powerio/format/

psse.rs

//! Read and write PSS/E `.raw` (revisions 33-35; see [`write_psse_rev`]).
//!
//! Covers the core sections — bus, load, fixed shunt, generator, branch, and the
//! 2- and 3-winding transformer records — which together carry a transmission
//! power flow case. A switched shunt keeps its steady-state susceptance `BINIT`
//! as the shunt `b` and carries its mode, voltage band, regulated bus, RMPCT, and
//! step blocks on [`SwitchedShuntControl`]. Transformer impedance and winding
//! bases (`CZ`/`CW`) are normalized to the system base and per unit tap ratios;
//! the writer emits the canonical `CZ = 1`, `CW = 1` form.
//! Two-terminal DC lines read and write as the neutral
//! [`Hvdc`] (power-setpoint model; converter firing-angle/transformer detail
//! rides through in extras). The other advanced sections (VSC and multi-terminal
//! DC, FACTS, GNE) are not modeled: on write they're emitted as empty sections,
//! on read they're skipped, and storage carried on the `BalancedNetwork` is reported as
//! dropped. Same-format round-trip is byte-exact via the retained source (see
//! [`crate::write_as`]); this serializer is the cross-format path.

use std::collections::{BTreeMap, BTreeSet};
use std::fmt::Write as _;
use std::sync::Arc;

use serde_json::Value;

use super::{
    Conversion, branch_rating_set_drop_warning, jnum, sanitize_quoted,
    warn_extra_branch_rating_sets,
};
use crate::network::{
    Area, BalancedNetwork, Branch, BranchCharging, BranchRatingSet, Bus, BusId, BusType, Extras,
    Generator, Hvdc, Impedance, Load, LoadVoltageModel, Shunt, ShuntBlock, SolverParams,
    SourceFormat, SwitchedShuntControl, SwitchedShuntMode, Transformer3W, TransformerControl,
    TransformerControlMode, Winding,
};
use crate::{Error, Result};

const FMT: &str = "PSS/E .raw";
const REV: u32 = 33;
const PSSE_EXTRA_BRANCH_RATINGS: usize = 9;

fn psse_extra_rating_name(slot: usize) -> String {
    format!("RATE{}", slot + 4)
}

fn psse_extra_rating_slot(name: &str) -> Option<usize> {
    let upper = name.trim().to_ascii_uppercase();
    let suffix = upper
        .strip_prefix("RATE")
        .or_else(|| upper.strip_prefix("RATING"))?
        .trim_start_matches([' ', '_']);
    let n = suffix.parse::<usize>().ok()?;
    (4..=12).contains(&n).then_some(n - 4)
}

fn read_extra_branch_ratings(
    fields: &[String],
    rating_start: usize,
    named_record: bool,
) -> Result<Vec<BranchRatingSet>> {
    if !named_record {
        return Ok(Vec::new());
    }
    let mut ratings = Vec::new();
    for slot in 0..PSSE_EXTRA_BRANCH_RATINGS {
        let rate_mva = num_at(fields, rating_start + 3 + slot, 0.0)?;
        if rate_mva.abs() > f64::EPSILON {
            ratings.push(BranchRatingSet::new(psse_extra_rating_name(slot), rate_mva));
        }
    }
    Ok(ratings)
}

fn psse_extra_rating_values(
    branch: &Branch,
    branch_index: usize,
    warnings: &mut Vec<String>,
) -> [f64; PSSE_EXTRA_BRANCH_RATINGS] {
    let mut values = [0.0; PSSE_EXTRA_BRANCH_RATINGS];
    let mut used = [false; PSSE_EXTRA_BRANCH_RATINGS];
    let mut deferred = Vec::new();

    for rating in &branch.rating_sets {
        if let Some(slot) = psse_extra_rating_slot(&rating.name) {
            if !used[slot] {
                values[slot] = rating.rate_mva;
                used[slot] = true;
                continue;
            }
        }
        deferred.push(rating);
    }

    for rating in deferred {
        if let Some(slot) = used.iter().position(|is_used| !*is_used) {
            values[slot] = rating.rate_mva;
            used[slot] = true;
            warnings.push(branch_rating_set_rename_warning(
                branch_index,
                branch,
                rating,
                &psse_extra_rating_name(slot),
            ));
        } else {
            warnings.push(branch_rating_set_drop_warning(
                "PSS/E v34/v35",
                branch_index,
                branch,
                rating,
            ));
        }
    }

    values
}

fn branch_rating_set_rename_warning(
    branch_index: usize,
    branch: &Branch,
    rating: &BranchRatingSet,
    emitted_name: &str,
) -> String {
    format!(
        "branch {} ({} to {}) rating set {}={} MVA emitted as {} in PSS/E v34/v35; rating set names outside RATE4-RATE12 are not preserved",
        branch_index + 1,
        branch.from,
        branch.to,
        rating.name,
        rating.rate_mva,
        emitted_name
    )
}

fn warn_psse_extra_branch_ratings_dropped(net: &BalancedNetwork, warnings: &mut Vec<String>) {
    warn_extra_branch_rating_sets("PSS/E v33", net, warnings);
}

/// Characters that would corrupt a single-quoted PSS/E name field. The quote
/// toggles the reader's quoted state early, and `/` truncates the record at the
/// inline-comment delimiter (a PSS/E record splits on `/` before tokenizing).
const NAME_FORBIDDEN: &[char] = &['\'', '/'];

// ---- Writer -----------------------------------------------------------------

/// Serialize `net` to PSS/E `.raw` at the default revision (33).
#[must_use]
pub fn write_psse(net: &BalancedNetwork) -> Conversion {
    write_psse_rev(net, REV)
}

/// Serialize `net` to PSS/E `.raw` at `rev` (33, 34, or 35).
///
/// Revisions 34 and 35 add the expanded system-wide header with its
/// end-of-system-wide-data marker, the named 12-rating branch record, the
/// 12-rating transformer winding line (COD at 15, NODE after CONT), and the
/// load distributed-generation / load-type trailing columns; 35 also inserts
/// the generator NREG/BASLOD columns and the switched shunt ID/NREG columns
/// with (S, N, B) step triples. The reader keys each layout off the header
/// revision. Any other `rev` falls back to the 33 layout. Same-format
/// byte-exact echo still rides the retained source (see [`crate::write_as`]);
/// this serializer is the cross format path.
#[must_use]
// A flat serializer: one stanza per PSS/E record type; splitting it would add
// indirection without clarity.
#[expect(clippy::too_many_lines)]
pub fn write_psse_rev(net: &BalancedNetwork, rev: u32) -> Conversion {
    // v34+ wraps the global parameters in a system-wide data section, names
    // branches and carries 12 ratings, and adds load DG / load-type columns.
    let modern = rev >= 34;
    let mut warnings = Vec::new();
    let mut nonfinite = false;
    let mut sanitized_quoted = 0usize;
    let mut s = String::new();
    // A formatter that records when a value can't be represented (PSS/E is fixed
    // numeric — no Inf/NaN).
    let mut num = |x: f64| -> String {
        if x.is_finite() {
            let s = format!("{x}");
            // PSS/E v33 readers treat a record whose first field is exactly "0" as
            // a section terminator (PowerModels' pti.jl). A transformer impedance
            // line can start with R = 0, so never emit a bare integer "0": give it
            // a decimal, matching PSS/E's own numeric convention.
            if s.bytes().all(|b| b.is_ascii_digit() || b == b'-') {
                format!("{s}.0")
            } else {
                s
            }
        } else {
            nonfinite = true;
            let sentinel = if x > 0.0 {
                1.0e10
            } else if x < 0.0 {
                -1.0e10
            } else {
                0.0
            };
            format!("{sentinel}.0")
        }
    };

    // The case name reaches the header line and the title line. Both are
    // single records, so an embedded terminator would make the rest of the
    // name parse as bus data.
    let case_name = sanitize_quoted(&net.name, NAME_FORBIDDEN, ' ');
    let _ = writeln!(
        s,
        "0, {}, {rev}, 0, {}, {}   / powerio export: {}",
        net.base_mva,
        i32::from(modern),
        num(net.base_frequency),
        case_name
    );
    let _ = writeln!(s, "{case_name}");
    let _ = writeln!(s);
    if modern {
        // v34+ system-wide block: emit the solver keyword lines (the fields that
        // are set), then close the block.
        if let Some(sp) = &net.solver {
            if let Some(t) = sp.zero_impedance_threshold {
                let _ = writeln!(s, "GENERAL, THRSHZ={}", num(t));
            }
            let mut newton = Vec::new();
            if let Some(t) = sp.newton_tolerance {
                newton.push(format!("TOLN={}", num(t)));
            }
            if let Some(n) = sp.max_iterations {
                newton.push(format!("ITMXN={n}"));
            }
            if !newton.is_empty() {
                let _ = writeln!(s, "NEWTON, {}", newton.join(", "));
            }
            let flags: Vec<String> = [
                ("ACTAPS", sp.adjust_taps),
                ("AREAIN", sp.adjust_area_interchange),
                ("PHSHFT", sp.adjust_phase_shift),
                ("DCTAPS", sp.adjust_dc_taps),
                ("SWSHNT", sp.adjust_switched_shunt),
            ]
            .into_iter()
            .filter_map(|(name, v)| v.map(|b| format!("{name}={}", i32::from(b))))
            .collect();
            if !flags.is_empty() {
                let _ = writeln!(s, "SOLVER, {}", flags.join(", "));
            }
        }
        let _ = writeln!(s, "0 / END OF SYSTEM-WIDE DATA, BEGIN BUS DATA");
    }

    // Bus, with area/zone kept for the load records that reference them.
    let mut bus_area: BTreeMap<BusId, (usize, usize)> = BTreeMap::new();
    for b in &net.buses {
        bus_area.insert(b.id, (b.area, b.zone));
        let raw_name = b.name.as_deref().unwrap_or("");
        let name = sanitize_quoted(raw_name, NAME_FORBIDDEN, ' ');
        if matches!(name, std::borrow::Cow::Owned(_)) {
            sanitized_quoted += 1;
        }
        // The last two columns are EVHI/EVLO; emit the emergency band when set,
        // else echo the normal band.
        let _ = writeln!(
            s,
            "{}, '{:<12}', {}, {}, {}, {}, 1, {}, {}, {}, {}, {}, {}",
            b.id,
            name,
            num(b.base_kv),
            ide(b.kind),
            b.area,
            b.zone,
            num(b.vm),
            num(b.va),
            num(b.vmax),
            num(b.vmin),
            num(b.evhi.unwrap_or(b.vmax)),
            num(b.evlo.unwrap_or(b.vmin))
        );
    }
    let _ = writeln!(s, "0 / END OF BUS DATA, BEGIN LOAD DATA");

    // v33 ends the load record at INTRPT; v34 adds PDGEN/QDGEN/STDG and v35 a
    // LOADTYPE string. PSS/E-sourced rows replay these from extras; other
    // sources get the documented defaults.
    // Per-bus circuit-id counters so parallel devices on a bus get distinct ids
    // (PSS/E requires (bus, id) to be unique); a captured `extras["id"]` wins.
    let mut load_ids: BTreeMap<BusId, BTreeSet<String>> = BTreeMap::new();
    for l in &net.loads {
        let (area, zone) = bus_area.get(&l.bus).copied().unwrap_or((1, 1));
        let id = quoted_device_id(&l.extras, l.bus, &mut load_ids, &mut sanitized_quoted);
        let (pl, ql, ip, iq, yp, yq) = load_components_for_write(l, &id, &mut warnings);
        let owner = extra_i64(&l.extras, "psse_owner").unwrap_or(1);
        let scal = typed_psse_scal(l, &id, &mut warnings)
            .or_else(|| extra_i64(&l.extras, "psse_scal"))
            .unwrap_or(1);
        let intrpt = extra_i64(&l.extras, "psse_intrpt").unwrap_or(0);
        let typed_load_type = l.voltage_model.as_ref().and_then(typed_psse_load_type);
        if rev < 35 && typed_load_type.is_some() {
            warnings.push(format!(
                "PSS/E load at bus {} id {id:?}: load type requires revision 35; dropped",
                l.bus
            ));
        }
        let modern_tail = if rev >= 35 {
            let pdgen = extra_f64(&l.extras, "psse_pdgen").unwrap_or(0.0);
            let qdgen = extra_f64(&l.extras, "psse_qdgen").unwrap_or(0.0);
            let flagstatus = extra_i64(&l.extras, "psse_flagstatus").unwrap_or(0);
            let raw_loadtype = typed_load_type.or_else(|| {
                l.extras
                    .get("psse_loadtype")
                    .and_then(Value::as_str)
                    .map(str::to_owned)
            });
            let loadtype =
                sanitize_quoted(raw_loadtype.as_deref().unwrap_or(""), NAME_FORBIDDEN, ' ');
            if matches!(loadtype, std::borrow::Cow::Owned(_)) {
                sanitized_quoted += 1;
            }
            format!(
                ", {}, {}, {flagstatus}, '{loadtype}'",
                num(pdgen),
                num(qdgen)
            )
        } else if modern {
            let pdgen = extra_f64(&l.extras, "psse_pdgen").unwrap_or(0.0);
            let qdgen = extra_f64(&l.extras, "psse_qdgen").unwrap_or(0.0);
            let flagstatus = extra_i64(&l.extras, "psse_flagstatus").unwrap_or(0);
            format!(", {}, {}, {flagstatus}", num(pdgen), num(qdgen))
        } else {
            String::new()
        };
        let _ = writeln!(
            s,
            "{}, '{id}', {}, {}, {}, {}, {}, {}, {}, {}, {}, {owner}, {scal}, {intrpt}{modern_tail}",
            l.bus,
            i32::from(l.in_service),
            area,
            zone,
            num(pl),
            num(ql),
            num(ip),
            num(iq),
            num(yp),
            num(yq)
        );
    }
    let _ = writeln!(s, "0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA");

    // Fixed shunts here; switched shunts (control = Some) go in their own section.
    let mut shunt_ids: BTreeMap<BusId, BTreeSet<String>> = BTreeMap::new();
    for sh in net.shunts.iter().filter(|s| s.control.is_none()) {
        let id = quoted_device_id(&sh.extras, sh.bus, &mut shunt_ids, &mut sanitized_quoted);
        let _ = writeln!(
            s,
            "{}, '{id}', {}, {}, {}",
            sh.bus,
            i32::from(sh.in_service),
            num(sh.g),
            num(sh.b)
        );
    }
    let _ = writeln!(s, "0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA");

    let mut gen_ids: BTreeMap<BusId, u32> = BTreeMap::new();
    for g in &net.generators {
        let id = positional_id(g.bus, &mut gen_ids);
        // IREG (field 7): the remote regulated bus, or 0 for own-terminal control.
        let ireg = g.regulated_bus.map_or(0, |b| b.0);
        // v35 inserts NREG after IREG and BASLOD after PB; v34 keeps the v33 layout.
        let (nreg, baslod) = if rev >= 35 { (" 0,", " 0,") } else { ("", "") };
        let _ = writeln!(
            s,
            "{}, '{id}', {}, {}, {}, {}, {}, {},{nreg} {}, 0, 1, 0, 0, 1, {}, 100, {}, {},{baslod} 1, 1",
            g.bus,
            num(g.pg),
            num(g.qg),
            num(g.qmax),
            num(g.qmin),
            num(g.vg),
            ireg,
            num(g.mbase),
            i32::from(g.in_service),
            num(g.pmax),
            num(g.pmin)
        );
    }
    let _ = writeln!(s, "0 / END OF GENERATOR DATA, BEGIN BRANCH DATA");

    // Non-transformer branches here; transformers go in their own section.
    // Parallel branches between the same bus pair get distinct circuit ids (PSS/E
    // keys a branch on (I, J, CKT)); a captured source CKT wins.
    let mut branch_ids: BTreeMap<(BusId, BusId), BTreeSet<String>> = BTreeMap::new();
    for (branch_index, br) in net
        .branches
        .iter()
        .enumerate()
        .filter(|(_, b)| !b.is_transformer())
    {
        let ckt = quoted_circuit_id(
            br.extras.get("id").and_then(Value::as_str),
            (br.from, br.to),
            &mut branch_ids,
            &mut sanitized_quoted,
        );
        let charging = br.terminal_charging();
        let b_total = charging.total_b();
        let b_mid = b_total / 2.0;
        let bi = charging.b_fr - b_mid;
        let bj = charging.b_to - b_mid;
        if modern {
            // v34+: a quoted line NAME at field 6, then twelve rating columns,
            // pushing STAT to field 23 (the layout the reader expects at rev>=34).
            // RATE4-RATE12 come from extra branch rating sets when present.
            let extra_ratings = psse_extra_rating_values(br, branch_index, &mut warnings);
            let _ = writeln!(
                s,
                "{}, {}, '{ckt}', {}, {}, {}, '            ', {}, {}, {}, \
                 {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, 1, 0, 1, 1",
                br.from,
                br.to,
                num(br.r),
                num(br.x),
                num(b_total),
                num(br.rate_a),
                num(br.rate_b),
                num(br.rate_c),
                num(extra_ratings[0]),
                num(extra_ratings[1]),
                num(extra_ratings[2]),
                num(extra_ratings[3]),
                num(extra_ratings[4]),
                num(extra_ratings[5]),
                num(extra_ratings[6]),
                num(extra_ratings[7]),
                num(extra_ratings[8]),
                num(charging.g_fr),
                num(bi),
                num(charging.g_to),
                num(bj),
                i32::from(br.in_service)
            );
        } else {
            let _ = writeln!(
                s,
                "{}, {}, '{ckt}', {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, 1, 0, 1, 1",
                br.from,
                br.to,
                num(br.r),
                num(br.x),
                num(b_total),
                num(br.rate_a),
                num(br.rate_b),
                num(br.rate_c),
                num(charging.g_fr),
                num(bi),
                num(charging.g_to),
                num(bj),
                i32::from(br.in_service)
            );
        }
    }
    let _ = writeln!(s, "0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA");

    for (branch_index, br) in net
        .branches
        .iter()
        .enumerate()
        .filter(|(_, b)| b.is_transformer())
    {
        // 2-winding, 4-line record. CW=1 (turns ratio p.u.), CZ=1 (Z on system
        // base). Record 1 carries the full owner block (O1..O4,F1..F4) and the
        // VECGRP string: PSS/E v33 readers count a 2-winding transformer as a
        // fixed 43-field record (21 + 3 + 17 + 2), so the owner padding matters.
        // MAG1/MAG2 = the branch charging projected to one magnetizing
        // admittance (CM = 1, so p.u. on the system base); a 2-winding
        // transformer that carries line charging keeps the total.
        let charging = br.terminal_charging();
        let _ = writeln!(
            s,
            "{}, {}, 0, '1', 1, 1, 1, {}, {}, 2, '            ', {}, 1, 1, 0, 1, 0, 1, 0, 1, '            '",
            br.from,
            br.to,
            num(charging.total_g()),
            num(charging.total_b()),
            i32::from(br.in_service)
        );
        // Winding-1 control columns (COD, CONT, RMA/RMI, VMA/VMI, NTP) come from
        // the regulating-control data when present, else the fixed defaults.
        let ctl = br.control.as_ref();
        let sbase = ctl
            .filter(|c| c.mva_base > 0.0)
            .map_or(net.base_mva, |c| c.mva_base);
        let cod = ctl.map_or(0, |c| mode_to_cod(c.mode));
        let cont = ctl.and_then(|c| c.controlled_bus).map_or(0, |b| b.0);
        let (rma, rmi, vma, vmi, ntp) = ctl.map_or((1.1, 0.9, 1.1, 0.9, 33), |c| {
            (c.tap_max, c.tap_min, c.band_max, c.band_min, c.ntp)
        });
        let _ = writeln!(s, "{}, {}, {}", num(br.r), num(br.x), num(sbase));
        if modern {
            // v34+ winding line: twelve ratings (RATE4-RATE12 from extra rating
            // sets), then COD, CONT, NODE, RMA, RMI, VMA, VMI, NTP, TAB, CR,
            // CX, CNXA — COD at 15, matching the reader.
            let extra_ratings = psse_extra_rating_values(br, branch_index, &mut warnings);
            let _ = writeln!(
                s,
                "{}, 0, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}, \
                 {cod}, {cont}, 0, {}, {}, {}, {}, {ntp}, 0, 0, 0, 0",
                num(br.effective_tap()),
                num(br.shift),
                num(br.rate_a),
                num(br.rate_b),
                num(br.rate_c),
                num(extra_ratings[0]),
                num(extra_ratings[1]),
                num(extra_ratings[2]),
                num(extra_ratings[3]),
                num(extra_ratings[4]),
                num(extra_ratings[5]),
                num(extra_ratings[6]),
                num(extra_ratings[7]),
                num(extra_ratings[8]),
                num(rma),
                num(rmi),
                num(vma),
                num(vmi)
            );
        } else {
            let _ = writeln!(
                s,
                "{}, 0, {}, {}, {}, {}, {cod}, {cont}, {}, {}, {}, {}, {ntp}, 0, 0, 0, 0",
                num(br.effective_tap()),
                num(br.shift),
                num(br.rate_a),
                num(br.rate_b),
                num(br.rate_c),
                num(rma),
                num(rmi),
                num(vma),
                num(vmi)
            );
        }
        let _ = writeln!(s, "1.0, 0");
    }

