const canvas = document.getElementById('gameCanvas');
const ctx = canvas.getContext('2d');

// 游戏窗口尺寸
const window_x = canvas.width;
const window_y = canvas.height;

// 定义颜色
const black = '#000000';
const white = '#FFFFFF';
const blue = '#0000FF';

// 球的属性
let ballRadius = 10;
let ballX = window_x / 2;
let ballY = window_y / 2;
let ballSpeedX = Math.random() > 0.5 ? 4 : -4;  // 随机方向
let ballSpeedY = Math.random() > 0.5 ? 4 : -4;

// 控制板的属性
let paddleWidth = 100;
let paddleHeight = 10;
let paddleX = (window_x - paddleWidth) / 2;
const paddleY = window_y - 30;
const paddleSpeed = 10;
let rightPressed = false;
let leftPressed = false;

// 分数
let score = 0;

// 游戏状态
let isPaused = false;

// 键盘控制
document.addEventListener('keydown', keyDownHandler);
document.addEventListener('keyup', keyUpHandler);

function keyDownHandler(e) {
    if (e.key === 'Right' || e.key === 'ArrowRight') {
        rightPressed = true;
    } else if (e.key === 'Left' || e.key === 'ArrowLeft') {
        leftPressed = true;
    } else if (e.key === 'p' || e.key === 'P') {
        isPaused = !isPaused; // 切换暂停状态
        if (!isPaused) {
            updateGame(); // 恢复游戏
        }
    }
}

function keyUpHandler(e) {
    if (e.key === 'Right' || e.key === 'ArrowRight') {
        rightPressed = false;
    } else if (e.key === 'Left' || e.key === 'ArrowLeft') {
        leftPressed = false;
    }
}

// 更新分数显示
function drawScore() {
    document.getElementById('score').textContent = `Score: ${score}`;
}

// 绘制球
function drawBall() {
    ctx.beginPath();
    ctx.arc(ballX, ballY, ballRadius, 0, Math.PI * 2);
    ctx.fillStyle = white;
    ctx.fill();
    ctx.closePath();
}

// 绘制控制板
function drawPaddle() {
    ctx.beginPath();
    ctx.rect(paddleX, paddleY, paddleWidth, paddleHeight);
    ctx.fillStyle = blue;
    ctx.fill();
    ctx.closePath();
}

// 更新游戏逻辑
function updateGame() {
    if (isPaused) return; // 如果游戏暂停，则不更新

    // 清空画布
    ctx.clearRect(0, 0, window_x, window_y);

    // 画球和控制板
    drawBall();
    drawPaddle();
    drawScore();

    // 碰撞检测：球碰到左右边界
    if (ballX + ballSpeedX > window_x - ballRadius || ballX + ballSpeedX < ballRadius) {
        ballSpeedX = -ballSpeedX;
    }
    
    // 碰撞检测：球碰到上边界
    if (ballY + ballSpeedY < ballRadius) {
        ballSpeedY = -ballSpeedY;
    }
    
    // 碰撞检测：球碰到控制板
    if (ballY + ballSpeedY > paddleY - ballRadius &&
        ballX > paddleX && ballX < paddleX + paddleWidth) {
        ballSpeedY = -ballSpeedY;
        score++; // 每次接住球得分
    }
    
    // 游戏结束：球触碰到下边界
    if (ballY + ballSpeedY > window_y) {
        alert('Game Over! Your Score: ' + score);
        resetGame(); // 重置游戏
        
    }

    // 更新球的位置
    ballX += ballSpeedX;
    ballY += ballSpeedY;

    // 控制板移动
    if (rightPressed && paddleX < window_x - paddleWidth) {
        paddleX += paddleSpeed;
    } else if (leftPressed && paddleX > 0) {
        paddleX -= paddleSpeed;
    }

    // 重新绘制
    requestAnimationFrame(updateGame);
}

// 重置游戏
function resetGame() {
    ballX = window_x / 2;
    ballY = window_y / 2;
    ballSpeedX = Math.random() > 0.5 ? 4 : -4;
    ballSpeedY = Math.random() > 0.5 ? 4 : -4;
    score = 0;
    drawScore();
}

// 启动游戏
updateGame();