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

import { GameContextInstance } from '../core/context';
import type { GameContextLike, RuleContext } from '../core/rule';
import { createRule, type InvokeYield, type RuleYield } from '../core/rule';
import type { Command } from '../utils/command';
import type { Part } from '../core/part';
import type { Region } from '../core/region';
import type { Context } from '../core/context';

export type TicTacToeState = Context & {
    type: 'tic-tac-toe';
    currentPlayer: 'X' | 'O';
    winner: 'X' | 'O' | 'draw' | null;
    moveCount: number;
};

type TurnResult = {
    winner: 'X' | 'O' | 'draw' | null;
};

function getBoardRegion(game: GameContextLike) {
    return game.regions.get('board');
}

function isCellOccupied(game: GameContextLike, row: number, col: number): boolean {
    const board = getBoardRegion(game);
    return board.value.children.some(
        (child: { value: { position: number[] } }) => child.value.position[0] === row && child.value.position[1] === col
    );
}

function checkWinner(game: GameContextLike): 'X' | 'O' | 'draw' | null {
    const parts = Object.values(game.parts.collection.value).map((s: { value: Part }) => s.value);

    const xPositions = parts.filter((_: Part, i: number) => i % 2 === 0).map((p: Part) => p.position);
    const oPositions = parts.filter((_: Part, i: number) => i % 2 === 1).map((p: Part) => p.position);

    if (hasWinningLine(xPositions)) return 'X';
    if (hasWinningLine(oPositions)) return 'O';

    return null;
}

function hasWinningLine(positions: number[][]): boolean {
    const lines = [
        [[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]],
    ];

    return lines.some(line =>
        line.every(([r, c]) =>
            positions.some(([pr, pc]) => pr === r && pc === c)
        )
    );
}

function placePiece(game: GameContextLike, row: number, col: number, moveCount: number) {
    const board = getBoardRegion(game);
    const piece: Part = {
        id: `piece-${moveCount}`,
        sides: 1,
        side: 0,
        region: board,
        position: [row, col],
    };
    game.parts.add(piece);
    board.value.children.push(game.parts.get(piece.id));
}

const playSchema = 'play <player> <row:number> <col:number>';

export function createSetupRule() {
    return createRule('start', function*() {
        this.pushContext({
            type: 'tic-tac-toe',
            currentPlayer: 'X',
            winner: null,
            moveCount: 0,
        } as TicTacToeState);

        this.regions.add({
            id: 'board',
            axes: [
                { name: 'x', min: 0, max: 2 },
                { name: 'y', min: 0, max: 2 },
            ],
            children: [],
        } as Region);

        let currentPlayer: 'X' | 'O' = 'X';
        let turnResult: TurnResult | undefined;

        while (true) {
            const yieldValue: InvokeYield = {
                type: 'invoke',
                rule: 'turn',
                command: { name: 'turn', params: [currentPlayer], flags: {}, options: {} } as Command,
            };
            const ctx = yield yieldValue as RuleYield;
            turnResult = (ctx as RuleContext<TurnResult>).resolution;
            if (turnResult?.winner) break;

            currentPlayer = currentPlayer === 'X' ? 'O' : 'X';
            const state = this.latestContext<TicTacToeState>('tic-tac-toe')!;
            state.value.currentPlayer = currentPlayer;
        }

        const state = this.latestContext<TicTacToeState>('tic-tac-toe')!;
        state.value.winner = turnResult?.winner ?? null;
        return { winner: state.value.winner };
    });
}

export function createTurnRule() {
    return createRule('turn <player>', function*(cmd) {
        while (true) {
            const received = yield playSchema;
            if ('resolution' in received) continue;

            const playCmd = received as Command;
            if (playCmd.name !== 'play') continue;

            const row = Number(playCmd.params[1]);
            const col = Number(playCmd.params[2]);

            if (isNaN(row) || isNaN(col) || row < 0 || row > 2 || col < 0 || col > 2) continue;
            if (isCellOccupied(this, row, col)) continue;

            const state = this.latestContext<TicTacToeState>('tic-tac-toe')!;
            if (state.value.winner) continue;

            placePiece(this, row, col, state.value.moveCount);
            state.value.moveCount++;

            const winner = checkWinner(this);
            if (winner) return { winner };

            if (state.value.moveCount >= 9) return { winner: 'draw' as const };
        }
    });
}

export function registerTicTacToeRules(game: GameContextInstance) {
    game.registerRule('start', createSetupRule());
    game.registerRule('turn', createTurnRule());
}

export function startTicTacToe(game: GameContextInstance) {
    game.dispatchCommand('start');
}