    // 3-winding transformers: a 5-line record. CW=1, CZ=1, CM=1 (same conventions
    // as the 2-winding record); line 2 carries the three pairwise impedances and
    // the star-point voltage, lines 3-5 the per-winding tap/angle/ratings.
    for t in &net.transformers_3w {
        let raw_name = t.name.as_deref().unwrap_or("");
        let name = sanitize_quoted(raw_name, NAME_FORBIDDEN, ' ');
        if matches!(name, std::borrow::Cow::Owned(_)) {
            sanitized_quoted += 1;
        }
        let _ = writeln!(
            s,
            "{}, {}, {}, '1', 1, 1, 1, {}, {}, 2, '{:<12}', {}, 1, 1, 0, 1, 0, 1, 0, 1, '            '",
            t.windings[0].bus,
            t.windings[1].bus,
            t.windings[2].bus,
            num(t.mag_g),
            num(t.mag_b),
            name,
            i32::from(t.in_service)
        );
        // Line 2: the three pairwise (R, X) on the system base (CZ=1), each with
        // its declared SBASE column, then the star voltage.
        let [z12, z23, z31] = t.z;
        let _ = writeln!(
            s,
            "{}, {}, {}, {}, {}, {}, {}, {}, {}, {}, {}",
            num(z12.r),
            num(z12.x),
            num(z12.base_mva),
            num(z23.r),
            num(z23.x),
            num(z23.base_mva),
            num(z31.r),
            num(z31.x),
            num(z31.base_mva),
            num(t.star_vm),
            num(t.star_va)
        );
        for w in &t.windings {
            if modern {
                // v34+ winding layout (twelve ratings, NODE after CONT); the
                // Winding model carries three ratings, so RATE4-RATE12 are 0.
                let _ = writeln!(
                    s,
                    "{}, {}, {}, {}, {}, {}, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, \
                     0, 0, 0, 1.1, 0.9, 1.1, 0.9, 33, 0, 0, 0, 0",
                    num(w.tap),
                    num(w.nominal_kv),
                    num(w.shift),
                    num(w.rate_a),
                    num(w.rate_b),
                    num(w.rate_c)
                );
            } else {
                let _ = writeln!(
                    s,
                    "{}, {}, {}, {}, {}, {}, 0, 0, 1.1, 0.9, 1.1, 0.9, 33, 0, 0, 0, 0",
                    num(w.tap),
                    num(w.nominal_kv),
                    num(w.shift),
                    num(w.rate_a),
                    num(w.rate_b),
                    num(w.rate_c)
                );
            }
        }
    }
    let _ = writeln!(s, "0 / END OF TRANSFORMER DATA, BEGIN AREA DATA");
    for a in &net.areas {
        let raw_name = a.name.as_deref().unwrap_or("");
        let name = sanitize_quoted(raw_name, NAME_FORBIDDEN, ' ');
        if matches!(name, std::borrow::Cow::Owned(_)) {
            sanitized_quoted += 1;
        }
        let _ = writeln!(
            s,
            "{}, {}, {}, {}, '{:<12}'",
            a.number,
            a.slack_bus.map_or(0, |b| b.0),
            num(a.net_interchange),
            num(a.tolerance),
            name
        );
    }

    // Two-terminal DC lines occupy the first of the otherwise-empty sections:
    // emit their 3-line records (if any) between the begin/end markers, then the
    // remaining sections as bare terminators so the file parses as a complete case.
    let _ = writeln!(s, "{}", EMPTY_SECTIONS[0]);
    for (i, dc) in net.hvdc.iter().enumerate() {
        let raw_name = dc_str(&dc.extras, "psse_dc_name").unwrap_or_else(|| format!("DC{}", i + 1));
        let name = sanitize_quoted(&raw_name, NAME_FORBIDDEN, ' ');
        if matches!(name, std::borrow::Cow::Owned(_)) {
            sanitized_quoted += 1;
        }
        let name = format!("'{name}'");
        let mdc = if dc.in_service {
            dc_int(&dc.extras, "psse_dc_mdc").unwrap_or(1)
        } else {
            0
        };
        let rdc = dc_f64(&dc.extras, "psse_dc_rdc").unwrap_or(0.0);
        let vschd = dc_f64(&dc.extras, "psse_dc_vschd").unwrap_or(0.0);
        let l1_tail = dc_tail(
            &dc.extras,
            "psse_dc_control_tail",
            "0.0, 0.0, 0.0, 'I', 0.0, 20, 1.0",
        );
        let rect_tail = dc_tail(&dc.extras, "psse_dc_rectifier_tail", DEFAULT_CONVERTER_TAIL);
        let inv_tail = dc_tail(&dc.extras, "psse_dc_inverter_tail", DEFAULT_CONVERTER_TAIL);
        let _ = writeln!(
            s,
            "{name}, {mdc}, {}, {}, {}, {l1_tail}",
            num(rdc),
            num(dc.pf),
            num(vschd)
        );
        let _ = writeln!(s, "{}, {rect_tail}", dc.from);
        let _ = writeln!(s, "{}, {inv_tail}", dc.to);
    }
    // Sections up to and including the SWITCHED SHUNT begin marker.
    for line in &EMPTY_SECTIONS[1..=9] {
        let _ = writeln!(s, "{line}");
    }
    // Switched shunts: BINIT becomes the susceptance, the control record the rest.
    // v35 inserts a quoted shunt ID at field 1 and NREG after SWREG, and its step
    // blocks are (S, N, B) triples with a leading per-block status; v33/34 have
    // neither and use (N, B) pairs. The writer must match the reader's layout at
    // each revision or every later field is read columns off.
    let mut sw_ids: BTreeMap<BusId, BTreeSet<String>> = BTreeMap::new();
    for sh in net.shunts.iter().filter(|s| s.control.is_some()) {
        let Some(c) = sh.control.as_ref() else {
            continue;
        };
        let swrem = c.control_bus.map_or(0, |b| b.0);
        let mut blocks = String::new();
        for blk in &c.blocks {
            if rev >= 35 {
                // The neutral model has no per-block status: every block is in
                // service (S = 1).
                let _ = write!(blocks, ", 1, {}, {}", blk.steps, num(blk.b));
            } else {
                let _ = write!(blocks, ", {}, {}", blk.steps, num(blk.b));
            }
        }
        if rev >= 35 {
            let id = quoted_device_id(&sh.extras, sh.bus, &mut sw_ids, &mut sanitized_quoted);
            let _ = writeln!(
                s,
                "{}, '{id}', {}, 0, {}, {}, {}, {swrem}, 0, {}, '', {}{blocks}",
                sh.bus,
                mode_to_modsw(c.mode),
                i32::from(sh.in_service),
                num(c.vhigh),
                num(c.vlow),
                num(c.rmpct),
                num(sh.b)
            );
        } else {
            let _ = writeln!(
                s,
                "{}, {}, 0, {}, {}, {}, {swrem}, {}, '', {}{blocks}",
                sh.bus,
                mode_to_modsw(c.mode),
                i32::from(sh.in_service),
                num(c.vhigh),
                num(c.vlow),
                num(c.rmpct),
                num(sh.b)
            );
        }
    }
    for line in &EMPTY_SECTIONS[10..] {
        let _ = writeln!(s, "{line}");
    }
    let _ = writeln!(s, "Q");

    if net
        .hvdc
        .iter()
        .any(|d| !d.extras.contains_key("psse_dc_name"))
    {
        warnings.push(
            "DC line converter detail (firing angles, converter transformer taps, reactive \
             output) defaulted: PSS/E two-terminal DC is written from the power setpoint and \
             line resistance only"
                .into(),
        );
    }
    if !net.storage.is_empty() {
        warnings.push(format!(
            "{} storage unit(s) dropped: PSS/E has no storage record",
            net.storage.len()
        ));
    }
    if net.generators.iter().any(|g| g.cost.is_some()) {
        warnings.push("generator cost curves dropped: PSS/E .raw has no cost data".into());
    }
    if net.branches.iter().any(Branch::has_angle_limits) {
        warnings.push(
            "branch angle limits (angmin/angmax) dropped: PSS/E branch records carry none".into(),
        );
    }
    let current_ratings = net
        .branches
        .iter()
        .filter(|b| b.current_ratings.is_some())
        .count();
    if current_ratings > 0 {
        warnings.push(format!(
            "{current_ratings} branch current rating record(s) dropped: PSS/E branch ratings are MVA ratings"
        ));
    }
    if !modern {
        warn_psse_extra_branch_ratings_dropped(net, &mut warnings);
    }
    let branch_solutions = net.branches.iter().filter(|b| b.solution.is_some()).count();
    if branch_solutions > 0 {
        warnings.push(format!(
            "{branch_solutions} branch solution value set(s) dropped: PSS/E RAW power flow result fields are not written"
        ));
    }
    let transformer_terminal_shunts = net
        .branches
        .iter()
        .filter(|b| {
            b.is_transformer()
                && b.charging
                    .is_some_and(|c| c.g_to.abs() > f64::EPSILON || c.b_to.abs() > f64::EPSILON)
        })
        .count();
    if transformer_terminal_shunts > 0 {
        warnings.push(format!(
            "{transformer_terminal_shunts} transformer terminal admittance record(s) collapsed to magnetizing admittance: PSS/E transformer records cannot preserve terminal side assignment"
        ));
    }
    if net.generators.iter().any(Generator::has_caps) {
        warnings.push(
            "generator ramp/capability columns dropped: PSS/E .raw has no equivalent fields".into(),
        );
    }
    if nonfinite {
        warnings.push("non-finite values written as ±1e10 sentinels (PSS/E has no Inf/NaN)".into());
    }
    if sanitized_quoted > 0 {
        warnings.push(format!(
            "{sanitized_quoted} quoted PSS/E field(s) contained a quote or '/' that would \
             corrupt a record; replaced with spaces"
        ));
    }

    Conversion { text: s, warnings }
}

/// MATPOWER/neutral bus kind → PSS/E bus type code (IDE).
fn ide(kind: BusType) -> u8 {
    kind as u8 // 1=PQ, 2=PV, 3=ref/swing, 4=isolated — same codes
}

/// The circuit id for an element: its sanitized `extras["id"]` when present and
/// still free on this bus, else the lowest positional id still free, so parallel
/// devices stay distinct and the PSS/E `(bus, id)` uniqueness rule holds even
/// when source ids collide before or after sanitation. `used` tracks the ids
/// already emitted per bus.
fn quoted_device_id(
    extras: &Extras,
    bus: BusId,
    used: &mut BTreeMap<BusId, BTreeSet<String>>,
    sanitized_quoted: &mut usize,
) -> String {
    quoted_circuit_id(
        extras.get("id").and_then(Value::as_str),
        bus,
        used,
        sanitized_quoted,
    )
}

fn quoted_circuit_id<K: Ord + Clone>(
    preferred: Option<&str>,
    key: K,
    used: &mut BTreeMap<K, BTreeSet<String>>,
    sanitized_quoted: &mut usize,
) -> String {
    let sanitized = preferred.map(|id| {
        let cleaned = sanitize_quoted(id, NAME_FORBIDDEN, ' ');
        if matches!(cleaned, std::borrow::Cow::Owned(_)) {
            *sanitized_quoted += 1;
        }
        cleaned.into_owned()
    });
    super::allocate_circuit_id(sanitized.as_deref(), key, used)
}

/// The next positional circuit id for `bus` (for elements with no extras to carry
/// a captured id, such as generators).
fn positional_id(bus: BusId, counters: &mut BTreeMap<BusId, u32>) -> String {
    let n = counters.entry(bus).or_insert(0);
    *n += 1;
    n.to_string()
}

/// Converter-line tail (everything after the AC terminal bus) for a synthesized
/// two-terminal DC record: NBR/NBI bridges, firing-angle limits, converter
/// transformer R/X and tap data, and the metered-end id. PSS/E-sourced lines
/// replay their own tail; these defaults serve a cross-format source.
const DEFAULT_CONVERTER_TAIL: &str =
    "1, 15.0, 5.0, 0.0, 0.0, 0.0, 1.0, 1.0, 1.5, 0.51, 0.00625, 0, 0, 0, '1', 0.0";

const EMPTY_SECTIONS: [&str; 13] = [
    "0 / END OF AREA DATA, BEGIN TWO-TERMINAL DC DATA",
    "0 / END OF TWO-TERMINAL DC DATA, BEGIN VSC DC LINE DATA",
    "0 / END OF VSC DC LINE DATA, BEGIN IMPEDANCE CORRECTION DATA",
    "0 / END OF IMPEDANCE CORRECTION DATA, BEGIN MULTI-TERMINAL DC DATA",
    "0 / END OF MULTI-TERMINAL DC DATA, BEGIN MULTI-SECTION LINE DATA",
    "0 / END OF MULTI-SECTION LINE DATA, BEGIN ZONE DATA",
    "0 / END OF ZONE DATA, BEGIN INTER-AREA TRANSFER DATA",
    "0 / END OF INTER-AREA TRANSFER DATA, BEGIN OWNER DATA",
    "0 / END OF OWNER DATA, BEGIN FACTS DEVICE DATA",
    "0 / END OF FACTS DEVICE DATA, BEGIN SWITCHED SHUNT DATA",
    "0 / END OF SWITCHED SHUNT DATA, BEGIN GNE DEVICE DATA",
    "0 / END OF GNE DEVICE DATA, BEGIN INDUCTION MACHINE DATA",
    "0 / END OF INDUCTION MACHINE DATA",
];

// ---- Reader -----------------------------------------------------------------

/// Parse a PSS/E `.raw` (revisions 33-35) into a [`BalancedNetwork`]. Reads bus/load/
/// fixed-shunt/generator/branch/2- and 3-winding transformer; skips the advanced
/// sections.
pub fn parse_psse(content: &str) -> Result<BalancedNetwork> {
    let mut warnings = Vec::new();
    parse_psse_source(Arc::new(content.to_owned()), None, &mut warnings)
}

/// The PSS/E revision declared in a retained `.raw` header (field 3, `REV`), or
/// 33 when it is absent or unparseable. The format hub uses it to decide whether
/// a same-format write can echo the source bytes or must re-emit at a different
/// revision.
pub(crate) fn header_rev(source: &str) -> u32 {
    let Some(header) = source
        .lines()
        .map(str::trim)
        .find(|line| !line.is_empty() && !is_comment(line))
    else {
        return 33;
    };
    fields(header)
        .get(2)
        .and_then(|f| f.parse::<f64>().ok())
        .filter(|v| v.is_finite() && *v >= 0.0)
        .map_or(33, |v| v as u32)
}

/// Owned-source entry used by the format hub: parse by borrowing `source`, then
/// move the buffer into the retained source (no copy). `name_hint` (e.g. a file
/// stem) names the network when the title line is blank.
// A flat reader: header parse plus one match arm per section. Splitting it would
// add indirection without clarity.
#[expect(clippy::too_many_lines)]
pub(crate) fn parse_psse_source(
    source: Arc<String>,
    name_hint: Option<&str>,
    warnings: &mut Vec<String>,
) -> Result<BalancedNetwork> {
    let content: &str = &source;
    let mut lines = content.lines();

    // Header line 1: IC, SBASE, REV, ...
    let header = lines
        .by_ref()
        .find(|line| {
            let line = line.trim();
            !line.is_empty() && !is_comment(line)
        })
        .ok_or_else(|| Error::FormatRead {
            format: FMT,
            message: "empty file".into(),
        })?;
    let header_fields = fields(header);
    let base_mva = header_fields
        .get(1)
        .and_then(|f| f.parse::<f64>().ok())
        .ok_or_else(|| Error::FormatRead {
            format: FMT,
            message: "missing SBASE in header".into(),
        })?;
    let raw_rev = header_fields
        .get(2)
        .and_then(|f| f.parse::<f64>().ok())
        .filter(|v| v.is_finite() && *v >= 0.0)
        .map_or(33, |v| v as u32);
    // BASFRQ is the sixth header field (IC, SBASE, REV, XFRRAT, NXFRAT, BASFRQ);
    // older revisions that carry only `SBASE, title` lack it, so default it.
    let base_frequency = header_fields
        .get(5)
        .and_then(|f| f.parse::<f64>().ok())
        .filter(|v| v.is_finite() && *v > 0.0)
        .unwrap_or(crate::network::DEFAULT_BASE_FREQUENCY);
    // Line 2 is the case title; we write the network name there, so read it back.
    let title = lines.next().unwrap_or("").trim();
    let name = if title.is_empty() {
        name_hint.unwrap_or("case").to_string()
    } else {
        title.to_string()
    };
    lines.next(); // line 3: second comment

    let mut buses = Vec::new();
    let mut loads = Vec::new();
    let mut shunts = Vec::new();
    let mut generators = Vec::new();
    let mut branches = Vec::new();
    let mut transformers_3w = Vec::new();
    let mut hvdc = Vec::new();
    let mut areas = Vec::new();
    let mut solver = SolverParams::default();
    let mut bus_base_kv: BTreeMap<BusId, f64> = BTreeMap::new();
    let mut unmodeled_sections: BTreeMap<String, usize> = BTreeMap::new();

