retro-arcade-games / chess.js
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// Chess Game for Retro Arcade - with AI Opponent
class ChessGame {
constructor(canvas, ctx) {
this.canvas = canvas;
this.ctx = ctx;
this.boardSize = Math.min(canvas.width, canvas.height) - 40;
this.squareSize = this.boardSize / 8;
this.board = this.initializeBoard();
this.selectedPiece = null;
this.currentPlayer = 'white';
this.gameOver = false;
this.moveHistory = [];
this.aiPlayer = 'black';
this.aiThinking = false;
this.validMoves = [];
}
initializeBoard() {
const board = [];
for (let row = 0; row < 8; row++) {
board[row] = [];
for (let col = 0; col < 8; col++) {
board[row][col] = this.getInitialPiece(row, col);
}
}
return board;
}
getInitialPiece(row, col) {
if (row === 1) return { type: 'pawn', color: 'black' };
if (row === 6) return { type: 'pawn', color: 'white' };
if (row === 0 || row === 7) {
const color = row === 0 ? 'black' : 'white';
const pieces = ['rook', 'knight', 'bishop', 'queen', 'king', 'bishop', 'knight', 'rook'];
return { type: pieces[col], color: color };
}
return null;
}
draw() {
this.ctx.fillStyle = '#8B4513';
this.ctx.fillRect(0, 0, this.canvas.width, this.canvas.height);
// Draw board
for (let row = 0; row < 8; row++) {
for (let col = 0; col < 8; col++) {
const x = col * this.squareSize + 20;
const y = row * this.squareSize + 20;
// Square color
this.ctx.fillStyle = (row + col) % 2 === 0 ? '#D2B48C' : '#8B4513';
this.ctx.fillRect(x, y, this.squareSize, this.squareSize);
// Highlight valid moves
if (this.validMoves.some(m => m.row === row && m.col === col)) {
this.ctx.fillStyle = 'rgba(0, 255, 0, 0.3)';
this.ctx.fillRect(x, y, this.squareSize, this.squareSize);
}
// Highlight selected piece
if (this.selectedPiece && this.selectedPiece.row === row && this.selectedPiece.col === col) {
this.ctx.strokeStyle = '#FFD700';
this.ctx.lineWidth = 3;
this.ctx.strokeRect(x, y, this.squareSize, this.squareSize);
}
// Draw piece
const piece = this.board[row][col];
if (piece) {
this.drawPiece(piece, x, y);
}
}
}
// Draw game info
this.ctx.fillStyle = '#FFF';
this.ctx.font = '16px Arial';
this.ctx.textAlign = 'left';
let statusText = `Current: ${this.currentPlayer}`;
if (this.aiThinking) statusText += ' (AI thinking...)';
this.ctx.fillText(statusText, 20, this.canvas.height - 10);
if (this.gameOver) {
this.ctx.fillStyle = 'rgba(0,0,0,0.7)';
this.ctx.fillRect(0, 0, this.canvas.width, this.canvas.height);
this.ctx.fillStyle = '#FFD700';
this.ctx.font = '30px Arial';
this.ctx.textAlign = 'center';
const winner = this.currentPlayer === 'white' ? 'Black' : 'White';
this.ctx.fillText(`${winner} Wins!`, this.canvas.width/2, this.canvas.height/2 - 20);
this.ctx.font = '16px Arial';
this.ctx.fillText('Click Restart to play again', this.canvas.width/2, this.canvas.height/2 + 20);
}
}
drawPiece(piece, x, y) {
this.ctx.font = `${this.squareSize * 0.7}px Arial`;
this.ctx.textAlign = 'center';
this.ctx.textBaseline = 'middle';
const pieces = {
'king': '♔', 'queen': '♕', 'rook': '♖',
'bishop': '♗', 'knight': '♘', 'pawn': '♙'
};
this.ctx.fillStyle = piece.color === 'white' ? '#FFF' : '#000';
this.ctx.fillText(
pieces[piece.type],
x + this.squareSize/2,
y + this.squareSize/2
);
}
handleClick(x, y) {
if (this.gameOver || this.aiThinking || this.currentPlayer === this.aiPlayer) return;
const col = Math.floor((x - 20) / this.squareSize);
const row = Math.floor((y - 20) / this.squareSize);
