/**
 * Plain-English narration for the replay viewer.
 *
 * Two jobs, and the second matters more than it looks:
 *
 *   1. `narrate()` — turn each engine event into a sentence a person can read.
 *   2. `impediments()` — say what is currently BLOCKED and why.
 *
 * Actions are easy to show. Blocked states are what diagnosis actually needs: the open questions
 * are all of the form "why is nothing happening?" — why is a train at the Office only 18% of
 * Stages, why do Laborers sit idle, why does a facility stop working. A log of things that did
 * happen answers none of those.
 *
 * The impediment checks call the engine's own predicates rather than reimplementing them, so the
 * panel cannot drift from the rules.
 */

import { MAINLINE_PROFILES, MAX_CONSIST, crewTrayCount } from '../engine/content.ts';
import { adTrackCount, coordKey, seatOf, turnOf } from '../engine/state.ts';
import type { GameState, GridCoord, PlayerIndex, RollingStock, SeatIndex, TrayId } from '../engine/state.ts';
import { areaOf, canAdvanceLoad, canBoard, canDetrain, canStartLoad, facilityCarType, facilityCarTypes, freightRuleSpentHere, isFreight, laborersLeft, movesFor, passengerRefusal, portersLeft } from '../engine/apply.ts';
import type { GameEvent } from '../engine/events.ts';
import { badlyMadeUp } from '../engine/advance.ts';
import type { CrewTray } from '../engine/state.ts';

// ---------------------------------------------------------------------------
// Small formatters
// ---------------------------------------------------------------------------

const CLOCK: readonly string[] = [
  'Midnight', '2:00 AM', '4:00 AM', '6:00 AM', '8:00 AM', '10:00 AM',
  'Noon', '2:00 PM', '4:00 PM', '6:00 PM', '8:00 PM', '10:00 PM',
];

export function clockTime(stage: number): string {
  return CLOCK[stage - 1] ?? `Stage ${stage}`;
}

/**
 * `homeSeat` is the district the page is being drawn for. Give it, and a load THIS district made
 * says so — the printed game's answer is to turn the chip upside down in the tray, and this is the
 * screen's. A load may not be broken in the Office Area that made it (state.ts `RollingStock.origin`),
 * so "loaded here" is the difference between a boxcar worth switching and one that has to leave the
 * district first. Omit it and the label is what it always was, which is what the replay viewers and
 * the history lines want: they describe a board, not a seat's view of one.
 */
export function carLabel(c: RollingStock, homeSeat?: SeatIndex): string {
  // A caboose carries the crew, not freight, so "loaded caboose" is nonsense on the page even
  // though the supply marks every caboose loaded. Name it plainly.
  if (c.type === 'caboose') return 'caboose';
  const label = `${c.loaded ? 'loaded' : 'empty'} ${c.type}`;
  return homeSeat !== undefined && c.origin === homeSeat ? `${label} (loaded here)` : label;
}

/**
 * "a loaded boxcar", "an empty tank" — the article the word actually takes.
 *
 * The make-up line hard-coded "a" and produced "a empty tank" at the table. Vowel-initial is the
 * whole rule here: every car word is ordinary English ('empty', 'loaded', and the car types), so
 * there is no 'an hour' case to special-case and inventing one would be the more fragile choice.
 */
export function indefinite(label: string): string {
  return `${/^[aeiou]/i.test(label) ? 'an' : 'a'} ${label}`;
}

/** "Train 10" / "Extra X18" — one spelling of a train's name for every line that mentions one. */
export function trainLabel(trainNumber: number | null, isExtra: boolean): string {
  if (trainNumber === null) return 'the local crew';
  return isExtra ? `Extra X${trainNumber}` : `Train ${trainNumber}`;
}

export function carsLabel(cars: RollingStock[]): string {
  if (cars.length === 0) return 'nothing';
  return cars.map(carLabel).join(', ');
}

/**
 * X,Y — EAST/WEST THEN NORTH/SOUTH, exactly as `view.ts` writes it, and NOT the internal row/col
 * storage order.
 *
 * These two disagreed until 2026-09-21: the action menu said "(1,-1)" and the log said "(-1,1)" for
 * the same square, side by side on the same screen. `view.ts` carried the comment explaining why
 * the display order is X,Y; this one had no comment at all and was simply the storage order
 * reaching the page. Jesse's call — the log and the action menu spell a square the same way.
 */
const at = (c: GridCoord): string => `(${c.col},${c.row})`;

const BOX_NAMES = ['MEN', 'AT', 'WORK'] as const;
const boxName = (i: number): string => BOX_NAMES[i] ?? `box ${i}`;

export function phaseLabel(phase: string): string {
  switch (phase) {
    case 'localOps':
      return 'Local Operations';
    case 'newTrain':
      return 'New Train';
    case 'mainline':
      return 'Mainline';
    case 'loadUnload':
      return 'Cargo';
    case 'shiftChange':
      return 'Supervisor Shift';
    default:
      return phase;
  }
}

// ---------------------------------------------------------------------------
// Event narration
// ---------------------------------------------------------------------------

export type Narration = {
  text: string;
  /** Colours the line in the viewer. */
  tone: 'plain' | 'good' | 'bad' | 'clock' | 'quiet' | 'phase';
  /** Board cell to highlight, if the event happened somewhere. */
  where?: GridCoord;
};

/**
 * Every member of `GameEvent` must produce a specific sentence. A test asserts the fallback is
 * never reached, so adding an event type without narrating it fails the build rather than quietly
 * degrading the replay.
 */
export type NarrateContext = {
  /** Resolves a card id to something a person can read, e.g. "Mine Tipple" or "Train 8". */
  cardName?: (id: string) => string;
  /**
   * Resolves a Crew Tray id to the train riding it. Without this the §8.1 clearance question read
   * "may tray2 follow tray3 into the next Subdivision?" — the most consequential decision in the
   * game, phrased in internal identifiers.
   */
  trainName?: (trayId: TrayId) => string;
  /**
   * Resolves a player index to their display name. Optional like the rest: an engine test narrating
   * events has no roster, and "Player 2" is a truthful fallback rather than a broken one.
   */
  playerName?: (player: PlayerIndex) => string;
  /**
   * Names the Facility standing on one of a player's squares, or null where there is none.
   *
   * Switching lines used to give the bare coordinate — "Set out a loaded hopper at (-1,1)" — which
   * is the grid's own notation and means nothing at a table where people are looking at cards. The
   * industry is the whole point of the move, so it is what the line should say.
   */
  facilityAt?: (player: PlayerIndex, at: GridCoord) => string | null;
};

export function narrate(e: GameEvent, ctx: NarrateContext = {}): Narration {
  const card = (id: string): string => ctx.cardName?.(id) ?? 'a card';
  const train = (id: TrayId): string => ctx.trainName?.(id) ?? String(id);
  // The industry on a square when there is one, and the coordinate when there is not — a crew works
  // plain track too, and "at nowhere" would be worse than the notation.
  const place = (player: PlayerIndex, c: GridCoord): string => ctx.facilityAt?.(player, c) ?? at(c);

