/**
 * One room: seats, spectators, chat, game runner, timers (docs/06, docs/03, docs/09 §4).
 * All mutations run on the single JS thread, so a room never sees concurrent updates.
 */
import { ulid } from 'ulid';
import { SeededRng, createSeed, seedToHex, type AnyGameDefinition, type GameResult, type RngState } from '@bg/engine';
import { maskProfanity, type PublicUser, type RoomView, type ServerMessage, type SeatView } from '@bg/shared';
import { sha256Hex } from '../auth/sessions';
import type { RoomStore } from './store';
import { applyLocks, type EffectiveGame, type SiteSettings } from '../admin/settings';

export interface Conn {
  userId: string;
  send(msg: ServerMessage): void;
  close(code: number, reason: string): void;
}

export interface RoomConfig {
  gameId: string;
  options: unknown;
  maxPlayers: number;
  visibility: 'private' | 'public';
  allowSpectators: boolean;
  chatEnabled: boolean;
  chatFilter: boolean;
  /** Seconds a disconnected player keeps their turn timer before auto actions kick in (docs/03 §6.2). */
  graceSec: number;
}

export interface Seat {
  userId: string;
  ready: boolean;
}

interface Presence {
  connected: boolean;
  since: number;
  joinedAt: number;
}

interface GameSlot {
  gameId: string;
  stateVersion: number;
  state: unknown;
  rng: RngState;
  gamePk: string;
  seedHex: string;
  seedHash: string;
  startedAt: number;
  players: string[];
  finished: boolean;
  /** After a restore, deadlines are not enforced before this time (docs/04 §3.3). */
  deadlineFloor: number | null;
}

/** Shape persisted to room_state.state_json. */
export interface RoomSnapshot {
  v: 1;
  config: RoomConfig;
  hostId: string;
  status: Room['status'];
  seats: (Seat | null)[];
  gameNo: number;
  sessionStats: Record<string, { played: number; wins: number }>;
  rematchVotes: string[];
  lastSeed: string | null;
  lastResult: GameResult | null;
  game: GameSlot | null;
  joinedAt: Record<string, number>;
}

export interface RoomDeps {
  store: RoomStore;
  games: Record<string, AnyGameDefinition>;
  users: { publicUser(id: string): PublicUser | null };
  now?: () => number;
  log?: (level: 'info' | 'warn' | 'error', msg: string, extra?: Record<string, unknown>) => void;
  onEmpty?: (room: Room) => void;
  onSeatChange?: (room: Room, userId: string, seated: boolean) => void;
  /** Admin settings (docs/14-admin.md). Optional so unit tests can run without them. */
  settings?: { game(id: string): EffectiveGame | null; getSite(): SiteSettings };
}

const CHAT_HISTORY = 30;
const ERROR_LIMIT = 3;

export class Room {
  status: 'lobby' | 'playing' | 'finished' | 'paused' | 'broken' = 'lobby';
  seq = 0;
  hostId: string;
  seats: (Seat | null)[];
  spectators = new Set<string>();
  presence = new Map<string, Presence>();
  conns = new Map<string, Conn>();
  kicked = new Set<string>();
  /** Players who left during a game; their seat is freed when the game ends. */
  leftDuringGame = new Set<string>();
  gameNo = 0;
  sessionStats: Record<string, { played: number; wins: number }> = {};
  rematchVotes = new Set<string>();
  lastSeed: string | null = null;
  lastResult: GameResult | null = null;
  game: GameSlot | null = null;
  chatLog: Extract<ServerMessage, { t: 'chat' }>[] = [];
  lastActiveAt: number;
  private timer: ReturnType<typeof setTimeout> | null = null;
  private recentCs = new Map<string, number[]>();
  private lastChatAt = new Map<string, number>();
  private consecutiveErrors = 0;
  private readonly now: () => number;

  constructor(
    readonly id: string,
    readonly code: string,
    public config: RoomConfig,
    hostId: string,
    private deps: RoomDeps,
  ) {
    this.hostId = hostId;
    this.seats = new Array(config.maxPlayers).fill(null);
    this.now = deps.now ?? Date.now;
    this.lastActiveAt = this.now();
  }

  get def(): AnyGameDefinition {
    const d = this.deps.games[this.config.gameId];
    if (!d) throw new Error(`unknown game ${this.config.gameId}`);
    return d;
  }

  playerRange(): { min: number; max: number } {
    return this.rangeFor(this.config.gameId, this.config.options);
  }

