blind_chess/packages/server/src/games.ts

import { Chess } from 'chess.js';
import { randomBytes } from 'node:crypto';
import type {
  Color, GameId, Mode, PlayerToken,
} from '@blind-chess/shared';
import type { BotDriver } from './bot/driver.js';
import { type Game, PRUNE_AFTER_FINISHED_MS, RATE_LIMIT } from './state.js';

const games = new Map<GameId, Game>();
const botDrivers = new Map<GameId, BotDriver>();

export function attachBotDriver(id: GameId, driver: BotDriver): void {
  botDrivers.set(id, driver);
}

export function getBotDriver(id: GameId): BotDriver | undefined {
  return botDrivers.get(id);
}

export function disposeBotDriver(id: GameId): void {
  botDrivers.delete(id);
}

export function newGameId(): GameId {
  const alphabet = 'abcdefghijklmnopqrstuvwxyz0123456789';
  let id = '';
  while (true) {
    const buf = randomBytes(8);
    id = '';
    for (let i = 0; i < 8; i++) id += alphabet[buf[i]! % alphabet.length];
    if (!games.has(id)) return id;
  }
}

export function newPlayerToken(): PlayerToken {
  return randomBytes(18).toString('base64url').slice(0, 24).toLowerCase().replace(/[^a-z0-9]/g, 'a');
}

export function chooseSide(side: Color | 'random'): Color {
  if (side === 'random') return Math.random() < 0.5 ? 'w' : 'b';
  return side;
}

export function createGame(opts: {
  mode: Mode;
  creatorSide: Color;
  highlightingEnabled: boolean;
  vsAi?: { brain: 'casual' | 'recon' };
}): { game: Game; creatorToken: PlayerToken } {
  const id = newGameId();
  const creatorToken = newPlayerToken();
  const now = Date.now();

  const botColor: Color | null = opts.vsAi
    ? (opts.creatorSide === 'w' ? 'b' : 'w')
    : null;

  const game: Game = {
    id,
    mode: opts.mode,
    highlightingEnabled: opts.highlightingEnabled,
    status: 'waiting',
    createdAt: now,
    chess: new Chess(),
    moveHistory: [],
    announcements: [],
    players: {
      w: opts.creatorSide === 'w' ? makeSlot(creatorToken, now)
        : (botColor === 'w' ? makeBotSlot(now) : null),
      b: opts.creatorSide === 'b' ? makeSlot(creatorToken, now)
        : (botColor === 'b' ? makeBotSlot(now) : null),
    },
    armed: null,
    drawOffer: null,
    disconnectAt: {},
    lastBroadcastIdx: { w: 0, b: 0 },
    aiOpponent: opts.vsAi && botColor
      ? { color: botColor, brain: opts.vsAi.brain }
      : undefined,
  };

  games.set(id, game);
  return { game, creatorToken };
}

function makeSlot(token: PlayerToken, now: number) {
  return {
    token,
    socket: null,
    joinedAt: now,
    rateBucket: { tokens: RATE_LIMIT.capacity, last: now },
  };
}

function makeBotSlot(now: number) {
  // Synthetic slot: occupies the player's color but never connects. The token
  // is randomized (same shape as a real client token) so a third party can't
  // hijack the bot's color by guessing a fixed placeholder.
  return {
    token: newPlayerToken(),
    socket: null,
    joinedAt: now,
    rateBucket: { tokens: RATE_LIMIT.capacity, last: now },
  };
}

export function getGame(id: GameId): Game | undefined {
  return games.get(id);
}

export function deleteGame(id: GameId): void {
  games.delete(id);
}

export function allGames(): IterableIterator<Game> {
  return games.values();
}

export function activeGameCount(): number {
  let n = 0;
  for (const g of games.values()) if (g.status !== 'finished') n++;
  return n;
}

/** Find game where this token is bound to a player slot; returns the slot color. */
export function findTokenInGame(game: Game, token: PlayerToken): Color | null {
  if (game.players.w?.token === token) return 'w';
  if (game.players.b?.token === token) return 'b';
  return null;
}

/** Claim the open slot in a game. Returns the color claimed or null if both filled. */
export function claimSlot(
  game: Game,
  joinAs: Color | 'auto',
): { color: Color; token: PlayerToken } | null {
  const tryClaim = (c: Color): { color: Color; token: PlayerToken } | null => {
    if (game.players[c]) return null;
    const token = newPlayerToken();
    game.players[c] = makeSlot(token, Date.now());
    return { color: c, token };
  };

  if (joinAs === 'w') return tryClaim('w');
  if (joinAs === 'b') return tryClaim('b');
  return tryClaim('w') ?? tryClaim('b');
}

export function pruneFinished(): number {
  const now = Date.now();
  let removed = 0;
  for (const [id, g] of games) {
    if (g.status === 'finished' && g.finishedAt && now - g.finishedAt > PRUNE_AFTER_FINISHED_MS) {
      games.delete(id);
      botDrivers.delete(id);
      removed++;
    }
  }
  return removed;
}