  switch (e.type) {
    // -- clock
    case 'stageBegan':
      return { tone: 'clock', text: `── Day ${e.day}, Stage ${e.stage} — ${clockTime(e.stage)} ──` };
    case 'seatsRotated':
      // Named players rather than seat numbers: the rule is that everyone MOVED, and a list of
      // indices does not say who is now next to whom.
      return {
        tone: 'clock',
        text: `Employee Rotation — everyone moves one chair left. West to East: ${e.seating
          .map((p) => ctx.playerName?.(p) ?? `Player ${p + 1}`)
          .join(' → ')}`,
      };
    case 'superintendentChanged':
      /**
       * The Fedora is the only thing in the game that changes hands on a clock rather than because
       * somebody did something, so it is the one handover nobody at the table watches happen.
       */
      return {
        tone: 'clock',
        text:
          `SUPERINTENDENT — the Fedora passes to ${ctx.playerName?.(e.player) ?? 'the next player'} ` +
          `at the end of Stage ${e.stage}. They rule on clearances, take the Yard Office and Red Flag ` +
          `questions, and every round that goes round the table now starts with them.`,
      };
    case 'phaseBegan':
      // Its own tone, not `quiet`. A phase marker sat in the same grey as the events inside it, so
      // the log read as one undifferentiated column and you could not see where a phase began.
      return { tone: 'phase', text: `▸ ${phaseLabel(e.phase)} phase` };
    case 'actorChanged':
      return {
        tone: 'quiet',
        text: e.player === null ? 'No player acts — automatic phase' : 'to act',
      };

    // -- local operations
    case 'localOpsOptionChosen':
      return {
        tone: 'plain',
        text:
          e.option === 'switch'
            ? 'Chose to SWITCH — six Moves to shunt cars around the yard. Watch the crew chip on the grid: it carries its consist with it, and cars it passes over are coupled automatically.'
            : e.option === 'draw'
              ? 'Chose to DRAW a card'
              /**
               * SAYS WHAT MAY BE DONE, NOT WHAT WAS. This read "one car moved to or from a
               * facility" — an assertion — and §6.3 requires no action at all, so when the Freight
               * Agent went idle the log claimed a car had moved and then fell silent about which.
               * Reported from a table on Day 1 Stage 3 of v0.8.0.16. The work itself is narrated by
               * `stockToOutbound`, `inboundCleared` and `facilityUnjammed`, each naming the car and
               * the industry; an idle Agent is narrated by `freightAgentIdled`.
               */
              : 'Chose FREIGHT AGENT work — may stock a green Outbound box, clear a red Inbound one, or free a jam',
      };
    case 'trayMoved':
      // `via` rides on the event only when there was another legal route to the same square
      // (docs/plans/switching-paths.md) — so naming it here says which one the crew actually took,
      // rather than leaving a real choice invisible in the crew's own history.
      return {
        tone: 'plain',
        where: e.to,
        // NO TUTORIAL TAIL. "The crew chip on the grid carries the whole train with it" was appended
        // to EVERY move — six times a turn, and the opener (`localOpsOptionChosen`) already says it
        // once. It also pushed the useful half of the line out of the caption row, which shows one
        // step at a time and is the place a player reads a move as it happens.
        text: `Moved ${train(e.trayId)} ${at(e.from)} → ${place(e.player, e.to)}${e.via ? ` via ${at(e.via)}` : ''} — ${e.movesRemaining} of ${e.movesAllowed} Moves left`,
      };
    case 'carsCoupled': {
      /**
       * TAKING YOUR OWN CUT BACK IS NOT THE SAME EVENT AS FINDING CARS ON THE LINE, and the history
       * read as though it were — "coupled 2 cars" told a player who had just set those very cars out
       * that the game had silently undone their work. It has not: they were standing at the end the
       * train pulled out through, and coupling is mandatory (§A.4).
       */
      const own = e.recoupled?.stock.length ?? 0;
      const found = e.stock.length - own;
      const parts: string[] = [];
      // `a loaded tank` for one, a bare list for several — "took loaded tank" reads as a telegram.
      const some = (cars: RollingStock[]): string =>
        cars.length === 1 ? indefinite(carLabel(cars[0]!)) : carsLabel(cars);
      if (own > 0) parts.push(`picked its own ${some(e.recoupled!.stock)} back up off ${at(e.recoupled!.at)} on the way out`);
      if (found > 0) parts.push(`took ${some(e.stock.slice(own))} standing there`);
      return {
        tone: 'plain',
        where: e.at,
        text:
          // "1 car(s)" was the plural of a machine. The count is already implied by the cars named
          // in `parts`, so the sentence leads with where and which end instead.
          `Coupled at ${place(e.player, e.at)}, ${e.toNose ? 'ONTO THE NOSE' : 'behind the train'}` +
          ` — ${parts.join(', and ')}`,
      };
    }
    case 'consistSorted': {
      /**
       * WHERE THE ENGINE ENDED UP, and whether the train can still run.
       *
       * ASKED OF `badlyMadeUp` RATHER THAN RE-DECIDED HERE, which matters because the obvious guess
       * is wrong: §8.2 is enforced direction-free, so a train with its WHOLE consist ahead of the
       * engine is a pushing train and perfectly fit to leave. What it may not be is broken-backed,
       * with the engine buried among its own cars. A copy of that rule in the narrator would have
       * told a player their pushing train was stranded when it was not.
       */
      const ahead = e.engineAt;
      const unfit = badlyMadeUp({ consist: e.after, engineAt: e.engineAt } as CrewTray);
      const where =
        ahead === 0
          ? 'so the right car is now on the end and can be spotted'
          : unfit === null
            ? `with the whole consist AHEAD of the engine — it runs as a pushing train`
            : `with ${ahead} car${ahead === 1 ? '' : 's'} ahead of the engine — ${unfit}, so it is held at the Office until it is sorted again (§8.2)`;
      return {
        tone: 'good',
        where: e.at,
        text: `Used the SMALL YARD — consist re-ordered from [${carsLabel(e.before)}] to [${carsLabel(e.after)}], ${where}`,
      };
    }
    case 'switchingEnded': {
      /**
       * The line that closes a switching turn, and the only one the history keeps from the middle of
       * it: what it cost, and where the crew was left standing.
       */
      const used = `${e.movesUsed} of ${e.movesAllowed} Move${e.movesAllowed === 1 ? '' : 's'} used`;
      if (e.movesUsed === 0) return { tone: 'quiet', text: 'Finished switching without moving a car' };
      if (!e.lastMove) return { tone: 'plain', text: `Finished switching — ${used}` };
      return {
        tone: 'plain',
        where: e.lastMove.to,
        text: `Finished switching — ${used}, leaving ${train(e.lastMove.trayId)} at ${place(e.player, e.lastMove.to)}`,
      };
    }
    case 'carsDropped':
      // WHICH END. A cut comes off an outer end (§A.3) and the end decides everything that follows:
      // the train may pull away from cars set out behind it and must couple back up to cars set out
      // in front. "Dropped 2 cars" left the one fact that matters out of the record.
      return {
        tone: 'plain',
        where: e.at,
        text:
          `Set out ${carsLabel(e.stock)} at ${place(e.player, e.at)}, off the ${e.fromNose ? 'NOSE — ahead of the engine, so pulling forward will couple them again' : 'TAIL — behind the engine, so it may pull away and leave them'}`,
      };