    // Sections appear in fixed order, each ended by a record whose first field is
    // `0`. We read the ones we model and treat the rest as skipped.
    let mut section = Section::Bus;
    let mut saw_bus_marker = false;
    let mut skipped_section_name: Option<String> = None;
    let mut lines = lines.peekable();
    while let Some(raw) = lines.next() {
        let line = raw.trim();
        if line.is_empty() {
            continue;
        }
        if is_comment(line) {
            continue;
        }
        if line == "Q" {
            break;
        }
        if is_terminator(line) {
            // The terminator names the section that begins next ("…, BEGIN
            // SWITCHED SHUNT DATA"); read that rather than counting, so the many
            // unmodeled sections between transformers and switched shunts don't
            // throw off the position.
            let next_section = section_after_marker(line);
            skipped_section_name =
                introduced_section_name(line).filter(|_| matches!(next_section, Section::Skip));
            section = next_section;
            saw_bus_marker |= matches!(section, Section::Bus);
            continue;
        }
        let f = fields(line);
        match section {
            Section::Bus if !saw_bus_marker && buses.is_empty() && is_system_wide_record(&f) => {
                // The v34+ system-wide block precedes the bus data; capture its
                // solver keyword lines (this is the first one that triggered).
                section = Section::SystemWide;
                parse_solver_line(&f, &mut solver);
            }
            Section::Bus => {
                let bus = read_bus(&f)?;
                bus_base_kv.insert(bus.id, bus.base_kv);
                buses.push(bus);
            }
            Section::Load => loads.push(read_load(&f, raw_rev, warnings)?),
            Section::FixedShunt => shunts.push(read_shunt(&f)?),
            Section::SwitchedShunt => shunts.push(read_switched_shunt(&f, raw_rev)?),
            Section::Generator => generators.push(read_gen(&f, raw_rev)?),
            Section::Branch => branches.push(read_branch(&f, raw_rev)?),
            Section::Transformer => {
                // 2-winding = 4 lines (K field == 0); 3-winding = 5 lines.
                // int_at parses through f64: v34/35 exporters write K in float
                // form ("0.00"), and an i64 parse would misclassify the record
                // as 3-winding and desynchronize the section.
                let two_winding = int_at(&f, 2, 0)? == 0;
                let l2 = next_continuation_line(
                    &mut lines,
                    "transformer",
                    "transformer impedance line",
                )?;
                let l3 = next_continuation_line(&mut lines, "transformer", "winding data line 1")?;
                let l4 = next_continuation_line(&mut lines, "transformer", "winding data line 2")?;
                if two_winding {
                    // MAG2 maps to the branch charging b only at CM = 1; a CM != 1
                    // record states magnetizing data in units this reader does not
                    // convert, so read_transformer drops it. Name the loss.
                    if int_at(&f, 6, 1)? != 1 && num_at(&f, 8, 0.0)? != 0.0 {
                        warnings.push(format!(
                            "transformer {}-{}: magnetizing data with CM != 1 dropped \
                             (only CM = 1 p.u. susceptance is read as branch charging)",
                            f.first().map_or("?", String::as_str),
                            f.get(1).map_or("?", String::as_str),
                        ));
                    }
                    branches.push(read_transformer(
                        &f,
                        &fields(l2),
                        &fields(l3),
                        &fields(l4),
                        raw_rev,
                        base_mva,
                        &bus_base_kv,
                        warnings,
                    )?);
                } else {
                    let l5 =
                        next_continuation_line(&mut lines, "transformer", "winding data line 3")?;
                    transformers_3w.push(read_transformer_3w(
                        &f,
                        &fields(l2),
                        &fields(l3),
                        &fields(l4),
                        &fields(l5),
                        base_mva,
                        &bus_base_kv,
                        warnings,
                    )?);
                }
            }
            Section::TwoTerminalDc => {
                // 3-line record: control line, then the rectifier and inverter
                // converter lines whose first field is the AC terminal bus.
                let rectifier =
                    next_continuation_line(&mut lines, "two-terminal DC", "rectifier line")?;
                let inverter =
                    next_continuation_line(&mut lines, "two-terminal DC", "inverter line")?;
                hvdc.push(read_dc_line(&f, &fields(rectifier), &fields(inverter))?);
            }
            Section::Area => areas.push(read_area(&f)?),
            Section::SystemWide => parse_solver_line(&f, &mut solver),
            Section::Skip => {
                if let Some(name) = skipped_section_name.as_ref() {
                    *unmodeled_sections.entry(name.clone()).or_default() += 1;
                }
            }
        }
    }

    warn_unmodeled_sections(unmodeled_sections, warnings);

    let mut net = BalancedNetwork {
        name,
        base_mva,
        base_frequency,
        geo: None,
        buses,
        loads,
        shunts,
        branches,
        switches: Vec::new(),
        generators,
        storage: Vec::new(),
        hvdc,
        transformers_3w,
        areas,
        solver: (!solver.is_empty()).then_some(solver),
        source_format: SourceFormat::Psse,
        source: Some(source),
    };
    drop_stale_control_pointers(&mut net, warnings);
    net.check_references(FMT)?;
    Ok(net)
}

#[derive(Clone, Copy)]
enum Section {
    Bus,
    Load,
    FixedShunt,
    SwitchedShunt,
    Generator,
    Branch,
    Transformer,
    TwoTerminalDc,
    Area,
    SystemWide,
    Skip,
}

/// The section a terminator introduces. Sections we don't model map to
/// [`Section::Skip`]. Case-insensitive on the marker text, so the number of
/// skipped sections between the modeled ones doesn't matter.
fn section_after_marker(line: &str) -> Section {
    match introduced_section_name(line).as_deref() {
        Some("BUS") => Section::Bus,
        Some("LOAD") => Section::Load,
        Some("FIXED SHUNT") => Section::FixedShunt,
        Some("SWITCHED SHUNT") => Section::SwitchedShunt,
        Some("GENERATOR" | "GEN") => Section::Generator,
        Some("BRANCH") => Section::Branch,
        Some("TRANSFORMER") => Section::Transformer,
        Some("TWO-TERMINAL DC" | "TWO TERMINAL DC" | "2-TERMINAL DC" | "2 TERMINAL DC") => {
            Section::TwoTerminalDc
        }
        Some("AREA" | "AREA INTERCHANGE") => Section::Area,
        _ => Section::Skip,
    }
}

/// A record line's first field is `0` (the section terminator).
fn is_terminator(line: &str) -> bool {
    fields(line).first().map(String::as_str) == Some("0")
}

fn next_continuation_line<'a>(
    lines: &mut std::iter::Peekable<std::str::Lines<'a>>,
    record: &str,
    expected: &str,
) -> Result<&'a str> {
    for line in lines.by_ref().map(str::trim) {
        if line.is_empty() || is_comment(line) {
            continue;
        }
        if line.eq_ignore_ascii_case("q") || is_section_marker(line) || is_bare_terminator(line) {
            return Err(Error::FormatRead {
                format: FMT,
                message: format!(
                    "PSS/E {record} record ended before {expected}: found section terminator `{line}`"
                ),
            });
        }
        return Ok(line);
    }
    Err(Error::FormatRead {
        format: FMT,
        message: format!("PSS/E {record} record ended before {expected}"),
    })
}

fn is_bare_terminator(line: &str) -> bool {
    let f = fields(line);
    f.len() == 1 && f.first().map(String::as_str) == Some("0")
}

fn transformer_basis_codes(f: &[String]) -> Result<(i64, i64)> {
    let cw = num_at(f, 4, 1.0)?;
    if cw.fract() != 0.0 {
        return Err(bad_field(4, f.get(4).map_or("", String::as_str)));
    }
    let cz = num_at(f, 5, 1.0)?;
    if cz.fract() != 0.0 {
        return Err(bad_field(5, f.get(5).map_or("", String::as_str)));
    }
    #[allow(clippy::cast_possible_truncation)]
    Ok((cw as i64, cz as i64))
}

fn transformer_label(f: &[String]) -> String {
    let i = f.first().map_or("?", String::as_str);
    let j = f.get(1).map_or("?", String::as_str);
    let k = f.get(2).map_or("?", String::as_str);
    let id = f.get(3).map_or("", String::as_str);
    format!("{i}-{j}-{k} id {id:?}")
}

#[expect(clippy::too_many_arguments)]
fn convert_transformer_impedance(
    r: f64,
    x: f64,
    sbase: f64,
    system_base: f64,
    cz: i64,
    label: &str,
    pair: &str,
    warnings: &mut Vec<String>,
) -> (f64, f64) {
    let base_ok = sbase.is_finite() && sbase > 0.0;
    match cz {
        1 => (r, x),
        2 => {
            if base_ok {
                let scale = system_base / sbase;
                (r * scale, x * scale)
            } else {
                warnings.push(format!(
                    "PSS/E transformer {label} pair {pair}: CZ=2 impedance has invalid SBASE {sbase}; read as system-base p.u."
                ));
                (r, x)
            }
        }
        3 => {
            if !base_ok {
                warnings.push(format!(
                    "PSS/E transformer {label} pair {pair}: CZ=3 impedance has invalid SBASE {sbase}; read as system-base p.u."
                ));
                return (r, x);
            }
            let r_pair = (r / 1_000_000.0) / sbase;
            let z_pair = x.abs();
            let x_pair = (z_pair.mul_add(z_pair, -(r_pair * r_pair)))
                .max(0.0)
                .sqrt()
                .copysign(x);
            let scale = system_base / sbase;
            (r_pair * scale, x_pair * scale)
        }
        other => {
            warnings.push(format!(
                "PSS/E transformer {label} pair {pair}: unsupported CZ={other}; read impedance as system-base p.u."
            ));
            (r, x)
        }
    }
}

fn default_windv(cw: i64, bus: BusId, bus_base_kv: &BTreeMap<BusId, f64>) -> f64 {
    if cw == 2 {
        bus_base_kv
            .get(&bus)
            .copied()
            .filter(|v| *v > 0.0)
            .unwrap_or(1.0)
    } else {
        1.0
    }
}

fn winding_ratio(
    w: &[String],
    bus: BusId,
    cw: i64,
    bus_base_kv: &BTreeMap<BusId, f64>,
    label: &str,
    winding: &str,
    warnings: &mut Vec<String>,
) -> Result<f64> {
    let windv = num_at(w, 0, default_windv(cw, bus, bus_base_kv))?;
    let nomv = num_at(w, 1, 0.0)?;
    let base_kv = bus_base_kv.get(&bus).copied().unwrap_or(0.0);
    let needs_base = matches!(cw, 2 | 3);
    if needs_base && !(base_kv.is_finite() && base_kv > 0.0) {
        warnings.push(format!(
            "PSS/E transformer {label} {winding}: CW={cw} needs a positive bus base kV for bus {bus}; read WINDV as a p.u. tap ratio"
        ));
        return Ok(windv);
    }
    match cw {
        1 => Ok(windv),
        2 => Ok(windv / base_kv),
        3 => {
            let nominal = if nomv.is_finite() && nomv > 0.0 {
                nomv
            } else {
                base_kv
            };
            Ok(windv * nominal / base_kv)
        }
        other => {
            warnings.push(format!(
                "PSS/E transformer {label} {winding}: unsupported CW={other}; read WINDV as a p.u. tap ratio"
            ));
            Ok(windv)
        }
    }
}

#[expect(clippy::too_many_arguments)]
fn two_winding_tap(
    l1: &[String],
    l3: &[String],
    l4: &[String],
    from: BusId,
    to: BusId,
    cw: i64,
    bus_base_kv: &BTreeMap<BusId, f64>,
    warnings: &mut Vec<String>,
) -> Result<f64> {
    let label = transformer_label(l1);
    let ratio1 = winding_ratio(l3, from, cw, bus_base_kv, &label, "winding 1", warnings)?;
    let ratio2 = winding_ratio(l4, to, cw, bus_base_kv, &label, "winding 2", warnings)?;
    if ratio2.abs() <= f64::EPSILON {
        warnings.push(format!(
            "PSS/E transformer {label}: winding 2 ratio is zero; used winding 1 ratio as the branch tap"
        ));
        Ok(ratio1)
    } else {
        Ok(ratio1 / ratio2)
    }
}

/// A terminator that also delimits a named section (`... END OF X DATA, BEGIN Y
/// DATA`), as opposed to the case header (whose first field is also `0`).
fn is_section_marker(line: &str) -> bool {
    if !is_terminator(line) {
        return false;
    }
    let u = line.to_ascii_uppercase();
    u.contains("END OF") || u.contains("BEGIN ") || u.contains("START OF ")
}

/// The upper-cased section name a `BEGIN <name> DATA` or `START OF <name> DATA`
/// marker introduces.
fn introduced_section_name(line: &str) -> Option<String> {
    let u = line.to_ascii_uppercase();
    let (start, prefix_len) = u
        .find("BEGIN ")
        .map(|idx| (idx, "BEGIN ".len()))
        .or_else(|| u.find("START OF ").map(|idx| (idx, "START OF ".len())))?;
    let start = start + prefix_len;
    let rest = &u[start..];
    let end = rest.find(" DATA")?;
    Some(rest[..end].trim().to_string())
}

/// Warn about non-empty PSS/E sections the reader does not model (VSC and
/// multi-terminal DC, impedance correction, substation/node, multi-section line,
/// induction machine, FACTS, GNE, owner/zone, ...). Counts come from the parser
/// pass itself, so bare `0` terminators and malformed continuation boundaries are
/// classified the same way as the records that get skipped.
fn warn_unmodeled_sections(totals: BTreeMap<String, usize>, warnings: &mut Vec<String>) {
    for (name, rows) in totals {
        warnings.push(format!(
            "PSS/E {name} section ({rows} record line(s)) is not modeled: preserved only in a \
             same-format .raw echo, dropped on any other write"
        ));
    }
}

fn drop_stale_control_pointers(net: &mut BalancedNetwork, warnings: &mut Vec<String>) {
    let bus_ids: BTreeSet<BusId> = net.buses.iter().map(|b| b.id).collect();
    let missing = |bus: BusId| !bus_ids.contains(&bus);

    for (idx, g) in net.generators.iter_mut().enumerate() {
        let Some(bus) = g.regulated_bus.filter(|b| missing(*b)) else {
            continue;
        };
        warnings.push(format!(
            "PSS/E GENERATOR DATA record {} at bus {}: IREG references missing bus id {}; dropped remote voltage control",
            idx + 1,
            g.bus,
            bus
        ));
        g.regulated_bus = None;
    }

    for (idx, br) in net.branches.iter_mut().enumerate() {
        let Some(control) = br.control.as_mut() else {
            continue;
        };
        let Some(bus) = control.controlled_bus.filter(|b| missing(*b)) else {
            continue;
        };
        warnings.push(format!(
            "PSS/E TRANSFORMER DATA record {} ({}-{}): CONT references missing bus id {}; dropped transformer control pointer",
            idx + 1,
            br.from,
            br.to,
            bus
        ));
        control.controlled_bus = None;
    }

    for (idx, shunt) in net.shunts.iter_mut().enumerate() {
        let Some(control) = shunt.control.as_mut() else {
            continue;
        };
        let Some(bus) = control.control_bus.filter(|b| missing(*b)) else {
            continue;
        };
        warnings.push(format!(
            "PSS/E SWITCHED SHUNT DATA record {} at bus {}: SWREM references missing bus id {}; dropped switched shunt control pointer",
            idx + 1,
            shunt.bus,
            bus
        ));
        control.control_bus = None;
    }

    for (idx, area) in net.areas.iter_mut().enumerate() {
        let Some(bus) = area.slack_bus.filter(|b| missing(*b)) else {
            continue;
        };
        warnings.push(format!(
            "PSS/E AREA DATA record {} area {}: ISW references missing bus id {}; dropped area swing pointer",
            idx + 1,
            area.number,
            bus
        ));
        area.slack_bus = None;
    }
}

fn is_comment(line: &str) -> bool {
    line.starts_with("@!") || line.starts_with('@')
}

fn is_system_wide_record(f: &[String]) -> bool {
    matches!(
        f.first().map(|s| s.to_ascii_uppercase()),
        Some(first) if matches!(first.as_str(), "GENERAL" | "RATING" | "NEWTON" | "SOLVER")
    )
}

/// Parse a v34+ system-wide keyword line (`GENERAL`/`NEWTON`/`SOLVER`, each a
/// keyword then `KEY=VALUE` tokens) into the solver record. Unrecognized
/// keywords (e.g. `RATING`) and keys are ignored.
fn parse_solver_line(f: &[String], solver: &mut SolverParams) {
    let Some(keyword) = f.first().map(|s| s.to_ascii_uppercase()) else {
        return;
    };
    for tok in &f[1..] {
        let Some((key, val)) = tok.split_once('=') else {
            continue;
        };
        let (key, val) = (key.trim().to_ascii_uppercase(), val.trim());
        match (keyword.as_str(), key.as_str()) {
            ("GENERAL", "THRSHZ") => solver.zero_impedance_threshold = val.parse().ok(),
            ("NEWTON", "TOLN") => solver.newton_tolerance = val.parse().ok(),
            ("NEWTON", "ITMXN") => solver.max_iterations = val.parse().ok(),
            ("SOLVER", "ACTAPS") => solver.adjust_taps = Some(parse_enable(val)),
            ("SOLVER", "AREAIN") => solver.adjust_area_interchange = Some(parse_enable(val)),
            ("SOLVER", "PHSHFT") => solver.adjust_phase_shift = Some(parse_enable(val)),
            ("SOLVER", "DCTAPS") => solver.adjust_dc_taps = Some(parse_enable(val)),
            ("SOLVER", "SWSHNT") => solver.adjust_switched_shunt = Some(parse_enable(val)),
            _ => {}
        }
    }
}

/// A `SOLVER` adjustment flag: numeric → nonzero is enabled; a keyword is enabled
/// unless it reads as off.
fn parse_enable(val: &str) -> bool {
    val.parse::<f64>().map_or_else(
        |_| !matches!(val.to_ascii_uppercase().as_str(), "DISABLED" | "OFF" | "NO"),
        |n| n != 0.0,
    )
}

/// Return the record body before an inline `/` comment, but only when the slash
/// is outside a single-quoted PSS/E field.
fn strip_inline_comment(line: &str) -> &str {
    let mut quoted = false;
    for (i, c) in line.char_indices() {
        match c {
            '\'' => quoted = !quoted,
            '/' if !quoted => return &line[..i],
            _ => {}
        }
    }
    line
}

/// Split a PSS/E record into trimmed, unquoted fields, dropping a trailing
/// `/comment`. Comma-delimited records keep empty fields (column position is
/// significant — a blank quoted name must not shift later columns); records with
/// no commas fall back to whitespace splitting.
fn fields(line: &str) -> Vec<String> {
    let code = strip_inline_comment(line);
    let comma_delimited = code.contains(',');
    // Size both buffers up front and keep `cur`'s capacity across fields.
    // Taking `cur` handed the buffer away, so every field regrew from empty
    // and then paid a second allocation to trim: two allocations and a
    // realloc chain per field, which dominated the cost of reading a `.raw`
    // (~950 allocations per KB of input).
    let mut out = Vec::with_capacity(if comma_delimited {
        code.bytes().filter(|b| *b == b',').count() + 1
    } else {
        8
    });
    let mut cur = String::with_capacity(32);
    let mut quoted = false;
    for c in code.chars() {
        match c {
            '\'' => quoted = !quoted,
            ',' if !quoted && comma_delimited => {
                out.push(cur.trim().to_owned());
                cur.clear();
            }
            c if c.is_whitespace() && !quoted && !comma_delimited => {
                if !cur.is_empty() {
                    out.push(cur.clone());
                    cur.clear();
                }
            }
            c => cur.push(c),
        }
    }
    let last = cur.trim().to_owned();
    if comma_delimited || !last.is_empty() {
        out.push(last);
    }
    out
}

fn bad_field(i: usize, tok: &str) -> Error {
    Error::FormatRead {
        format: FMT,
        message: format!("field {i} {tok:?} is not a number"),
    }
}

