/**
 * Build order step 4 — "A full solitaire game runs to completion, headless."
 * See architecture/components.md §4. This is the milestone that proves the rules before a single
 * pixel is drawn.
 */

import { describe, it } from 'node:test';
import assert from 'node:assert/strict';

import { advance, pump } from '../src/engine/advance.ts';
import { applyIntent, areaOf, check, isBeingMadeUp } from '../src/engine/apply.ts';
import { EXPEDITE_FAULT_PENALTY, HAND_LIMIT, MAX_CONSIST, STAGES_PER_DAY, TOTAL_ROLLING_STOCK } from '../src/engine/content.ts';
import { legalActions } from '../src/engine/legal.ts';
import { createGame } from '../src/engine/setup.ts';
import { developerBot } from '../src/sim/bot.ts';
import type { CrewTray, DivisionNode, GameConfig, GameState } from '../src/engine/state.ts';
import { coordKey, railFacingOf } from '../src/engine/state.ts';

const baseConfig = (over: Partial<GameConfig> = {}): GameConfig => ({
  mode: 'solitaire',
  days: 3,
  minCombinedRevenue: 0,
  maxCollisionsPerDay: 0,
  maxCollisionsTotal: 0,
  pvpCardsAllowed: false,
  optionalRules: {
    reducedVisibility: false,
    employeeRotation: false,
    emergencyToolbox: false,
  },
  ...over,
});

const game = (seed = 1, over: Partial<GameConfig> = {}): GameState =>
  createGame({ id: 'g', seed, config: baseConfig(over), playerNames: ['Jesse'] });

type PlayStats = { turns: number; scheduled: number; collisions: number; cardsPlayed: number };

/**
 * A deliberately simple bot — the seed of component 17. It draws, then plays, then ends its turn.
 *
 * The draw-first ordering matters: an earlier version never drew, so it burned its three opening
 * cards and then held an empty hand for the rest of the game. Every seed still "completed", but
 * nothing ever happened — no trains, no revenue. That is why the milestone tests below assert on
 * what the game DID, not merely that it terminated.
 */
function playToCompletion(s: GameState, seed = 1, maxTurns = 20_000): PlayStats {
  let rng = seed >>> 0;
  const pick = <T,>(xs: T[]): T => {
    rng = (rng * 1103515245 + 12345) >>> 0;
    return xs[rng % xs.length]!;
  };

  const stats: PlayStats = { turns: 0, scheduled: 0, collisions: 0, cardsPlayed: 0 };
  const tally = (events: { type: string }[]): void => {
    for (const e of events) {
      if (e.type === 'trainScheduled') stats.scheduled++;
      if (e.type === 'cardPlayed') stats.cardsPlayed++;
      if (e.type === 'revenueChanged' && 'reason' in e && String(e.reason).startsWith('collision')) {
        stats.collisions++;
      }
    }
  };

  for (; stats.turns < maxTurns; stats.turns++) {
    tally(pump(s));
    if (s.status === 'finished') break;

    const actor = s.clock.pendingDecision !== null ? s.clock.superintendent : s.clock.currentActor;
    if (actor === null) break;

    const options = legalActions(s, actor);
    if (options.length === 0) break;

    const draws = options.filter((i) => i.type.startsWith('draw.from'));
    const plays = options.filter((i) => i.type === 'card.play');
    const enders = options.filter(
      (i) =>
        i.type === 'switch.end' ||
        i.type === 'draw.end' ||
        i.type === 'loadUnload.end' ||
        i.type === 'mainline.clearance',
    );

    const choice =
      draws.length > 0
        ? pick(draws)
        : plays.length > 0
          ? pick(plays)
          : enders.length > 0
            ? pick(enders)
            : pick(options);

    const r = applyIntent(s, actor, choice);
    assert.ok(r.ok, `bot chose an illegal action: ${choice.type}`);
    tally(r.events);
  }
  return stats;
}

// ---------------------------------------------------------------------------

describe('phase sequencing (Gap 1)', () => {
  it('waits for the actor in a player-driven phase', () => {
    const s = game();
    const r = advance(s);
    assert.equal(r.needsInput, true);
    assert.equal(s.clock.phase, 'localOps');
    assert.equal(s.clock.currentActor, 0);
  });

  it('runs the phases in order once the player finishes', () => {
    const s = game();
    const seen: string[] = [];
    for (let i = 0; i < 40 && s.status === 'active'; i++) {
      const r = advance(s);
      seen.push(...r.events.filter((e) => e.type === 'phaseBegan').map(() => s.clock.phase));
      if (r.needsInput) {
        applyIntent(s, 0, { type: 'localOps.choose', option: 'draw' });
        // The opening deal is six cards against a limit of three (§6.2), so a turn cannot be ended
        // until the hand is played or discarded down. Only the first turn actually has anything to
        // shed; after that this loop is a no-op.
        while ((s.decks.hands.get(0) ?? []).length > HAND_LIMIT) {
          applyIntent(s, 0, { type: 'card.discard', cardId: s.decks.hands.get(0)![0]!, toSlot: 0 });
        }
        applyIntent(s, 0, { type: 'draw.end' });
      }
    }
    // Phase-major: the whole sequence runs per Stage, with no player acting in mainline.
    assert.ok(seen.includes('newTrain'));
    assert.ok(seen.includes('mainline'));
    assert.ok(seen.includes('loadUnload'));
  });

  it('has no current actor on entering the automatic Mainline Phase', () => {
    // Entering `mainline` nulls the actor — nobody acts in turn order there (Gap 1). With no
    // trains running the phase then completes immediately, so this checks the moment of entry.
    const s = game();
    s.clock.phase = 'newTrain';
    advance(s);
    assert.equal(s.clock.phase, 'mainline');
    assert.equal(s.clock.currentActor, null);
  });

  it('advances the Stage and resets per-Stage worker usage', () => {
    // §9.1 — Laborers and Porters reset at the start of each Stage, not each Phase.
    const s = game();
    const office = s.officeAreas.get(0)!.grid.get('0,0')!;
    office.facility!.usedThisStage = { laborers: 2, porters: 1 };
    s.clock.phase = 'shiftChange';
    advance(s);
    assert.deepEqual(office.facility!.usedThisStage, { laborers: 0, porters: 0 });
    assert.equal(s.clock.stage, 2);
  });

  it('rolls over into a new Day after twelve Stages', () => {
    const s = game();
    s.clock.stage = STAGES_PER_DAY;
    s.clock.phase = 'shiftChange';
    advance(s);
    assert.equal(s.clock.day, 2);
    assert.equal(s.clock.stage, 1);
  });

  it('passes the Fedora every three Stages', () => {
    // §5 — shift changes at Stages 3, 6, 9 and 12. With one player it returns to them.
    const s = createGame({
      id: 'g',
      seed: 3,
      config: baseConfig({ mode: 'competitive' }),
      playerNames: ['A', 'B', 'C'],
    });
    const before = s.clock.superintendent;
    s.clock.stage = 3;
    s.clock.phase = 'shiftChange';
    advance(s);
    assert.equal(s.clock.superintendent, (before + 1) % 3);
  });

  it('does not pass the Fedora on a non-shift-change Stage', () => {
    const s = createGame({
      id: 'g',
      seed: 3,
      config: baseConfig({ mode: 'competitive' }),
      playerNames: ['A', 'B', 'C'],
    });
    const before = s.clock.superintendent;
    s.clock.stage = 4;
    s.clock.phase = 'shiftChange';
    advance(s);
    assert.equal(s.clock.superintendent, before);
  });

  it('resets the collision count each Day', () => {
    // §3.4 — the counter resets at the start of each Day.
    const s = game();
    s.collisionsToday = 2;
    s.clock.stage = STAGES_PER_DAY;
    s.clock.phase = 'shiftChange';
    advance(s);
    assert.equal(s.collisionsToday, 0);
  });
});