    // -- cards
    case 'cardDrawn':
      return {
        tone: 'plain',
        text:
          e.source === 'homeOffice'
            ? `Drew ${card(e.cardId)} from the Home Office deck`
            : `Took ${card(e.cardId)} from Department slot ${(e.slot ?? 0) + 1}`,
      };
    case 'cardPlayed':
      return {
        tone: 'plain',
        ...(e.placement ? { where: e.placement } : {}),
        text: e.placement
          ? `Played ${card(e.cardId)} onto ${at(e.placement)}`
          : `Played ${card(e.cardId)}`,
      };
    case 'mainlineModified': {
      // WHICH CARD, NOT JUST WHICH WAY IT WENT. "Mainline card 3 converted to plains" left the reader
      // to remember what card 3 had been (playtest, 2026-09-15), and the card it WAS is the half that
      // says what the play was worth.
      const kindName = (k: string | undefined): string =>
        MAINLINE_PROFILES.find((m) => m.kind === k)?.name ?? k ?? 'that card';
      return {
        tone: 'plain',
        text: e.became
          ? `Realignment: Mainline card ${e.node}, ${kindName(e.from)}, converted to ${kindName(e.became)}`
          : `Played ${e.key} on Mainline card ${e.node}${e.from ? ` (${kindName(e.from)})` : ''}`,
      };
    }
    case 'redFlagSpent':
      return {
        tone: 'good',
        text: `RED FLAG — Train ${e.trainNumber} stopped short of the ${e.side === 'east' ? 'Eastern' : 'Western'} Limits. The flag comes down with it.`,
      };
    case 'redFlagRuled':
      return e.flag
        ? { tone: 'plain', text: 'Flagged the approaching train' }
        : { tone: 'plain', text: 'Waved the train through' };
    case 'redFlagsSet':
      return {
        tone: 'good',
        text: `RED FLAGS set out on the ${e.side === 'east' ? 'Eastern' : 'Western'} Limits — the next train from that way is held short`,
      };
    case 'flyingSwitch':
      return {
        tone: 'good',
        where: e.to,
        text: `Flying Switch — ${e.stock.length} car(s) cut loose and rolled into the industry at ${at(e.to)} without the engine entering`,
      };
    case 'officeUpgraded':
      return { tone: 'good', text: `OFFICE UPGRADED — ${e.from} → ${e.to}` };
    case 'cardDiscarded':
      return {
        tone: 'quiet',
        text: `Discarded ${card(e.cardId)} face-up on top of Department ${e.toSlot + 1}`,
      };
    case 'deckReshuffled':
      return {
        tone: 'quiet',
        text:
          `Home Office deck ran out — the Salvage Yard and all three Department decks ` +
          `(${e.order.length} cards) were collected, reshuffled and dealt back out`,
      };
    case 'departmentRefilled':
      return {
        tone: 'quiet',
        text: `Department slot ${e.slot + 1} refilled with ${card(e.cardId)}`,
      };

    // -- train lifecycle
    case 'extraQueued':
      return {
        tone: 'good',
        text: `Extra X${e.trainNumber} played — it is NOT scheduled; it runs once as soon as a Crew Tray frees up, then its card is gone`,
      };
    case 'enhancementPlaced': {
      const name = e.key.replace(/([A-Z])/g, ' $1');
      // Out on the Mainline is not a square in anyone's district, so it is named rather than
      // given a coordinate the Office Area does not have.
      if (e.at === undefined) {
        return { tone: 'good', text: `ENHANCEMENT built: ${name} on Mainline card ${e.node}` };
      }
      return { tone: 'good', where: e.at, text: `ENHANCEMENT built: ${name} at ${at(e.at)}` };
    }
    case 'secondSectionOrdered':
      return {
        tone: 'bad',
        text: `SECOND SECTION ordered on Train ${e.trainNumber} — an identical train will run right behind it, which forces the Superintendent to rule on a following train`,
      };
    /**
     * WHERE THE PLAYER PUT IT, not where its number would have sent it.
     *
     * An Extra's direction comes from its start now (§7, Jesse's ruling), so the line that used to
     * explain the number's parity would be explaining a rule that no longer applies to this train.
     */
    case 'extraStarted': {
      const where =
        e.at.kind === 'divisionPoint'
          ? `the ${e.at.side === 'west' ? 'Western' : 'Eastern'} Division Point`
          : e.at.kind === 'mainline'
            ? "the Interchange's yard"
            : `the Control Point in seat ${e.at.seat}`;
      const why =
        e.at.kind === 'divisionPoint'
          ? 'the end it runs away from — an Extra may start at either, and the end chooses the run'
          : e.at.kind === 'mainline'
            ? 'made up off the running line, so it highballs onto the Mainline once the Subdivision ' +
              'is clear and may be held in the yard until it is'
            : 'an Extra may begin at any Office above a Whistle Post, and the player chooses the run';
      return {
        tone: 'good',
        text: `EXTRA X${e.trainNumber} started at ${where}, running ${e.direction} — ${why}`,
      };
    }
    case 'trainMadeUp':
      return {
        tone: 'good',
        text: `${e.isExtra ? `EXTRA X${e.trainNumber}` : `TRAIN ${e.trainNumber}`} MADE UP at the ${e.at}, running ${e.direction} — crew assigned, now taking cars`,
      };
    case 'trainStoodStill':
      return {
        tone: 'good',
        text:
          `Train ${e.trainNumber} stood still for a whole Stage at ${e.where} and earned a point — ` +
          'its card pays for the stop, not for the run (circus set-up)',
      };
    case 'trainHeld':
      return {
        tone: 'bad',
        text: `Train ${e.trainNumber} was due out but is HELD — ${e.reason}`,
      };
    case 'trainHighballed':
      // The RULE that released it, not a restatement of the move. "Some trains seem to be moving
      // before I can switch them" was reported against a log in which every departure read alike.
      return {
        tone: 'plain',
        text: `Train ${e.trainNumber} HIGHBALLED — departed ${e.from} onto ${e.to}. Why now: ${e.why}`,
      };
    case 'trainArrived':
      /**
       * AN EXPEDITED ARRIVAL IS AN ORDINARY ARRIVAL, WITH ONE STANDING OBLIGATION.
       *
       * This used to say the train stands through Cargo and is forced out at the end of the Stage —
       * true once, and wrong: Q3 means the train must not be PARKED anywhere but the station, not
       * that it is rushed out early. It is switched, worked and released exactly like any other
       * arrival; the only difference is what happens if it is left on Secondary Track when the next
       * Mainline Phase begins (`expediteFault`).
       */
      /**
       * WHOSE OFFICE, AND WHOSE TRAIN TO WORK — Jesse, playtest 2026-09-16.
       *
       * This said "ARRIVED at the Whistle Post" and then "You can work it in Cargo now". Both halves
       * are wrong at a table of four: every seat has an Office, so the tier alone does not say which
       * district the train is standing in, and the reader is usually NOT its Station Master — the
       * line was telling three players they could work a train they cannot touch.
       */
      {
        const name = ctx.playerName?.(e.owner) ?? null;
        const whose = name === null ? `the ${e.office}` : `${name}'s ${e.office}`;
        const worker = name === null ? 'Its Station Master' : name;
        return {
          tone: 'plain',
          text: e.expedited
            ? `Train ${e.trainNumber} ARRIVED at ${whose} carrying ${carsLabel(e.consist)} — its card prints EXPEDITE, so it must stay on the Office square: parked anywhere else in that district when the next Mainline Phase begins costs a Revenue point. It works and switches normally in the meantime.`
            : `Train ${e.trainNumber} ARRIVED at ${whose} carrying ${carsLabel(e.consist)} — it stands there for the rest of this Stage. ${worker} can work it in Cargo now and switch it in the NEXT Stage's Local Operations, and it departs in that Stage's Mainline Phase.`,
        };
      }
    case 'expediteFault':
      return {
        tone: 'bad',
        text: `Train ${e.trainNumber} was left at ${e.where}, off the station, when the Mainline Phase began — an expedited train must be kept ready to highball. Station Master fault.`,
      };
    case 'trainDiverted':
      return {
        tone: 'good',
        text: `Train ${e.trainNumber} DIVERTED to ${e.to} — ${e.reason}`,
      };
    case 'trainCompleted':
      // The one line in the log that is good news for everybody, so it is not 'quiet'.
      return {
        tone: 'good',
        text:
          `Train ${e.isExtra ? 'X' : ''}${e.trainNumber} has completed its run, leaving via the ` +
          `${e.side === 'east' ? 'Eastern' : 'Western'} Division Point carrying ${carsLabel(e.consist)}. ` +
          `All players get 1 Revenue. The crew is free again.`,
      };

