boardgame-core/src/samples/tic-tac-toe.ts

import { Part } from "@/core/part";
import { createRegion } from "@/core/region";
import {
  createGameCommandRegistry,
  createPromptDef,
  IGameContext,
} from "@/core/game";

const BOARD_SIZE = 3;
const MAX_TURNS = BOARD_SIZE * BOARD_SIZE;
const WINNING_LINES: number[][][] = [
  [
    [0, 0],
    [0, 1],
    [0, 2],
  ],
  [
    [1, 0],
    [1, 1],
    [1, 2],
  ],
  [
    [2, 0],
    [2, 1],
    [2, 2],
  ],
  [
    [0, 0],
    [1, 0],
    [2, 0],
  ],
  [
    [0, 1],
    [1, 1],
    [2, 1],
  ],
  [
    [0, 2],
    [1, 2],
    [2, 2],
  ],
  [
    [0, 0],
    [1, 1],
    [2, 2],
  ],
  [
    [0, 2],
    [1, 1],
    [2, 0],
  ],
];

export type PlayerType = "X" | "O";
export type WinnerType = PlayerType | "draw" | null;
export type TicTacToePart = Part<{ player: PlayerType }>;

export function createInitialState() {
  return {
    board: createRegion("board", [
      { name: "x", min: 0, max: BOARD_SIZE - 1 },
      { name: "y", min: 0, max: BOARD_SIZE - 1 },
    ]),
    parts: {} as Record<string, TicTacToePart>,
    currentPlayer: "X" as PlayerType,
    winner: null as WinnerType,
    turn: 0,
  };
}
export type TicTacToeState = ReturnType<typeof createInitialState>;
export type TicTacToeGame = IGameContext<TicTacToeState>;
export const registry = createGameCommandRegistry<TicTacToeState>();
export const prompts = {
  play: createPromptDef<[PlayerType, number, number]>(
    "play <player> <row:number> <col:number>",
  ),
};

export async function start(game: TicTacToeGame) {
  while (true) {
    const currentPlayer = game.value.currentPlayer;
    const turnNumber = game.value.turn + 1;
    const turnOutput = await turn(game, currentPlayer, turnNumber);

    game.produce((state) => {
      state.winner = turnOutput.winner;
      if (!state.winner) {
        state.currentPlayer = state.currentPlayer === "X" ? "O" : "X";
        state.turn = turnNumber;
      }
    });
    if (game.value.winner) break;
  }

  return game.value;
}

const turn = registry.register({
  schema: "turn <player> <turnNumber:number>",
  async run(game: TicTacToeGame, turnPlayer: PlayerType, turnNumber: number) {
    const { player, row, col } = await game.prompt(
      prompts.play,
      (player, row, col) => {
        if (player !== turnPlayer) {
          throw `Invalid player: ${player}. Expected ${turnPlayer}.`;
        } else if (!isValidMove(row, col)) {
          throw `Invalid position: (${row}, ${col}). Must be between 0 and ${BOARD_SIZE - 1}.`;
        } else if (isCellOccupied(game, row, col)) {
          throw `Cell (${row}, ${col}) is already occupied.`;
        } else {
          return { player, row, col };
        }
      },
      game.value.currentPlayer,
    );

    placePiece(game, row, col, turnPlayer);

    const winner = checkWinner(game);
    if (winner) return { winner };
    if (turnNumber >= MAX_TURNS) return { winner: "draw" as WinnerType };

    return { winner: null };
  },
});

function isValidMove(row: number, col: number): boolean {
  return (
    !isNaN(row) &&
    !isNaN(col) &&
    row >= 0 &&
    row < BOARD_SIZE &&
    col >= 0 &&
    col < BOARD_SIZE
  );
}

export function isCellOccupied(
  host: TicTacToeGame,
  row: number,
  col: number,
): boolean {
  return !!host.value.board.partMap[`${row},${col}`];
}

export function hasWinningLine(positions: number[][]): boolean {
  return WINNING_LINES.some((line) =>
    line.every(([r, c]) => positions.some(([pr, pc]) => pr === r && pc === c)),
  );
}

export function checkWinner(host: TicTacToeGame): WinnerType {
  const parts = host.value.parts;
  const partsArray = Object.values(parts);

  const xPositions = partsArray
    .filter((p: TicTacToePart) => p.player === "X")
    .map((p: TicTacToePart) => p.position);
  const oPositions = partsArray
    .filter((p: TicTacToePart) => p.player === "O")
    .map((p: TicTacToePart) => p.position);

  if (hasWinningLine(xPositions)) return "X";
  if (hasWinningLine(oPositions)) return "O";
  if (partsArray.length >= MAX_TURNS) return "draw";

  return null;
}

export function placePiece(
  host: TicTacToeGame,
  row: number,
  col: number,
  player: PlayerType,
) {
  const board = host.value.board;
  const moveNumber = Object.keys(host.value.parts).length + 1;
  const piece: TicTacToePart = {
    regionId: "board",
    position: [row, col],
    player,
    id: `piece-${player}-${moveNumber}`,
  };
  host.produce((state) => {
    state.parts[piece.id] = piece;
    board.childIds.push(piece.id);
    board.partMap[`${row},${col}`] = piece.id;
  });
}