/// Field `i` as f64. Absent or empty → `default` (a genuinely optional column).
/// Present but unparseable → a hard error: a malformed number must not silently
/// become a plausible default (e.g. a garbled reactance collapsing to 0.0, which
/// would drop the branch from every matrix) and corrupt the result.
fn num_at(f: &[String], i: usize, default: f64) -> Result<f64> {
    match f.get(i).map(String::as_str) {
        None | Some("") => Ok(default),
        Some(s) => s.parse().map_err(|_| bad_field(i, s)),
    }
}
/// Field `i` as a bus id (parsed as f64 then truncated, the PSS/E convention).
fn id_at(f: &[String], i: usize, default: usize) -> Result<usize> {
    match f.get(i).map(String::as_str) {
        None | Some("") => Ok(default),
        #[allow(clippy::cast_possible_truncation, clippy::cast_sign_loss)]
        Some(s) => s
            .parse::<f64>()
            .map(|v| v as usize)
            .map_err(|_| bad_field(i, s)),
    }
}
/// Field `i` as a status flag (nonzero = in service).
fn on_at(f: &[String], i: usize, default: bool) -> Result<bool> {
    match f.get(i).map(String::as_str) {
        None | Some("") => Ok(default),
        Some(s) => s
            .parse::<f64>()
            .map(|v| v != 0.0)
            .map_err(|_| bad_field(i, s)),
    }
}
/// Field `i` as an integer code (bus type, etc.).
fn int_at(f: &[String], i: usize, default: i64) -> Result<i64> {
    match f.get(i).map(String::as_str) {
        None | Some("") => Ok(default),
        // v34/35 exporters write integer fields in float form (`0.00` for `0`), so
        // parse through f64 and truncate, the way `id_at` already does.
        #[allow(clippy::cast_possible_truncation)]
        Some(s) => s
            .parse::<f64>()
            .map(|v| v as i64)
            .map_err(|_| bad_field(i, s)),
    }
}

fn bustype(code: i64) -> BusType {
    match code {
        2 => BusType::Pv,
        3 => BusType::Ref,
        4 => BusType::Isolated,
        _ => BusType::Pq,
    }
}

// The EVHI/EVLO equality below is an exact compare on purpose: the emergency
// band is typed only when its token differs from the normal-band token.
#[allow(clippy::float_cmp)]
fn read_bus(f: &[String]) -> Result<Bus> {
    // I, NAME, BASKV, IDE, AREA, ZONE, OWNER, VM, VA, NVHI, NVLO, EVHI, EVLO
    let id = f
        .first()
        .and_then(|x| x.parse::<f64>().ok())
        .ok_or_else(|| Error::FormatRead {
            format: FMT,
            message: "bus record missing numeric id (field I)".into(),
        })? as usize;
    let name = f
        .get(1)
        .filter(|n| !n.is_empty())
        .map(|n| n.trim().to_string());
    let vmax = num_at(f, 9, 1.1)?;
    let vmin = num_at(f, 10, 0.9)?;
    // EVHI/EVLO (v31+); default to the normal band when absent. Keep them typed
    // only when they actually differ, so the common equal-band case stays `None`.
    let evhi = num_at(f, 11, vmax)?;
    let evlo = num_at(f, 12, vmin)?;
    Ok(Bus {
        id: BusId(id),
        kind: bustype(int_at(f, 3, 1)?),
        vm: num_at(f, 7, 1.0)?,
        va: num_at(f, 8, 0.0)?,
        base_kv: num_at(f, 2, 0.0)?,
        vmax,
        vmin,
        evhi: (evhi != vmax).then_some(evhi),
        evlo: (evlo != vmin).then_some(evlo),
        area: id_at(f, 4, 0)?,
        zone: id_at(f, 5, 0)?,
        name,
        uid: None,
        location: None,
        extras: Extras::new(),
    })
}

/// Capture an element's circuit id (field `i`, a quoted 1-2 char string) into its
/// extras under `"id"`, so a round trip keeps the id and parallel devices on a bus
/// stay distinguishable.
fn device_extras(f: &[String], i: usize) -> Extras {
    let mut extras = Extras::new();
    if let Some(id) = f.get(i).map(|s| s.trim()).filter(|s| !s.is_empty()) {
        extras.insert("id".into(), Value::String(id.to_string()));
    }
    extras
}

fn read_load(f: &[String], raw_rev: u32, warnings: &mut Vec<String>) -> Result<Load> {
    // I, ID, STATUS, AREA, ZONE, PL, QL, ...
    let bus = id_at(f, 0, 0)?;
    let id = f.get(1).map_or("", |s| s.trim());
    let pl = num_at(f, 5, 0.0)?;
    let ql = num_at(f, 6, 0.0)?;
    let ip = num_at(f, 7, 0.0)?;
    let iq = num_at(f, 8, 0.0)?;
    let yp = num_at(f, 9, 0.0)?;
    let yq = num_at(f, 10, 0.0)?;
    let mut extras = device_extras(f, 1);
    for (key, value) in [
        ("psse_pl", pl),
        ("psse_ql", ql),
        ("psse_ip", ip),
        ("psse_iq", iq),
        ("psse_yp", yp),
        ("psse_yq", yq),
    ] {
        extras.insert(key.into(), jnum(value));
    }
    for (field, key, default) in [
        (11, "psse_owner", 1_i64),
        (12, "psse_scal", 1_i64),
        (13, "psse_intrpt", 0_i64),
    ] {
        let value = int_at(f, field, default)?;
        if value != default {
            extras.insert(key.into(), Value::from(value));
        }
    }
    if raw_rev >= 34 {
        for (field, key) in [(14, "psse_pdgen"), (15, "psse_qdgen")] {
            let value = num_at(f, field, 0.0)?;
            if value != 0.0 {
                extras.insert(key.into(), jnum(value));
            }
        }
        let flag = int_at(f, 16, 0)?;
        if flag != 0 {
            extras.insert("psse_flagstatus".into(), Value::from(flag));
        }
    }
    if raw_rev >= 35 {
        if let Some(loadtype) = f.get(17).map(|s| s.trim()).filter(|s| !s.is_empty()) {
            extras.insert("psse_loadtype".into(), Value::String(loadtype.to_string()));
        }
    }
    let scal = int_at(f, 12, 1)?;
    let load_type = f.get(17).and_then(|s| s.trim().parse::<i32>().ok());
    let has_zip_components = [ip, iq, yp, yq].iter().any(|v| *v != 0.0);
    let voltage_model =
        (has_zip_components || scal != 1 || load_type.is_some()).then_some(LoadVoltageModel::Zip {
            p_constant_power: pl,
            q_constant_power: ql,
            p_constant_current: ip,
            q_constant_current: iq,
            p_constant_impedance: yp,
            q_constant_impedance: yq,
            v_nom: None,
            load_type,
            scaling: (scal != 1).then_some(scal as f64),
        });
    let has_load_options = extras.contains_key("psse_intrpt")
        || extras.contains_key("psse_pdgen")
        || extras.contains_key("psse_qdgen")
        || extras.contains_key("psse_flagstatus");
    if has_load_options {
        warnings.push(format!(
            "PSS/E load at bus {bus} id {id:?}: interruptible/DG/flag fields are retained in extras"
        ));
    }
    Ok(Load {
        bus: BusId(bus),
        p: pl + ip + yp,
        q: ql + iq + yq,
        voltage_model,
        in_service: on_at(f, 2, true)?,
        uid: None,
        extras,
    })
}

fn read_shunt(f: &[String]) -> Result<Shunt> {
    // I, ID, STATUS, GL, BL
    Ok(Shunt {
        bus: BusId(id_at(f, 0, 0)?),
        g: num_at(f, 3, 0.0)?,
        b: num_at(f, 4, 0.0)?,
        in_service: on_at(f, 2, true)?,
        control: None,
        uid: None,
        extras: device_extras(f, 1),
    })
}

fn read_switched_shunt(f: &[String], rev: u32) -> Result<Shunt> {
    // v33/34: I, MODSW, ADJM, STAT, VSWHI, VSWLO, SWREM, RMPCT, RMIDNT, BINIT(9),
    // then (Ni, Bi) step pairs. v35: I, ID, MODSW, ADJM, ST, VSWHI, VSWLO,
    // SWREG, NREG, RMPCT, RMIDNT, BINIT(11), then (Si, Ni, Bi) triples — the ID
    // shifts everything by one and NREG shifts the fields after SWREG by another.
    // BINIT becomes the shunt `b` (gs = 0); the mode, voltage band, regulated
    // bus, RMPCT, and step blocks ride on the switching-control record.
    let o = usize::from(rev >= 35);
    let o2 = 2 * o;
    let bus = id_at(f, 0, 0)?;
    let swrem = id_at(f, 6 + o, 0)?;
    // Step blocks follow BINIT; stop at the first empty (padding) block or the
    // end of the record. The v35 per-block status Si leads each triple; the
    // neutral ShuntBlock carries no block status, so keep the block either way.
    let mut blocks = Vec::new();
    let mut i = 10 + o2;
    let stride = 2 + o;
    while i + stride <= f.len() {
        let steps = int_at(f, i + o, 0)?;
        let b = num_at(f, i + o + 1, 0.0)?;
        if steps == 0 && b == 0.0 {
            break;
        }
        blocks.push(ShuntBlock {
            steps: steps.clamp(0, i64::from(u32::MAX)) as u32,
            b,
        });
        i += stride;
    }
    let control = SwitchedShuntControl {
        mode: modsw_to_mode(int_at(f, 1 + o, 1)?),
        vhigh: num_at(f, 4 + o, 0.0)?,
        vlow: num_at(f, 5 + o, 0.0)?,
        control_bus: (swrem != 0 && swrem != bus).then_some(BusId(swrem)),
        rmpct: num_at(f, 7 + o2, 100.0)?,
        blocks,
    };
    Ok(Shunt {
        bus: BusId(bus),
        g: 0.0,
        b: num_at(f, 9 + o2, 0.0)?,
        in_service: on_at(f, 3 + o, true)?,
        control: Some(control),
        uid: None,
        // Keep the v35 shunt ID so it survives a round trip.
        extras: if rev >= 35 {
            device_extras(f, 1)
        } else {
            Extras::new()
        },
    })
}

/// PSS/E `MODSW` switched-shunt mode code → neutral mode.
fn modsw_to_mode(modsw: i64) -> SwitchedShuntMode {
    match modsw {
        0 => SwitchedShuntMode::Locked,
        1 => SwitchedShuntMode::Continuous,
        _ => SwitchedShuntMode::Discrete,
    }
}

/// Neutral switched-shunt mode → PSS/E `MODSW` (the 0/1/2 codes; modes beyond
/// discrete collapse to 2).
fn mode_to_modsw(mode: SwitchedShuntMode) -> i64 {
    match mode {
        SwitchedShuntMode::Locked => 0,
        SwitchedShuntMode::Continuous => 1,
        SwitchedShuntMode::Discrete => 2,
    }
}

fn read_area(f: &[String]) -> Result<Area> {
    // I, ISW, PDES, PTOL, 'ARNAME'
    let isw = id_at(f, 1, 0)?;
    Ok(Area {
        number: id_at(f, 0, 0)?,
        slack_bus: (isw != 0).then_some(BusId(isw)),
        net_interchange: num_at(f, 2, 0.0)?,
        tolerance: num_at(f, 3, 0.0)?,
        name: f
            .get(4)
            .filter(|n| !n.trim().is_empty())
            .map(|n| n.trim().to_string()),
    })
}

fn read_gen(f: &[String], raw_rev: u32) -> Result<Generator> {
    // v33/34: I, ID, PG, QG, QT, QB, VS, IREG, MBASE(8), ..., STAT(14), ...,
    // PT(16), PB(17). v35 inserts NREG after IREG (and BASLOD after PB),
    // shifting MBASE through PB by one; v34 keeps the v33 layout.
    let o = usize::from(raw_rev >= 35);
    let bus = id_at(f, 0, 0)?;
    // IREG names a remote regulated bus; 0 (or the generator's own bus) means it
    // regulates its own terminal, which the neutral model leaves as `None`.
    let ireg = id_at(f, 7, 0)?;
    Ok(Generator {
        bus: BusId(bus),
        pg: num_at(f, 2, 0.0)?,
        qg: num_at(f, 3, 0.0)?,
        qmax: num_at(f, 4, 0.0)?,
        qmin: num_at(f, 5, 0.0)?,
        vg: num_at(f, 6, 1.0)?,
        mbase: num_at(f, 8 + o, 100.0)?,
        in_service: on_at(f, 14 + o, true)?,
        pmax: num_at(f, 16 + o, 0.0)?,
        pmin: num_at(f, 17 + o, 0.0)?,
        cost: None,
        caps: Default::default(),
        regulated_bus: (ireg != 0 && ireg != bus).then_some(BusId(ireg)),
        uid: None,
    })
}

fn read_branch(f: &[String], raw_rev: u32) -> Result<Branch> {
    // v33: I, J, CKT, R, X, B, RATEA, RATEB, RATEC, GI,BI,GJ,BJ, ST(13)
    // v34 exports insert NAME before twelve rating columns, putting STAT after
    // GI/BI/GJ/BJ. v33 can still have a long owner/fraction tail, so the RAW
    // revision, not RATEA parseability, decides the long named layout.
    let named_record = raw_rev >= 34 && f.len() >= 24;
    let rating = if named_record { 7 } else { 6 };
    let status = if named_record { 23 } else { 13 };
    let shunt = if named_record { 19 } else { 9 };
    let br_b = num_at(f, 5, 0.0)?;
    let g_fr = num_at(f, shunt, 0.0)?;
    let b_fr_extra = num_at(f, shunt + 1, 0.0)?;
    let g_to = num_at(f, shunt + 2, 0.0)?;
    let b_to_extra = num_at(f, shunt + 3, 0.0)?;
    let b_fr = br_b / 2.0 + b_fr_extra;
    let b_to = br_b / 2.0 + b_to_extra;
    Ok(Branch {
        from: BusId(id_at(f, 0, 0)?),
        to: BusId(id_at(f, 1, 0)?),
        r: num_at(f, 3, 0.0)?,
        x: num_at(f, 4, 0.0)?,
        b: b_fr + b_to,
        charging: Some(BranchCharging {
            g_fr,
            b_fr,
            g_to,
            b_to,
        }),
        rate_a: num_at(f, rating, 0.0)?,
        rate_b: num_at(f, rating + 1, 0.0)?,
        rate_c: num_at(f, rating + 2, 0.0)?,
        rating_sets: read_extra_branch_ratings(f, rating, named_record)?,
        current_ratings: None,
        tap: 0.0,
        shift: 0.0,
        in_service: on_at(f, status, true)?,
        angmin: -360.0,
        angmax: 360.0,
        control: None,
        solution: None,
        uid: None,
        route: None,
        // Capture CKT (field 2) so parallel circuits stay distinct on write-back.
        extras: device_extras(f, 2),
    })
}

#[expect(clippy::too_many_arguments)]
fn read_transformer(
    l1: &[String],
    l2: &[String],
    l3: &[String],
    l4: &[String],
    raw_rev: u32,
    system_base: f64,
    bus_base_kv: &BTreeMap<BusId, f64>,
    warnings: &mut Vec<String>,
) -> Result<Branch> {
    // l1: I, J, K, CKT, CW, CZ, CM, MAG1, MAG2, NMETR, NAME, STAT(11)
    // l2: R1-2, X1-2, SBASE1-2
    // l3 at v33: WINDV1, NOMV1, ANG1, RATA1, RATB1, RATC1, COD1(6), CONT1,
    //     RMA1, RMI1, VMA1, VMI1, NTP1(12), ...
    // v34/35 widen the winding line to twelve ratings (RATE1..3 succeed
    // RATA/B/C in place) and insert NODE after CONT: COD1 lands at 15, CONT1
    // at 16, and RMA1..NTP1 at 18..22.
    // A nonzero control code COD1 marks a regulating winding; capture its limits
    // and regulated bus, else leave the branch's control unset.
    let (cw, cz) = transformer_basis_codes(l1)?;
    let from = BusId(id_at(l1, 0, 0)?);
    let to = BusId(id_at(l1, 1, 0)?);
    let sbase = num_at(l2, 2, system_base)?;
    let label = transformer_label(l1);
    let (r, x) = convert_transformer_impedance(
        num_at(l2, 0, 0.0)?,
        num_at(l2, 1, 0.0)?,
        sbase,
        system_base,
        cz,
        &label,
        "1-2",
        warnings,
    );
    let tap = two_winding_tap(l1, l3, l4, from, to, cw, bus_base_kv, warnings)?;
    let modern = raw_rev >= 34;
    let (cod_i, cont_i, rma_i) = if modern { (15, 16, 18) } else { (6, 7, 8) };
    let cod = int_at(l3, cod_i, 0)?;
    let control = (cod != 0)
        .then(|| -> Result<TransformerControl> {
            let cont = id_at(l3, cont_i, 0)?;
            Ok(TransformerControl {
                mode: cod_to_mode(cod),
                controlled_bus: (cont != 0).then_some(BusId(cont)),
                tap_max: num_at(l3, rma_i, 1.1)?,
                tap_min: num_at(l3, rma_i + 1, 0.9)?,
                band_max: num_at(l3, rma_i + 2, 1.1)?,
                band_min: num_at(l3, rma_i + 3, 0.9)?,
                ntp: int_at(l3, rma_i + 4, 33)?.clamp(0, i64::from(u32::MAX)) as u32,
                mva_base: sbase,
            })
        })
        .transpose()?;
    let mag_g = if int_at(l1, 6, 1)? == 1 {
        num_at(l1, 7, 0.0)?
    } else {
        0.0
    };
    let mag_b = if int_at(l1, 6, 1)? == 1 {
        num_at(l1, 8, 0.0)?
    } else {
        0.0
    };
    Ok(Branch {
        from,
        to,
        r,
        x,
        b: mag_b,
        charging: Some(BranchCharging {
            g_fr: mag_g,
            b_fr: mag_b,
            g_to: 0.0,
            b_to: 0.0,
        }),
        rate_a: num_at(l3, 3, 0.0)?,
        rate_b: num_at(l3, 4, 0.0)?,
        rate_c: num_at(l3, 5, 0.0)?,
        rating_sets: read_extra_branch_ratings(l3, 3, modern)?,
        current_ratings: None,
        tap,
        shift: num_at(l3, 2, 0.0)?,
        in_service: on_at(l1, 11, true)?,
        angmin: -360.0,
        angmax: 360.0,
        control,
        solution: None,
        uid: None,
        route: None,
        extras: Extras::new(),
    })
}