    // -- freight agent
    /**
     * THE INDUSTRY, NOT THE COORDINATE — `place` over `at`, for the reason its own comment gives:
     * "(-1,1)" is the grid's notation and means nothing at a table where people are looking at
     * cards. The switching lines were moved to it and these three were missed, so a Freight Agent
     * turn was the one place the log still spoke in coordinates. Asked directly from a table on
     * Day 1 Stage 3 of v0.8.0.16: "can we tell what car, what facility and whether it was to or
     * from." The car and the direction were already here; the facility was not.
     */
    case 'stockToOutbound':
      return {
        tone: 'plain',
        where: e.at,
        text: `Freight Agent loaded a ${carLabel(e.stock)} INTO the green Outbound box at ${place(e.player, e.at)}`,
      };
    case 'inboundCleared':
      return {
        tone: 'plain',
        where: e.at,
        text: `Freight Agent cleared a ${carLabel(e.stock)} OUT of the red Inbound box at ${place(e.player, e.at)}`,
      };
    case 'facilityUnjammed':
      return {
        tone: 'bad',
        text: `UNJAMMED ${place(e.player, e.at)} — pulled a ${carLabel(e.stock)} out of ${e.from} to free the facility`,
        where: e.at,
      };
    case 'freightAgentIdled':
      return {
        tone: 'quiet',
        text:
          'Freight Agent found nothing worth doing — no green box could be stocked, no red box needed ' +
          'clearing, and no load was jammed. §6.3 requires no action, and unjamming a healthy box ' +
          'would destroy a load that cost a whole action to stock.',
      };

    // -- trains
    case 'trainScheduled': {
      // §7 — roll 1D12 for the slot; if it is taken, work down the column. Reporting only the roll
      // makes a bumped train look like an arithmetic error.
      const bumped = e.slot + 1 !== e.roll;
      return {
        tone: 'good',
        text: bumped
          ? `Train ${e.trainNumber} SCHEDULED at Stage ${e.slot + 1} — rolled ${e.roll}, but Stage ${e.roll} was already taken, so it moved down the column to the next free Stage`
          : `Train ${e.trainNumber} SCHEDULED to depart at Stage ${e.slot + 1} (rolled ${e.roll}) — it will run at this time EVERY Day from now on`,
      };
    }
    case 'carPlacedOnTrain':
      // NAMES THE TRAIN. "the train being made up" was true and useless: a player looking back for
      // what happened to train 10 found four lines that never said 10 (playtest, 2026-09-16).
      return {
        tone: 'plain',
        text: `Added ${indefinite(carLabel(e.stock))} to ${trainLabel(e.trainNumber, e.isExtra)}`,
      };
    case 'carPassed':
      return {
        tone: 'quiet',
        text: `Passed on ${trainLabel(e.trainNumber, e.isExtra)} — no suitable car in the Division Yard`,
      };
    case 'makeUpShort': {
      // What it wanted, in the words the card uses, so the line can be checked against the card.
      const names: Record<'freight' | 'coach' | 'caboose', string> = {
        freight: 'freight car',
        coach: 'coach',
        caboose: 'caboose',
      };
      const wants = e.missing.map((m) => names[m]).join(' or ');
      const got = e.placed === 0 ? 'NO CARS AT ALL' : `only ${e.placed} of the ${e.wanted} its card calls for`;
      // §2.2 is the whole explanation and it is not guessable from the board: the cars are visible
      // in the Classification Yard, and why they will not come back is not.
      const why =
        e.waiting > 0
          ? ` ${e.waiting} sit in the Classification Yard, which comes back only when the Division Yard is bare — and it still holds ${e.divisionYardHolds} cars.`
          : ' There are none in the Classification Yard either.';
      return {
        tone: 'bad',
        text:
          `${trainLabel(e.trainNumber, e.isExtra).toUpperCase()} WAS MADE UP WITH ${got} — the ` +
          `Division Yard holds no ${wants} it can take, so nobody was asked for one.${why}`,
      };
    }
    case 'dispatchBonusUsed':
      return {
        tone: 'good',
        text: `${e.key.toUpperCase()} used (+${e.bonus}) — Train ${e.trainNumber} wins the meet against Train ${e.againstTrain}, which now counts as number ${e.againstTrain + e.bonus}. Once a Day only.`,
      };
    case 'trainsDestroyed': {
      // Say what hit what, where, and what was written off. "COLLISION: NO FREE A/D TRACK" told a
      // player the score had changed and nothing else.
      const why =
        e.reason === 'no free A/D track'
          ? `it arrived at ${e.where} with every A/D track already occupied — there was nowhere to put it`
          : e.reason === 'cars fouling the Running Track'
            ? `it ran into cars left standing on ${e.where} between the Limits and the Office`
            : e.reason;
      const wrecked = e.trains
        .map((t) => `${t.label} (${t.consist.length ? carsLabel(t.consist) : 'no cars'})`)
        .join(' and ');
      /**
       * WHOSE OFFICE, AND WHO PAYS (playtest, 2026-09-16: "it doesn't say who suffers the revenue
       * loss… we need to know which player received the penalty and why").
       *
       * `player` is the seat at fault, and for everything that happens inside a district that is the
       * district's owner — so it names the place as well as the payer. A Mainline collision is the
       * Superintendent's by rule (§10), which is a different sentence: it happened on open road, not
       * in anybody's Office. The 5 points ride in a separate `revenueChanged`, which is why the line
       * never mentioned them; a player should not have to add two log entries together.
       */
      const who = ctx.playerName?.(e.player) ?? null;
      const mainline = e.where === 'the Mainline';
      const place = who === null || mainline ? e.where : `${who}'s ${e.where.replace(/^the /, '')}`;
      const cost =
        who === null
          ? ' 5 Revenue is lost.'
          : mainline
            ? ` ${who} loses 5 Revenue: §10 makes a Mainline collision the Superintendent's fault.`
            : ` ${who} loses 5 Revenue — it happened in their district.`;
      return {
        tone: 'bad',
        text:
          `COLLISION at ${place} — ${wrecked} destroyed: ${why}.${cost} Engines and cabooses go back ` +
          `to the Division Yard, all other cars to the Classification Yard. A Timetabled train card ` +
          `returns to its slot and runs again next Day; an Extra is gone for good.`,
      };
    }