// ---------------------------------------------------------------------------

describe('Mainline Phase (§8)', () => {
  function scheduleTrain(s: GameState, stage: number, number: number): void {
    s.timetable[stage - 1] = number;
  }

  it('makes up a train due this Stage at the correct Division Point', () => {
    const s = game();
    scheduleTrain(s, 1, 2); // train 2 is even, therefore eastbound
    s.clock.phase = 'newTrain';
    advance(s);
    const trays = [...s.trays.values()];
    assert.equal(trays.length, 1);
    assert.equal(trays[0]!.trainNumber, 2);
    assert.equal(trays[0]!.direction, 'east');
    // An eastbound train starts in the west.
    assert.deepEqual(trays[0]!.position, { at: 'divisionPoint', side: 'west' });
  });

  it('holds a train when no Crew Tray is free (§7)', () => {
    const s = game();
    s.freeTrays = [];
    scheduleTrain(s, 1, 2);
    s.clock.phase = 'newTrain';
    advance(s);
    assert.equal(s.trays.size, 0, 'the train is held, not made up');
    assert.equal(s.clock.phase, 'mainline', 'and the Stage moves on');
  });

  it('moves trains one region per Stage (§8.2)', () => {
    const s = game();
    /**
     * PIN THE TERRAIN. This used to rely on whatever card the seed happened to lay down, and the
     * moment the RNG stream moved — a different opening deal draws a different number of cards
     * before the Division is built — seed 1 dealt a 60 card instead of a 30 and the train crossed in
     * one Stage. What is under test is that crossing takes the card's time, so the card has to be
     * the test's own: Curves is a 30, which is two Stages for a fast train.
     */
    for (const n of s.division.nodes) if (n.kind === 'mainline') n.card = 'curves';
    scheduleTrain(s, 1, 2);
    s.clock.phase = 'newTrain';
    pump(s);

    const id = [...s.trays.keys()][0]!;
    s.trays.get(id)!.consist = [{ type: 'coach', loaded: false }];
    s.clock.phase = 'mainline';
    s.movedThisPhase = new Set();
    advance(s);
    const pos = s.trays.get(id)!.position;
    assert.equal(pos.at, 'mainline', 'the train highballed onto the mainline');

    s.clock.phase = 'mainline';
    s.movedThisPhase = new Set();
    advance(s);
    // Q1/Q2 — crossing time is counted in Stages by card speed and Fast/Slow class, so the train
    // stays on the card until its transit expires rather than stepping through printed cells.
    const pos2 = s.trays.get(id)!.position;
    assert.equal(pos2.at, 'mainline', 'still crossing');
  });

  it('orders movement by train number, Timetabled before Extra on a tie (Gap 5)', () => {
    const s = game();
    const order: number[] = [];
    for (const [i, spec] of [
      { n: 9, extra: true },
      { n: 9, extra: false },
      { n: 3, extra: false },
    ].entries()) {
      s.trays.set(`t${i}`, {
        id: `t${i}`,
        trainNumber: spec.n,
        trainIsExtra: spec.extra,
        engineAt: 0,
        consist: [],
        direction: 'east',
        position: { at: 'divisionPoint', side: 'west' },
        movesUsed: 0,
      });
    }
    const sorted = [...s.trays.values()].sort((a, b) => {
      const d = (a.trainNumber ?? 0) - (b.trainNumber ?? 0);
      return d !== 0 ? d : Number(a.trainIsExtra) - Number(b.trainIsExtra);
    });
    for (const t of sorted) order.push(t.trainIsExtra ? -t.trainNumber! : t.trainNumber!);
    assert.deepEqual(order, [3, 9, -9], 'train 3, then Timetabled 9, then Extra X9');
  });
});

// ---------------------------------------------------------------------------

describe('collisions are automatic (Gap 2)', () => {
  it('collides when a train arrives with every A/D track occupied', () => {
    // Gap 2d — no room at the station, the local player's fault, −5 Revenue.
    const s = game();
    const area = s.officeAreas.get(0)!;
    area.adOccupancy = ['blocker']; // a Whistle Post has exactly one A/D track

    const id = 'inbound';
    s.trays.set(id, {
      id,
      trainNumber: 2,
      trainIsExtra: false,
      engineAt: 0,
      consist: [{ type: 'coach', loaded: true }],
      direction: 'east',
      position: { at: 'mainline', index: 1 },
      movesUsed: 0,
    });
    const ml = s.division.nodes[1];
    if (ml?.kind === 'mainline') {
      // Pin the terrain. Mainline types are drawn from the SHUFFLED deck, so deck composition
      // would otherwise decide this test's outcome — and Double Track / Uncontrolled Siding set
      // `trainsMayPass`, which legitimately removes the §8.1 bar being asserted here.
      ml.card = 'plains';
      ml.transits.push({ tray: id, stagesRemaining: 1, stagesTotal: 1, direction: 'east' });
    }

    s.clock.phase = 'mainline';
    s.movedThisPhase = new Set();
    advance(s);

    assert.equal(s.players[0]!.revenue, -5, 'the fault is the local player’s (§10)');
    assert.equal(s.collisionsToday, 1);
    assert.ok(!s.trays.has(id), 'the train is removed');
  });

  it('does not collide when a coach is legally parked at the Office (v0.5.0 §A.4 exception)', () => {
    // A coach may now be set out at the Office (§A.4's carve-out). It must not become a hazard to
    // the next train in — that would punish exactly the thing the rule was written to allow.
    const s = game();
    const area = s.officeAreas.get(0)!;
    area.adOccupancy = []; // an A/D track is free — only the fouling check is under test
    const officeCard = area.grid.get(coordKey(area.officeCoord))!;
    officeCard.standing = [{ type: 'coach', loaded: false }];

    const id = 'inbound';
    s.trays.set(id, {
      id,
      trainNumber: 2,
      trainIsExtra: false,
      engineAt: 0,
      consist: [{ type: 'coach', loaded: true }],
      direction: 'east',
      position: { at: 'mainline', index: 1 },
      movesUsed: 0,
    });
    const ml = s.division.nodes[1];
    if (ml?.kind === 'mainline') {
      ml.card = 'plains';
      ml.transits.push({ tray: id, stagesRemaining: 1, stagesTotal: 1, direction: 'east' });
    }

    s.clock.phase = 'mainline';
    s.movedThisPhase = new Set();
    advance(s);

    assert.equal(s.collisionsToday, 0, 'a legally parked coach is not a hazard to the next arrival');
    assert.ok(s.trays.has(id), 'the train is not written off');
  });