/// PSS/E transformer control code `COD` → neutral control mode. The sign encodes
/// an enable/disable flag PSS/E carries separately; only the magnitude selects
/// the regulation kind.
fn cod_to_mode(cod: i64) -> TransformerControlMode {
    // `int_at` parses through f64 and saturates, so an extreme COD field can
    // reach i64::MIN, whose magnitude exceeds i64::MAX; `cod.abs()` would
    // overflow (panic under overflow checks). unsigned_abs never overflows,
    // and only the small magnitudes 1..=3 select a nonfixed mode anyway.
    match cod.unsigned_abs() {
        1 => TransformerControlMode::Voltage,
        2 => TransformerControlMode::ReactiveFlow,
        3 => TransformerControlMode::ActiveFlow,
        _ => TransformerControlMode::Fixed,
    }
}

/// Neutral control mode → PSS/E `COD` (positive; the enable-flag sign is not modeled).
fn mode_to_cod(mode: TransformerControlMode) -> i64 {
    match mode {
        TransformerControlMode::Fixed => 0,
        TransformerControlMode::Voltage => 1,
        TransformerControlMode::ReactiveFlow => 2,
        TransformerControlMode::ActiveFlow => 3,
    }
}

/// Read a 5-line 3-winding transformer record into a [`Transformer3W`].
#[expect(clippy::too_many_arguments)]
fn read_transformer_3w(
    l1: &[String],
    l2: &[String],
    l3: &[String],
    l4: &[String],
    l5: &[String],
    system_base: f64,
    bus_base_kv: &BTreeMap<BusId, f64>,
    warnings: &mut Vec<String>,
) -> Result<Transformer3W> {
    // l1: I, J, K, CKT, CW, CZ, CM, MAG1, MAG2, NMETR, NAME, STAT(11)
    // l2: R1-2,X1-2,SBASE1-2, R2-3,X2-3,SBASE2-3, R3-1,X3-1,SBASE3-1, VMSTAR, ANSTAR
    // l3/l4/l5: WINDVk, NOMVk, ANGk, RATAk, RATBk, RATCk, ...
    let (cw, cz) = transformer_basis_codes(l1)?;
    let label = transformer_label(l1);
    let buses = [
        BusId(id_at(l1, 0, 0)?),
        BusId(id_at(l1, 1, 0)?),
        BusId(id_at(l1, 2, 0)?),
    ];
    let z = {
        let mut imp = |off: usize, pair: &str| -> Result<Impedance> {
            let sbase = num_at(l2, off + 2, system_base)?;
            let (r, x) = convert_transformer_impedance(
                num_at(l2, off, 0.0)?,
                num_at(l2, off + 1, 0.0)?,
                sbase,
                system_base,
                cz,
                &label,
                pair,
                warnings,
            );
            Ok(Impedance {
                r,
                x,
                base_mva: sbase,
            })
        };
        [imp(0, "1-2")?, imp(3, "2-3")?, imp(6, "3-1")?]
    };
    let windings = {
        let mut winding = |idx: usize, w: &[String]| -> Result<Winding> {
            let bus = buses[idx];
            let tap = winding_ratio(
                w,
                bus,
                cw,
                bus_base_kv,
                &label,
                match idx {
                    0 => "winding 1",
                    1 => "winding 2",
                    _ => "winding 3",
                },
                warnings,
            )?;
            Ok(Winding {
                bus,
                tap,
                shift: num_at(w, 2, 0.0)?,
                nominal_kv: num_at(w, 1, 0.0)?,
                rate_a: num_at(w, 3, 0.0)?,
                rate_b: num_at(w, 4, 0.0)?,
                rate_c: num_at(w, 5, 0.0)?,
            })
        };
        [winding(0, l3)?, winding(1, l4)?, winding(2, l5)?]
    };
    Ok(Transformer3W {
        windings,
        z,
        star_vm: num_at(l2, 9, 1.0)?,
        star_va: num_at(l2, 10, 0.0)?,
        mag_g: num_at(l1, 7, 0.0)?,
        mag_b: num_at(l1, 8, 0.0)?,
        // STAT 0 = out of service; 1-4 mark which windings are in service. Treat
        // any nonzero status as the transformer being in service.
        in_service: int_at(l1, 11, 1)? != 0,
        name: l1
            .get(10)
            .filter(|n| !n.is_empty())
            .map(|n| n.trim().to_string()),
        uid: None,
        extras: Extras::new(),
    })
}

/// Read a 3-line two-terminal DC line record into an [`Hvdc`].
///
/// The control line `l1` gives the operating mode (`MDC`), the DC line resistance
/// (`RDC`), the power/current demand (`SETVL`), and the scheduled DC voltage
/// (`VSCHD`). The rectifier and inverter lines' first field is the AC terminal
/// bus, which becomes the HVDC from/to. The HVDC is read as a power-setpoint
/// model (`pf = pt = SETVL`, no reactive output); the converter detail beyond the
/// buses (firing angles, converter transformer taps) is retained in extras for a
/// faithful write-back, not modeled electrically.
fn read_dc_line(l1: &[String], rect: &[String], inv: &[String]) -> Result<Hvdc> {
    let mdc = int_at(l1, 1, 1)?;
    let rdc = num_at(l1, 2, 0.0)?;
    let setvl = num_at(l1, 3, 0.0)?;
    let vschd = num_at(l1, 4, 0.0)?;
    let mut extras = Extras::new();
    if let Some(name) = l1.first().filter(|n| !n.is_empty()) {
        extras.insert("psse_dc_name".into(), Value::String(name.clone()));
    }
    extras.insert("psse_dc_mdc".into(), Value::from(mdc));
    extras.insert("psse_dc_rdc".into(), jnum(rdc));
    extras.insert("psse_dc_vschd".into(), jnum(vschd));
    extras.insert("psse_dc_control_tail".into(), tail_array(l1, 5));
    extras.insert("psse_dc_rectifier_tail".into(), tail_array(rect, 1));
    extras.insert("psse_dc_inverter_tail".into(), tail_array(inv, 1));
    Ok(Hvdc {
        from: BusId(id_at(rect, 0, 0)?),
        to: BusId(id_at(inv, 0, 0)?),
        in_service: mdc != 0,
        pf: setvl,
        pt: setvl,
        qf: 0.0,
        qt: 0.0,
        vf: 1.0,
        vt: 1.0,
        pmin: 0.0,
        pmax: setvl.abs(),
        qminf: 0.0,
        qmaxf: 0.0,
        qmint: 0.0,
        qmaxt: 0.0,
        loss0: 0.0,
        loss1: 0.0,
        cost: None,
        uid: None,
        extras,
    })
}

/// The fields of `f` from index `start` as a JSON string array (for extras).
fn tail_array(f: &[String], start: usize) -> Value {
    Value::Array(
        f.iter()
            .skip(start)
            .map(|s| Value::String(s.clone()))
            .collect(),
    )
}

/// A string-valued DC extra.
fn dc_str(extras: &Extras, key: &str) -> Option<String> {
    extras.get(key).and_then(Value::as_str).map(str::to_owned)
}

/// An integer-valued DC extra.
fn dc_int(extras: &Extras, key: &str) -> Option<i64> {
    extras.get(key).and_then(Value::as_i64)
}

/// A float-valued DC extra.
fn dc_f64(extras: &Extras, key: &str) -> Option<f64> {
    extras.get(key).and_then(Value::as_f64)
}

/// A finite float extra carried by a read side passthrough field.
fn extra_f64(extras: &Extras, key: &str) -> Option<f64> {
    extras
        .get(key)
        .and_then(Value::as_f64)
        .filter(|v| v.is_finite())
}

/// An integer extra carried by a read side passthrough field.
fn extra_i64(extras: &Extras, key: &str) -> Option<i64> {
    extras.get(key).and_then(Value::as_i64)
}

fn same_load_total(a: f64, b: f64) -> bool {
    (a - b).abs() <= 1e-9 * a.abs().max(b.abs()).max(1.0)
}

fn typed_psse_scal(l: &Load, id: &str, warnings: &mut Vec<String>) -> Option<i64> {
    let Some(LoadVoltageModel::Zip {
        scaling: Some(scaling),
        ..
    }) = &l.voltage_model
    else {
        return None;
    };
    let scaling = *scaling;
    if !scaling.is_finite() {
        warnings.push(format!(
            "PSS/E load at bus {} id {id:?}: non-finite typed scaling has no SCAL value; used source/default SCAL",
            l.bus
        ));
        return None;
    }
    let rounded = scaling.round();
    if (scaling - rounded).abs() > 1e-9 || rounded < i64::MIN as f64 || rounded > i64::MAX as f64 {
        warnings.push(format!(
            "PSS/E load at bus {} id {id:?}: non-integer typed scaling {scaling} has no SCAL value; used source/default SCAL",
            l.bus
        ));
        return None;
    }
    Some(rounded as i64)
}

fn typed_psse_load_type(model: &LoadVoltageModel) -> Option<String> {
    match model {
        LoadVoltageModel::Zip {
            load_type: Some(load_type),
            ..
        } => Some(load_type.to_string()),
        _ => None,
    }
}

fn load_components_for_write(
    l: &Load,
    id: &str,
    warnings: &mut Vec<String>,
) -> (f64, f64, f64, f64, f64, f64) {
    if let Some(LoadVoltageModel::Zip {
        p_constant_power,
        q_constant_power,
        p_constant_current,
        q_constant_current,
        p_constant_impedance,
        q_constant_impedance,
        v_nom,
        ..
    }) = &l.voltage_model
    {
        if same_load_total(
            p_constant_power + p_constant_current + p_constant_impedance,
            l.p,
        ) && same_load_total(
            q_constant_power + q_constant_current + q_constant_impedance,
            l.q,
        ) {
            if v_nom.is_some() {
                warnings.push(format!(
                    "PSS/E load at bus {} id {id:?}: nominal voltage has no load record field; dropped",
                    l.bus
                ));
            }
            return (
                *p_constant_power,
                *q_constant_power,
                *p_constant_current,
                *q_constant_current,
                *p_constant_impedance,
                *q_constant_impedance,
            );
        }
        warnings.push(format!(
            "PSS/E load at bus {} id {id:?}: stale voltage model components did not match \
             typed p/q; wrote typed p/q as constant power",
            l.bus
        ));
        return (l.p, l.q, 0.0, 0.0, 0.0, 0.0);
    }
    if matches!(l.voltage_model, Some(LoadVoltageModel::Exponential { .. })) {
        warnings.push(format!(
            "PSS/E load at bus {} id {id:?}: exponential voltage model has no load record fields; wrote typed p/q as constant power",
            l.bus
        ));
        return (l.p, l.q, 0.0, 0.0, 0.0, 0.0);
    }

    let pl = extra_f64(&l.extras, "psse_pl").unwrap_or(l.p);
    let ql = extra_f64(&l.extras, "psse_ql").unwrap_or(l.q);
    let ip = extra_f64(&l.extras, "psse_ip").unwrap_or(0.0);
    let iq = extra_f64(&l.extras, "psse_iq").unwrap_or(0.0);
    let yp = extra_f64(&l.extras, "psse_yp").unwrap_or(0.0);
    let yq = extra_f64(&l.extras, "psse_yq").unwrap_or(0.0);
    let has_components = [
        "psse_pl", "psse_ql", "psse_ip", "psse_iq", "psse_yp", "psse_yq",
    ]
    .iter()
    .any(|key| l.extras.contains_key(*key));
    if has_components
        && (!same_load_total(pl + ip + yp, l.p) || !same_load_total(ql + iq + yq, l.q))
    {
        warnings.push(format!(
            "PSS/E load at bus {} id {id:?}: stale PL/QL/IP/IQ/YP/YQ extras did not match \
             typed p/q; wrote typed p/q as constant power",
            l.bus
        ));
        (l.p, l.q, 0.0, 0.0, 0.0, 0.0)
    } else {
        (pl, ql, ip, iq, yp, yq)
    }
}

/// A retained converter-line tail joined back into a record fragment, or
/// `default` when the element carries none (a cross-format source).
fn dc_tail(extras: &Extras, key: &str, default: &str) -> String {
    match extras.get(key).and_then(Value::as_array) {
        Some(arr) if !arr.is_empty() => arr
            .iter()
            .filter_map(Value::as_str)
            // These come from a source file's `extras` and are replayed into
            // a record, so they go through the quoting seam like every other
            // interpolated string: a terminator here would forge a whole DC
            // record or a section end.
            .map(|f| sanitize_quoted(f, NAME_FORBIDDEN, ' ').into_owned())
            .collect::<Vec<_>>()
            .join(", "),
        _ => default.to_string(),
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    fn close(actual: f64, expected: f64) {
        assert!((actual - expected).abs() < 1e-12, "{actual} != {expected}");
    }

    #[test]
    fn extreme_transformer_cod_does_not_overflow() {
        // `int_at` parses COD through f64 and saturates, so `-1e300` becomes
        // i64::MIN; the old `cod.abs()` would overflow (panic under overflow
        // checks). The field decodes to Fixed instead.
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / synthetic
CASE
COMMENT
1,'BUS1        ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
2,'BUS2        ', 115.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
1,2,0,'1 ',2,2,1,0,0,1,'xf',1
0.01,0.10,50.0
241.5,230.0,0.0,100.0,90.0,80.0,-1e300,0,1.1,0.9,1.1,0.9,33
115.0,115.0
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
";
        let parsed = crate::parse_str(raw, "psse").unwrap();
        let control = parsed.network.branches[0].control.as_ref().unwrap();
        assert_eq!(control.mode, TransformerControlMode::Fixed);
    }

    fn test_bus(id: usize, kind: BusType) -> Bus {
        Bus {
            id: BusId(id),
            kind,
            vm: 1.0,
            va: 0.0,
            base_kv: 230.0,
            vmax: 1.1,
            vmin: 0.9,
            evhi: None,
            evlo: None,
            area: 1,
            zone: 1,
            name: None,
            uid: None,
            location: None,
            extras: Extras::default(),
        }
    }

    fn branch_with_terminal_charging() -> Branch {
        Branch {
            from: BusId(1),
            to: BusId(2),
            r: 0.01,
            x: 0.1,
            b: 0.0,
            charging: Some(BranchCharging {
                g_fr: 0.01,
                b_fr: 0.02,
                g_to: 0.03,
                b_to: 0.05,
            }),
            rate_a: 100.0,
            rate_b: 110.0,
            rate_c: 120.0,
            rating_sets: Vec::new(),
            current_ratings: None,
            tap: 0.0,
            shift: 0.0,
            in_service: true,
            angmin: -360.0,
            angmax: 360.0,
            control: None,
            solution: None,
            uid: None,
            route: None,
            extras: Extras::default(),
        }
    }

    fn transformer_with_terminal_charging(charging: BranchCharging) -> Branch {
        Branch {
            from: BusId(1),
            to: BusId(2),
            r: 0.01,
            x: 0.1,
            b: 0.0,
            charging: Some(charging),
            rate_a: 100.0,
            rate_b: 110.0,
            rate_c: 120.0,
            rating_sets: Vec::new(),
            current_ratings: None,
            tap: 1.05,
            shift: 0.0,
            in_service: true,
            angmin: -360.0,
            angmax: 360.0,
            control: None,
            solution: None,
            uid: None,
            route: None,
            extras: Extras::default(),
        }
    }

    fn assert_terminal_charging_round_trip(text: &str) {
        let back = parse_psse(text).unwrap();
        let charging = back.branches[0].terminal_charging();
        close(charging.g_fr, 0.01);
        close(charging.b_fr, 0.02);
        close(charging.g_to, 0.03);
        close(charging.b_to, 0.05);
        close(back.branches[0].b, 0.07);
    }

    #[test]
    fn branch_terminal_charging_writes_gi_bi_gj_bj() {
        let mut net = BalancedNetwork::in_memory(
            "terminal-shunts",
            100.0,
            vec![test_bus(1, BusType::Ref), test_bus(2, BusType::Pq)],
            Vec::new(),
        );
        net.branches.push(branch_with_terminal_charging());

        let rev33 = write_psse(&net);
        assert!(rev33.warnings.is_empty(), "{:?}", rev33.warnings);
        assert_terminal_charging_round_trip(&rev33.text);

        let rev35 = write_psse_rev(&net, 35);
        assert!(rev35.warnings.is_empty(), "{:?}", rev35.warnings);
        assert_terminal_charging_round_trip(&rev35.text);
    }

    #[test]
    fn transformer_magnetizing_admittance_writes_mag1_mag2() {
        let mut net = BalancedNetwork::in_memory(
            "xfmr-mag",
            100.0,
            vec![test_bus(1, BusType::Ref), test_bus(2, BusType::Pq)],
            Vec::new(),
        );
        net.branches
            .push(transformer_with_terminal_charging(BranchCharging {
                g_fr: 0.01,
                b_fr: 0.02,
                g_to: 0.0,
                b_to: 0.0,
            }));

        let conv = write_psse(&net);
        assert!(
            !conv
                .warnings
                .iter()
                .any(|w| w.contains("magnetizing admittance")),
            "{:?}",
            conv.warnings
        );
        let back = parse_psse(&conv.text).unwrap();
        let charging = back.branches[0].terminal_charging();
        close(charging.g_fr, 0.01);
        close(charging.b_fr, 0.02);
        close(charging.g_to, 0.0);
        close(charging.b_to, 0.0);
        close(back.branches[0].b, 0.02);
    }

    #[test]
    fn transformer_to_side_terminal_admittance_warns_and_collapses_to_mag() {
        let mut net = BalancedNetwork::in_memory(
            "xfmr-mag-collapse",
            100.0,
            vec![test_bus(1, BusType::Ref), test_bus(2, BusType::Pq)],
            Vec::new(),
        );
        net.branches
            .push(transformer_with_terminal_charging(BranchCharging {
                g_fr: 0.01,
                b_fr: 0.02,
                g_to: 0.03,
                b_to: 0.05,
            }));

        let conv = write_psse(&net);
        assert!(
            conv.warnings
                .iter()
                .any(|w| w.contains("magnetizing admittance")),
            "{:?}",
            conv.warnings
        );
        let back = parse_psse(&conv.text).unwrap();
        let charging = back.branches[0].terminal_charging();
        close(charging.g_fr, 0.04);
        close(charging.b_fr, 0.07);
        close(charging.g_to, 0.0);
        close(charging.b_to, 0.0);
        close(back.branches[0].b, 0.07);
    }

    #[test]
    fn slash_inside_a_quoted_field_is_not_a_comment() {
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / synthetic
CASE
COMMENT
1,'A/B         ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
Q
";

        let net = parse_psse(raw).unwrap();

        assert_eq!(net.buses.len(), 1);
        assert_eq!(net.buses[0].name.as_deref(), Some("A/B"));
    }