if (col < 0 || col > 7 || row < 0 || row > 7) return;
const piece = this.board[row][col];
if (this.selectedPiece) {
// Try to move
if (this.isValidMove(this.selectedPiece, row, col)) {
this.movePiece(this.selectedPiece, row, col);
this.selectedPiece = null;
this.validMoves = [];
this.currentPlayer = this.aiPlayer;
this.draw();
// Trigger AI after a short delay
setTimeout(() => this.makeAIMove(), 300);
} else {
this.selectedPiece = null;
this.validMoves = [];
}
} else if (piece && piece.color === this.currentPlayer) {
this.selectedPiece = { row, col, piece };
this.validMoves = this.getValidMovesForPiece(row, col);
}
}
getValidMovesForPiece(row, col) {
const moves = [];
const piece = this.board[row][col];
if (!piece) return moves;
for (let r = 0; r < 8; r++) {
for (let c = 0; c < 8; c++) {
if (this.isValidMove({row, col, piece}, r, c)) {
moves.push({row: r, col: c});
}
}
}
return moves;
}
isValidMove(from, toRow, toCol) {
const piece = from.piece;
const rowDiff = Math.abs(toRow - from.row);
const colDiff = Math.abs(toCol - from.col);
if (toRow < 0 || toRow > 7 || toCol < 0 || toCol > 7) return false;
if (from.row === toRow && from.col === toCol) return false;
const targetPiece = this.board[toRow][toCol];
if (targetPiece && targetPiece.color === piece.color) return false;
// Check path for sliding pieces
if (['rook', 'bishop', 'queen'].includes(piece.type)) {
if (!this.isPathClear(from.row, from.col, toRow, toCol)) return false;
}
switch(piece.type) {
case 'pawn':
const direction = piece.color === 'white' ? -1 : 1;
if (colDiff === 0 && !targetPiece) {
if (toRow === from.row + direction) return true;
if ((from.row === 6 || from.row === 1) && toRow === from.row + 2 * direction) {
return this.isPathClear(from.row, from.col, toRow, toCol);
}
}
if (colDiff === 1 && toRow === from.row + direction && targetPiece) return true;
return false;
case 'rook':
return (rowDiff === 0 || colDiff === 0);
case 'bishop':
return rowDiff === colDiff;
case 'queen':
return (rowDiff === 0 || colDiff === 0 || rowDiff === colDiff);
case 'king':
return rowDiff <= 1 && colDiff <= 1;
case 'knight':
return (rowDiff === 2 && colDiff === 1) || (rowDiff === 1 && colDiff === 2);
default:
return false;
}
}
isPathClear(fromRow, fromCol, toRow, toCol) {
const rowStep = Math.sign(toRow - fromRow);
const colStep = Math.sign(toCol - fromCol);
let r = fromRow + rowStep;
let c = fromCol + colStep;
while (r !== toRow || c !== toCol) {
if (this.board[r][c] !== null) return false;
r += rowStep;
c += colStep;
}
return true;
}
movePiece(from, toRow, toCol) {
this.board[toRow][toCol] = from.piece;
this.board[from.row][from.col] = null;
this.moveHistory.push({
from: { row: from.row, col: from.col },
to: { row: toRow, col: toCol },
piece: from.piece
});
// Check for pawn promotion
if (from.piece.type === 'pawn' && (toRow === 0 || toRow === 7)) {
this.board[toRow][toCol] = { type: 'queen', color: from.piece.color };
}
// Check for king capture (win condition)
if (this.isKingCaptured()) {
this.gameOver = true;
}
}
isKingCaptured() {
let whiteKing = false;
let blackKing = false;
for (let r = 0; r < 8; r++) {
for (let c = 0; c < 8; c++) {
const p = this.board[r][c];
if (p && p.type === 'king') {
if (p.color === 'white') whiteKing = true;
else blackKing = true;
}
}
}
return !whiteKing || !blackKing;
}
// ========== AI OPPONENT ==========
makeAIMove() {
if (this.gameOver) return;