    case 'clearanceRequested':
      return {
        tone: 'bad',
        text:
          `SUPERINTENDENT MUST RULE: ${train(e.trainId)} wants to enter the Mainline card ` +
          `that ${train(e.occupiedBy)} is still crossing. Allow it and ${train(e.trainId)} may run ` +
          `into the back of ${train(e.occupiedBy)} — a collision costs 5 Revenue. Hold it and it ` +
          `waits where it is, losing time but safe.`,
      };
    case 'clearanceGiven':
      return {
        tone: e.allow ? 'bad' : 'plain',
        text: e.allow
          ? `Clearance GRANTED — ${train(e.trainId)} follows into the occupied Subdivision`
          : `Clearance DENIED — ${train(e.trainId)} holds where it is`,
      };

    // -- passengers
    // §9.2 — "One Porter will allow you to do any ONE of the following actions", so a Depot with a
    // single Porter works exactly one coach per Stage. That is a limit, not a bug.
    case 'passengersBoarded':
      return {
        tone: 'good',
        where: e.at,
        text: `Porter boarded passengers at ${at(e.at)} — one coach per Porter per Stage`,
      };
    case 'passengersDetrained':
      return {
        tone: 'good',
        where: e.at,
        text: `Porter de-trained passengers at ${at(e.at)} — one coach per Porter per Stage`,
      };

    // -- freight pipeline
    case 'loadStarted':
      return {
        tone: 'plain',
        where: e.at,
        text: `Laborer moved a ${e.carType} load from the green box onto MEN`,
      };
    case 'loadAdvanced':
      return {
        tone: 'plain',
        where: e.at,
        text: `Laborer advanced the load ${boxName(e.fromBox)} → ${boxName(e.toBox)}`,
      };
    case 'loadCompleted':
      return {
        tone: 'good',
        where: e.at,
        text: `LOAD FINISHED — ${e.carType} loaded onto the spotted car`,
      };
    case 'unloadBegan':
      return {
        tone: 'plain',
        where: e.at,
        text: `Laborer began unloading a ${e.carType} — load lifted onto WORK`,
      };
    case 'unloadCompleted':
      return {
        tone: 'good',
        where: e.at,
        text: `UNLOAD FINISHED — ${e.carType} delivered into the red Inbound box`,
      };

    // -- consequences
    case 'revenueChanged':
      return e.delta < 0
        ? { tone: 'bad', text: `${e.reason.toUpperCase()} · ${e.delta} Revenue (now ${e.total})` }
        : { tone: 'good', text: `+${e.delta} Revenue (now ${e.total}) — ${e.reason}` };
    case 'phaseEnded':
      return { tone: 'quiet', text: `Finished ${phaseLabel(e.phase)}` };

    // -- §3.3, extended play (Gitea#11)
    case 'extensionVoted':
      return e.agree
        ? { tone: 'plain', text: 'Would play one more Day' }
        : { tone: 'plain', text: 'Called time — the game ends here' };
    case 'dayExtended':
      return { tone: 'clock', text: `── The table plays on: Day ${e.day} is added to the timetable ──` };
    case 'playConcluded':
      return { tone: 'clock', text: '── The railroad is put to bed. Final results stand. ──' };

    // -- §11, the Yard Office (Gitea#5)
    case 'yardOfficeRuled':
      return e.take
        ? { tone: 'plain', text: `Sent ${train(e.trainId)} into the Yard Office` }
        : { tone: 'plain', text: `Kept ${train(e.trainId)} at the Train Order Office` };
  }
}

/** Events that change nothing a viewer can see. Skipped when capturing frames. */
export function isVisible(e: GameEvent): boolean {
  return e.type !== 'actorChanged';
}

/**
 * A phase that ended with nothing done needs saying so explicitly. "Player 0 finished Load/Unload"
 * with no preceding action reads as a gap in the replay when it is actually the game reporting that
 * there was no work available.
 */
export function idleNote(phase: string): string {
  switch (phase) {
    case 'loadUnload':
      return 'Nothing to do this Load/Unload — no load ready to advance, and no train at the platform with passengers to work.';
    case 'localOps':
      return 'Nothing useful to do this Local Operations.';
    default:
      return `Nothing to do this ${phaseLabel(phase)}.`;
  }
}

// ---------------------------------------------------------------------------
// Impediments — "why is nothing happening?"
// ---------------------------------------------------------------------------

export type Impediment = { where: string; why: string; severity: 'stuck' | 'waiting' | 'risk' };

/**
 * Everything currently preventing progress. Derived live from engine predicates, never cached.
 *
 * This is the panel that should answer the standing questions: whether facilities jam, whether
 * trains are held for want of a crew, whether the Office is about to cause a collision.
 */
/** `coordKey`'s inverse — the grid is keyed by string and the engine predicates take coordinates. */
function uncoordKey(key: string): GridCoord {
  const [row, col] = key.split(',').map(Number);
  return { row: row ?? 0, col: col ?? 0 };
}