  /** Game's own range (per options) intersected with the admin-configured range. */
  private rangeFor(gameId: string, options: unknown): { min: number; max: number } {
    const d = this.deps.games[gameId]!;
    const base = d.playersFor ? d.playersFor(options) : { min: d.minPlayers, max: d.maxPlayers };
    const eff = this.deps.settings?.game(gameId);
    if (!eff) return base;
    const min = Math.max(base.min, eff.minPlayers);
    const max = Math.min(base.max, eff.maxPlayers);
    return min <= max ? { min, max } : base;
  }

  private locked(gameId: string): { defaults: unknown; paths: string[] } {
    const eff = this.deps.settings?.game(gameId);
    return { defaults: eff?.defaultOptions, paths: eff?.lockedOptions ?? [] };
  }

  seatOf(userId: string): number {
    return this.seats.findIndex((s) => s?.userId === userId);
  }

  isParticipant(userId: string): boolean {
    return this.seatOf(userId) >= 0 || this.spectators.has(userId);
  }

  seatedIds(): string[] {
    return this.seats.filter((s): s is Seat => s !== null).map((s) => s.userId);
  }

  inGame(userId: string): boolean {
    return !!this.game && !this.game.finished && this.game.players.includes(userId);
  }

  // ---------------------------------------------------------------- snapshot

  snapshot(): RoomSnapshot {
    const joinedAt: Record<string, number> = {};
    for (const [u, p] of this.presence) if (this.seatOf(u) >= 0) joinedAt[u] = p.joinedAt;
    return {
      v: 1,
      config: this.config,
      hostId: this.hostId,
      status: this.status,
      seats: this.seats,
      gameNo: this.gameNo,
      sessionStats: this.sessionStats,
      rematchVotes: [...this.rematchVotes],
      lastSeed: this.lastSeed,
      lastResult: this.lastResult,
      game: this.game,
      joinedAt,
    };
  }

  static restore(id: string, code: string, seq: number, snap: RoomSnapshot, deps: RoomDeps): Room {
    const room = new Room(id, code, snap.config, snap.hostId, deps);
    room.seq = seq;
    room.status = snap.status;
    room.seats = snap.seats;
    room.gameNo = snap.gameNo;
    room.sessionStats = snap.sessionStats;
    room.rematchVotes = new Set(snap.rematchVotes);
    room.lastSeed = snap.lastSeed;
    room.lastResult = snap.lastResult;
    room.game = snap.game;
    const now = room.now();
    for (const s of room.seats) {
      if (s) room.presence.set(s.userId, { connected: false, since: now, joinedAt: snap.joinedAt[s.userId] ?? now });
    }
    if (room.game && !room.game.finished) {
      const def = room.def;
      if (def.stateVersion !== room.game.stateVersion) {
        if (!def.migrate) throw new Error(`state version mismatch for ${def.id}`);
        room.game.state = def.migrate(room.game.state, room.game.stateVersion);
        room.game.stateVersion = def.stateVersion;
      }
      // 30s to reconnect, plus up to 30s jitter so thousands of restored rooms don't all time out
      // in the same instant (thundering herd after a restart, docs/04 §3).
      room.game.deadlineFloor = now + 30_000 + Math.floor(Math.random() * 30_000);
      room.scheduleTimer();
    }
    return room;
  }

  private persist(log: { actorId: string | null; kind: string; data: unknown } | null): void {
    const nextSeq = this.seq + 1;
    this.deps.store.save(
      this.id,
      nextSeq,
      JSON.stringify(this.snapshot()),
      { hostId: this.hostId, gameId: this.config.gameId, status: this.status, visibility: this.config.visibility, config: this.config },
      log ? { seq: nextSeq, gameNo: this.gameNo, at: this.now(), ...log } : null,
    );
    this.seq = nextSeq;
    this.lastActiveAt = this.now();
  }