  it('still collides when a non-coach car is left fouling the Office track', () => {
    // Reachable only by poking state directly — `canDropCarsAt` already refuses every non-coach
    // drop at the Office, so this backstops the collision check itself, not a state a legal game
    // can reach.
    const s = game();
    const area = s.officeAreas.get(0)!;
    area.adOccupancy = [];
    const officeCard = area.grid.get(coordKey(area.officeCoord))!;
    officeCard.standing = [{ type: 'boxcar', loaded: false }];

    const id = 'inbound';
    s.trays.set(id, {
      id,
      trainNumber: 2,
      trainIsExtra: false,
      engineAt: 0,
      consist: [{ type: 'coach', loaded: true }],
      direction: 'east',
      position: { at: 'mainline', index: 1 },
      movesUsed: 0,
    });
    const ml = s.division.nodes[1];
    if (ml?.kind === 'mainline') {
      ml.card = 'plains';
      ml.transits.push({ tray: id, stagesRemaining: 1, stagesTotal: 1, direction: 'east' });
    }

    s.clock.phase = 'mainline';
    s.movedThisPhase = new Set();
    advance(s);

    assert.equal(s.collisionsToday, 1);
    assert.ok(!s.trays.has(id), 'the train is removed');
  });

  it('returns cabooses to the Division Yard and other stock to Classification (Gap 2c)', () => {
    const s = game();
    s.officeAreas.get(0)!.adOccupancy = ['blocker'];
    const classBefore = s.yards.classificationYard.length;

    const mlx = s.division.nodes[1];
    if (mlx?.kind === 'mainline') {
      // Pin the terrain. Mainline types are drawn from the SHUFFLED deck, so deck composition
      // would otherwise decide this test's outcome — and Double Track / Uncontrolled Siding set
      // `trainsMayPass`, which legitimately removes the §8.1 bar being asserted here.
      mlx.card = 'plains';
      mlx.transits.push({ tray: 'x', stagesRemaining: 1, stagesTotal: 1, direction: 'east' });
    }
    s.trays.set('x', {
      id: 'x',
      trainNumber: 8,
      trainIsExtra: false,
      engineAt: 0,
      consist: [
        { type: 'hopper', loaded: true },
        { type: 'caboose', loaded: true },
      ],
      direction: 'east',
      position: { at: 'mainline', index: 1 },
      movesUsed: 0,
    });
    s.clock.phase = 'mainline';
    s.movedThisPhase = new Set();
    advance(s);

    assert.equal(s.yards.classificationYard.length, classBefore + 1, 'the hopper');
    assert.ok(
      s.yards.divisionYard.some((c) => c.type === 'caboose'),
      'the caboose goes straight back to the Division Yard',
    );
  });
});

// ---------------------------------------------------------------------------

describe('the Superintendent clearance interrupt (§8.1)', () => {
  it('pauses the Mainline Phase for a following-train decision', () => {
    const s = game();
    // A train already on the first Mainline card, moving east.
    s.trays.set('ahead', {
      id: 'ahead',
      trainNumber: 4,
      trainIsExtra: false,
      engineAt: 0,
      consist: [],
      direction: 'east',
      position: { at: 'mainline', index: 1 },
      movesUsed: 0,
    });
    const ml = s.division.nodes[1];
    if (ml?.kind === 'mainline') {
      // Pin the terrain. Mainline types are drawn from the SHUFFLED deck, so deck composition
      // would otherwise decide this test's outcome — and Double Track / Uncontrolled Siding set
      // `trainsMayPass`, which legitimately removes the §8.1 bar being asserted here.
      ml.card = 'plains';
      ml.transits.push({ tray: 'ahead', stagesRemaining: 2, stagesTotal: 2, direction: 'east' });
    }

    // A second train at the Western Division Point wanting to follow it.
    s.trays.set('behind', {
      id: 'behind',
      trainNumber: 2,
      trainIsExtra: false,
      engineAt: 0,
      consist: [],
      direction: 'east',
      position: { at: 'divisionPoint', side: 'west' },
      movesUsed: 0,
    });

    s.clock.phase = 'mainline';
    s.movedThisPhase = new Set();
    const r = advance(s);

    assert.equal(r.needsInput, true, 'the phase must stop and ask');
    assert.notEqual(s.clock.pendingDecision, null);
    assert.equal(s.clock.pendingDecision!.train, 'behind');
    assert.equal(s.clock.pendingDecision!.occupiedBy, 'ahead');
  });

  it('does not ask when the train ahead is coming the other way — that is an absolute bar', () => {
    const s = game();
    s.trays.set('oncoming', {
      id: 'oncoming',
      trainNumber: 3,
      trainIsExtra: false,
      engineAt: 0,
      consist: [],
      direction: 'west',
      position: { at: 'mainline', index: 1 },
      movesUsed: 0,
    });
    const ml = s.division.nodes[1];
    if (ml?.kind === 'mainline') {
      // Pin the terrain. Mainline types are drawn from the SHUFFLED deck, so deck composition
      // would otherwise decide this test's outcome — and Double Track / Uncontrolled Siding set
      // `trainsMayPass`, which legitimately removes the §8.1 bar being asserted here.
      ml.card = 'plains';
      ml.transits.push({ tray: 'oncoming', stagesRemaining: 2, stagesTotal: 2, direction: 'west' });
    }

    s.trays.set('waiting', {
      id: 'waiting',
      trainNumber: 2,
      trainIsExtra: false,
      engineAt: 0,
      consist: [],
      direction: 'east',
      position: { at: 'divisionPoint', side: 'west' },
      movesUsed: 0,
    });

    s.clock.phase = 'mainline';
    s.movedThisPhase = new Set();
    advance(s);

    assert.equal(s.clock.pendingDecision, null, 'no judgment call — the train simply holds');
    assert.deepEqual(s.trays.get('waiting')!.position, { at: 'divisionPoint', side: 'west' });
  });

  it('clears the decision once the Superintendent rules', () => {
    const s = game();
    s.clock.phase = 'mainline';
    s.clock.pendingDecision = { train: 'a', occupiedBy: 'b' };
    const r = applyIntent(s, 0, { type: 'mainline.clearance', allow: false });
    assert.ok(r.ok);
    assert.equal(s.clock.pendingDecision, null);
  });
});

// ---------------------------------------------------------------------------

describe('victory conditions (§3, Gap 10e) — unified 2026-08-20', () => {
  it('loses a timed Solitaire game that misses minCombinedRevenue', () => {
    // minCombinedRevenue doubles as a MINIMUM in Solitaire: below it you lose regardless of score.
    const s = game(1, { minCombinedRevenue: 10 });
    s.clock.day = s.config.days + 1;
    s.clock.stage = STAGES_PER_DAY;
    s.clock.phase = 'shiftChange';
    s.players[0]!.revenue = 0;
    advance(s);
    assert.equal(s.status, 'finished');
    assert.equal(s.outcome!.result, 'loss');
    assert.equal(s.outcome!.reason, 'revenueFloor');
  });

  it('wins a timed Solitaire game that clears minCombinedRevenue', () => {
    const s = game(1, { minCombinedRevenue: 10 });
    s.clock.day = s.config.days + 1;
    s.clock.stage = STAGES_PER_DAY;
    s.clock.phase = 'shiftChange';
    s.players[0]!.revenue = 10;
    advance(s);
    assert.equal(s.status, 'finished');
    assert.equal(s.outcome!.result, 'win');
  });

