script.js

const canvas = document.getElementById("gameCanvas");
const ctx = canvas.getContext("2d");
const scoreEl = document.getElementById("score");
const messageEl = document.getElementById("message");
const restartBtn = document.getElementById("restartBtn");
const wrapAroundCheckbox = document.getElementById("wrapAroundCheckbox"); // 新增：穿墙复选框

const gridSize = 20;
const tileCount = canvas.width / gridSize;
const gameSpeedMs = 120;

let snake;
let direction;
let queuedDirection;
let inputQueue; // 新增：输入队列，用于缓存按键指令
let food;
let score;
let isGameOver;
let isGameStarted; // 新增：游戏是否已开始
let isPaused; // 新增：游戏是否暂停
let gameLoopId;

function randomTile() {
 return Math.floor(Math.random() * tileCount);
}

function spawnFood() {
 let nextFood = { x: randomTile(), y: randomTile() };
 while (snake.some((part) => part.x === nextFood.x && part.y === nextFood.y)) {
 nextFood = { x: randomTile(), y: randomTile() };
 }
 food = nextFood;
}

function resetGame() {
 snake = [
 { x: 10, y: 10 },
 { x: 9, y: 10 },
 { x: 8, y: 10 },
 ];
 direction = { x: 1, y: 0 };
 queuedDirection = { x: 1, y: 0 };
 inputQueue = []; // 初始化输入队列
 score = 0;
 isGameOver = false;
 isGameStarted = false; // 重置后不自动开始
 isPaused = false; // 重置暂停状态
 scoreEl.textContent = "0";
 messageEl.textContent = "按Enter开始游戏"; // 显示开始提示
 spawnFood();

 if (gameLoopId) {
 clearInterval(gameLoopId);
 }
 draw(); // 只绘制初始画面，不启动游戏循环
}

function startGame() {
 if (isGameStarted || isGameOver) return;
 
 isGameStarted = true;
 isPaused = false;
 messageEl.textContent = ""; // 清除提示
 
 if (gameLoopId) {
 clearInterval(gameLoopId);
 }
 gameLoopId = setInterval(update, gameSpeedMs);
}

function togglePause() {
 if (!isGameStarted || isGameOver) return;
 
 isPaused = !isPaused;
 
 if (isPaused) {
 clearInterval(gameLoopId);
 messageEl.textContent = "已暂停 - 按P继续";
 } else {
 messageEl.textContent = "";
 gameLoopId = setInterval(update, gameSpeedMs);
 }
}

function setDirection(nextX, nextY) {
 if (isGameOver || !isGameStarted) return;

 // Prevent turning directly into your own body.
 if (direction.x === -nextX && direction.y === -nextY) {
 return;
 }

 // 将方向加入输入队列，而不是直接设置
 const lastQueued = inputQueue.length > 0 
 ? inputQueue[inputQueue.length - 1] 
 : queuedDirection;
 
 // 防止在同一帧内连续转向自身
 if (lastQueued.x === -nextX && lastQueued.y === -nextY) {
 return;
 }

 inputQueue.push({ x: nextX, y: nextY });
}

function update() {
 if (isGameOver || !isGameStarted) return;

 // 从输入队列中取出下一个方向（如果有的话）
 if (inputQueue.length > 0) {
 queuedDirection = inputQueue.shift();
 }
 
 direction = queuedDirection;
 let newHead = {
 x: snake[0].x + direction.x,
 y: snake[0].y + direction.y,
 };

 // 处理穿墙逻辑
 const wrapAround = wrapAroundCheckbox.checked;
 if (wrapAround) {
 // 穿墙模式：从一边出去，从另一边进来
 if (newHead.x < 0) newHead.x = tileCount - 1;
 if (newHead.x >= tileCount) newHead.x = 0;
 if (newHead.y < 0) newHead.y = tileCount - 1;
 if (newHead.y >= tileCount) newHead.y = 0;
 }

 const hitWall = !wrapAround && (
 newHead.x < 0 ||
 newHead.x >= tileCount ||
 newHead.y < 0 ||
 newHead.y >= tileCount
 );
 const hitSelf = snake.some((part) => part.x === newHead.x && part.y === newHead.y);

 if (hitWall || hitSelf) {
 isGameOver = true;
 isGameStarted = false;
 clearInterval(gameLoopId);
 messageEl.textContent = "游戏结束 - 按Enter或Restart以重新开始";
 draw();
 return;
 }

 snake.unshift(newHead);

 if (newHead.x === food.x && newHead.y === food.y) {
 score += 1;
 scoreEl.textContent = String(score);
 spawnFood();
 } else {
 snake.pop();
 }

 draw();
}

function draw() {
 ctx.fillStyle = "#0b1220";
 ctx.fillRect(0, 0, canvas.width, canvas.height);

 ctx.fillStyle = "#ef4444";
 ctx.fillRect(food.x * gridSize, food.y * gridSize, gridSize, gridSize);

 snake.forEach((part, index) => {
 ctx.fillStyle = index === 0 ? "#22c55e" : "#4ade80";
 ctx.fillRect(part.x * gridSize, part.y * gridSize, gridSize, gridSize);
 });

 // Draw light grid lines for easier visual tracking.
 ctx.strokeStyle = "rgba(255,255,255,0.06)";
 for (let i = 0; i <= tileCount; i += 1) {
 ctx.beginPath();
 ctx.moveTo(i * gridSize, 0);
 ctx.lineTo(i * gridSize, canvas.height);
 ctx.stroke();
 ctx.beginPath();
 ctx.moveTo(0, i * gridSize);
 ctx.lineTo(canvas.width, i * gridSize);
 ctx.stroke();
 }
}

window.addEventListener("keydown", (event) => {
 const key = event.key.toLowerCase();

 // 处理Enter键开始游戏
 if (key === "enter") {
 if (!isGameStarted && !isGameOver) {
 startGame();
 } else if (isGameOver) {
 resetGame();
 setTimeout(() => startGame(), 100); // 短暂延迟后开始
 }
 return;
 }

 // 处理P键暂停/继续
 if (key === "p") {
 togglePause();
 return;
 }

 // 方向键处理（暂停时不允许移动）
 if (key === "arrowup" || key === "w") setDirection(0, -1);
 if (key === "arrowdown" || key === "s") setDirection(0, 1);
 if (key === "arrowleft" || key === "a") setDirection(-1, 0);
 if (key === "arrowright" || key === "d") setDirection(1, 0);
});

restartBtn.addEventListener("click", () => {
 resetGame();
});

resetGame();