  // ---------------------------------------------------------------- views

  roomView(): RoomView {
    const pub = (id: string): PublicUser => this.deps.users.publicUser(id) ?? { id, nickname: '알 수 없음', avatar: null, kind: 'guest' };
    const seats: (SeatView | null)[] = this.seats.map((s) => {
      if (!s) return null;
      const p = this.presence.get(s.userId);
      const connected = !!p?.connected;
      const away = !connected && !!p && this.now() - p.since > this.config.graceSec * 1000;
      return { user: pub(s.userId), ready: s.ready, connected, away };
    });
    const range = this.playerRange();
    return {
      code: this.code,
      hostId: this.hostId,
      gameId: this.config.gameId,
      options: this.config.options,
      maxPlayers: this.config.maxPlayers,
      minPlayers: range.min,
      visibility: this.config.visibility,
      turnSeconds: null,
      allowSpectators: this.config.allowSpectators,
      chatEnabled: this.config.chatEnabled,
      chatFilter: this.config.chatFilter,
      seats,
      spectators: [...this.spectators].map(pub),
      status: this.status,
      gameNo: this.gameNo,
      rematchVotes: [...this.rematchVotes],
      sessionStats: this.sessionStats,
      seedHash: this.game?.seedHash ?? null,
      lockedOptions: this.locked(this.config.gameId).paths,
      lastSeed: this.lastSeed,
    };
  }

  private stateMessage(viewer: string, cs?: number): ServerMessage | null {
    if (!this.game) return null;
    const def = this.def;
    const asPlayer = this.game.players.includes(viewer) ? viewer : null;
    let view: unknown;
    try {
      view = def.view(this.game.state, asPlayer);
    } catch (err) {
      this.deps.log?.('error', 'view failed', { room: this.code, viewer, err: String(err) });
      return { t: 'error', code: 'view-failed', message: '화면을 그리는 중 오류가 발생했어요.' };
    }
    return {
      t: 'state',
      seq: this.seq,
      view,
      events: [],
      active: this.game.finished ? [] : def.activePlayers(this.game.state),
      deadline: this.game.finished ? null : this.effectiveDeadline(),
      ...(cs !== undefined ? { cs } : {}),
    };
  }

  broadcastRoom(): void {
    const msg: ServerMessage = { t: 'room', seq: this.seq, room: this.roomView() };
    for (const c of this.conns.values()) c.send(msg);
  }

  private broadcastState(events: unknown[], actor?: string, cs?: number): void {
    if (!this.game) return;
    let spectatorMsg: ServerMessage | null = null;
    for (const c of this.conns.values()) {
      let msg: ServerMessage | null;
      if (this.game.players.includes(c.userId)) {
        msg = this.stateMessage(c.userId, c.userId === actor ? cs : undefined);
      } else {
        spectatorMsg ??= this.stateMessage('');
        msg = spectatorMsg;
      }
      if (msg && msg.t === 'state') c.send({ ...msg, events });
      else if (msg) c.send(msg);
    }
  }

  notice(code: string, message: string): void {
    for (const c of this.conns.values()) c.send({ t: 'notice', code, message });
  }

  // ---------------------------------------------------------------- membership

  /** Returns an error message, or null on success. */
  join(conn: Conn, as: 'player' | 'spectator'): string | null {
    const u = conn.userId;
    if (this.kicked.has(u)) return '방장이 내보낸 방에는 다시 들어갈 수 없어요.';
    if (this.status === 'broken') return '서버 업데이트로 이 게임을 이어갈 수 없어요. 새로 시작해 주세요.';
    const old = this.conns.get(u);
    if (old && old !== conn) {
      old.send({ t: 'bye', reason: 'replaced' });
      old.close(4000, 'replaced');
    }
    const now = this.now();
    const wasSeated = this.seatOf(u) >= 0;
    if (!wasSeated && !this.spectators.has(u)) {
      const seatable = as === 'player' && (this.status === 'lobby' || this.status === 'finished') && this.seats.some((s) => s === null);
      if (seatable) {
        const idx = this.seats.findIndex((s) => s === null);
        this.seats[idx] = { userId: u, ready: false };
        this.deps.onSeatChange?.(this, u, true);
      } else {
        if (!this.config.allowSpectators && !this.inGame(u)) return '이 방은 가득 찼어요.';
        this.spectators.add(u);
      }
    }
    const prev = this.presence.get(u);
    this.leftDuringGame.delete(u);
    this.presence.set(u, { connected: true, since: now, joinedAt: prev?.joinedAt || now });
    this.conns.set(u, conn);
    if (wasSeated && prev && !prev.connected && this.inGame(u)) {
      this.notice('reconnected', `${this.nick(u)}님이 다시 연결됐어요.`);
    }
    this.persist(wasSeated ? null : { actorId: u, kind: 'join', data: { as } });
    this.broadcastRoom();
    const st = this.stateMessage(u);
    if (st) conn.send(st);
    if (this.status === 'finished' && this.lastResult) conn.send({ t: 'result', seq: this.seq, result: this.lastResult });
    for (const m of this.chatLog) conn.send(m);
    this.scheduleTimer();
    return null;
  }