  it('minCombinedRevenue = 0 disables the floor — any score wins once days run out', () => {
    const s = game(1, { minCombinedRevenue: 0 });
    s.clock.day = s.config.days + 1;
    s.clock.stage = STAGES_PER_DAY;
    s.clock.phase = 'shiftChange';
    s.players[0]!.revenue = 0;
    advance(s);
    assert.equal(s.status, 'finished');
    assert.equal(s.outcome!.result, 'win');
  });

  it('everyone loses in Competitive when the TABLE misses minCombinedRevenue, whoever scored best', () => {
    const s = createGame({
      id: 'g', seed: 2, config: baseConfig({ mode: 'competitive', minCombinedRevenue: 20 }),
      playerNames: ['A', 'B'],
    });
    s.clock.day = s.config.days + 1;
    s.clock.stage = STAGES_PER_DAY;
    s.clock.phase = 'shiftChange';
    s.players[0]!.revenue = 5; // best individual score...
    s.players[1]!.revenue = 3; // ...but combined (8) still misses the floor (20).
    advance(s);
    assert.equal(s.status, 'finished');
    assert.equal(s.outcome!.result, 'loss');
    assert.equal(s.outcome!.reason, 'revenueFloor');
  });

  it('Co-op wins as one table score (summed Revenue), winner stays null', () => {
    const s = createGame({
      id: 'g', seed: 3, config: baseConfig({ mode: 'coop', minCombinedRevenue: 10 }),
      playerNames: ['A', 'B'],
    });
    s.clock.day = s.config.days + 1;
    s.clock.stage = STAGES_PER_DAY;
    s.clock.phase = 'shiftChange';
    s.players[0]!.revenue = 4;
    s.players[1]!.revenue = 6; // combined 10 clears the floor, neither alone would.
    advance(s);
    assert.equal(s.status, 'finished');
    assert.equal(s.outcome!.result, 'win');
    assert.equal(s.outcome!.winner, null, 'Co-op names an individual winner instead of a shared one');
  });

  it('ends immediately, mid-Stage, when collisions reach maxCollisionsPerDay', () => {
    // Competitive/coop only, and immediate — not gated on the day boundary the way the revenue
    // floor is. Stage 1, well short of STAGES_PER_DAY, proves it fires mid-day.
    const s = game(1, { mode: 'competitive', maxCollisionsPerDay: 2 });
    s.collisionsToday = 2;
    s.clock.stage = 1;
    s.clock.phase = 'shiftChange';
    advance(s);
    assert.equal(s.status, 'finished');
    assert.equal(s.outcome!.result, 'loss');
    assert.equal(s.outcome!.reason, 'collisionFloor');
  });

  it('ends immediately when the running total reaches maxCollisionsTotal, even under the per-day cap', () => {
    const s = game(1, { mode: 'coop', maxCollisionsPerDay: 0, maxCollisionsTotal: 3 });
    s.collisionsTotal = 3;
    s.clock.stage = 1;
    s.clock.phase = 'shiftChange';
    advance(s);
    assert.equal(s.status, 'finished');
    assert.equal(s.outcome!.reason, 'collisionFloor');
  });

  it('maxCollisionsPerDay = 0 and maxCollisionsTotal = 0 disable the collision floor entirely', () => {
    const s = game(1, { mode: 'competitive', maxCollisionsPerDay: 0, maxCollisionsTotal: 0 });
    s.collisionsToday = 99;
    s.collisionsTotal = 99;
    s.clock.stage = 1;
    s.clock.phase = 'shiftChange';
    advance(s);
    assert.notEqual(s.status, 'finished');
  });

  it('solitaire never checks the collision floor, whatever the counts', () => {
    const s = game(1, { mode: 'solitaire', maxCollisionsPerDay: 1, maxCollisionsTotal: 1 });
    s.collisionsToday = 99;
    s.collisionsTotal = 99;
    s.clock.stage = 1;
    s.clock.phase = 'shiftChange';
    advance(s);
    assert.notEqual(s.status, 'finished');
  });
});

// ---------------------------------------------------------------------------

describe('MILESTONE: a full solitaire game runs headless', () => {
  it('plays a short game to completion', () => {
    const s = game(42);
    playToCompletion(s, 42);
    assert.equal(s.status, 'finished', 'the game must reach an outcome');
    assert.ok(s.outcome, 'and record one');
    assert.ok(s.clock.day >= 1);
  });

  it('terminates from many different seeds', () => {
    // The driver must settle regardless of how the deck falls.
    for (const seed of [1, 7, 23, 99, 256, 1013]) {
      const s = game(seed);
      playToCompletion(s, seed);
      assert.equal(s.status, 'finished', `seed ${seed} did not finish`);
    }
  });

  it('is fully reproducible from a seed', () => {
    const a = game(555);
    const b = game(555);
    playToCompletion(a, 555);
    playToCompletion(b, 555);
    assert.equal(a.clock.day, b.clock.day);
    assert.equal(a.players[0]!.revenue, b.players[0]!.revenue);
    assert.deepEqual(a.outcome, b.outcome);
  });

  it('never offers the bot an illegal action along the way', () => {
    // playToCompletion asserts this on every step; this test states the guarantee explicitly.
    const s = game(31);
    const stats = playToCompletion(s, 31);
    assert.ok(stats.turns > 0, 'the game should take at least one turn');
  });

  it('actually plays the game — trains get scheduled and cards get played', () => {
    // GUARD. An earlier bot completed every seed while doing nothing at all: no trains, no
    // revenue, every game a loss. Asserting only on termination hid two real bugs. These assert
    // the game DEVELOPS.
    let scheduled = 0;
    let cardsPlayed = 0;
    for (const seed of [7, 42, 99, 256]) {
      const s = game(seed);
      const stats = playToCompletion(s, seed);
      scheduled += stats.scheduled;
      cardsPlayed += stats.cardsPlayed;
    }
    assert.ok(scheduled > 0, 'no train was ever scheduled across four games');
    assert.ok(cardsPlayed > 4, `only ${cardsPlayed} cards played across four games`);
  });

  it('terminates even when the Superintendent denies clearance repeatedly', () => {
    // A denied ruling must be CONSUMED. Without that the driver re-evaluates the same train and
    // asks the same question forever — a livelock that only showed up on one seed.
    const s = game(7);
    const stats = playToCompletion(s, 7, 5_000);
    assert.equal(s.status, 'finished');
    assert.ok(stats.turns < 5_000, `took ${stats.turns} turns — probable livelock`);
  });

  it('conserves rolling stock across a whole game', () => {
    // Nothing may be created or destroyed: every piece in the roster, wherever it sits.
    const s = game(88);
    playToCompletion(s, 88);

    let count = s.yards.divisionYard.length + s.yards.classificationYard.length;
    for (const tray of s.trays.values()) count += tray.consist.length;
    for (const area of s.officeAreas.values()) {
      for (const card of area.grid.values()) {
        count += card.standing.length;
        if (card.facility) {
          count += card.facility.outboundBox.length;
          count += card.facility.inboundBox.length;
          count += card.facility.industryTrack.cars.length;
        }
      }
    }
    assert.equal(count, TOTAL_ROLLING_STOCK, 'rolling stock leaked or was duplicated');
  });
});

