class SnakeGame {
    constructor(canvasId, scoreId) {
        this.canvas = document.getElementById(canvasId);
        this.ctx = this.canvas.getContext('2d');
        this.scoreElement = document.getElementById(scoreId);
        
        this.gridSize = 20;
        this.tileCount = this.canvas.width / this.gridSize;
        
        this.reset();
        
        window.addEventListener('keydown', this.handleKeyDown.bind(this));
    }

    reset() {
        this.snake = [
            { x: 10, y: 10 },
            { x: 10, y: 11 },
            { x: 10, y: 12 }
        ];
        this.food = this.getRandomFood();
        this.dx = 0;
        this.dy = -1;
        this.score = 0;
        this.updateScore();
        this.gameOver = false;
    }

    getRandomFood() {
        let newFood;
        while (true) {
            newFood = {
                x: Math.floor(Math.random() * this.tileCount),
                y: Math.floor(Math.random() * this.tileCount)
            };
            // 确保食物不生成在蛇身上
            let collision = this.snake.some(segment => segment.x === newFood.x && segment.y === newFood.y);
            if (!collision) break;
        }
        return newFood;
    }

    handleKeyDown(e) {
        switch (e.key) {
            case 'ArrowUp':
                if (this.dy === 0) { this.dx = 0; this.dy = -1; }
                break;
            case 'ArrowDown':
                if (this.dy === 0) { this.dx = 0; this.dy = 1; }
                break;
            case 'ArrowLeft':
                if (this.dx === 0) { this.dx = -1; this.dy = 0; }
                break;
            case 'ArrowRight':
                if (this.dx === 0) { this.dx = 1; this.dy = 0; }
                break;
        }
    }

    update() {
        if (this.gameOver) return;

        const head = { x: this.snake[0].x + this.dx, y: this.snake[0].y + this.dy };

        // 碰撞墙壁检测
        if (head.x < 0 || head.x >= this.tileCount || head.y < 0 || head.y >= this.tileCount) {
            this.endGame();
            return;
        }

        // 碰撞自身检测
        if (this.snake.some(segment => segment.x === head.x && segment.y === head.y)) {
            this.endGame();
            return;
        }

        this.snake.unshift(head);

        // 进食检测
        if (head.x === this.food.x && head.y === this.food.y) {
            this.score += 10;
            this.updateScore();
            this.food = this.getRandomFood();
        } else {
            this.snake.pop();
        }
    }

    draw() {
        // 清屏
        this.ctx.fillStyle = '#1a1a1a';
        this.ctx.fillRect(0, 0, this.canvas.width, this.canvas.height);

        // 画网格背景 (可选)
        this.ctx.strokeStyle = 'rgba(255, 255, 255, 0.03)';
        this.ctx.lineWidth = 1;
        for (let i = 0; i <= this.tileCount; i++) {
            this.ctx.beginPath();
            this.ctx.moveTo(i * this.gridSize, 0);
            this.ctx.lineTo(i * this.gridSize, this.canvas.height);
            this.ctx.stroke();
            this.ctx.beginPath();
            this.ctx.moveTo(0, i * this.gridSize);
            this.ctx.lineTo(this.canvas.width, i * this.gridSize);
            this.ctx.stroke();
        }

        // 画食物
        const foodX = this.food.x * this.gridSize + this.gridSize / 2;
        const foodY = this.food.y * this.gridSize + this.gridSize / 2;
        const foodRadius = this.gridSize / 2 - 2;

        const gradient = this.ctx.createRadialGradient(foodX, foodY, 2, foodX, foodY, foodRadius);
        gradient.addColorStop(0, '#ff7675');
        gradient.addColorStop(1, '#d63031');
        
        this.ctx.fillStyle = gradient;
        this.ctx.shadowBlur = 15;
        this.ctx.shadowColor = '#d63031';
        this.ctx.beginPath();
        this.ctx.arc(foodX, foodY, foodRadius, 0, Math.PI * 2);
        this.ctx.fill();
        this.ctx.shadowBlur = 0;

        // 画蛇
        this.snake.forEach((segment, index) => {
            const isHead = index === 0;
            const x = segment.x * this.gridSize;
            const y = segment.y * this.gridSize;
            const size = this.gridSize - 2;
            const radius = isHead ? 8 : 4;

            this.ctx.fillStyle = isHead ? '#55efc4' : '#00b894';
            
            // 蛇头阴影
            if (isHead) {
                this.ctx.shadowBlur = 10;
                this.ctx.shadowColor = '#55efc4';
            }

            this.ctx.beginPath();
            this.ctx.roundRect(x + 1, y + 1, size, size, radius);
            this.ctx.fill();
            this.ctx.shadowBlur = 0;

            // 眼睛
            if (isHead) {
                this.ctx.fillStyle = '#2d3436';
                const eyeSize = 3;
                const offset = 5;
                
                // 根据方向画眼睛
                if (this.dy === -1) { // Up
                    this.ctx.fillRect(x + offset, y + offset, eyeSize, eyeSize);
                    this.ctx.fillRect(x + size - offset - eyeSize, y + offset, eyeSize, eyeSize);
                } else if (this.dy === 1) { // Down
                    this.ctx.fillRect(x + offset, y + size - offset - eyeSize, eyeSize, eyeSize);
                    this.ctx.fillRect(x + size - offset - eyeSize, y + size - offset - eyeSize, eyeSize, eyeSize);
                } else if (this.dx === -1) { // Left
                    this.ctx.fillRect(x + offset, y + offset, eyeSize, eyeSize);
                    this.ctx.fillRect(x + offset, y + size - offset - eyeSize, eyeSize, eyeSize);
                } else { // Right
                    this.ctx.fillRect(x + size - offset - eyeSize, y + offset, eyeSize, eyeSize);
                    this.ctx.fillRect(x + size - offset - eyeSize, y + size - offset - eyeSize, eyeSize, eyeSize);
                }
            }
        });

        if (this.gameOver) {
            this.ctx.fillStyle = 'rgba(0, 0, 0, 0.75)';
            this.ctx.fillRect(0, 0, this.canvas.width, this.canvas.height);
            
            this.ctx.shadowBlur = 20;
            this.ctx.shadowColor = 'rgba(255, 255, 255, 0.5)';
            this.ctx.fillStyle = 'white';
            this.ctx.textAlign = 'center';
            this.ctx.font = 'bold 40px Segoe UI';
            this.ctx.fillText('GAME OVER', this.canvas.width / 2, this.canvas.height / 2);
            
            this.ctx.font = '20px Segoe UI';
            this.ctx.fillStyle = '#bdc3c7';
            this.ctx.fillText('按空格重新开始', this.canvas.width / 2, this.canvas.height / 2 + 50);
            this.ctx.shadowBlur = 0;
            this.ctx.textAlign = 'start';
        }
    }

    updateScore() {
        this.scoreElement.innerText = this.score;
    }

    endGame() {
        this.gameOver = true;
    }

    run() {
        this.update();
        this.draw();
    }
}

const game = new SnakeGame('snakeGame', 'score');
setInterval(() => game.run(), 100);

window.addEventListener('keydown', (e) => {
    if (e.code === 'Space' && game.gameOver) {
        game.reset();
    }
});