.content{
 width: 640px;
 height: 640px;
 margin: 50px auto;
 position: relative;
}
.btn{
 width: 100%;
 height: 100%;
 position: absolute;
 left: 0;
 top: 0;
 background-color: rgba(0,0,0,0);
 z-index: 1;
}
.btn button{
 background: none;
 border:none;
 background-size: 100% 100%;
 cursor: pointer;
 outline: none;
 position: absolute;
 left: 50%;
 top: 50%;
}
.startBtn button{
 width: 200px;
 height: 150px;
 background-image: url('../images/btn1.gif');
 margin-left: -100px;
 margin-top: -75px;
}
.pauseBtn{
 display: none;
}
.pauseBtn button{
 width: 70px;
 height: 70px;
 background-image: url('../images/btn4.png');
 margin-left: -35px;
 margin-top: -35px;
}
#snakeWrap{
 position: relative;
 width: 600px;
 height: 600px;
 background: #FCE4EC;
 border: 20px solid #F8BBD0;
}
.snakeHead{
 background-image: url('../images/snake.png');
 background-size: cover;
}
.snakeBody{
 background-color: #9CCC65;
 border-radius: 50%;
}
.food{
 background: url('../images/food2.png') no-repeat;
 background-size: 100% 100%;
}

var sw = 20, // 一个方块的宽度
 sh = 20, // 高度
 tr = 30, // 行数
 td = 30; // 列数

var snake = null, // 蛇的实例
 food = null, // 食物的实例
 game = null; // 游戏实例

// 方块构造函数
function Square(x,y,classname) {
 this.x = x*sw;
 this.y = y*sh;
 this.class = classname;

 this.viewContent = document.createElement('div');
 this.viewContent.className = this.class;
 this.parent = document.getElementById('snakeWrap');

}

Square.prototype.create = function(){ // 创建方块dom
 this.viewContent.style.position='absolute';
 this.viewContent.style.width = sw+'px';
 this.viewContent.style.height = sh + 'px';
 this.viewContent.style.left = this.x +'px';
 this.viewContent.style.top = this.y + 'px';

 this.parent.appendChild(this.viewContent)

}

Square.prototype.remove = function() {
 this.parent.removeChild(this.viewContent);
}

// 蛇
function Snake () {
 this.head = null; //蛇头
 this.tail = null; // 蛇尾
 this.pos = []; // 存储蛇身上的每一个方块的位置
 this.directionNum = { // 存储蛇走的方向，用一个对象来表示
 left:{
 x:-1,
 y:0,
 rotate:180 // 蛇头旋转角度
 },
 right:{
 x:1,
 y:0,
 rotate:0
 },
 up:{
 x:0,
 y:-1,
 rotate:-90
 },
 down:{
 x:0,
 y:1,
 rotate:90
 }
 }
}

Snake.prototype.init = function() {
 // 创建蛇头
 var snakeHead = new Square(2,0,'snakeHead');
 snakeHead.create();
 this.head = snakeHead; // 存储蛇头信息
 this.pos.push([2,0]) // 存储蛇头位置
 // 创建蛇身体
 var snakeBody1 = new Square(1,0,'snakeBody');
 snakeBody1.create();
 this.pos.push([1,0]) // 存储蛇身1位置

 var snakeBody2 = new Square(0,0,'snakeBody');
 snakeBody2.create();
 this.tail = snakeBody2; // 存储蛇尾信息
 this.pos.push([0,0]) // 存储蛇身1位置

 // 形成链表关系
 snakeHead.last = null;
 snakeHead.next = snakeBody1;
 
 snakeBody1.last = snakeHead;
 snakeBody1.next = snakeBody2;

 snakeBody2.last = snakeBody1;
 snakeBody2.next = null;

 // 给蛇添加一个属性，用来表示蛇走的方向
 this.direction = this.directionNum.right; // 默认往右走

}

// 获取蛇头的下一个位置对应的元素，要根据元素做不同的事情
Snake.prototype.getNextPos = function() {
 var nextPos = [
 this.head.x/sw+this.direction.x,
 this.head.y/sh+this.direction.y
 ]
 // 下个点是自己，游戏结束
 var selfCollied = false; //是否撞到了自己
 this.pos.forEach(function(value) {
 if(value[0]==nextPos[0] && value[1]==nextPos[1]){
 selfCollied = true;
 }
 });
 if(selfCollied){
 console.log('撞到了自己');

 this.strategies.die.call(this);
 return;
 }
 // 下个点是围墙，游戏结束
 if(nextPos[0]<0 || nextPos[1]<0 || nextPos[0]>td-1 || nextPos[1]>tr-1){
 console.log('撞到了墙');

 this.strategies.die.call(this);
 return;
 }

 // 下个点是食物，吃
 if(food && food.pos[0]==nextPos[0] && food.pos[1]==nextPos[1]){
 // 如果这个条件成立说明现在蛇头要走的下一个点是食物的那个点；
 console.log('吃到食物了');
 this.strategies.eat.call(this);
 return;
 }