/**
 * One of `passengerRefusal`'s codes, in words a player can act on.
 *
 * `NO_EMPTY_COACH_IN_YARD` gets the longest answer because it is the one that looks like a broken
 * game: the Division Yard is visibly full of cars, and the single type that has run out is the one
 * §9.2 needs. Where the missing coaches ARE, and the condition that brings them back, is the whole
 * of what the player needs to know — §2.2 returns the Classification Yard only when the Division
 * Yard is bare, so a yard with fifty freight cars in it will not refill for a long time.
 */
function passengerReason(
  s: GameState,
  player: PlayerIndex,
  at: GridCoord,
  dir: 'board' | 'detrain',
): string {
  const code = passengerRefusal(s, player, at, dir);
  switch (code) {
    case 'NO_TRAIN_AT_OFFICE':
      return dir === 'board'
        ? 'passengers waiting, no train at the platform to take them'
        : 'no train at the platform';
    case 'NOT_A_TERMINAL':
      return 'the only train here stops at Terminals only — Porters may not work it at this Office';
    case 'NO_PASSENGER_WORK':
      return 'the only train here is one its card bars Porters from working';
    case 'NO_EMPTY_COACH':
      return 'passengers waiting, but every coach on the train is already full';
    case 'INBOUND_BOX_FULL':
      return 'arrivals aboard, but the red Unloading slots are all occupied';
    case 'LOADED_IN_THIS_DISTRICT':
      return 'the loaded coaches all boarded here — passengers must be carried to another Office ' +
        'Area before they can alight';
    case 'NO_EMPTY_COACH_IN_YARD': {
      const stuck = s.yards.classificationYard.filter((c) => c.type === 'coach').length;
      const total = s.yards.divisionYard.length;
      return (
        'arrivals aboard, but §9.2 needs a white empty coach from the Division Yard to swap in and ' +
        `there is none left${stuck > 0 ? ` — ${stuck} ${stuck === 1 ? 'coach is' : 'coaches are'} in the Classification Yard` : ''}. ` +
        `Classification returns only when the Division Yard is bare, and it still holds ${total} cars.`
      );
    }
    default:
      return `Porters cannot work here (${code})`;
  }
}

export function impediments(s: GameState, player: PlayerIndex = 0): Impediment[] {
  const out: Impediment[] = [];
  const area = areaOf(s, player);

  for (const [key, card] of area.grid) {
    const f = card.facility;
    if (!f) continue;
    /**
     * A Freight Facility names itself off its own card; a Passenger Facility does NOT — it rides on
     * the `office` card, so `geometry.kind` is `'office'` and it fell through to the literal
     * "facility". Every passenger impediment therefore read `facility 0,0`, next to a freight row
     * saying `mineTipple 1,-3`. The Office Area's tier is the name it should carry, and there is
     * exactly one Office per Area, so `area.tier` is that card's own.
     */
    const name =
      card.geometry.kind === 'facility'
        ? card.geometry.facility
        : card.geometry.kind === 'office'
          ? area.tier
          : 'facility';

    /**
     * WHY THE PORTERS ARE STANDING THERE (Gitea#2).
     *
     * "Note that the sparrow (with two loaded coaches) pulled into the station. There are two
     * passengers on the platform. Four porters. My thought was to unload two and load two. I never
     * get the chance to load the last two."
     *
     * The engine was right — §9.2 needs a white coach out of the Division Yard to de-train into,
     * §2.2 returns the Classification Yard only when the Division Yard is BARE, and the Division
     * Yard was one empty coach short with eight more sitting in Classification unable to come back.
     * Jesse's ruling is that the shortage stays: "it is possible to run out — that's part of the
     * strategy." What was missing was any way to SEE it. A Porter action that cannot be taken is
     * simply absent from the menu, and this panel — the one that answers "why is nothing moving?" —
     * covered freight facilities only, so the platform had nothing to say for itself at all.
     *
     * The reason comes from `passengerRefusal`, the engine's own, so what is on screen is the rule
     * that actually refused rather than a second guess at it.
     */
    if (f.kind === 'passenger') {
      /**
       * NOBODY TO PUT ON THE PLATFORM, AND NO WAY TO SEE WHY (playtest, 2026-09-16).
       *
       * "He would like to have two passengers waiting in his depot… but the only option he had was
       * bringing a tank load into the refinery." His Depot had a Restaurant and a Hotel beside it and
       * three outbound slots — capacity was never the problem. §6.3 stocking takes a LOADED car of
       * the facility's type out of the Division Yard, and there was not a loaded coach in it: six
       * were sitting in Classification, which §2.2 returns only when the Division Yard runs bare.
       *
       * Jesse's ruling (2026-09-16) is the same one Gitea#2 got: the shortage stays, because running
       * out is part of the game. What must not stay is the silence — an action with no legal target
       * is simply absent from the menu, so the player is left to guess whether they misunderstood the
       * rules or the game is broken.
       */
      if (f.allows.outbound && f.outboundBox.length < f.capacity.outbound) {
        const loadedCoaches = s.yards.divisionYard.filter((c) => c.type === 'coach' && c.loaded).length;
        if (loadedCoaches === 0) {
          const waiting = s.yards.classificationYard.filter((c) => c.type === 'coach' && c.loaded).length;
          out.push({
            where: `${name} ${key}`,
            why:
              `room for ${f.capacity.outbound - f.outboundBox.length} more passenger` +
              `${f.capacity.outbound - f.outboundBox.length === 1 ? '' : 's'} to wait, but no loaded ` +
              `coach in the Division Yard for the Freight Agent to bring over` +
              (waiting > 0
                ? ` — ${waiting} ${waiting === 1 ? 'is' : 'are'} in the Classification Yard, which comes ` +
                  'back only when the Division Yard is bare'
                : ''),
            severity: 'waiting',
          });
        }
      }
      if (portersLeft(f) > 0) {
        const coord = uncoordKey(key);
        // Passengers standing on the platform with nothing carrying them away.
        if (f.outboundBox.some((c) => c.type === 'coach' && c.loaded) && !canBoard(s, player, coord)) {
          out.push({
            where: `${name} ${key}`,
            why: passengerReason(s, player, coord, 'board'),
            severity: 'waiting',
          });
        }
        // A coach full of arrivals that cannot be emptied.
        const arriving = area.adOccupancy.some((id) =>
          s.trays.get(id)?.consist.some((c) => c.type === 'coach' && c.loaded && c.origin !== seatOf(s, player)),
        );
        if (arriving && !canDetrain(s, player, coord)) {
          out.push({
            where: `${name} ${key}`,
            why: passengerReason(s, player, coord, 'detrain'),
            severity: 'stuck',
          });
        }
      }
      continue;
    }

    if (f.kind !== 'freight') continue;
    const want = facilityCarType(f);

    // A load that cannot move, with Laborers standing by, is the worst state a facility reaches:
    // it also strips the industry track of Operational Rail status (§9.3), so no car can be
    // brought in to rescue it.
    for (let box = 0; box < (f.menAtWork?.length ?? 0); box++) {
      const load = f.menAtWork![box];
      if (!load || canAdvanceLoad(f, box)) continue;
      const reason =
        laborersLeft(f) < 1
          ? 'all Laborers already used this Stage'
          : load.dir === 'out'
            ? `no empty ${want} spotted to load onto`
            : 'red Inbound box is full';
      out.push({
        where: `${name} ${key}`,
        why: `load STUCK on ${boxName(box)} — ${reason}`,
        severity: laborersLeft(f) < 1 ? 'waiting' : 'stuck',
      });
    }

    if (f.outboundBox.length > 0 && !canStartLoad(f) && laborersLeft(f) > 0) {
      // Two quite different reasons, and telling a player "MEN is occupied" when the real answer is
      // "there is no car to load onto" sends them to fix the wrong thing.
      const blockedByBox = f.menAtWork?.[0] != null;
      out.push({
        where: `${name} ${key}`,
        why: blockedByBox
          ? 'green box has a load but MEN is occupied'
          : `a load is staged but no empty ${want} is spotted on this industry's track — it stays ` +
            'in the green box until a crew sets one out here',
        severity: blockedByBox ? 'waiting' : 'stuck',
      });
    }

