script.js

const canvas = document.getElementById('gameCanvas');
const ctx = canvas.getContext('2d');
canvas.width = 400;
canvas.height = 400;

const box = 20;
let snake = [];
snake[0] = { x: 9 * box, y: 10 * box };

let food = {
    x: Math.floor(Math.random() * 19 + 1) * box,
    y: Math.floor(Math.random() * 19 + 1) * box
};

let score = 0;
let d;
let speed = 150; // Độ trễ của game - giảm số này để rắn di chuyển nhanh hơn

document.addEventListener("keydown", direction);

function direction(event) {
    if (event.keyCode === 37 && d !== "RIGHT") {
        d = "LEFT";
    } else if (event.keyCode === 38 && d !== "DOWN") {
        d = "UP";
    } else if (event.keyCode === 39 && d !== "LEFT") {
        d = "RIGHT";
    } else if (event.keyCode === 40 && d !== "UP") {
        d = "DOWN";
    }
}

function collision(newHead, snake) {
    for (let i = 0; i < snake.length; i++) {
        if (newHead.x === snake[i].x && newHead.y === snake[i].y) {
            return true;
        }
    }
    return false;
}

function draw() {
    ctx.clearRect(0, 0, canvas.width, canvas.height);

    for (let i = 0; i < snake.length; i++) {
        ctx.fillStyle = (i === 0) ? "#4CAF50" : "#c8e6c9";
        ctx.fillRect(snake[i].x, snake[i].y, box, box);

        ctx.strokeStyle = "#388e3c";
        ctx.strokeRect(snake[i].x, snake[i].y, box, box);
    }

    ctx.fillStyle = "#d32f2f";
    ctx.fillRect(food.x, food.y, box, box);

    let snakeX = snake[0].x;
    let snakeY = snake[0].y;

    if (d === "LEFT") snakeX -= box;
    if (d === "UP") snakeY -= box;
    if (d === "RIGHT") snakeX += box;
    if (d === "DOWN") snakeY += box;

    if (snakeX === food.x && snakeY === food.y) {
        score++;
        food = {
            x: Math.floor(Math.random() * 19 + 1) * box,
            y: Math.floor(Math.random() * 19 + 1) * box
        };
    } else {
        snake.pop();
    }

    let newHead = { x: snakeX, y: snakeY };

    if (snakeX < 0 || snakeY < 0 || snakeX >= canvas.width || snakeY >= canvas.height || collision(newHead, snake)) {
        clearInterval(game);
        alert("Game Over");
    }

    snake.unshift(newHead);

    document.getElementById('score').innerHTML = "Score: " + score;
}

function startGame() {
    d = undefined;
    snake = [{ x: 9 * box, y: 10 * box }];
    score = 0;
    food = {
        x: Math.floor(Math.random() * 19 + 1) * box,
        y: Math.floor(Math.random() * 19 + 1) * box
    };
    game = setInterval(draw, speed); // Đặt tốc độ rắn theo biến "speed"
}