    #[test]
    fn load_zip_components_are_typed_and_round_trip() {
        let raw = r"0, 100.00, 35, 0, 1, 60.00 / synthetic
CASE
COMMENT
0 / END OF SYSTEM-WIDE DATA, BEGIN BUS DATA
1,'BUS1        ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
2,'BUS2        ', 230.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
2,'L1',1,1,1,10.0,3.0,1.0,0.5,2.0,1.5,1,0,1,4.0,2.0,1,'industrial'
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
Q
";
        let mut warnings = Vec::new();
        let net =
            parse_psse_source(std::sync::Arc::new(raw.to_string()), None, &mut warnings).unwrap();

        assert_eq!(net.loads.len(), 1);
        close(net.loads[0].p, 13.0);
        close(net.loads[0].q, 5.0);
        let Some(LoadVoltageModel::Zip {
            p_constant_power,
            q_constant_current,
            p_constant_impedance,
            ..
        }) = &net.loads[0].voltage_model
        else {
            panic!("missing typed ZIP load model");
        };
        close(*p_constant_power, 10.0);
        close(*q_constant_current, 0.5);
        close(*p_constant_impedance, 2.0);
        assert!(
            warnings.iter().any(|w| w.contains("interruptible/DG/flag")),
            "missing load option warning: {warnings:?}"
        );

        let text = write_psse_rev(&net, 35).text;
        assert!(
            text.contains("10.0, 3.0, 1.0, 0.5, 2.0, 1.5"),
            "ZIP components were not replayed: {text}"
        );
        assert!(
            text.contains("4.0, 2.0, 1, 'industrial'"),
            "modern load tail was not replayed: {text}"
        );
        let net2 = parse_psse(&text).unwrap();
        close(net2.loads[0].p, 13.0);
        close(net2.loads[0].q, 5.0);
    }

    #[test]
    fn tiny_nonzero_zip_components_are_preserved_as_typed_fields() {
        let raw = r"0, 100.00, 35, 0, 1, 60.00 / synthetic
CASE
COMMENT
0 / END OF SYSTEM-WIDE DATA, BEGIN BUS DATA
1,'BUS1        ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
2,'BUS2        ', 230.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
2,'L1',1,1,1,10.0,3.0,1e-20,0.0,0.0,0.0,1,1,0,0.0,0.0,0,''
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
Q
";
        let net = parse_psse(raw).unwrap();
        let Some(LoadVoltageModel::Zip {
            p_constant_current, ..
        }) = &net.loads[0].voltage_model
        else {
            panic!("tiny nonzero ZIP component was not typed");
        };
        assert_eq!(p_constant_current.to_bits(), 1.0e-20_f64.to_bits());

        let matpower = crate::format::matpower::write_matpower_conversion(&net);
        assert!(
            matpower
                .warnings
                .iter()
                .any(|w| w.contains("voltage dependent load model")),
            "missing MATPOWER voltage model warning: {:?}",
            matpower.warnings
        );
    }

    #[test]
    fn typed_psse_load_scaling_and_type_write_without_extras() {
        let raw = r"0, 100.00, 35, 0, 1, 60.00 / synthetic
CASE
COMMENT
0 / END OF SYSTEM-WIDE DATA, BEGIN BUS DATA
1,'BUS1        ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
2,'BUS2        ', 230.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
2,'L1',1,1,1,10.0,3.0,1.0,0.5,2.0,1.5,1,1,0,0.0,0.0,0,''
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
Q
";
        let mut net = parse_psse(raw).unwrap();
        let Some(LoadVoltageModel::Zip {
            scaling,
            load_type,
            v_nom,
            ..
        }) = &mut net.loads[0].voltage_model
        else {
            panic!("missing typed ZIP load model");
        };
        *scaling = Some(0.0);
        *load_type = Some(7);
        *v_nom = Some(230_000.0);
        net.loads[0].extras.remove("psse_scal");
        net.loads[0].extras.remove("psse_loadtype");

        let conv = write_psse_rev(&net, 35);

        assert!(
            conv.text.contains(", 1, 0, 0, 0.0, 0.0, 0, '7'"),
            "typed SCAL/LOADTYPE were not written: {}",
            conv.text
        );
        assert!(
            conv.warnings.iter().any(|w| w.contains("nominal voltage")),
            "missing nominal voltage warning: {:?}",
            conv.warnings
        );
        let rev33 = write_psse(&net);
        assert!(
            rev33
                .warnings
                .iter()
                .any(|w| w.contains("load type requires revision 35")),
            "missing rev33 load type warning: {:?}",
            rev33.warnings
        );
        let reparsed = parse_psse(&conv.text).unwrap();
        let Some(LoadVoltageModel::Zip {
            scaling, load_type, ..
        }) = &reparsed.loads[0].voltage_model
        else {
            panic!("missing reparsed ZIP load model");
        };
        assert_eq!(*scaling, Some(0.0));
        assert_eq!(*load_type, Some(7));
    }

    #[test]
    fn mutated_load_does_not_replay_stale_psse_zip_extras() {
        let raw = r"0, 100.00, 35, 0, 1, 60.00 / synthetic
CASE
COMMENT
0 / END OF SYSTEM-WIDE DATA, BEGIN BUS DATA
1,'BUS1        ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
2,'BUS2        ', 230.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
2,'L1',1,1,1,10.0,3.0,1.0,0.5,2.0,1.5,1,0,1,4.0,2.0,1,'industrial'
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
Q
";
        let mut net = parse_psse(raw).unwrap();
        net.loads[0].p = 20.0;
        net.loads[0].q = 7.0;

        let conv = write_psse_rev(&net, 35);

        assert!(
            conv.text.contains("20.0, 7.0, 0.0, 0.0, 0.0, 0.0"),
            "typed p/q were not written as constant power: {}",
            conv.text
        );
        assert!(
            conv.warnings
                .iter()
                .any(|w| w.contains("stale voltage model components")),
            "missing stale voltage model warning: {:?}",
            conv.warnings
        );
        let reparsed = parse_psse(&conv.text).unwrap();
        close(reparsed.loads[0].p, 20.0);
        close(reparsed.loads[0].q, 7.0);
    }

    #[test]
    fn transformer_continuation_rejects_section_terminator() {
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / synthetic
CASE
COMMENT
1,'BUS1        ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
2,'BUS2        ', 230.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
1,2,0,'1 ',1,1,1,0,0,1,'xf'
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
";
        let err = parse_psse(raw).unwrap_err().to_string();
        assert!(
            err.contains("transformer record ended before transformer impedance line"),
            "{err}"
        );
    }

    #[test]
    fn transformer_impedance_line_can_start_with_zero_resistance() {
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / synthetic
CASE
COMMENT
1,'BUS1        ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
2,'BUS2        ', 230.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
1,2,0,'1 ',1,1,1,0,0,1,'xf',1
0,0.10,100.0
1.0,230.0,0.0,100.0,90.0,80.0,0,0,1.1,0.9,1.1,0.9,33
1.0,230.0
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
";
        let net = parse_psse(raw).unwrap();

        assert_eq!(net.branches.len(), 1);
        close(net.branches[0].r, 0.0);
        close(net.branches[0].x, 0.10);
    }

    #[test]
    fn transformer_non_integral_cz_is_a_hard_error() {
        // A malformed CZ like `2.9` must not silently truncate to a valid
        // looking code `2`; that would apply the wrong impedance base
        // conversion without ever surfacing an "unsupported CZ" warning.
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / synthetic
CASE
COMMENT
1,'BUS1        ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
2,'BUS2        ', 115.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
1,2,0,'1 ',1,2.9,1,0,0,1,'xf',1
0,0.10,100.0
1.0,230.0,0.0,100.0,90.0,80.0,0,0,1.1,0.9,1.1,0.9,33
1.0,230.0
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
";
        let err = parse_psse(raw).unwrap_err().to_string();
        assert!(err.contains("field 5") && err.contains("2.9"), "{err}");
    }

    #[test]
    fn non_unit_two_winding_transformer_bases_are_converted() {
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / synthetic
CASE
COMMENT
1,'BUS1        ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
2,'BUS2        ', 115.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
1,2,0,'1 ',2,2,1,0,0,1,'xf',1
0.01,0.10,50.0
241.5,230.0,0.0,100.0,90.0,80.0,0,0,1.1,0.9,1.1,0.9,33
115.0,115.0
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
";
        let parsed = crate::parse_str(raw, "psse").unwrap();
        assert!(
            !parsed
                .warnings
                .iter()
                .any(|w| w.contains("unsupported CZ") || w.contains("unsupported CW")),
            "unexpected transformer base warning: {:?}",
            parsed.warnings
        );
        let br = &parsed.network.branches[0];
        close(br.r, 0.02);
        close(br.x, 0.20);
        close(br.tap, 1.05);
    }

    #[test]
    fn cz3_load_loss_and_cw3_nominal_voltage_are_converted() {
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / synthetic
CASE
COMMENT
1,'BUS1        ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
2,'BUS2        ', 115.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
1,2,0,'1 ',3,3,1,0,0,1,'xf',1
250000.0,0.10,50.0
1.05,230.0,0.0,100.0,90.0,80.0,0,0,1.1,0.9,1.1,0.9,33
1.0,115.0
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
";
        let parsed = crate::parse_str(raw, "psse").unwrap();
        assert!(
            !parsed
                .warnings
                .iter()
                .any(|w| w.contains("unsupported CZ") || w.contains("unsupported CW")),
            "unexpected transformer base warning: {:?}",
            parsed.warnings
        );
        let br = &parsed.network.branches[0];
        close(br.r, 0.01);
        close(br.x, (0.10_f64 * 0.10 - 0.005_f64 * 0.005).sqrt() * 2.0);
        close(br.tap, 1.05);
    }

    #[test]
    fn non_unit_three_winding_transformer_bases_are_converted() {
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / synthetic
CASE
COMMENT
1,'BUS1        ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
2,'BUS2        ', 115.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
3,'BUS3        ', 13.8,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
1,2,3,'1 ',2,2,1,0,0,1,'xf3',1
0.01,0.10,50.0,0.02,0.20,100.0,0.03,0.30,200.0,1.0,0.0
241.5,230.0,0.0,100.0,90.0,80.0,0,0,1.1,0.9,1.1,0.9,33
115.0,115.0,0.0,100.0,90.0,80.0,0,0,1.1,0.9,1.1,0.9,33
13.8,13.8,0.0,100.0,90.0,80.0,0,0,1.1,0.9,1.1,0.9,33
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
";
        let parsed = crate::parse_str(raw, "psse").unwrap();
        assert!(
            !parsed
                .warnings
                .iter()
                .any(|w| w.contains("unsupported CZ") || w.contains("unsupported CW")),
            "unexpected transformer base warning: {:?}",
            parsed.warnings
        );
        let t = &parsed.network.transformers_3w[0];
        close(t.z[0].r, 0.02);
        close(t.z[0].x, 0.20);
        close(t.z[1].r, 0.02);
        close(t.z[1].x, 0.20);
        close(t.z[2].r, 0.015);
        close(t.z[2].x, 0.15);
        close(t.windings[0].tap, 1.05);
        close(t.windings[1].tap, 1.0);
        close(t.windings[2].tap, 1.0);
    }

    #[test]
    fn dc_continuation_rejects_section_terminator() {
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / synthetic
CASE
COMMENT
0 / END OF SYSTEM-WIDE DATA, BEGIN TWO-TERMINAL DC DATA
'DC1',1
0 / END OF TWO-TERMINAL DC DATA, BEGIN VSC DC LINE DATA
Q
";
        let err = parse_psse(raw).unwrap_err().to_string();
        assert!(
            err.contains("two-terminal DC record ended before rectifier line"),
            "{err}"
        );
    }

    #[test]
    fn reads_comment_headers_system_wide_block_and_named_branch_records() {
        let raw = r#"@!IC, SBASE,REV,XFRRAT,NXFRAT,BASFRQ
0, 100.00, 34, 0, 0, 60.00 / synthetic v34 export


GENERAL, THRSHZ=0.0002
RATING, 1, "      ", "                                "
0 / END OF SYSTEM-WIDE DATA, BEGIN BUS DATA
@!   I,'NAME        ', BASKV, IDE,AREA,ZONE,OWNER, VM,        VA,    NVHI,   NVLO,   EVHI,   EVLO
1,'BUS1        ', 230.0000,3,1,1,1,1.00000,0.0000,1.1000,0.9000,1.1000,0.9000
2,'BUS2        ', 230.0000,1,1,1,1,1.00000,0.0000,1.1000,0.9000,1.1000,0.9000
0 / END OF BUS DATA, BEGIN LOAD DATA
@!   I,'ID',STAT,AREA,ZONE,      PL,        QL
2,'1 ',1,1,1,10.0,5.0
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
@!   I,'ID',      PG,        QG,        QT,        QB,     VS,    IREG,     MBASE,     ZR,         ZX,         RT,         XT,     GTAP,STAT, RMPCT,      PT,        PB
1,'1 ',50.0,5.0,20.0,-10.0,1.0,0,100.0,0.0,1.0,0.0,0.0,1.0,1,100.0,80.0,10.0
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
@!   I,     J,'CKT',     R,          X,         B,                    'N A M E'                 ,   RATE1,   RATE2,   RATE3,   RATE4,   RATE5,   RATE6,   RATE7,   RATE8,   RATE9,  RATE10,  RATE11,  RATE12,    GI,       BI,       GJ,       BJ,STAT,MET,  LEN
1,2,'1 ',0.01,0.05,0.001,'named branch',100.0,90.0,80.0,70.0,0.0,60.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,1,1,0.0
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
"#;

        let mut net = parse_psse(raw).unwrap();

        close(net.base_mva, 100.0);
        assert_eq!(net.buses.len(), 2);
        assert_eq!(net.loads.len(), 1);
        assert_eq!(net.generators.len(), 1);
        assert_eq!(net.branches.len(), 1);
        close(net.branches[0].rate_a, 100.0);
        assert_eq!(net.branches[0].rating_sets.len(), 2);
        assert_eq!(net.branches[0].rating_sets[0].name, "RATE4");
        close(net.branches[0].rating_sets[0].rate_mva, 70.0);
        assert_eq!(net.branches[0].rating_sets[1].name, "RATE6");
        close(net.branches[0].rating_sets[1].rate_mva, 60.0);
        assert!(net.branches[0].in_service);

        net.source = None;
        let written = write_psse_rev(&net, 34);
        assert!(
            !written.warnings.iter().any(|w| w.contains("rating set")),
            "v34 should carry RATE4-RATE12, got {:?}",
            written.warnings
        );
        let back = parse_psse(&written.text).unwrap();
        assert_eq!(back.branches[0].rating_sets.len(), 2);
        assert_eq!(back.branches[0].rating_sets[0].name, "RATE4");
        close(back.branches[0].rating_sets[0].rate_mva, 70.0);
        assert_eq!(back.branches[0].rating_sets[1].name, "RATE6");
        close(back.branches[0].rating_sets[1].rate_mva, 60.0);
    }

    #[test]
    fn v34_transformer_reads_float_k_and_modern_winding_columns() {
        // v34/35 exporters write K in float form: "0.00" must classify the
        // record as 2-winding (4 lines), or the reader consumes a fifth line and
        // desynchronizes every later section. The winding line uses the v34
        // layout (twelve ratings, NODE after CONT), putting COD at 15 and
        // RMA..NTP at 18..22.
        let raw = r"0, 100.00, 34, 0, 0, 60.00 / synthetic v34 export
CASE
COMMENT
0 / END OF SYSTEM-WIDE DATA, BEGIN BUS DATA
1,'B1          ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
2,'B2          ', 18.0,2,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
1, 2, 0.00, '1', 1, 1, 1, 0.0, 0.0, 2, 'T1          ', 1, 1, 1.0, 0, 1, 0, 1, 0, 1, '            '
0.01, 0.10, 100.0
1.05, 0.0, 0.0, 100.0, 90.0, 80.0, 70.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1, 2, 0, 1.08, 0.92, 1.05, 0.98, 17, 0, 0, 0, 0
1.0, 0.0
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
1, 1, 0.0, 0.0, 'AREA        '
Q
";
        let net = parse_psse(raw).unwrap();
        assert_eq!(net.branches.len(), 1, "K = 0.00 is a 2-winding record");
        assert!(net.transformers_3w.is_empty());
        assert_eq!(
            net.areas.len(),
            1,
            "the section after the transformer parsed"
        );
        let br = &net.branches[0];
        close(br.tap, 1.05);
        close(br.rate_a, 100.0);
        assert_eq!(br.rating_sets.len(), 1);
        assert_eq!(br.rating_sets[0].name, "RATE4");
        close(br.rating_sets[0].rate_mva, 70.0);
        let c = br.control.as_ref().expect("COD at 15 marks the control");
        assert_eq!(c.mode, TransformerControlMode::Voltage);
        assert_eq!(c.controlled_bus, Some(BusId(2)));
        close(c.tap_max, 1.08);
        close(c.tap_min, 0.92);
        close(c.band_max, 1.05);
        close(c.band_min, 0.98);
        assert_eq!(c.ntp, 17);
    }

    #[test]
    fn v34_warns_when_custom_rating_name_is_emitted_as_rate_slot() {
        let mut net = BalancedNetwork::in_memory(
            "ratings",
            100.0,
            vec![
                Bus::new(BusId(1), BusType::Ref, 230.0),
                Bus::new(BusId(2), BusType::Pq, 230.0),
            ],
            Vec::new(),
        );
        let mut branch = Branch::new(BusId(1), BusId(2), 0.01, 0.05);
        branch.rate_a = 100.0;
        branch
            .rating_sets
            .push(BranchRatingSet::new("emergency", 125.0));
        net.branches.push(branch);

        let written = write_psse_rev(&net, 34);

        assert!(
            written.warnings.iter().any(|w| {
                w.contains("rating set emergency=125")
                    && w.contains("emitted as RATE4")
                    && w.contains("names outside RATE4-RATE12 are not preserved")
            }),
            "missing rating rename warning: {:?}",
            written.warnings
        );
        let back = parse_psse(&written.text).unwrap();
        assert_eq!(back.branches[0].rating_sets.len(), 1);
        assert_eq!(back.branches[0].rating_sets[0].name, "RATE4");
        close(back.branches[0].rating_sets[0].rate_mva, 125.0);
    }

    #[test]
    fn reads_start_of_section_markers_and_gen_alias() {
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / synthetic v33 export
CASE
COMMENT
1,'BUS1        ', 230.0000,3,1,1,1,1.00000,0.0000,1.1000,0.9000,1.1000,0.9000
2,'BUS2        ', 230.0000,1,1,1,1,1.00000,0.0000,1.1000,0.9000,1.1000,0.9000
0 / End of Bus Data, Start of Load Data
2,'1 ',1,1,1,10.0,5.0
0 / End of Load Data, Start of Fixed Shunt Data
0 / End of Fixed Shunt Data, Start of Gen Data
1,'1 ',50.0,5.0,20.0,-10.0,1.0,0,100.0,0.0,1.0,0.0,0.0,1.0,1,100.0,80.0,10.0
0 / End of Gen Data, Start of Branch Data
1,2,'1 ',0.01,0.05,0.001,100.0,90.0,80.0,0.0,0.0,0.0,0.0,1,1,0.0,1,1
0 / End of Branch Data, Start of Transformer Data
0 / End of Transformer Data, Start of Area Interchange Data
Q
";

        let net = parse_psse(raw).unwrap();

        assert_eq!(net.buses.len(), 2);
        assert_eq!(net.loads.len(), 1);
        assert_eq!(net.generators.len(), 1);
        assert_eq!(net.branches.len(), 1);
    }

    #[test]
    fn v33_long_branch_with_blank_ratea_keeps_v33_columns() {
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / synthetic v33 export
CASE
COMMENT
1,'BUS1        ', 230.0000,3,1,1,1,1.00000,0.0000,1.1000,0.9000,1.1000,0.9000
2,'BUS2        ', 230.0000,1,1,1,1,1.00000,0.0000,1.1000,0.9000,1.1000,0.9000
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
1,2,'1 ',0.01,0.05,0.001,,90.0,80.0,0.0,0.0,0.0,0.0,1,1,0.0,1,1.0,2,0.0,3,0.0,4,0.0
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
";

        let net = parse_psse(raw).unwrap();

        assert_eq!(net.branches.len(), 1);
        close(net.branches[0].rate_a, 0.0);
        close(net.branches[0].rate_b, 90.0);
        close(net.branches[0].rate_c, 80.0);
        assert!(net.branches[0].in_service);
    }