    if (f.allows.outbound && f.outboundBox.length === 0) {
      /**
       * WHAT TO DO NEXT — AND THE TWO STEPS CAN BE DONE IN EITHER ORDER.
       *
       * §6.3 stocking needs only a car in the Division Yard; §9.3's "Load the car" is what needs an
       * empty car of the commodity standing on the industry's track. So an empty siding is not a
       * reason to hold the Freight Agent back — it is a second errand to run before the Laborers can
       * start. Saying "bring a car in FIRST" sent players to do them in a fixed order they are not
       * bound by, and wasted the Stage's one Freight Agent action.
       */
      const spotted = f.industryTrack.cars.some((c) => !c.loaded && facilityCarTypes(f).includes(c.type));
      out.push({
        where: `${name} ${key}`,
        why: spotted
          ? 'green box empty — nothing to load (needs a Freight Agent action)'
          : `green box empty — the Freight Agent can stage a load now, but no empty ${want} is ` +
            'spotted here, so a crew must set one out before Laborers can work it',
        severity: 'waiting',
      });
    }

    // Four cars is the whole of any track card, industry or not — the same limit that caps a
    // consist. It is no longer the industry's box count, which is what used to make a one-box
    // industry report itself full with a single car standing on it.
    if (f.industryTrack.cars.length >= MAX_CONSIST) {
      out.push({
        where: `${name} ${key}`,
        why: `industry track full (${MAX_CONSIST} cars) — no room to spot another`,
        severity: 'stuck',
      });
    }
  }

  /**
   * WHY THE CREW CANNOT GET THERE.
   *
   * The panel is called "why nothing is moving" and covered everything except movement: jammed
   * facilities, held trains, a full Office. A crew standing one card short of an industry it cannot
   * enter had nothing here at all — reported as trains being blocked "in certain conditions", with
   * no way to find out which.
   *
   * Only while switching, and only the cards actually in the crew's way: `movesFor` reports the
   * squares the movement walk reached and refused, not every square on the board.
   */
  /**
   * WHY A CAR WILL NOT COME OFF (Gitea#21).
   *
   * "I dropped the first tank car, but that was all I was allowed to do" — and this panel, asked
   * why, talked about the refinery's green box. The rule that actually refused is printed on the
   * train: trains 3/4, the Express, "may drop or pick up one freight car at every location". The
   * refusal was correct. Nothing said it.
   *
   * That is a worse failure than a missing button, because the panel did not stay silent — it
   * offered a true statement about the FACILITY, which sent the player to spend a Freight Agent
   * action that could not have helped. The rule was on the train card's tooltip, which is not
   * where anyone looks when a button they expected is simply absent.
   *
   * Only when the crew has a freight car it could otherwise set out. A budget spent by a train
   * with nothing left to drop is not blocking anything, and this panel earns its keep by being
   * short enough to read.
   */
  const turnNow = turnOf(s, player);
  if (s.clock.phase === 'localOps' && turnNow.option === 'switch') {
    for (const [id, tray] of s.trays) {
      if (tray.position.at !== 'grid' || tray.position.seat !== seatOf(s, player)) continue;
      if (!tray.consist.some(isFreight)) continue;
      if (!freightRuleSpentHere(s, player, id)) continue;
      const { row, col } = tray.position.coord;
      out.push({
        where: `Train ${tray.trainNumber} at (${col},${row})`,
        why:
          'ONE FREIGHT CAR PER LOCATION — this train has already worked a freight car on this ' +
          'square, so no more come off or on here until next turn. It may still work one at the ' +
          'next square it reaches.',
        // The printed rule doing its job, and it lifts by itself. Amber, not red.
        severity: 'waiting',
      });
    }
  }

  const turn = turnOf(s, player);
  if (s.clock.phase === 'localOps' && turn.option === 'switch' && turn.movesRemaining > 0) {
    for (const [id, tray] of s.trays) {
      if (tray.position.at !== 'grid' || tray.position.seat !== seatOf(s, player)) continue;
      const { blocked } = movesFor(s, player, id);
      for (const b of blocked) {
        // A turnout is not an obstruction — a train runs through one all day and simply may not
        // STOP on it. Listing every one would bury the four reasons that are genuinely in the way;
        // the board says it on the card instead.
        if (b.kind === 'noStopping') continue;
        out.push({
          where: `${tray.trainNumber === null ? 'crew' : `Train ${tray.trainNumber}`} → (${b.coord.col},${b.coord.row})`,
          why: b.why,
          // Not "stuck": these are the shape of the district and of the other trains in it, which is
          // the puzzle rather than a fault. Amber, not red.
          severity: 'waiting',
        });
      }
    }
  }

  /**
   * WHY THE PASSENGERS ARE NOT MOVING — boarding as well as de-training.
   *
   * Reported first as "I can't figure out how to have a train with three passenger coaches unload
   * all three at my depot." You cannot — a Depot has ONE Porter and ONE red slot, so it works one
   * coach a Stage and then needs a Freight Agent action to clear the box before the next. A Station
   * does two and a Terminal three. That is the Office ladder doing its job, and nothing on screen
   * said so.
   *
   * Reported again as "passenger trains arrive at my Office and move on before I can load or unload
   * them", which turned out to be two separate silences. This block only looked at trains carrying
   * a LOADED coach, so a train arriving to PICK UP said nothing at all. A Whistle Post's Office card
   * carries a passenger facility with zero Porters, so the engine answered `RESOURCE_SPENT` — "all
   * Porters used" — to a player who had used none.
   *
   * §9.2 also requires an empty coach in the DIVISION YARD to swap into the train, which no panel
   * mentioned at all.
   */
  const office = area.grid.get(coordKey(area.officeCoord));
  const pf = office?.facility;
  if (pf && pf.kind === 'passenger') {
    const coachTrains = area.adOccupancy
      .map((id) => s.trays.get(id))
      .filter((t): t is NonNullable<typeof t> => !!t && t.consist.some((c) => c.type === 'coach'));

    if (coachTrains.length > 0) {
      const say = (why: string, severity: Impediment['severity'] = 'waiting'): void => {
        out.push({ where: 'Office — passengers', why, severity });
      };

      const boarding = pf.outboundBox.some((c) => c.type === 'coach' && c.loaded);
      const emptyOnTrain = coachTrains.some((t) => t.consist.some((c) => c.type === 'coach' && !c.loaded));
      const loadedOnTrain = coachTrains.some((t) => t.consist.some((c) => c.type === 'coach' && c.loaded));

      if (pf.porters < 1) {
        say(
          'this Office has NO Porters — a Whistle Post is not a Passenger Facility and cannot ' +
            'work passengers at all. Upgrade it to a Depot or better.',
          'stuck',
        );
      } else if (portersLeft(pf) < 1) {
        say(
          `all ${pf.porters} Porter${pf.porters === 1 ? '' : 's'} used this Stage — one works one coach, ` +
            'and the Office tier is the Porter count (Depot 1, Station 2, Terminal 3)',
        );
      } else {
        if (boarding && !emptyOnTrain) {
          say('passengers are waiting to board, but every coach standing here is already full');
        }
        if (!boarding && !loadedOnTrain) {
          say('nobody waiting to travel and no loaded coach to set down — stock the platform with a Freight Agent action');
        }
        if (loadedOnTrain && pf.inboundBox.length >= pf.capacity.inbound) {
          say(
            `the red Unloading box is full (${pf.capacity.inbound} slot${pf.capacity.inbound === 1 ? '' : 's'}) — ` +
              'a Freight Agent action clears it, which costs a whole Local Operations turn',
          );
        }
        if (loadedOnTrain && !s.yards.divisionYard.some((c) => c.type === 'coach' && !c.loaded)) {
          say('no EMPTY coach in the Division Yard to swap into the train — one is required');
        }
      }
    }
  }