  /** Connection dropped (not an intentional leave). */
  disconnect(conn: Conn): void {
    const u = conn.userId;
    if (this.conns.get(u) !== conn) return;
    this.conns.delete(u);
    const p = this.presence.get(u);
    if (p) {
      p.connected = false;
      p.since = this.now();
    }
    if (this.spectators.has(u)) {
      this.spectators.delete(u);
      this.presence.delete(u);
    } else if (this.inGame(u)) {
      this.notice('disconnected', `${this.nick(u)}님의 연결이 끊겼어요.`);
    }
    this.broadcastRoom();
    this.scheduleTimer();
    if (this.conns.size === 0) this.deps.onEmpty?.(this);
  }

  leave(userId: string): void {
    const conn = this.conns.get(userId);
    this.conns.delete(userId);
    this.spectators.delete(userId);
    this.presence.delete(userId);
    const seat = this.seatOf(userId);
    if (seat >= 0) {
      if (this.inGame(userId)) {
        // Stay in the seat as "away" until the game ends so the game state stays consistent.
        this.leftDuringGame.add(userId);
        this.presence.set(userId, { connected: false, since: 0, joinedAt: 0 });
        const action = this.def.onLeave?.(this.game!.state, userId);
        if (action) this.runAction(userId, action, undefined, true);
      } else {
        this.seats[seat] = null;
        this.rematchVotes.delete(userId);
        this.deps.onSeatChange?.(this, userId, false);
      }
    }
    if (this.hostId === userId) this.pickNewHost();
    this.persist({ actorId: userId, kind: 'leave', data: null });
    this.broadcastRoom();
    conn?.send({ t: 'bye', reason: 'closed' });
    if (this.conns.size === 0) this.deps.onEmpty?.(this);
  }

  private pickNewHost(): void {
    const candidates = [...this.presence.entries()]
      .filter(([u, p]) => this.seatOf(u) >= 0 && p.connected)
      .sort((a, b) => a[1].joinedAt - b[1].joinedAt);
    const next = candidates[0]?.[0] ?? this.seatedIds()[0] ?? [...this.spectators][0];
    if (next) this.hostId = next;
  }

  // ---------------------------------------------------------------- lobby commands

  private requireLobby(): string | null {
    return this.status === 'lobby' || this.status === 'finished' ? null : '게임 중에는 바꿀 수 없어요.';
  }

  seat(userId: string, seat?: number): string | null {
    const err = this.requireLobby();
    if (err) return err;
    const target = seat ?? this.seats.findIndex((s) => s === null);
    if (target < 0 || target >= this.seats.length) return '빈자리가 없어요.';
    if (this.seats[target] && this.seats[target]!.userId !== userId) return '이미 다른 사람이 앉은 자리예요.';
    const cur = this.seatOf(userId);
    if (cur === target) return null;
    const ready = cur >= 0 ? this.seats[cur]!.ready : false;
    if (cur >= 0) this.seats[cur] = null;
    this.seats[target] = { userId, ready };
    this.spectators.delete(userId);
    if (cur < 0) this.deps.onSeatChange?.(this, userId, true);
    this.persist({ actorId: userId, kind: 'seat', data: { seat: target } });
    this.broadcastRoom();
    return null;
  }

  unseat(userId: string): string | null {
    const err = this.requireLobby();
    if (err) return err;
    const cur = this.seatOf(userId);
    if (cur < 0) return null;
    if (!this.config.allowSpectators) return '이 방은 관전을 허용하지 않아요.';
    this.seats[cur] = null;
    this.spectators.add(userId);
    this.rematchVotes.delete(userId);
    this.deps.onSeatChange?.(this, userId, false);
    this.persist({ actorId: userId, kind: 'unseat', data: null });
    this.broadcastRoom();
    return null;
  }

  ready(userId: string, ready: boolean): string | null {
    const cur = this.seatOf(userId);
    if (cur < 0) return '자리에 앉아야 준비할 수 있어요.';
    if (this.requireLobby()) return this.requireLobby();
    this.seats[cur]!.ready = ready;
    this.persist(null);
    this.broadcastRoom();
    return null;
  }