this.aiThinking = true;
this.draw();
// Use setTimeout to allow UI update before AI calculates
setTimeout(() => {
const move = this.findBestMove(3); // Depth 3 for balance
if (move) {
this.movePiece(move.from, move.to.row, move.to.col);
this.currentPlayer = 'white';
this.aiThinking = false;
this.draw();
} else {
this.aiThinking = false;
this.draw();
}
}, 100);
}
findBestMove(depth) {
let bestMove = null;
let bestValue = -Infinity;
const moves = this.getAllPossibleMoves(this.aiPlayer);
for (const move of moves) {
// Make move
const captured = this.board[move.to.row][move.to.col];
const piece = this.board[move.from.row][move.from.col];
this.board[move.to.row][move.to.col] = piece;
this.board[move.from.row][move.from.col] = null;
// Evaluate
const value = this.minimax(depth - 1, -Infinity, Infinity, false);
// Undo move
this.board[move.from.row][move.from.col] = piece;
this.board[move.to.row][move.to.col] = captured;
if (value > bestValue) {
bestValue = value;
bestMove = move;
}
}
return bestMove;
}
minimax(depth, alpha, beta, isMaximizing) {
if (depth === 0 || this.isKingCaptured()) {
return this.evaluateBoard();
}
const player = isMaximizing ? this.aiPlayer : 'white';
const moves = this.getAllPossibleMoves(player);
if (moves.length === 0) return isMaximizing ? -1000 : 1000;
if (isMaximizing) {
let maxEval = -Infinity;
for (const move of moves) {
const captured = this.board[move.to.row][move.to.col];
const piece = this.board[move.from.row][move.from.col];
this.board[move.to.row][move.to.col] = piece;
this.board[move.from.row][move.from.col] = null;
const eval_ = this.minimax(depth - 1, alpha, beta, false);
this.board[move.from.row][move.from.col] = piece;
this.board[move.to.row][move.to.col] = captured;
maxEval = Math.max(maxEval, eval_);
alpha = Math.max(alpha, eval_);
if (beta <= alpha) break;
}
return maxEval;
} else {
let minEval = Infinity;
for (const move of moves) {
const captured = this.board[move.to.row][move.to.col];
const piece = this.board[move.from.row][move.from.col];
this.board[move.to.row][move.to.col] = piece;
this.board[move.from.row][move.from.col] = null;
const eval_ = this.minimax(depth - 1, alpha, beta, true);
this.board[move.from.row][move.from.col] = piece;
this.board[move.to.row][move.to.col] = captured;
minEval = Math.min(minEval, eval_);
beta = Math.min(beta, eval_);
if (beta <= alpha) break;
}
return minEval;
}
}
getAllPossibleMoves(color) {
const moves = [];
for (let r = 0; r < 8; r++) {
for (let c = 0; c < 8; c++) {
const piece = this.board[r][c];
if (piece && piece.color === color) {
for (let tr = 0; tr < 8; tr++) {
for (let tc = 0; tc < 8; tc++) {
if (this.isValidMove({row: r, col: c, piece}, tr, tc)) {
moves.push({
from: {row: r, col: c, piece},
to: {row: tr, col: tc}
});
}
}
}
}
}
}
return moves;
}
evaluateBoard() {
const pieceValues = {
'pawn': 100,
'knight': 320,
'bishop': 330,
'rook': 500,
'queen': 900,
'king': 20000
};
let score = 0;
for (let r = 0; r < 8; r++) {
for (let c = 0; c < 8; c++) {
const piece = this.board[r][c];
if (piece) {
const value = pieceValues[piece.type] || 0;
if (piece.color === this.aiPlayer) {
score += value;
// Bonus for advanced pawns
if (piece.type === 'pawn') {
score += (piece.color === 'black' ? r : (7 - r)) * 10;
}
} else {
score -= value;
}
}
}
}
return score;
}
}
// Export for use in main games.js
if (typeof module !== 'undefined' && module.exports) {
module.exports = ChessGame;
}