 // 下个点什么都不是，走
 this.strategies.move.call(this);
 
};

// 处理碰撞后要做的事
Snake.prototype.strategies = {
 move:function(format) { // 该参数用于决定是否删除蛇尾
 // 创建新身体，在旧蛇头的位置
 var newBody = new Square(this.head.x/sw,this.head.y/sh,'snakeBody');
 // 更新链表的关系
 newBody.next = this.head.next;
 newBody.next.last = newBody;
 newBody.last = null;

 this.head.remove(); // 把旧蛇头从原来的位置删除
 newBody.create();

 // 创建蛇头:蛇头下一个点
 var newHead = new Square(this.head.x/sw+this.direction.x,this.head.y/sh+this.direction.y,'snakeHead');
 
 // 更新链表的关系
 newHead.next = newBody;
 newHead.last = null;
 newBody.last = newHead;

 newHead.viewContent.style.transform = 'rotate('+this.direction.rotate+'deg)';
 
 newHead.create();

 // 更新蛇身上每一个方块的坐标
 this.pos.splice(0,0,[this.head.x/sw+this.direction.x,this.head.y/sh+this.direction.y]);
 this.head = newHead; //更新this.head
 
 if(!format){ // false: 需要删除（处理吃之外的操作）
 this.tail.remove();
 this.tail = this.tail.last;
 this.pos.pop();

 }
 


 },
 eat:function(){
 this.strategies.move.call(this,true);
 createFood();
 game.score++;
 },
 die:function(){
 game.over();
 }
}

snake = new Snake();
// snake.init();

// 创建食物
function createFood(){
 // 食物的随机坐标
 var x = null;
 var y = null;
 var include = true; // 循环跳出的条件,true表示食物坐标在蛇身上，false:表示不在
 while(include){
 x = Math.round(Math.random()*(td-1));
 y = Math.round(Math.random()*(tr-1));

 snake.pos.forEach(function(value){
 if(x!=value[0] && y!=value[1]){
 // 坐标不在蛇身上
 include = false;
 }
 })
 // 生成食物
 food = new Square(x,y,'food');
 food.pos = [x,y]; // 存储食物的坐标，用于跟蛇头下一个走的点作对比

 var foodDom = document.querySelector('.food');
 if(foodDom){
 foodDom.style.left = x*sw +'px';
 foodDom.style.top = y*sh +'px';
 }else{
 food.create();
 }
 
 }

}


// 创建游戏逻辑
function Game(){
 this.timer = null;
 this.score = 0;

}
Game.prototype.init = function(){
 snake.init();
 createFood();

 document.onkeydown = function(ev) {
 // 用户按下左键， 蛇不能是正在往右走的
 if(ev.which == 37 && snake.direction != snake.directionNum.right){
 snake.direction = snake.directionNum.left;
 }else if(ev.which == 38 && snake.direction != snake.directionNum.down){
 snake.direction = snake.directionNum.up;
 }else if(ev.which == 39 && snake.direction != snake.directionNum.left){
 snake.direction = snake.directionNum.right;
 }else if(ev.which == 40 && snake.direction != snake.directionNum.up){
 snake.direction = snake.directionNum.down;
 }
 }

 this.start();

}

Game.prototype.start = function(){
 // 开始游戏
 this.timer = setInterval(function(){
 snake.getNextPos();
 
 },200);
}
Game.prototype.pause = function() {
 clearInterval(this.timer);
}
Game.prototype.over = function() {
 clearInterval(this.timer);
 alert('你的得分为：'+ this.score);

 // 游戏回到最初始的状态
 var snakeWrap = document.getElementById('snakeWrap');
 snakeWrap.innerHTML = '';
 snake = new Snake();
 game = new Game();

 var startBtnWrap = document.querySelector('.startBtn');
 startBtnWrap.style.display = 'block';
}


// 开启游戏
game = new Game();

var startBtn = document.querySelector('.startBtn button');
startBtn.onclick = function(){
 startBtn.parentNode.style.display = 'none';
 game.init();
}

// 暂停游戏
var snakeWrap = document.getElementById('snakeWrap');
var pauseBtn = document.querySelector('.pauseBtn button');
snakeWrap.onclick = function() {
 game.pause();
 pauseBtn.parentNode.style.display='block';
}
pauseBtn.onclick = function() {
 game.start();
 pauseBtn.parentNode.style.display='none';
}