  configure(
    userId: string,
    patch: Partial<Omit<RoomConfig, 'graceSec'>> & { gameId?: string },
  ): string | null {
    if (userId !== this.hostId) return '방장만 설정을 바꿀 수 있어요.';
    const err = this.requireLobby();
    if (err) return err;
    const next: RoomConfig = { ...this.config };
    if (patch.gameId !== undefined && patch.gameId !== this.config.gameId) {
      const def = this.deps.games[patch.gameId];
      const eff = this.deps.settings?.game(patch.gameId);
      if (!def || (eff && !eff.enabled)) return '없는 게임이에요.';
      next.gameId = patch.gameId;
      next.options = eff?.defaultOptions ?? def.defaultOptions;
      next.maxPlayers = eff?.maxPlayers ?? def.maxPlayers;
    }
    const def = this.deps.games[next.gameId]!;
    if (patch.options !== undefined) {
      const parsed = def.optionsSchema.safeParse(patch.options);
      if (!parsed.success) return '설정 값이 올바르지 않아요.';
      next.options = parsed.data;
    }
    // Admin-locked options always keep the admin value (docs/14-admin.md §4).
    const lk = this.locked(next.gameId);
    if (lk.paths.length) next.options = def.optionsSchema.parse(applyLocks(next.options, lk.defaults, lk.paths));
    const range = this.rangeFor(next.gameId, next.options);
    if (patch.maxPlayers !== undefined) next.maxPlayers = patch.maxPlayers;
    // A room that had every seat its game allows keeps doing so when an option changes the range (e.g. 윷놀이 팀전 8명).
    else if (next.gameId === this.config.gameId && this.config.maxPlayers === this.playerRange().max) next.maxPlayers = range.max;
    next.maxPlayers = Math.min(Math.max(next.maxPlayers, range.min), range.max);
    if (next.maxPlayers < this.seatedIds().length) return `이미 ${this.seatedIds().length}명이 앉아 있어요.`;
    for (const k of ['visibility', 'allowSpectators', 'chatEnabled', 'chatFilter'] as const) {
      if (patch[k] !== undefined) (next as unknown as Record<string, unknown>)[k] = patch[k];
    }
    // Resize seats, compacting occupied seats to the front if needed.
    if (next.maxPlayers !== this.seats.length) {
      const occupied = this.seats.filter((s): s is Seat => s !== null);
      const seats: (Seat | null)[] = new Array(next.maxPlayers).fill(null);
      let i = 0;
      for (let k = 0; k < this.seats.length && k < next.maxPlayers; k++) if (this.seats[k]) seats[k] = this.seats[k]!;
      const placed = new Set(seats.filter(Boolean).map((s) => s!.userId));
      for (const s of occupied) {
        if (placed.has(s.userId)) continue;
        while (seats[i]) i++;
        seats[i] = s;
      }
      this.seats = seats;
    }
    this.config = next;
    for (const s of this.seats) if (s) s.ready = false;
    this.persist({ actorId: userId, kind: 'config', data: patch });
    this.broadcastRoom();
    return null;
  }

  kick(userId: string, target: string): string | null {
    if (userId !== this.hostId) return '방장만 내보낼 수 있어요.';
    if (target === userId) return '자기 자신은 내보낼 수 없어요.';
    if (!this.isParticipant(target)) return '방에 없는 사람이에요.';
    const conn = this.conns.get(target);
    this.kicked.add(target);
    this.leave(target);
    conn?.send({ t: 'bye', reason: 'kicked' });
    conn?.close(4001, 'kicked');
    return null;
  }

  transferHost(userId: string, target: string): string | null {
    if (userId !== this.hostId) return '방장만 넘길 수 있어요.';
    if (this.seatOf(target) < 0 && !this.spectators.has(target)) return '방에 없는 사람이에요.';
    this.hostId = target;
    this.persist({ actorId: userId, kind: 'host', data: { target } });
    this.broadcastRoom();
    return null;
  }