describe('X18 Circus Train — a point for standing still', () => {
  it('pays once for a Stage spent stopped, and never again', () => {
    /**
     * REPORTED: "Circus train TX18 was stopped on a siding for a full Stage and I did not get my
     * Revenue point." It never could: `stopEarnsPoint` was declared on the profile and read
     * NOWHERE, along with eight other special-train rules. The one card in the deck that pays for
     * standing still paid nothing.
     */
    const s = game();
    s.clock.phase = 'mainline';
    s.trays.set('circus', {
      id: 'circus', trainNumber: 18, trainIsExtra: true, engineAt: 0,
      consist: [], direction: 'east',
      position: { at: 'grid', seat: 0, coord: { row: -1, col: 0 } },
      movesUsed: 0,
    } as never);
    // A card under it, so the crew is somewhere real rather than off the grid.
    areaOf(s, 0).grid.set('-1,0', {
      geometry: { kind: 'track', geometry: 'straight' },
      baseOperationalRail: true, standing: [], facility: null, modifiers: [], enhancements: [],
    } as never);

    const before = s.players[0]!.revenue;
    const first = pump(s);
    assert.ok(
      first.some((e) => e.type === 'trainStoodStill' && e.trainNumber === 18),
      'the Circus Train stood still for a Stage and earned nothing',
    );
    assert.equal(s.players[0]!.revenue, before + 1, 'the point was not paid');

    // "One turn stopped" — once. A train that goes on standing there does not keep earning.
    const paidAgain = () => {
      s.clock.phase = 'mainline';
      s.movedThisPhase = new Set();
      return pump(s).some((e) => e.type === 'trainStoodStill');
    };
    assert.ok(!paidAgain(), 'the Circus Train collected a second time for the same set-up');
  });
});

// ---------------------------------------------------------------------------

describe('a train on the Division points the way it is running', () => {
  /**
   * Nothing reset `facing` when a train left a district, so a crew that had been shunted onto a
   * north-south spur carried a compass port — 'n' or 's' — out onto the Division with it.
   *
   * The Division is east-west, and so is every Office card, so that port exists nowhere the train is
   * about to be. `movesFor` explores from `facing` and from its opposite, and a card with neither
   * yields nothing at all: the train arrived at the next Office **unable to switch at all**. It also
   * drew a ▲ on the Division map, where there is no north.
   *
   * A train running the Division has its engine at one end of an east-west railroad, so this is not
   * a repair applied after the fact — it is the only thing `facing` can mean out there.
   */
  const runningOnTheDivision = (spurFacing: 'n' | 's', direction: 'east' | 'west'): CrewTray => {
    const s = game();
    // Straight onto the Mainline card west of the first Office, as a departure would.
    const index = s.division.nodes.findIndex((n) => n.kind === 'mainline');
    const node = s.division.nodes[index]!;
    assert.equal(node.kind, 'mainline');
    const id = 'shunted';
    s.trays.set(id, {
      id, trainNumber: 2, trainIsExtra: false, engineAt: 0, consist: [],
      direction,
      // What a Move round a district leaves behind: a real port on the card it was standing on.
      facing: spurFacing,
      railFacing: 'w',
      position: { at: 'grid', seat: 0, coord: areaOf(s, 0).officeCoord },
      movesUsed: 0,
    });
    const tray = s.trays.get(id)!;
    // Depart it: the Mainline Phase's own path onto the card.
    s.clock.phase = 'mainline';
    s.movedThisPhase = new Set();
    for (let i = 0; i < 3 && tray.position.at === 'grid'; i++) {
      s.clock.phase = 'mainline';
      s.movedThisPhase = new Set();
      advance(s);
    }
    assert.notEqual(tray.position.at, 'grid', 'the train never left the district');
    return tray;
  };

  it('drops the spur port the moment it reaches the Mainline', () => {
    for (const spur of ['n', 's'] as const) {
      for (const direction of ['east', 'west'] as const) {
        const tray = runningOnTheDivision(spur, direction);
        assert.equal(
          tray.facing,
          direction === 'east' ? 'e' : 'w',
          `a ${direction}bound train left the district still facing ${spur}`,
        );
        assert.equal(railFacingOf(tray), direction === 'east' ? 'e' : 'w');
      }
    }
  });
});

// ---------------------------------------------------------------------------

describe('the history says WHY a train moved, and says it truthfully', () => {
  /**
   * REPORTED from play: "some trains seem to be moving before I can switch or do other operations on
   * them — it may be the rules are wrong, or it may be my perception."
   *
   * It was perception, but the log was actively feeding it. Every departure read alike, and the
   * arrival line for an Expedited train said there was "no turn in which to work it" — which was
   * false under the OLD (v0.4.8 and earlier) same-stage-departure reading of Q3, and cost the player
   * the Cargo turn they did have.
   *
   * v0.4.9 CORRECTED Q3 ITSELF, not just the narration: Expedite does not change when a train
   * leaves — it is released by the ordinary §8.1 rules exactly like any other train, and may be
   * switched normally while it stands. What it means is that the train must not be PARKED anywhere
   * but the station; leaving it on Secondary Track when a Mainline Phase begins is a Station Master
   * fault (`expediteFault`, `EXPEDITE_FAULT_PENALTY`). These pin that behaviour, so a phase-order
   * change cannot silently bring back the old forced departure.
   */
  /**
   * Drop one named train at the Western Division Point and follow it, counting the DISTINCT phases
   * it spends standing in a district — `advance` is called many times inside one phase, so a raw
   * count would say nothing. Driven by the developer bot rather than a hand-rolled phase-ender,
   * which deadlocks the moment Local Operations wants an option chosen before it can be ended.
   */
  const phasesWith = (trainNumber: number): { localOps: number; loadUnload: number; leftIn: string } => {
    const s = game(7, { days: 5 });
    for (const n of s.division.nodes) if (n.kind === 'mainline') n.card = 'plains';
    /**
     * A DIVISION WITH NOTHING ELSE ON IT. §8.1 can still hold any train, Expedited or not, on a
     * same-direction meet — with the bot's own traffic running, Train 6 was held four Stages and
     * collected four Local Operations turns. Correct behaviour, but it is traffic noise for what
     * this test is trying to pin, so clearing the timetable isolates the rule from it.
     */
    s.timetable = s.timetable.map(() => null);
    const id = 'watched';
    s.trays.set(id, {
      id, trainNumber, trainIsExtra: false, engineAt: 0,
      consist: [{ type: 'coach', loaded: true }] as never,
      direction: 'east', facing: 'e',
      position: { at: 'divisionPoint', side: 'west' }, movesUsed: 0,
    });
    const dp = s.division.nodes.find((n) => n.kind === 'divisionPoint' && n.side === 'west');
    if (dp?.kind === 'divisionPoint') dp.holding.push(id);

    const standingIn = new Set<string>();
    let reachedOffice = false;
    let leftIn = '';

    for (let i = 0; i < 20_000; i++) {
      const phase = s.clock.phase;
      const onGrid = s.trays.get(id)?.position.at === 'grid';
      if (onGrid) {
        reachedOffice = true;
        standingIn.add(`${s.clock.day}|${s.clock.stage}|${phase}`);
      }

      const r = advance(s);

