Juegoland/server/games/parchis.mjs

import { randomInt } from 'node:crypto';
import { nextPlayingSeat, withdrawParchis } from './turns.mjs';

export const starts = [4, 21, 38, 55];
const safe = new Set([4, 11, 16, 21, 28, 33, 38, 45, 50, 55, 62, 67]);
const square = (seat, progress) => (starts[seat] + progress) % 68;
const occupants = (state, cell) =>
  state.pieces.flatMap((pieces, seat) =>
    pieces.flatMap((p, piece) =>
      p >= 0 && p < 64 && square(seat, p) === cell ? [{ seat, piece }] : [],
    ),
  );

function canMove(state, seat, piece) {
  const p = state.pieces[seat][piece];
  const distance = state.die;
  if (
    !distance ||
    p === 71 ||
    (p === -1 && distance !== 5) ||
    p + distance > 71
  )
    return false;
  const target = p === -1 ? 0 : p + distance;
  if (p !== -1)
    for (let step = p + 1; step <= Math.min(target, 63); step++) {
      const group = occupants(state, square(seat, step));
      if (group.length >= 2 && group[0].seat === group[1].seat) return false;
    }
  if (target < 64) {
    const group = occupants(state, square(seat, target));
    if (group.length >= 2) return false;
    if (
      group.length &&
      group[0].seat !== seat &&
      safe.has(square(seat, target))
    )
      return false;
  } else if (target < 71 && state.pieces[seat].includes(target)) return false;
  return true;
}

export const parchis = {
  withdraw: withdrawParchis,
  id: 'parchis',
  version: '1.0.0',
  minPlayers: 2,
  maxPlayers: 4,
  /** @returns {{pieces: number[][], turn: number, die: number|null, rolled: number|null, bonus: boolean, extraTurn: boolean}} */
  create(players = 4) {
    return {
      pieces: Array.from({ length: players }, () => [-1, -1, -1, -1]),
      turn: 0,
      die: null,
      rolled: null,
      bonus: false,
      extraTurn: false,
    };
  },
  /** @returns {{type: string, piece?: number}[]} */
  legal(state, seat) {
    if (seat !== state.turn) return [];
    if (state.die === null) return [{ type: 'roll' }];
    let moves = state.pieces[seat].flatMap((_, piece) =>
      canMove(state, seat, piece) ? [{ type: 'move', piece }] : [],
    );
    // In this explicit basic variant, leaving home on a five is compulsory.
    if (
      !state.bonus &&
      state.die === 5 &&
      moves.some((m) => state.pieces[seat][m.piece] === -1)
    )
      moves = moves.filter((m) => state.pieces[seat][m.piece] === -1);
    return moves.length ? moves : [{ type: 'pass' }];
  },
  apply(state, action, seat, rng = () => randomInt(1, 7)) {
    if (
      !this.legal(state, seat).some(
        (a) =>
          a.type === action.type &&
          (a.type !== 'move' || a.piece === action.piece),
      )
    )
      throw new Error('Esa acción no está disponible.');
    const next = structuredClone(state);
    if (action.type === 'roll') {
      const die = rng();
      if (!Number.isInteger(die) || die < 1 || die > 6)
        throw new Error('Dado no válido.');
      next.die = die;
      next.rolled = die;
      next.extraTurn = die === 6;
      if (this.legal(next, seat).every((a) => a.type === 'pass')) {
        next.die = null;
        next.turn = next.extraTurn ? seat : nextPlayingSeat(next, seat);
        next.extraTurn = false;
      }
      return {
        state: next,
        label: `Dado: ${die}`,
        result: null,
        sound: 'roll',
      };
    }
    let reward = null;
    let label = 'Sin movimientos: pasa el turno';
    if (action.type === 'move') {
      const piece = action.piece;
      const p = state.pieces[seat][piece];
      const target = p === -1 ? 0 : p + state.die;
      next.pieces[seat][piece] = target;
      label = `Ficha ${piece + 1}: ${p === -1 ? 'sale de casa' : `avanza ${state.die}`}`;
      if (target < 64 && !safe.has(square(seat, target))) {
        for (const other of occupants(next, square(seat, target)))
          if (other.seat !== seat) {
            next.pieces[other.seat][other.piece] = -1;
            reward = 20;
            label += ' · captura';
          }
      }
      if (target === 71) {
        reward = 10;
        label += ' · llega a meta';
      }
      if (next.pieces[seat].every((p) => p === 71))
        return {
          state: next,
          label,
          result: { winner: seat, reason: 'cuatro fichas en meta' },
          sound: 'finish',
        };
    }
    if (reward !== null) {
      next.die = reward;
      next.bonus = true;
      if (this.legal(next, seat).every((a) => a.type === 'pass')) {
        next.die = null;
        next.bonus = false;
        next.turn = next.extraTurn ? seat : nextPlayingSeat(next, seat);
        next.extraTurn = false;
      }
    } else {
      next.die = null;
      next.bonus = false;
      next.turn = state.extraTurn ? seat : nextPlayingSeat(next, seat);
      next.extraTurn = false;
    }
    return {
      state: next,
      label,
      result: null,
      sound:
        action.type === 'pass'
          ? 'pass'
          : reward === 20
            ? 'capture'
            : reward === 10
              ? 'goal'
              : 'move',
    };
  },
  view(state) {
    return { ...state, starts, safe: [...safe] };
  },
};