  chat(userId: string, text: string): string | null {
    if (!this.config.chatEnabled) return '이 방은 채팅을 쓰지 않아요.';
    if (!this.isParticipant(userId)) return '방에 들어와야 채팅할 수 있어요.';
    const now = this.now();
    if (now - (this.lastChatAt.get(userId) ?? 0) < 500) return '조금 천천히 보내 주세요.';
    this.lastChatAt.set(userId, now);
    const clean = text.replace(/[\u0000-\u001f\u007f]/g, ' ').trim();
    if (!clean) return null;
    const msg: Extract<ServerMessage, { t: 'chat' }> = {
      t: 'chat',
      from: this.deps.users.publicUser(userId),
      text: this.config.chatFilter ? maskProfanity(clean, this.deps.settings?.getSite().bannedWords ?? []) : clean,
      at: now,
    };
    this.chatLog.push(msg);
    if (this.chatLog.length > CHAT_HISTORY) this.chatLog.shift();
    for (const c of this.conns.values()) c.send(msg);
    return null;
  }

  emote(userId: string, id: string): void {
    if (!this.isParticipant(userId)) return;
    const now = this.now();
    if (now - (this.lastChatAt.get(`e:${userId}`) ?? 0) < 500) return;
    this.lastChatAt.set(`e:${userId}`, now);
    for (const c of this.conns.values()) c.send({ t: 'emote', from: userId, id });
  }

  // ---------------------------------------------------------------- game lifecycle

  start(userId: string): string | null {
    if (userId !== this.hostId) return '방장만 시작할 수 있어요.';
    const err = this.requireLobby();
    if (err) return err;
    const players = this.orderedPlayers();
    const range = this.playerRange();
    if (players.length < range.min) return `${range.min - players.length}명 더 필요해요.`;
    if (players.length > range.max) return `최대 ${range.max}명까지 할 수 있어요.`;
    return this.startGame(players);
  }

  rematch(userId: string): string | null {
    if (this.status !== 'finished') return '게임이 끝난 뒤에 누를 수 있어요.';
    if (this.seatOf(userId) < 0) return '자리에 앉아야 해요.';
    this.rematchVotes.add(userId);
    const seated = this.seatedIds();
    const range = this.playerRange();
    if (seated.length >= range.min && seated.every((u) => this.rematchVotes.has(u))) {
      return this.startGame(this.orderedPlayers());
    }
    this.persist(null);
    this.broadcastRoom();
    return null;
  }

  /** Seated players in seat order, rotated so the host (if seated) comes first. */
  private orderedPlayers(): string[] {
    const ids = this.seatedIds();
    const h = ids.indexOf(this.hostId);
    return h > 0 ? [...ids.slice(h), ...ids.slice(0, h)] : ids;
  }

  private startGame(players: string[]): string | null {
    const def = this.def;
    const lk = this.locked(def.id);
    const parsed = def.optionsSchema.safeParse(lk.paths.length ? applyLocks(this.config.options, lk.defaults, lk.paths) : this.config.options);
    if (!parsed.success) return '설정 값이 올바르지 않아요.';
    const countErr = def.playerCountError?.(parsed.data, players.length);
    if (countErr) return countErr;
    const eff = this.deps.settings?.game(def.id);
    if (eff && !eff.enabled) return '관리자가 이 게임을 잠시 막아 두었어요.';
    this.config = { ...this.config, options: parsed.data };
    const seed = createSeed();
    const seedHex = seedToHex(seed);
    const rng = SeededRng.fromSeed(seed);
    const now = this.now();
    const gameNo = this.gameNo + 1;
    let state: unknown;
    try {
      state = def.setup({ players, options: parsed.data, rng, now, gameNo });
    } catch (err) {
      this.deps.log?.('error', 'setup failed', { room: this.code, err: String(err) });
      return '게임을 시작하지 못했어요.';
    }
    const gamePk = ulid(now);
    const seedHash = sha256Hex(seedHex);
    this.deps.store.insertGame({ id: gamePk, roomId: this.id, gameNo, gameId: def.id, options: parsed.data, seedHash, startedAt: now });
    this.gameNo = gameNo;
    this.game = {
      gameId: def.id,
      stateVersion: def.stateVersion,
      state,
      rng: rng.state(),
      gamePk,
      seedHex,
      seedHash,
      startedAt: now,
      players,
      finished: false,
      deadlineFloor: null,
    };
    this.status = 'playing';
    this.rematchVotes.clear();
    this.lastResult = null;
    this.consecutiveErrors = 0;
    for (const s of this.seats) if (s) s.ready = false;
    this.persist({ actorId: this.hostId, kind: 'start', data: { gameId: def.id, players, seedHash } });
    this.broadcastRoom();
    this.broadcastState([{ type: 'gameStarted' }]);
    this.scheduleTimer();
    return null;
  }