      if (reachedOffice && onGrid && s.trays.get(id)?.position.at !== 'grid' && leftIn === '') {
        leftIn = phase;
        break;
      }
      if (s.status === 'finished') break;
      if (r.needsInput) {
        /**
         * A PLAYER WHO DOES NOTHING. The developer bot plays train cards, and a train card rolls
         * itself onto the Timetable — so clearing the Timetable above achieved nothing while the bot
         * was driving, and the watched train kept meeting traffic it had to be cleared past. This
         * ends every turn without playing anything, which is the only way to isolate one train.
         */
        const actor = s.clock.pendingDecision !== null ? s.clock.superintendent : s.clock.currentActor;
        if (actor === null) break;
        const options = legalActions(s, actor);
        if (options.length === 0) break;
        const pick =
          options.find((x) => x.type === 'mainline.clearance') ??
          options.find(
            (x) =>
              x.type === 'switch.end' ||
              x.type === 'draw.end' ||
              x.type === 'loadUnload.end' ||
              x.type === 'freightAgent.end',
          ) ??
          options.find((x) => x.type === 'localOps.choose') ??
          options[0]!;
        if (!applyIntent(s, actor, pick).ok) break;
      }
    }

    const count = (phase: string): number => [...standingIn].filter((k) => k.endsWith(`|${phase}`)).length;
    assert.ok(reachedOffice, `train ${trainNumber} never reached a district at all`);
    return { localOps: count('localOps'), loadUnload: count('loadUnload'), leftIn };
  };

  it('gives an ordinary train a Local Operations turn before it goes', () => {
    // Train 12 Drag Freight — no Expedite. Arrives in a Mainline Phase, stands, and the player gets
    // a Local Operations turn with it in the NEXT Stage. This is what the arrival line promises.
    const r = phasesWith(12);
    assert.ok(r.localOps >= 1, `an ordinary train got ${r.localOps} Local Operations turns`);
    assert.equal(r.leftIn, 'mainline', 'an ordinary train should leave in a Mainline Phase');
  });

  it('gives an Expedited train a Local Operations turn too, exactly like an ordinary one', () => {
    // Train 6 The Sparrow — Expedite. v0.4.9 corrected Q3: Expedite no longer forces a same-stage
    // departure, so an Expedited train is released by the ordinary §8.1 rule and stands for a
    // Local Operations turn the same as Train 12 above.
    const r = phasesWith(6);
    assert.ok(r.localOps >= 1, `an Expedited train got ${r.localOps} Local Operations turns`);
    assert.ok(r.loadUnload >= 1, 'an Expedited train never stood through a Cargo phase');
    assert.equal(r.leftIn, 'mainline', 'an Expedited train should leave in a Mainline Phase, like any other');
  });

  it('faults an Expedited train left off the station when a Mainline Phase begins', () => {
    // What Expedite actually restricts now: not WHEN the train leaves, but WHERE it may be left
    // standing in the meantime. Parked on Secondary Track — cleared there to make way for other
    // switching, say — it must not still be there when the next Mainline Phase begins.
    const s = game(7, { days: 5 });
    const area = areaOf(s, 0);
    const id = 'expedited';
    const secondary = { row: area.officeCoord.row, col: area.officeCoord.col + 1 };
    s.trays.set(id, {
      id, trainNumber: 6, trainIsExtra: false, engineAt: 0, consist: [],
      direction: 'east', facing: 'e',
      position: { at: 'grid', seat: 0, coord: secondary }, movesUsed: 0,
    });

    s.clock.phase = 'mainline';
    const before = s.players[0]!.revenue;
    const r = advance(s);

    assert.ok(
      r.events.some((e) => e.type === 'expediteFault' && e.trainNumber === 6),
      'no fault was raised for an Expedited train left off the station',
    );
    assert.equal(
      s.players[0]!.revenue,
      before - EXPEDITE_FAULT_PENALTY,
      'the fault did not cost Revenue',
    );
  });

  it('does not fault an Expedited train legitimately held at the station itself', () => {
    // A train sitting on the Office square is not "left" anywhere — including one §8.1 is holding
    // for a same-direction meet, which is an ordinary hold, not a Station Master failure.
    const s = game(7, { days: 5 });
    const area = areaOf(s, 0);
    const id = 'expedited';
    s.trays.set(id, {
      id, trainNumber: 6, trainIsExtra: false, engineAt: 0, consist: [],
      direction: 'east', facing: 'e',
      position: { at: 'grid', seat: 0, coord: area.officeCoord }, movesUsed: 0,
    });
    area.adOccupancy.push(id);

    // A train ahead of it in the same Subdivision, running the SAME way — §8.1's fourth condition,
    // which is the Superintendent's call rather than an absolute bar.
    const ahead = s.division.nodes.findIndex((n) => n.kind === 'mainline');
    const node = s.division.nodes[ahead];
    assert.equal(node?.kind, 'mainline');
    s.trays.set('ahead', {
      id: 'ahead', trainNumber: 12, trainIsExtra: false, engineAt: 0, consist: [],
      direction: 'east', facing: 'e', position: { at: 'mainline', index: ahead }, movesUsed: 0,
    });
    if (node?.kind === 'mainline') {
      node.transits.push({ tray: 'ahead', stagesRemaining: 2, stagesTotal: 2, direction: 'east' });
    }

    s.clock.phase = 'mainline';
    const before = s.players[0]!.revenue;
    const r = advance(s);

    assert.ok(
      r.events.some((e) => e.type === 'clearanceRequested' && e.trainId === id),
      'the departure was not put to the Superintendent',
    );
    assert.ok(
      !r.events.some((e) => e.type === 'expediteFault'),
      'a train properly parked at the station was faulted anyway',
    );
    assert.equal(
      s.players[0]!.revenue,
      before,
      'Revenue changed for a train legitimately held at the station',
    );
  });
});

// ---------------------------------------------------------------------------

describe('an Extra starts where the player puts it (Gitea#4)', () => {
  /**
   * REPORTED, v0.4.9e: "When extras are played the player doing so may choose where the extra
   * starts. They may choose either division point. And if the interchange mainline card has been
   * played, they may start the extra on that card and choose the direction from there. If there is
   * potential for conflict with other trains in that area the superintendent may hold the extra."
   *
   * This SUPERSEDES the earlier ruling these tests used to assert — "the number decides, like
   * everything else on the timetable" — for Extras only. The number still decides for a timetabled
   * train. The reason the two cannot both hold: an odd (westbound) Extra placed at the WEST end
   * would leave the Division on its first move having crossed nothing, and be paid for the run.
   *
   * So: the start decides the direction. A Division Point runs the train away from itself; in the
   * middle of the railroad — an Interchange, a Control Point — the player says which way.
   */
  const pending = (trainNumber: number, tier?: 'depot' | 'station'): GameState => {
    const s = game(11);
    s.pendingExtras = [trainNumber];
    s.timetable = s.timetable.map(() => null);
    if (tier) s.officeAreas.get(0)!.tier = tier;
    s.clock.phase = 'newTrain';
    advance(s);
    return s;
  };

  const started = (s: GameState): CrewTray => {
    const tray = [...s.trays.values()].find((t) => t.trainIsExtra);
    assert.ok(tray, 'the Extra never took a Crew Tray');
    return tray;
  };