    #[test]
    fn captured_load_ids_round_trip_and_parallel_loads_stay_distinct() {
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / x
CASE
COMMENT
1,'B1          ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
2,'B2          ', 230.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
2,'A',1,1,1,10.0,5.0,0,0,0,0,1,1,0
2,'B',1,1,1,20.0,8.0,0,0,0,0,1,1,0
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
";
        let id = |l: &Load| {
            l.extras
                .get("id")
                .and_then(|v| v.as_str())
                .map(str::to_owned)
        };
        let net = parse_psse(raw).unwrap();
        assert_eq!(net.loads.len(), 2);
        assert_eq!(id(&net.loads[0]).as_deref(), Some("A"));
        assert_eq!(id(&net.loads[1]).as_deref(), Some("B"));

        // A round trip keeps the captured ids.
        let net2 = parse_psse(&write_psse(&net).text).unwrap();
        assert_eq!(id(&net2.loads[0]).as_deref(), Some("A"));
        assert_eq!(id(&net2.loads[1]).as_deref(), Some("B"));

        // With the ids stripped (a synthesized network, e.g. from MATPOWER), the
        // two loads on bus 2 still write with distinct positional ids, so the
        // output is valid PSS/E rather than two colliding (bus, '1') records.
        let mut synth = net.clone();
        for l in &mut synth.loads {
            l.extras.remove("id");
        }
        let net3 = parse_psse(&write_psse(&synth).text).unwrap();
        let ids: Vec<_> = net3.loads.iter().filter_map(&id).collect();
        assert_eq!(ids, vec!["1".to_string(), "2".to_string()]);
    }

    #[test]
    fn sanitized_load_ids_are_allocated_after_cleaning() {
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / x
CASE
COMMENT
1,'B1          ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
2,'B2          ', 230.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
2,'A',1,1,1,10.0,5.0,0,0,0,0,1,1,0
2,'B',1,1,1,20.0,8.0,0,0,0,0,1,1,0
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
";
        let mut net = parse_psse(raw).unwrap();
        net.loads[0]
            .extras
            .insert("id".into(), Value::String("A/B".into()));
        net.loads[1]
            .extras
            .insert("id".into(), Value::String("A'B".into()));

        let conv = write_psse(&net);
        let reparsed = parse_psse(&conv.text).unwrap();
        let ids: Vec<_> = reparsed
            .loads
            .iter()
            .filter_map(|l| l.extras.get("id").and_then(Value::as_str))
            .collect();

        assert_eq!(ids, vec!["A B", "1"]);
        assert!(
            conv.warnings
                .iter()
                .any(|w| w.contains("2 quoted PSS/E field")),
            "missing sanitation warning: {:?}",
            conv.warnings
        );
    }

    #[test]
    fn two_winding_transformer_charging_round_trips_via_mag2() {
        // MAG2 (line-1 field 8) carries the transformer's magnetizing susceptance;
        // at CM = 1 it maps to the branch charging b and must survive a round trip.
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / x
CASE
COMMENT
1,'B1          ', 230.0,3,1,1,1,1.00000,0.0,1.1,0.9,1.1,0.9
2,'B2          ', 138.0,1,1,1,1,1.00000,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
1, 2, 0, '1', 1, 1, 1, 0, 0.04, 2, 'XF          ', 1, 1, 1, 0, 1, 0, 1, 0, 1, '            '
0.01, 0.10, 100.0
1.025, 0, 0.0, 100.0, 90.0, 80.0, 0, 0, 1.1, 0.9, 1.1, 0.9, 33, 0, 0, 0, 0
1.0, 0
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
";
        let net = parse_psse(raw).unwrap();
        assert_eq!(net.branches.len(), 1);
        assert!(net.branches[0].is_transformer());
        close(net.branches[0].b, 0.04);

        let net2 = parse_psse(&write_psse(&net).text).unwrap();
        close(net2.branches[0].b, 0.04);
    }

    #[test]
    fn parallel_branches_round_trip_and_stay_distinct() {
        // Two circuits between buses 1 and 2: each keeps a distinct CKT so the
        // output is valid PSS/E rather than two colliding (I, J, '1') records.
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / x
CASE
COMMENT
1,'B1          ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
2,'B2          ', 230.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
1,2,'1 ',0.01,0.05,0.001,0,0,0,0,0,0,0,1,1,0.0
1,2,'2 ',0.02,0.06,0.002,0,0,0,0,0,0,0,1,1,0.0
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
";
        let ckt = |b: &Branch| {
            b.extras
                .get("id")
                .and_then(|v| v.as_str())
                .map(str::to_owned)
        };
        let net = parse_psse(raw).unwrap();
        assert_eq!(net.branches.len(), 2);
        assert_eq!(ckt(&net.branches[0]).as_deref(), Some("1"));
        assert_eq!(ckt(&net.branches[1]).as_deref(), Some("2"));

        // Round trip keeps both circuits distinct.
        let net2 = parse_psse(&write_psse(&net).text).unwrap();
        assert_eq!(net2.branches.len(), 2);
        assert_eq!(ckt(&net2.branches[0]).as_deref(), Some("1"));
        assert_eq!(ckt(&net2.branches[1]).as_deref(), Some("2"));

        // With the captured ids stripped (a synthesized network), the two parallel
        // branches still write with distinct positional circuit ids.
        let mut synth = net.clone();
        for b in &mut synth.branches {
            b.extras.remove("id");
        }
        let net3 = parse_psse(&write_psse(&synth).text).unwrap();
        let ids: Vec<_> = net3.branches.iter().filter_map(&ckt).collect();
        assert_eq!(ids, vec!["1".to_string(), "2".to_string()]);
    }

    #[test]
    fn reads_and_writes_solver_params() {
        let raw = r"0, 100.00, 34, 0, 1, 60.00 / x
CASE
COMMENT
GENERAL, THRSHZ=0.0001
NEWTON, TOLN=0.1, ITMXN=25
SOLVER, ACTAPS=1, AREAIN=0, PHSHFT=1, DCTAPS=1, SWSHNT=0
0 / END OF SYSTEM-WIDE DATA, BEGIN BUS DATA
1,'B1          ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
Q
";
        let net = parse_psse(raw).unwrap();
        let sp = net.solver.as_ref().expect("solver params parsed");
        close(sp.zero_impedance_threshold.unwrap(), 0.0001);
        close(sp.newton_tolerance.unwrap(), 0.1);
        assert_eq!(sp.max_iterations, Some(25));
        assert_eq!(sp.adjust_taps, Some(true));
        assert_eq!(sp.adjust_area_interchange, Some(false));
        assert_eq!(sp.adjust_phase_shift, Some(true));
        assert_eq!(sp.adjust_switched_shunt, Some(false));

        // Round trip at rev 34 keeps the tolerances and the adjustment flags.
        let net2 = parse_psse(&write_psse_rev(&net, 34).text).unwrap();
        let sp2 = net2
            .solver
            .as_ref()
            .expect("solver params survive the write");
        close(sp2.newton_tolerance.unwrap(), 0.1);
        assert_eq!(sp2.max_iterations, Some(25));
        assert_eq!(sp2.adjust_taps, Some(true));
        assert_eq!(sp2.adjust_area_interchange, Some(false));
    }

    #[test]
    fn reads_and_writes_area_records() {
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / x
CASE
COMMENT
1,'B1          ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
5,'B5          ', 230.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
1, 5, 100.0, 10.0, 'AREA-ONE    '
0 / END OF AREA DATA, BEGIN TWO-TERMINAL DC DATA
Q
";
        let net = parse_psse(raw).unwrap();
        assert_eq!(net.areas.len(), 1, "the area record was read");
        let a = &net.areas[0];
        assert_eq!(a.number, 1);
        assert_eq!(a.slack_bus, Some(BusId(5)));
        close(a.net_interchange, 100.0);
        close(a.tolerance, 10.0);
        assert_eq!(a.name.as_deref(), Some("AREA-ONE"));

        // Round trip: write and re-read keeps the interchange and swing bus.
        let net2 = parse_psse(&write_psse(&net).text).unwrap();
        assert_eq!(net2.areas.len(), 1);
        let a2 = &net2.areas[0];
        assert_eq!(a2.number, 1);
        assert_eq!(a2.slack_bus, Some(BusId(5)));
        close(a2.net_interchange, 100.0);
        assert_eq!(a2.name.as_deref(), Some("AREA-ONE"));
    }

    #[test]
    fn reads_and_writes_a_switched_shunt() {
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / x
CASE
COMMENT
1,'B1          ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
3,'B3          ', 230.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
7,'B7          ', 230.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
0 / END OF AREA DATA, BEGIN SWITCHED SHUNT DATA
3, 2, 0, 1, 1.05, 0.95, 7, 100.0, '', 19.0, 2, 25.0, 1, 50.0
0 / END OF SWITCHED SHUNT DATA, BEGIN GNE DEVICE DATA
Q
";
        let net = parse_psse(raw).unwrap();
        assert_eq!(net.shunts.len(), 1);
        let sh = &net.shunts[0];
        assert_eq!(sh.bus, BusId(3));
        close(sh.b, 19.0);
        let c = sh.control.as_ref().expect("switched-shunt control parsed");
        assert_eq!(c.mode, SwitchedShuntMode::Discrete);
        close(c.vhigh, 1.05);
        close(c.vlow, 0.95);
        assert_eq!(c.control_bus, Some(BusId(7)));
        close(c.rmpct, 100.0);
        assert_eq!(c.blocks.len(), 2);
        assert_eq!(c.blocks[0].steps, 2);
        close(c.blocks[0].b, 25.0);
        assert_eq!(c.blocks[1].steps, 1);
        close(c.blocks[1].b, 50.0);

        // Round trip: written to the SWITCHED SHUNT section and re-read intact.
        let text = write_psse(&net).text;
        assert!(text.contains("BEGIN SWITCHED SHUNT DATA"));
        let net2 = parse_psse(&text).unwrap();
        assert_eq!(net2.shunts.len(), 1);
        let c2 = net2.shunts[0]
            .control
            .as_ref()
            .expect("control survives the write");
        assert_eq!(c2.mode, SwitchedShuntMode::Discrete);
        assert_eq!(c2.control_bus, Some(BusId(7)));
        assert_eq!(c2.blocks.len(), 2);
        close(c2.blocks[0].b, 25.0);
        close(net2.shunts[0].b, 19.0);
    }

    #[test]
    fn v35_switched_shunt_write_round_trips_through_the_id_column() {
        // v35 inserts a quoted shunt ID at field 1 and NREG after SWREG, and its
        // step blocks are (S, N, B) triples; the writer must emit that layout or
        // the reader misplaces every later field. Build a switched shunt, write
        // the v35 layout, and confirm it reads back intact.
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / x
CASE
COMMENT
3,'B3          ', 230.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
7,'B7          ', 230.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
0 / END OF AREA DATA, BEGIN SWITCHED SHUNT DATA
3, 2, 0, 1, 1.05, 0.95, 7, 100.0, '', 19.0, 2, 25.0, 1, 50.0
0 / END OF SWITCHED SHUNT DATA, BEGIN GNE DEVICE DATA
Q
";
        let net = parse_psse(raw).unwrap();
        let text = write_psse_rev(&net, 35).text;
        let net2 = parse_psse(&text).unwrap();
        assert_eq!(net2.shunts.len(), 1);
        let sh = &net2.shunts[0];
        assert_eq!(sh.bus, BusId(3));
        close(sh.b, 19.0);
        let c = sh
            .control
            .as_ref()
            .expect("v35 switched-shunt control survives the write");
        assert_eq!(c.mode, SwitchedShuntMode::Discrete);
        close(c.vhigh, 1.05);
        close(c.vlow, 0.95);
        assert_eq!(c.control_bus, Some(BusId(7)));
        close(c.rmpct, 100.0);
        assert_eq!(c.blocks.len(), 2);
        close(c.blocks[0].b, 25.0);
        close(c.blocks[1].b, 50.0);
    }

    #[test]
    fn reads_and_writes_a_generator_remote_regulated_bus() {
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / x
CASE
COMMENT
1,'B1          ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
3,'B3          ', 18.0,2,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
7,'B7          ', 230.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
3,'1', 50.0, 5.0, 30.0, -20.0, 1.02, 7, 100.0, 0, 1, 0, 0, 1, 1, 100.0, 80.0, 0.0, 1, 1
1,'1', 10.0, 0.0, 10.0, -10.0, 1.0, 0, 100.0, 0, 1, 0, 0, 1, 1, 100.0, 50.0, 0.0, 1, 1
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
";
        let net = parse_psse(raw).unwrap();
        assert_eq!(net.generators.len(), 2);
        let g3 = net.generators.iter().find(|g| g.bus == BusId(3)).unwrap();
        assert_eq!(
            g3.regulated_bus,
            Some(BusId(7)),
            "IREG names the remote regulated bus"
        );
        // IREG 0 means own-terminal control: no remote bus.
        let g1 = net.generators.iter().find(|g| g.bus == BusId(1)).unwrap();
        assert_eq!(g1.regulated_bus, None);

        // Round trip: IREG is written at field 7 and re-read intact.
        let text = write_psse(&net).text;
        let net2 = parse_psse(&text).unwrap();
        let g3b = net2.generators.iter().find(|g| g.bus == BusId(3)).unwrap();
        assert_eq!(g3b.regulated_bus, Some(BusId(7)));
        let g1b = net2.generators.iter().find(|g| g.bus == BusId(1)).unwrap();
        assert_eq!(g1b.regulated_bus, None);
    }

    #[test]
    fn reads_a_v35_generator_record_with_nreg() {
        // v35 inserts NREG after IREG (and BASLOD after PB), shifting MBASE,
        // STAT, PT, and PB by one. Reading at the v33 offsets takes NREG as
        // MBASE and GTAP (1.0) as STAT, silently returning this out of service
        // unit to service.
        let raw = "0, 100.00, 35, 0, 0, 60.00 / x
CASE
COMMENT
1,'B1          ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
1,'1 ',50.0,5.0,20.0,-10.0,1.0,0,2,900.0,0.0,1.0,0.0,0.0,1.0,0,100.0,80.0,10.0,0.0,1,1.0
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
";
        let net = parse_psse(raw).unwrap();
        assert_eq!(net.generators.len(), 1);
        let g = &net.generators[0];
        close(g.mbase, 900.0);
        assert!(!g.in_service, "STAT = 0 at the shifted index");
        close(g.pmax, 80.0);
        close(g.pmin, 10.0);
        assert_eq!(g.regulated_bus, None, "IREG stays at field 7");

        // The v35 writer emits NREG and BASLOD, so the record reads back intact.
        let net2 = parse_psse(&write_psse_rev(&net, 35).text).unwrap();
        let g2 = &net2.generators[0];
        close(g2.mbase, 900.0);
        assert!(!g2.in_service);
        close(g2.pmax, 80.0);
        close(g2.pmin, 10.0);
    }

    #[test]
    fn stale_control_pointers_warn_and_drop() {
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / x
CASE
COMMENT
1,'B1          ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
2,'B2          ', 18.0,2,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
1,'1', 50.0, 5.0, 30.0, -20.0, 1.02, 99, 100.0, 0, 1, 0, 0, 1, 1, 100.0, 80.0, 0.0, 1, 1
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
1, 2, 0, '1', 1, 1, 1, 0, 0, 2, 'REG         ', 1, 1, 1, 0, 1, 0, 1, 0, 1, '            '
0.01, 0.10, 100.0
1.025, 0, 2.5, 100.0, 90.0, 80.0, 1, 98, 1.08, 0.92, 1.05, 0.98, 17, 0, 0, 0, 0
1.0, 0
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
1, 97, 0.0, 0.0, 'AREA        '
0 / END OF AREA DATA, BEGIN TWO-TERMINAL DC DATA
0 / END OF TWO-TERMINAL DC DATA, BEGIN VSC DC LINE DATA
0 / END OF VSC DC LINE DATA, BEGIN IMPEDANCE CORRECTION DATA
0 / END OF IMPEDANCE CORRECTION DATA, BEGIN MULTI-TERMINAL DC DATA
0 / END OF MULTI-TERMINAL DC DATA, BEGIN MULTI-SECTION LINE DATA
0 / END OF MULTI-SECTION LINE DATA, BEGIN ZONE DATA
0 / END OF ZONE DATA, BEGIN INTER-AREA TRANSFER DATA
0 / END OF INTER-AREA TRANSFER DATA, BEGIN OWNER DATA
0 / END OF OWNER DATA, BEGIN FACTS DEVICE DATA
0 / END OF FACTS DEVICE DATA, BEGIN SWITCHED SHUNT DATA
2, 2, 0, 1, 1.05, 0.95, 96, 100.0, '', 19.0, 2, 25.0
0 / END OF SWITCHED SHUNT DATA, BEGIN GNE DEVICE DATA
Q
";
        let mut warnings = Vec::new();
        let net =
            parse_psse_source(std::sync::Arc::new(raw.to_string()), None, &mut warnings).unwrap();

        assert_eq!(net.generators[0].regulated_bus, None);
        assert_eq!(
            net.branches[0]
                .control
                .as_ref()
                .and_then(|c| c.controlled_bus),
            None
        );
        assert_eq!(
            net.shunts[0].control.as_ref().and_then(|c| c.control_bus),
            None
        );
        assert_eq!(net.areas[0].slack_bus, None);
        assert!(
            warnings.iter().any(|w| w.contains("GENERATOR DATA")
                && w.contains("IREG")
                && w.contains("missing bus id 99")),
            "missing IREG warning: {warnings:?}"
        );
        assert!(
            warnings.iter().any(|w| w.contains("TRANSFORMER DATA")
                && w.contains("CONT")
                && w.contains("missing bus id 98")),
            "missing CONT warning: {warnings:?}"
        );
        assert!(
            warnings.iter().any(|w| w.contains("SWITCHED SHUNT DATA")
                && w.contains("SWREM")
                && w.contains("missing bus id 96")),
            "missing SWREM warning: {warnings:?}"
        );
        assert!(
            warnings.iter().any(|w| w.contains("AREA DATA")
                && w.contains("ISW")
                && w.contains("missing bus id 97")),
            "missing ISW warning: {warnings:?}"
        );
    }

    #[test]
    fn truncated_transformer_continuation_names_expected_line() {
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / x
CASE
COMMENT
1,'B1          ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
2,'B2          ', 18.0,2,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
1, 2, 0, '1', 1, 1, 1, 0, 0, 2, 'REG         ', 1, 1, 1, 0, 1, 0, 1, 0, 1, '            '
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
";
        let err = parse_psse(raw).unwrap_err().to_string();
        assert!(
            err.contains("transformer record ended before transformer impedance line"),
            "got {err}"
        );
    }