  /** Client action entry. `cs` dedupes retransmissions (docs/03 §5). */
  act(userId: string, cs: number, action: unknown): void {
    const conn = this.conns.get(userId);
    const reject = (reason: string) => conn?.send({ t: 'reject', cs, reason });
    const recent = this.recentCs.get(userId) ?? [];
    if (recent.includes(cs)) return;
    recent.push(cs);
    if (recent.length > 50) recent.shift();
    this.recentCs.set(userId, recent);
    if (!this.game || this.game.finished || this.status !== 'playing') return reject('진행 중인 게임이 없어요.');
    if (!this.game.players.includes(userId)) return reject('이 게임의 플레이어가 아니에요.');
    const parsed = this.def.actionSchema.safeParse(action);
    if (!parsed.success) return reject('잘못된 요청이에요.');
    const err = this.runAction(userId, parsed.data, cs, false);
    if (err) reject(err);
  }

  /** Validates and applies one action; returns an error message on rejection. */
  private runAction(userId: string, action: unknown, cs: number | undefined, system: boolean): string | null {
    const g = this.game;
    if (!g || g.finished) return '진행 중인 게임이 없어요.';
    const def = this.def;
    let next: { state: unknown; events: unknown[] };
    const rng = new SeededRng(g.rng);
    try {
      const v = def.validate(g.state, userId, action);
      if (!v.ok) return v.reason;
      next = def.apply(g.state, userId, action, { rng, now: this.now() });
    } catch (err) {
      this.consecutiveErrors++;
      this.deps.log?.('error', 'game apply failed', { room: this.code, game: def.id, seq: this.seq, action, err: String(err), stack: (err as Error)?.stack });
      if (this.consecutiveErrors >= ERROR_LIMIT) {
        this.status = 'paused';
        this.clearTimer();
        this.persist({ actorId: null, kind: 'paused', data: null });
        this.broadcastRoom();
        this.notice('paused', '오류가 반복되어 게임을 멈췄어요. 방장은 게임을 끝낼 수 있어요.');
      }
      return '알 수 없는 오류가 발생했어요.';
    }
    this.consecutiveErrors = 0;
    g.state = next.state;
    g.rng = rng.state();
    g.deadlineFloor = null;
    this.persist({ actorId: userId, kind: system ? 'auto' : 'act', data: action });
    this.broadcastState(next.events, userId, cs);
    const result = def.result(g.state);
    if (result) this.finishGame(result);
    else this.scheduleTimer();
    return null;
  }

  /** Host ends a paused/broken game without counting it. */
  voidGame(userId: string): string | null {
    if (userId !== this.hostId) return '방장만 할 수 있어요.';
    if (!this.game || this.game.finished) return '진행 중인 게임이 없어요.';
    this.finishGame({ ranking: [this.game.players], summary: '게임이 무효 처리됐어요.', reason: 'abandoned' }, true);
    return null;
  }

  private finishGame(result: GameResult, voided = false): void {
    const g = this.game!;
    g.finished = true;
    this.clearTimer();
    const rankOf = new Map<string, number>();
    let rank = 1;
    for (const group of result.ranking) {
      for (const u of group) rankOf.set(u, rank);
      rank += group.length;
    }
    const players = g.players.map((u) => ({
      userId: u,
      seat: this.seatOf(u),
      rank: rankOf.get(u) ?? null,
      score: result.scores?.[u] ?? null,
    }));
    this.deps.store.finishGame({
      id: g.gamePk,
      gameId: g.gameId,
      seed: g.seedHex,
      endedAt: this.now(),
      endReason: voided ? 'void' : result.reason,
      result,
      players,
    });
    const allFirst = players.every((p) => p.rank === 1);
    if (!voided) {
      for (const p of players) {
        const st = (this.sessionStats[p.userId] ??= { played: 0, wins: 0 });
        st.played++;
        if (p.rank === 1 && !allFirst) st.wins++;
      }
    }
    this.lastSeed = g.seedHex;
    this.lastResult = result;
    this.status = 'finished';
    // Players who left during the game lose their seat now.
    for (let i = 0; i < this.seats.length; i++) {
      const s = this.seats[i];
      if (s && this.leftDuringGame.has(s.userId)) {
        this.seats[i] = null;
        this.presence.delete(s.userId);
        this.deps.onSeatChange?.(this, s.userId, false);
      }
    }
    this.leftDuringGame.clear();
    this.persist({ actorId: null, kind: 'finish', data: { result, voided } });
    this.broadcastState([{ type: 'gameOver' }]);
    for (const c of this.conns.values()) c.send({ t: 'result', seq: this.seq, result });
    this.broadcastRoom();
  }