  /** Turn one Mainline card into an Interchange, and say which node it is. */
  const withInterchange = (s: GameState): number => {
    const i = s.division.nodes.findIndex((n) => n.kind === 'mainline');
    const node = s.division.nodes[i]!;
    if (node.kind === 'mainline') node.card = 'interchange';
    return i;
  };

  it('stops for the decision instead of launching the train itself', () => {
    const s = pending(17);
    assert.equal(s.clock.phase, 'newTrain');
    assert.equal(s.trays.size, 0, 'the Extra was placed without anyone choosing where');
    assert.ok(
      legalActions(s, s.clock.currentActor ?? 0).some((i) => i.type === 'newTrain.startExtra'),
      'the placement was never offered',
    );
  });

  it('offers BOTH Division Points, not the one the number would dictate', () => {
    const s = pending(17);
    const sides = legalActions(s, 0)
      .filter((i) => i.type === 'newTrain.startExtra' && i.start?.kind === 'divisionPoint')
      .map((i) => (i.type === 'newTrain.startExtra' && i.start?.kind === 'divisionPoint' ? i.start.side : ''));
    assert.deepEqual([...sides].sort(), ['east', 'west']);
  });

  it('runs an Extra AWAY from the Division Point it was placed at, whatever its number', () => {
    // X17 is odd. Under the superseded rule it could only ever start at the East end and run west.
    for (const [side, direction] of [['west', 'east'], ['east', 'west']] as const) {
      const s = pending(17);
      const r = applyIntent(s, 0, {
        type: 'newTrain.startExtra', trainNumber: 17, start: { kind: 'divisionPoint', side },
      });
      assert.ok(r.ok, `the ${side} Division Point was refused: ${r.ok ? '' : r.code}`);
      const tray = started(s);
      assert.equal(tray.direction, direction, `an Extra at the ${side} end must run ${direction}`);
      assert.equal(tray.position.at === 'divisionPoint' && tray.position.side, side);
    }
  });

  it('refuses a Whistle Post, which is not a Control Point, at every setting of the house rule', () => {
    for (const extraStart of ['divisionPointsOnly', 'ownOffice', 'anyOffice'] as const) {
      const s = pending(18);
      s.config = { ...s.config, houseRules: { ...s.config.houseRules, extraStart } };
      assert.equal(s.officeAreas.get(0)!.tier, 'whistlePost');
      const code = check(s, 0, {
        type: 'newTrain.startExtra', trainNumber: 18, start: { kind: 'office', seat: 0 }, direction: 'east',
      });
      assert.ok(code !== null, `a Whistle Post was allowed under ${extraStart}`);
    }
  });

  it('starts at a Control Point when the player picks one, taking an A/D track', () => {
    // Upgrading the Office is what buys this: a Depot is a Control Point, a Whistle Post is not.
    const s = pending(18, 'depot');
    const r = applyIntent(s, 0, {
      type: 'newTrain.startExtra', trainNumber: 18, start: { kind: 'office', seat: 0 }, direction: 'west',
    });
    assert.ok(r.ok, `starting at the Depot was refused: ${r.ok ? '' : r.code}`);
    const tray = started(s);
    const area = s.officeAreas.get(0)!;
    assert.equal(tray.position.at, 'grid');
    assert.deepEqual(
      tray.position.at === 'grid' ? tray.position.coord : null,
      area.officeCoord,
      'the Extra did not start on the Office card',
    );
    assert.ok(area.adOccupancy.includes(tray.id), 'it did not take an A/D track');
    // The point of the change: an EVEN Extra running WEST, because the player said so.
    assert.equal(tray.direction, 'west', 'the direction the player chose was not honoured');
  });

  it('needs a direction anywhere that is not an end of the Division', () => {
    const s = pending(18, 'depot');
    assert.equal(
      check(s, 0, { type: 'newTrain.startExtra', trainNumber: 18, start: { kind: 'office', seat: 0 } }),
      'NO_DIRECTION_CHOSEN',
    );
  });

  it('honours the extraStart house rule for Office starts, and never for the shared ground', () => {
    for (const [extraStart, code] of [
      ['divisionPointsOnly', 'OFFICE_STARTS_NOT_ALLOWED'],
      ['anyOffice', null],
    ] as const) {
      const s = pending(18, 'depot');
      s.config = { ...s.config, houseRules: { ...s.config.houseRules, extraStart } };
      assert.equal(
        check(s, 0, {
          type: 'newTrain.startExtra', trainNumber: 18, start: { kind: 'office', seat: 0 }, direction: 'east',
        }),
        code,
        `office start under ${extraStart}`,
      );
      // The Division Points belong to nobody, so no setting ever closes them.
      assert.equal(
        check(s, 0, { type: 'newTrain.startExtra', trainNumber: 18, start: { kind: 'divisionPoint', side: 'west' } }),
        null,
      );
    }
  });

  it('starts at an Interchange in the players yard, not out on the running line', () => {
    const s = pending(18);
    const node = withInterchange(s);
    const r = applyIntent(s, 0, {
      type: 'newTrain.startExtra', trainNumber: 18, start: { kind: 'mainline', node }, direction: 'east',
    });
    assert.ok(r.ok, `the Interchange was refused: ${r.ok ? '' : r.code}`);
    const tray = started(s);
    const card = s.division.nodes[node]!;
    assert.equal(tray.direction, 'east');
    assert.deepEqual(tray.position, { at: 'mainline', index: node });
    assert.ok(card.kind === 'mainline' && card.holding?.includes(tray.id), 'it is not in the yard');
    assert.equal(card.kind === 'mainline' && card.transits.length, 0, 'it was put on the running line');
  });

  it('refuses any Mainline card that is not an Interchange', () => {
    const s = pending(18);
    const plains = s.division.nodes.findIndex((n) => n.kind === 'mainline');
    const node = s.division.nodes[plains]!;
    if (node.kind === 'mainline') node.card = 'plains';
    assert.equal(
      check(s, 0, { type: 'newTrain.startExtra', trainNumber: 18, start: { kind: 'mainline', node: plains }, direction: 'east' }),
      'NOT_AN_INTERCHANGE',
    );
  });

  it('may be started at an Interchange however busy the card is — the yard forces no collision', () => {
    const s = pending(18);
    const node = withInterchange(s);
    const card = s.division.nodes[node]!;
    // Nose to tail with opposing traffic. §7: placing here still must not force a collision.
    if (card.kind === 'mainline') {
      card.transits.push({ tray: 'tray9', stagesRemaining: 2, stagesTotal: 2, direction: 'west' });
    }
    assert.equal(
      check(s, 0, { type: 'newTrain.startExtra', trainNumber: 18, start: { kind: 'mainline', node }, direction: 'east' }),
      null,
    );
  });