    #[test]
    fn unmodeled_section_counts_skip_bare_terminators() {
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / x
CASE
COMMENT
1,'B1          ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
0 / END OF AREA DATA, BEGIN TWO-TERMINAL DC DATA
0 / END OF TWO-TERMINAL DC DATA, BEGIN VSC DC LINE DATA
'VSC1', 1
2, 3
0
0 / END OF VSC DC LINE DATA, BEGIN IMPEDANCE CORRECTION DATA
Q
";
        let mut warnings = Vec::new();
        parse_psse_source(std::sync::Arc::new(raw.to_string()), None, &mut warnings).unwrap();
        assert!(
            warnings
                .iter()
                .any(|w| w.contains("VSC DC LINE section (2 record line(s))")),
            "bare terminator should not be counted as skipped data: {warnings:?}"
        );
    }

    #[test]
    fn reads_a_v35_switched_shunt_with_an_id_column() {
        // v35: I, ID, MODSW, ADJM, ST, VSWHI, VSWLO, SWREG, NREG, RMPCT, RMIDNT,
        // BINIT, then (S, N, B) triples. Reading it at the v33 offsets misparses
        // VSWLO as SWREM (regression: a real v35 case pointed switched-shunt
        // control at a nonexistent bus 1) and NREG as RMPCT.
        let raw = "0, 100.00, 35, 0, 0, 60.00 / x
CASE
COMMENT
5,'B5          ', 230.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
7,'B7          ', 230.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
0 / END OF AREA DATA, BEGIN SWITCHED SHUNT DATA
5,'1 ',2,0,1,1.05,0.95,7,3,80.0,'',19.0,1,2,25.0,0,1,50.0
0 / END OF SWITCHED SHUNT DATA, BEGIN GNE DEVICE DATA
Q
";
        let net = parse_psse(raw).unwrap();
        assert_eq!(net.shunts.len(), 1);
        let sh = &net.shunts[0];
        assert_eq!(sh.bus, BusId(5));
        close(sh.b, 19.0);
        assert!(sh.in_service);
        let c = sh.control.as_ref().expect("switched-shunt control parsed");
        assert_eq!(c.mode, SwitchedShuntMode::Discrete);
        close(c.vhigh, 1.05);
        close(c.vlow, 0.95);
        assert_eq!(
            c.control_bus,
            Some(BusId(7)),
            "SWREG at field 7, not NREG at 8"
        );
        close(c.rmpct, 80.0);
        // Both (S, N, B) blocks are kept; the leading status column is skipped.
        assert_eq!(c.blocks.len(), 2);
        assert_eq!(c.blocks[0].steps, 2);
        close(c.blocks[0].b, 25.0);
        assert_eq!(c.blocks[1].steps, 1);
        close(c.blocks[1].b, 50.0);
    }

    #[test]
    fn reads_and_writes_a_two_terminal_dc_line() {
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / x
CASE
COMMENT
1,'B1          ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
4,'B4          ', 230.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
5,'B5          ', 230.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
0 / END OF AREA DATA, BEGIN TWO-TERMINAL DC DATA
'DCLINE1', 1, 2.5, 350.0, 500.0, 0.0, 0.0, 0.0, 'I', 0.0, 20, 1.0
4, 1, 15.0, 5.0, 0.0, 0.0, 0.0, 1.0, 1.0, 1.5, 0.51, 0.00625, 0, 0, 0, '1', 0.0
5, 1, 15.0, 5.0, 0.0, 0.0, 0.0, 1.0, 1.0, 1.5, 0.51, 0.00625, 0, 0, 0, '1', 0.0
0 / END OF TWO-TERMINAL DC DATA, BEGIN VSC DC LINE DATA
Q
";
        let net = parse_psse(raw).unwrap();
        assert_eq!(net.hvdc.len(), 1, "the two-terminal DC line was read");
        let dc = &net.hvdc[0];
        assert_eq!(dc.from, BusId(4), "rectifier bus is the from end");
        assert_eq!(dc.to, BusId(5), "inverter bus is the to end");
        assert!(dc.in_service);
        close(dc.pf, 350.0);
        close(dc.pt, 350.0);

        // Round trip: write and re-read keeps the buses and the power setpoint.
        let net2 = parse_psse(&write_psse(&net).text).unwrap();
        assert_eq!(net2.hvdc.len(), 1, "the DC line survives the write");
        let dc2 = &net2.hvdc[0];
        assert_eq!(dc2.from, BusId(4));
        assert_eq!(dc2.to, BusId(5));
        assert!(dc2.in_service);
        close(dc2.pf, 350.0);
    }

    #[test]
    fn reads_and_writes_a_regulating_transformer_control() {
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / x
CASE
COMMENT
1,'B1          ', 230.0,3,1,1,1,1.00000,0.0,1.1,0.9,1.1,0.9
2,'B2          ', 138.0,1,1,1,1,1.00000,0.0,1.1,0.9,1.1,0.9
3,'B3          ', 13.8,1,1,1,1,1.00000,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
1, 2, 0, '1', 1, 1, 1, 0, 0, 2, 'REG         ', 1, 1, 1, 0, 1, 0, 1, 0, 1, '            '
0.01, 0.10, 100.0
1.025, 0, 2.5, 100.0, 90.0, 80.0, 1, 3, 1.08, 0.92, 1.05, 0.98, 17, 0, 0, 0, 0
1.0, 0
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
";
        let net = parse_psse(raw).unwrap();
        assert_eq!(net.branches.len(), 1);
        let c = net.branches[0].control.as_ref().expect("control parsed");
        assert_eq!(c.mode, TransformerControlMode::Voltage);
        assert_eq!(c.controlled_bus, Some(BusId(3)));
        close(c.tap_max, 1.08);
        close(c.tap_min, 0.92);
        close(c.band_min, 0.98);
        assert_eq!(c.ntp, 17);
        close(c.mva_base, 100.0);

        // Round trip: write and re-read keeps the control block and the tap/shift.
        let net2 = parse_psse(&write_psse(&net).text).unwrap();
        let c2 = net2.branches[0].control.as_ref().expect("control survives");
        assert_eq!(c2.mode, TransformerControlMode::Voltage);
        assert_eq!(c2.controlled_bus, Some(BusId(3)));
        close(c2.tap_max, 1.08);
        assert_eq!(c2.ntp, 17);
        close(net2.branches[0].tap, 1.025);
        close(net2.branches[0].shift, 2.5);
    }

    #[test]
    fn reads_and_writes_a_three_winding_transformer() {
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / x
CASE
COMMENT
1,'B1          ', 230.0,3,1,1,1,1.00000,0.0,1.1,0.9,1.1,0.9
2,'B2          ', 138.0,1,1,1,1,1.00000,0.0,1.1,0.9,1.1,0.9
3,'B3          ', 13.8,1,1,1,1,1.00000,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
1, 2, 3, '1', 1, 1, 1, 0.0, 0.0, 2, 'T3W         ', 1, 1, 1, 0, 1, 0, 1, 0, 1, '            '
0.01, 0.10, 100.0, 0.02, 0.20, 100.0, 0.03, 0.30, 100.0, 0.98, -1.5
1.0, 230.0, 0.0, 100.0, 90.0, 80.0, 0, 0, 1.1, 0.9, 1.1, 0.9, 33, 0, 0, 0, 0
1.025, 138.0, 0.0, 110.0, 0, 0, 0, 0, 1.1, 0.9, 1.1, 0.9, 33, 0, 0, 0, 0
0.95, 13.8, 30.0, 50.0, 0, 0, 0, 0, 1.1, 0.9, 1.1, 0.9, 33, 0, 0, 0, 0
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
";
        let net = parse_psse(raw).unwrap();
        assert_eq!(
            net.transformers_3w.len(),
            1,
            "the 3-winding record was read"
        );
        assert!(net.branches.is_empty(), "a 3W is not folded into branches");
        let t = &net.transformers_3w[0];
        assert_eq!(
            [t.windings[0].bus, t.windings[1].bus, t.windings[2].bus],
            [BusId(1), BusId(2), BusId(3)]
        );
        close(t.z[0].r, 0.01);
        close(t.z[2].x, 0.30);
        close(t.windings[0].rate_a, 100.0);
        close(t.windings[1].tap, 1.025);
        close(t.windings[2].shift, 30.0);
        close(t.star_vm, 0.98);
        close(t.star_va, -1.5);

        // Round trip: write and re-read keeps the windings and the star voltage.
        let net2 = parse_psse(&write_psse(&net).text).unwrap();
        assert_eq!(net2.transformers_3w.len(), 1);
        assert!(net2.branches.is_empty());
        let t2 = &net2.transformers_3w[0];
        close(t2.z[1].x, 0.20);
        close(t2.windings[2].tap, 0.95);
        close(t2.star_va, -1.5);
        assert_eq!(t2.name.as_deref(), Some("T3W"));
    }

    #[test]
    fn three_winding_cross_format_warns_and_survives_normalization() {
        // Same 3-winding record plus a slack generator so to_normalized has a
        // reference to anchor.
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / x
CASE
COMMENT
1,'B1          ', 230.0,3,1,1,1,1.00000,0.0,1.1,0.9,1.1,0.9
2,'B2          ', 138.0,1,1,1,1,1.00000,0.0,1.1,0.9,1.1,0.9
3,'B3          ', 13.8,1,1,1,1,1.00000,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
1,'1 ',50.0,5.0,20.0,-10.0,1.0,0,100.0,0.0,1.0,0.0,0.0,1.0,1,100.0,80.0,10.0
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
1, 2, 3, '1', 1, 1, 1, 0.0, 0.0, 2, 'T3W         ', 1, 1, 1, 0, 1, 0, 1, 0, 1, '            '
0.01, 0.10, 100.0, 0.02, 0.20, 100.0, 0.03, 0.30, 100.0, 0.98, -1.5
1.0, 230.0, 0.0, 100.0, 90.0, 80.0, 0, 0, 1.1, 0.9, 1.1, 0.9, 33, 0, 0, 0, 0
1.025, 138.0, 0.0, 110.0, 0, 0, 0, 0, 1.1, 0.9, 1.1, 0.9, 33, 0, 0, 0, 0
0.95, 13.8, 30.0, 50.0, 0, 0, 0, 0, 1.1, 0.9, 1.1, 0.9, 33, 0, 0, 0, 0
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
";
        let net = parse_psse(raw).unwrap();
        assert_eq!(net.transformers_3w.len(), 1);

        // Cross-format write to MATPOWER drops the 3W but must report it, not drop
        // it silently.
        let mpc = net.to_format(crate::TargetFormat::Matpower).unwrap();
        assert!(
            mpc.warnings.iter().any(|w| w.contains("3-winding")),
            "MATPOWER write must warn on the dropped 3-winding transformer, got {:?}",
            mpc.warnings
        );

        // The normalized form keeps the 3-winding transformer.
        let norm = net.to_normalized().unwrap();
        assert_eq!(norm.transformers_3w.len(), 1, "to_normalized keeps the 3W");
        norm.validate().unwrap();
    }

    #[test]
    fn writing_a_different_revision_re_emits_instead_of_echoing() {
        // A PSS/E v33 source echoes byte-for-byte when written back as v33, but a
        // request for v34 must re-emit the v34 layout, not return the v33 bytes.
        let raw = "0, 100.00, 33, 0, 0, 60.00 / x
CASE
COMMENT
1,'B1          ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
";
        let parsed = crate::parse_str(raw, "psse").unwrap();
        let same = crate::write_as(&parsed.network, crate::TargetFormat::Psse { rev: 33 }).unwrap();
        assert_eq!(same.text, raw, "same revision echoes the retained source");
        let v34 = crate::write_as(&parsed.network, crate::TargetFormat::Psse { rev: 34 }).unwrap();
        assert_ne!(v34.text, raw, "a different revision must re-emit, not echo");
        assert!(
            v34.text.contains("END OF SYSTEM-WIDE DATA"),
            "v34 output carries the system-wide marker, got:\n{}",
            v34.text
        );
    }

    #[test]
    fn warns_on_a_nonempty_unmodeled_section() {
        // A substation (node-breaker) section is not modeled; reading must report
        // it rather than drop it silently.
        let raw = "0, 100.00, 34, 0, 0, 60.00 / x
CASE
COMMENT
1,'B1          ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
0 / END OF AREA DATA, BEGIN SUBSTATION DATA
1, 'SUB1', 21.3, -157.8, 0.001
0 / END OF SUBSTATION DATA, BEGIN GNE DEVICE DATA
Q
";
        let parsed = crate::parse_str(raw, "psse").unwrap();
        assert!(
            parsed
                .warnings
                .iter()
                .any(|w| w.contains("SUBSTATION") && w.contains("not modeled")),
            "an unmodeled substation section must be reported, got {:?}",
            parsed.warnings
        );
    }

    #[test]
    fn reads_writes_and_drops_an_emergency_voltage_band() {
        // Bus 1 has a distinct EVHI/EVLO (1.2/0.8) vs the normal band (1.1/0.9);
        // bus 2's emergency band equals its normal band.
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / x
CASE
COMMENT
1,'B1          ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.2,0.8
2,'B2          ', 230.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
1,'1 ',50.0,5.0,20.0,-10.0,1.0,0,100.0,0.0,1.0,0.0,0.0,1.0,1,100.0,80.0,10.0
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
";
        let net = parse_psse(raw).unwrap();
        let b1 = net.buses.iter().find(|b| b.id == BusId(1)).unwrap();
        assert!(
            b1.evhi.is_some() && b1.evlo.is_some(),
            "distinct band typed"
        );
        close(b1.evhi.unwrap(), 1.2);
        close(b1.evlo.unwrap(), 0.8);
        let b2 = net.buses.iter().find(|b| b.id == BusId(2)).unwrap();
        assert!(
            b2.evhi.is_none() && b2.evlo.is_none(),
            "an emergency band equal to the normal band stays None"
        );

        // Round trip through the PSS/E writer keeps the distinct band.
        let net2 = parse_psse(&write_psse(&net).text).unwrap();
        let r1 = net2.buses.iter().find(|b| b.id == BusId(1)).unwrap();
        close(r1.evhi.unwrap(), 1.2);
        close(r1.evlo.unwrap(), 0.8);

        // A cross-format write to MATPOWER (single voltage band) reports the drop.
        let mpc = net.to_format(crate::TargetFormat::Matpower).unwrap();
        assert!(
            mpc.warnings
                .iter()
                .any(|w| w.contains("emergency voltage band")),
            "MATPOWER write must warn on the dropped emergency band, got {:?}",
            mpc.warnings
        );
    }

    #[test]
    fn a_case_name_with_a_terminator_cannot_forge_a_bus_record() {
        // The case name reaches the header and title lines verbatim. A
        // terminator inside it used to end the record, so the rest parsed as
        // bus data and the written file described a network the source never
        // had.
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / x
CASE
COMMENT
1,'B1          ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
";
        let mut net = parse_psse(raw).unwrap();
        net.name =
            "A\n42, 'INJECTED   ', 500.0, 2, 9, 9, 1, 1.0, 0.0, 1.1, 0.9, 1.1, 0.9".to_owned();
        net.source = None; // force a real write, not the byte-exact echo
        let text = write_psse(&net).text;
        let back = parse_psse(&text).unwrap();
        assert_eq!(back.buses.len(), 1, "forged bus record in:\n{text}");
    }

    #[test]
    fn writes_v34_v35_layouts_that_round_trip() {
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / x
CASE
COMMENT
1,'B1          ', 230.0,3,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
2,'B2          ', 230.0,1,1,1,1,1.0,0.0,1.1,0.9,1.1,0.9
0 / END OF BUS DATA, BEGIN LOAD DATA
2,'1',1,1,1,10.0,5.0,0,0,0,0,1,1,0
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
1,2,'1 ',0.01,0.05,0.001,111.0,90.0,80.0,0,0,0,0,1,1,0,1,1
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
";
        let net = parse_psse(raw).unwrap();

        for rev in [34u32, 35] {
            let text = write_psse_rev(&net, rev).text;
            // v34+ wraps the globals in a system-wide section with its end marker.
            assert!(
                text.contains("END OF SYSTEM-WIDE DATA, BEGIN BUS DATA"),
                "rev {rev} missing the system-wide marker"
            );
            let header = text.lines().next().unwrap();
            assert!(header.contains(&format!(", {rev}, ")), "header {header:?}");
            // The branch uses the named 12-rating layout (>= 24 comma fields).
            let branch = text.lines().find(|l| l.starts_with("1, 2, '1'")).unwrap();
            assert!(
                branch.split(',').count() >= 24,
                "rev {rev} branch is not the named layout: {branch:?}"
            );

            let back = parse_psse(&text).unwrap();
            assert_eq!(back.buses.len(), 2);
            assert_eq!(back.loads.len(), 1);
            assert_eq!(back.branches.len(), 1);
            close(back.branches[0].rate_a, 111.0);
            close(back.loads[0].p, 10.0);
            assert!(back.branches[0].in_service);
        }

        // The v35 load record carries the trailing LOADTYPE field.
        assert!(
            write_psse_rev(&net, 35).text.contains(", ''"),
            "v35 load should carry a LOADTYPE field"
        );
    }

    #[test]
    fn writer_sanitizes_bus_names_that_would_corrupt_a_record() {
        // A name with an apostrophe closes the single-quoted field early; a name
        // with '/' truncates the record at the inline-comment delimiter. Either
        // shifts every later column. The writer replaces both and warns, so the
        // second bus's base kV survives the round trip.
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / x
CASE
COMMENT
1,'BUS1        ', 230.0000,3,1,1,1,1.00000,0.0000,1.1000,0.9000,1.1000,0.9000
2,'BUS2        ', 138.0000,1,1,1,1,1.00000,0.0000,1.1000,0.9000,1.1000,0.9000
0 / END OF BUS DATA, BEGIN LOAD DATA
0 / END OF LOAD DATA, BEGIN FIXED SHUNT DATA
0 / END OF FIXED SHUNT DATA, BEGIN GENERATOR DATA
0 / END OF GENERATOR DATA, BEGIN BRANCH DATA
0 / END OF BRANCH DATA, BEGIN TRANSFORMER DATA
0 / END OF TRANSFORMER DATA, BEGIN AREA DATA
Q
";
        let mut net = parse_psse(raw).unwrap();
        net.buses[0].name = Some("O'Brien/X".to_string());

        let conv = write_psse(&net);
        let reparsed = parse_psse(&conv.text).unwrap();

        assert_eq!(reparsed.buses.len(), 2);
        close(reparsed.buses[0].base_kv, 230.0);
        close(reparsed.buses[1].base_kv, 138.0);
        let name = reparsed.buses[0].name.as_deref().unwrap();
        assert!(!name.contains('\'') && !name.contains('/'), "got {name:?}");
        assert!(
            conv.warnings
                .iter()
                .any(|w| w.contains("quoted PSS/E field")),
            "expected a sanitization warning, got {:?}",
            conv.warnings
        );
    }

    #[test]
    fn malformed_first_bus_id_is_not_treated_as_system_wide_data() {
        let raw = r"0, 100.00, 33, 0, 0, 60.00 / synthetic malformed export
CASE
COMMENT
BAD,'BUS1        ', 230.0000,3,1,1,1,1.00000,0.0000,1.1000,0.9000,1.1000,0.9000
0 / END OF BUS DATA, BEGIN LOAD DATA
Q
";

        let err = parse_psse(raw).unwrap_err();

        assert!(
            err.to_string().contains("bus record missing numeric id"),
            "malformed bus id should be reported directly: {err}"
        );
    }
}