  // ---------------------------------------------------------------- timers

  /** Earliest time any timed player must be auto-acted for. */
  effectiveDeadline(): number | null {
    const g = this.game;
    if (!g || g.finished || this.status !== 'playing') return null;
    const def = this.def;
    const base = def.deadline?.(g.state) ?? null;
    const notBefore = def.timeoutNotBefore?.(g.state) ?? null;
    const timed = def.timeoutPlayers ? def.timeoutPlayers(g.state) : def.activePlayers(g.state);
    let best: number | null = null;
    for (const u of timed) {
      let d = base;
      const p = this.presence.get(u);
      if (p && !p.connected) {
        const grace = p.since + this.config.graceSec * 1000;
        d = d === null ? grace : Math.min(d, grace);
      }
      if (d === null) continue;
      if (g.deadlineFloor !== null) d = Math.max(d, g.deadlineFloor);
      if (notBefore !== null) d = Math.max(d, notBefore);
      best = best === null ? d : Math.min(best, d);
    }
    return best;
  }

  scheduleTimer(): void {
    this.clearTimer();
    const at = this.effectiveDeadline();
    if (at === null) return;
    const delay = Math.max(0, at - this.now());
    this.timer = setTimeout(() => this.onTimer(), Math.min(delay, 2 ** 31 - 1));
  }

  clearTimer(): void {
    if (this.timer) clearTimeout(this.timer);
    this.timer = null;
  }

  /** Fires due timeouts. Public for tests. */
  onTimer(): void {
    this.timer = null;
    const g = this.game;
    if (!g || g.finished || this.status !== 'playing') return;
    const def = this.def;
    const now = this.now();
    const base = def.deadline?.(g.state) ?? null;
    const notBefore = def.timeoutNotBefore?.(g.state) ?? null;
    const timed = def.timeoutPlayers ? def.timeoutPlayers(g.state) : def.activePlayers(g.state);
    for (const u of timed) {
      let d = base;
      const p = this.presence.get(u);
      if (p && !p.connected) {
        const grace = p.since + this.config.graceSec * 1000;
        d = d === null ? grace : Math.min(d, grace);
      }
      if (g.deadlineFloor !== null && d !== null) d = Math.max(d, g.deadlineFloor);
      if (notBefore !== null && d !== null) d = Math.max(d, notBefore);
      if (d === null || d > now) continue;
      const action = def.onTimeout(g.state, u);
      const err = this.runAction(u, action, undefined, true);
      if (err) this.deps.log?.('warn', 'timeout action rejected', { room: this.code, user: u, err });
      break; // state changed; re-evaluate via scheduleTimer
    }
    if (!this.game?.finished) this.scheduleTimer();
  }

  // ---------------------------------------------------------------- misc

  private nick(u: string): string {
    return this.deps.users.publicUser(u)?.nickname ?? '알 수 없음';
  }

  sendSync(conn: Conn): void {
    conn.send({ t: 'room', seq: this.seq, room: this.roomView() });
    const st = this.stateMessage(conn.userId);
    if (st) conn.send(st);
  }

  /** Admin closes the room: void any running game, tell everyone, disconnect. */
  closeByAdmin(): void {
    if (this.game && !this.game.finished) {
      this.finishGame({ ranking: [this.game.players], summary: '관리자가 방을 닫아 무효 처리됐어요.', reason: 'abandoned' }, true);
    }
    this.notice('closed', '관리자가 방을 닫았어요.');
    this.clearTimer();
    for (const c of this.conns.values()) {
      c.send({ t: 'bye', reason: 'closed' });
      c.close(4002, 'closed');
    }
    this.conns.clear();
  }

  shutdown(): void {
    this.clearTimer();
    for (const c of this.conns.values()) {
      c.send({ t: 'bye', reason: 'restart' });
      c.close(1012, 'restart');
    }
  }
}