  /**
   * §7's last clause, and the reason the Interchange start is modelled as a yard at all: "If there
   * is potential for conflict with other trains in that area the superintendent may hold the extra."
   *
   * Jesse's split: a GUARANTEED collision holds the train at the Interchange for another Stage and
   * it tries again; a POTENTIAL one is the Superintendent's to rule on. Those are exactly §8.1's
   * two answers, so the Extra highballs out of the yard through `evaluateClearance` — the same
   * check a train leaving a Division Point goes through — rather than through anything new.
   */
  describe('highballing out of the Interchange yard', () => {
    /** A pending X18 sitting in the yard of an Interchange, with the terrain pinned. */
    const inYard = (): { s: GameState; node: number; tray: CrewTray } => {
      const s = pending(18);
      const node = withInterchange(s);
      const r = applyIntent(s, 0, {
        type: 'newTrain.startExtra', trainNumber: 18, start: { kind: 'mainline', node }, direction: 'east',
      });
      assert.ok(r.ok, `the Interchange was refused: ${r.ok ? '' : r.code}`);
      s.clock.phase = 'mainline';
      s.movedThisPhase = new Set();
      return { s, node, tray: started(s) };
    };

    const card = (s: GameState, node: number): Extract<DivisionNode, { kind: 'mainline' }> => {
      const n = s.division.nodes[node]!;
      assert.equal(n.kind, 'mainline');
      return n as Extract<DivisionNode, { kind: 'mainline' }>;
    };

    it('pulls out onto the card at the next Mainline Phase when the Subdivision is clear', () => {
      const { s, node, tray } = inYard();
      advance(s);
      const n = card(s, node);
      assert.deepEqual(n.holding, [], 'it never left the yard');
      assert.ok(n.transits.some((t) => t.tray === tray.id), 'it is not on the running line');
    });

    it('is held in the yard by a facing train, and tries again the next Stage', () => {
      const { s, node, tray } = inYard();
      // Westbound, against an eastbound Extra: §8.1 calls that an absolute bar, not a judgment call.
      card(s, node).transits.push({ tray: 'facing', stagesRemaining: 2, stagesTotal: 2, direction: 'west' });
      s.trays.set('facing', {
        id: 'facing', trainNumber: 3, trainIsExtra: false, engineAt: 0, consist: [],
        direction: 'west', position: { at: 'mainline', index: node }, movesUsed: 0,
      });

      const r = advance(s);
      assert.equal(r.needsInput ?? false, false, 'a guaranteed collision is not a question to ask');
      assert.equal(s.clock.pendingDecision, null);
      assert.ok(card(s, node).holding?.includes(tray.id), 'it was not held in the yard');
      assert.ok(
        !card(s, node).transits.some((t) => t.tray === tray.id),
        'it pulled out in front of a train coming the other way',
      );
      assert.ok(s.trays.has(tray.id), 'the Extra was destroyed rather than held');

      // AND IT TRIES AGAIN. The Extra waits in the yard, not on the pending list, so once the road
      // clears the next Mainline Phase takes it out with no further intervention.
      s.trays.delete('facing');
      card(s, node).transits = [];
      s.clock.phase = 'mainline';
      s.movedThisPhase = new Set();
      advance(s);
      assert.deepEqual(card(s, node).holding, [], 'it did not try again once the road was clear');
      assert.ok(card(s, node).transits.some((t) => t.tray === tray.id), 'it never pulled out');
    });

    it('puts a following train to the Superintendent rather than holding it automatically', () => {
      const { s, node, tray } = inYard();
      // Same direction: §8.1's judgment call, which is what "may hold the extra" means.
      card(s, node).transits.push({ tray: 'ahead', stagesRemaining: 2, stagesTotal: 2, direction: 'east' });
      s.trays.set('ahead', {
        id: 'ahead', trainNumber: 4, trainIsExtra: false, engineAt: 0, consist: [],
        direction: 'east', position: { at: 'mainline', index: node }, movesUsed: 0,
      });

      const r = advance(s);
      assert.equal(r.needsInput, true, 'the phase must stop and ask');
      assert.equal(s.clock.pendingDecision?.train, tray.id);
      assert.equal(s.clock.pendingDecision?.occupiedBy, 'ahead');

      // HOLD keeps it in the yard.
      assert.ok(applyIntent(s, s.clock.superintendent, { type: 'mainline.clearance', allow: false }).ok);
      advance(s);
      assert.ok(card(s, node).holding?.includes(tray.id), 'the Superintendent held it and it left anyway');
    });
  });

  /**
   * FOUND BY PLAYING IT, not by the tests above: an Extra started anywhere but a Division Point was
   * never offered a car and ran empty.
   *
   * `isBeingMadeUp` asked only "is this tray standing at a Division Point", which was the whole
   * truth while that was the only place to build a train. The Control Point start has therefore
   * shipped since it was added with a train that could not be loaded, and the Interchange start
   * would have shipped the same way — against Jesse's report, which says an Extra started at the
   * Interchange "would be Loaded with cars".
   */
  describe('an Extra started away from a Division Point can still be made up', () => {
    const fill = (s: GameState): string[] => {
      for (let i = 0; i < MAX_CONSIST + 1; i++) {
        const options = legalActions(s, s.clock.currentActor ?? 0).filter((a) => a.type === 'newTrain.placeCar');
        if (options.length === 0) break;
        assert.ok(applyIntent(s, s.clock.currentActor ?? 0, options[0]!).ok);
      }
      return started(s).consist.map((c) => c.type);
    };

    it('takes a consist in the Interchange yard', () => {
      const s = pending(18);
      const node = withInterchange(s);
      assert.ok(applyIntent(s, 0, {
        type: 'newTrain.startExtra', trainNumber: 18, start: { kind: 'mainline', node }, direction: 'east',
      }).ok);
      assert.ok(fill(s).length > 0, 'the Extra was never offered a car and would have run empty');
    });

    it('takes a consist at a Control Point', () => {
      const s = pending(18, 'depot');
      assert.ok(applyIntent(s, 0, {
        type: 'newTrain.startExtra', trainNumber: 18, start: { kind: 'office', seat: 0 }, direction: 'east',
      }).ok);
      assert.ok(fill(s).length > 0, 'the Extra was never offered a car and would have run empty');
    });

    it('stops being made up the moment it starts running', () => {
      // Otherwise a train out on the Mainline could be handed cars from the Division Yard — the
      // "cars appearing on a train nobody was making up" bug `isBeingMadeUp` exists to prevent.
      const s = pending(18);
      const node = withInterchange(s);
      assert.ok(applyIntent(s, 0, {
        type: 'newTrain.startExtra', trainNumber: 18, start: { kind: 'mainline', node }, direction: 'east',
      }).ok);
      const tray = started(s);
      s.clock.phase = 'mainline';
      s.movedThisPhase = new Set();
      advance(s);
      assert.equal(s.trays.get(tray.id)?.beingMadeUp, undefined, 'a running train is still being made up');
      assert.equal(isBeingMadeUp(s.trays.get(tray.id)!), false);
    });
  });

  it('replays a save written before the choice existed exactly as it meant it', () => {
    /**
     * A save is a seed and a list of intents, so an intent whose meaning moves is a save that
     * quietly replays as a different game. The legacy shape carried only `atSeat`: null meant the
     * Division Point the NUMBER sent it to, running in the number's direction.
     */
    const s = pending(17);
    assert.ok(applyIntent(s, 0, { type: 'newTrain.startExtra', trainNumber: 17, atSeat: null }).ok);
    const tray = started(s);
    assert.equal(tray.direction, 'west', 'the legacy intent stopped meaning what it meant');
    assert.equal(tray.position.at === 'divisionPoint' && tray.position.side, 'east');
  });

  it('takes the Extra off the pending list once, whichever end it started from', () => {
    const s = pending(17);
    const at = { type: 'newTrain.startExtra', trainNumber: 17, start: { kind: 'divisionPoint', side: 'east' } } as const;
    assert.ok(applyIntent(s, 0, at).ok);
    assert.deepEqual(s.pendingExtras, []);
    assert.equal(check(s, 0, at), 'NO_EXTRA_PENDING');
  });
});