  /**
   * TRAINS HELD FOR WANT OF A CREW TRAY (§7) — the scarcity mechanic, made visible (#98).
   *
   * This covered the TIMETABLED train due out this Stage and nothing else, which meant the two
   * other things that queue for the same pool reported nothing at all. A player who spent a card on
   * an Extra, or ordered a second section, got an EMPTY panel while their train sat behind an
   * exhausted pool — and each had been announced once in the log in a line that promised a future
   * event ("as soon as a Crew Tray frees up") which nothing then confirmed.
   *
   * All three are one condition, so they are written as one block: no free tray, and something
   * waiting for one. The count rides along because "no free Crew Tray" reads like a permanent fact
   * about the game rather than a state that will pass.
   */
  // `crewTrayCount` is the pool's size, asked rather than re-derived. `trays.size + freeTrays.length`
  // gives the same number in play — `retireTrain` moves a tray back — but it is a second way to know
  // one fact, which is the shape of every bug this release fixed.
  const trays = `${s.freeTrays.length} of ${crewTrayCount(s.players.length)} Crew Trays free`;
  if (s.freeTrays.length === 0) {
    const due = s.timetable[s.clock.stage - 1];
    if (due !== null && due !== undefined) {
      out.push({
        where: `Train ${due}`,
        why: `due to depart but HELD — no free Crew Tray (${trays})`,
        severity: 'stuck',
      });
    }

    // An Extra belongs to the player who played the card (§7), so it is their errand and it is
    // reported to them. A second section is the table's, like any Timetabled train.
    for (const x of s.pendingExtras) {
      if (x.player !== player) continue;
      out.push({
        where: `Extra X${x.trainNumber}`,
        why: `played and waiting to be made up — no free Crew Tray (${trays})`,
        severity: 'stuck',
      });
    }

    for (const n of s.pendingSecondSections) {
      out.push({
        where: `Train ${n}`,
        why: `second section ordered and waiting to be made up — no free Crew Tray (${trays})`,
        severity: 'stuck',
      });
    }
  }

  /**
   * A TRAIN HELD AT THE LIMITS BY AN INTERLOCKING (#99).
   *
   * It is inside the player's Limits, not on an A/D track, and it takes the first track that frees
   * ahead of any newcomer. The map now draws it on the Limits square; this says what it is waiting
   * for, which is the Office emptying rather than anything the held train itself can do.
   */
  for (const id of area.heldAtLimits) {
    const t = s.trays.get(id);
    if (!t) continue;
    out.push({
      where: `Train ${t.trainIsExtra ? 'X' : ''}${t.trainNumber ?? '—'}`,
      why:
        'held at your Limits by the Interlocking instead of colliding — it takes the first A/D ' +
        'track that frees, ahead of any train arriving after it',
      severity: 'waiting',
    });
  }

  // A full Office means the next arrival is an automatic collision (Gap 2d).
  const cap = adTrackCount(s, seatOf(s, player));
  if (area.adOccupancy.length >= cap) {
    out.push({
      where: 'Office',
      why: `all ${cap} A/D track(s) occupied — the next arrival COLLIDES`,
      severity: 'risk',
    });
  }

  if (s.clock.pendingDecision) {
    out.push({
      where: 'Superintendent',
      why: 'must rule on a following-train clearance before the Mainline Phase continues',
      severity: 'waiting',
    });
  }

  return out;
}

/** A one-line summary of where every train currently is. */
export function trainPositions(s: GameState): { id: TrayId; label: string; where: string }[] {
  const out: { id: TrayId; label: string; where: string }[] = [];
  for (const [id, tray] of s.trays) {
    const label = tray.trainNumber === null ? 'local crew' : `Train ${tray.trainIsExtra ? 'X' : ''}${tray.trainNumber}`;
    let where: string;
    switch (tray.position.at) {
      case 'divisionPoint':
        where = `${tray.position.side === 'west' ? 'West' : 'East'} Division Point`;
        break;
      case 'mainline':
        where = `Mainline card ${tray.position.index}`;
        break;
      case 'grid':
        where = `Office Area ${at(tray.position.coord)}`;
        break;
    }
    out.push({ id, label, where });
  }
  return out;
}

export { coordKey };


/**
 * What a batch of events should SOUND like.
 *
 * Shared between the live game and the replay so the two cannot disagree about when a Stage ended.
 * The model names what happened; the page decides what it sounds like.
 */
export function cuesFor(events: readonly GameEvent[]): string[] {
  const out: string[] = [];
  for (const e of events) {
    if (e.type === 'trainMadeUp') out.push('train');
    // Coupling and setting out are what a switching move IS, and both were silent. A car leaving the
    // board with only a line of history to say where it went is the thing that most needs a noise.
    if (e.type === 'carsCoupled') out.push('couple');
    if (e.type === 'carsDropped' || e.type === 'flyingSwitch') out.push('drop');
    // The 1D12 that sets a train's departure Stage. It is the one roll a player makes and it landed
    // silently, so the card was gone and the answer to "when does it run?" was a line of history.
    if (e.type === 'trainScheduled') out.push('schedule');
    // A train running the whole length of the Division pays every player, and it is the one event
    // nobody made happen on the turn it lands. It should be heard, not found in the log.
    if (e.type === 'trainCompleted') out.push('completed');
    // A train pulling into an Office. `trainDiverted` (the Yard Office siding) is deliberately not
    // included — that one goes straight to a work track without the A/D stop `arrive` depicts.
    if (e.type === 'trainArrived') out.push('arrive');
    // Only an OFFICE departure, not every highball: a fresh make-up leaving a Division Point already
    // sounds `train` ("All aboard"), and a train clearing the whole Division already sounds
    // `completed` — this is the one case neither of those covers.
    if (e.type === 'trainHighballed' && e.from === 'the Office') out.push('depart');
    // §10 — the one event nobody wants to hear and everybody needs to.
    if (e.type === 'trainsDestroyed') out.push('crash');
    if (e.type === 'stageBegan') {
      // A Stage BEGINNING is the previous one ending — except the first, which is the game opening
      // and has nothing behind it. A Day boundary rings the bell only: sounding both would collide,
      // and the bell is the bigger event.
      if (e.day > 1 && e.stage === 1) out.push('day');
      else if (e.day > 1 || e.stage > 1) out.push('stage');
    }
  }
  return out;
}