var config = {
 width: 20, //一个格子的宽度
 height: 20, //一个格子的高度
 tr: 30, //行数
 td: 30 //列数
}
var snake = null, //Snake的实例
 food = null, //Food的实例
 game = null; //游戏的实例

//我们把蛇移动的整个区域设置成一个具有30列30行的网格坐标
//方块(格子)坐标位置
/**
0,0 (0,0)
20,0 (1,0)
40,0 (2,0)
*/
function Square(x, y, className) {
 this.x = x*config.width;
 this.y = y*config.height;
 this.className = className;
 this.contentDom = document.createElement('div');//该位置的方块对应的DOM元素
 this.contentDom.className = this.className;
 this.parent = document.getElementsByClassName("innerSnake")[0];

}
Square.prototype.create = function() { //创建方块并添加到页面
 this.contentDom.style.position = 'absolute';
 this.contentDom.style.width = config.width + 'px';
 this.contentDom.style.height = config.height + 'px';
 this.contentDom.style.left = this.x + 'px';
 this.contentDom.style.top = this.y + 'px';

 this.parent.appendChild(this.contentDom);
};
Square.prototype.remove = function() { //移除方块
 this.parent.removeChild(this.contentDom);
};

//蛇
function Snake() {
 this.head = null; //蛇头
 this.tail = null; //蛇尾
 this.pos = []; //二维数组，存储蛇身上每个节点（方块）
 this.directionKey = { //存储蛇走的方向
 left: { //往左走
 x: -1, //横坐标减1，一个坐标表示一个格子
 y: 0, //纵坐标不变
 rotate: 90
 },
 right: { //往右走
 x: 1,
 y: 0,
 rotate: -90
 },
 up: { //往上走
 x: 0,
 y: -1,
 rotate: 180
 },
 down: { //往下走
 x: 0,
 y: 1,
 rotate: 0 //蛇头图片方向，顺时针为正
 }
 }
}
Snake.prototype.init = function() { //初始化蛇
 //蛇头
 var snakeHead = new Square(2,0,"head");
 snakeHead.create(); //将蛇头添加到界面
 this.head = snakeHead; //存储蛇头信息
 this.pos.push([2,0]); //存储蛇头坐标

 //蛇的第1节身体
 var snakeBody1 = new Square(1,0,"body");
 snakeBody1.create(); //将蛇的第一节身体添加到界面
 this.pos.push([1,0]);

 //蛇的尾巴
 var snakeTail = new Square(0,0,"body");
 snakeTail.create(); //将蛇尾添加到界面
 this.tail = snakeTail; //存储蛇尾信息
 this.pos.push([0,0]);

 //形成链表关系
 snakeHead.prev = null; //蛇头的前面没有元素，指向null
 snakeHead.next = snakeBody1; //蛇头的后面有一节身体，其.next指针指向后面那节身体

 snakeBody1.prev = snakeHead; //蛇的第一节身体，.prev指向前面的蛇头snakeHead
 snakeBody1.next = snakeTail; //蛇的第一节身体，.next指向后面的身体，此时是蛇尾snakeTail

 snakeTail.prev = snakeBody1; //蛇尾，.prev指向前面的蛇身体snakeBody1
 snakeTail.next = null; //蛇尾后面没有元素，指向Null

 //初始蛇的走向，后面想改变蛇的走向即改变this.direction
 this.direction = this.directionKey.right; //默认向右走

};

//获取蛇头下一个位置对应的元素,根据元素做下一个动作
Snake.prototype.getNextPos = function() {
 var nextPos = [ //获取蛇头走的下一个点的坐标
  this.head.x / config.width + this.direction.x,
  this.head.y / config.height + this.direction.y
 ];

 //判断下一个点是自己or食物or围墙or无障碍"body");
 //更新链表关系
 newBody.next = this.head.next;
 newBody.next.prev = newBody;
 newBody.prev = null;

 this.head.remove(); //删除旧蛇头
 newBody.create(); //添加蛇身体,替代在旧蛇头位置

 //声明一个新蛇头(下一个走的点)
  var newHead = new Square(x, y, "head");
  //更新链表关系
  newHead.prev = null;
  newHead.next = newBody;
  newBody.prev = newHead;

  this.pos.unshift([x, y]); //更新蛇节点的坐标this.pos
  this.head = newHead; //更新this.head的信息
  
  newHead.contentDom.style.transform = `rotate(${this.direction.rotate}deg)`
  newHead.create(); //添加蛇头

  //删除蛇尾：吃食物则不删
  if(!isEat) { //没有吃食物,删除蛇尾
  this.tail.remove();
  this.tail = this.tail.prev;

  this.pos.pop(); //更新蛇节点坐标
  }
  // console.log(this.pos); //打印数组,验证
 },
 eat: function() {
 this.collide.move.call(this, true); //传参true,表示此时为吃操作
 food.remove(); //删除被吃掉的食物
 game.score ++; //记录分数
 createFood(); //此时再随机产生一个食物
 },
 end: function() {
 console.log('end');
 game.gameOver();
 }

}

snake = new Snake();

//创建食物
function createFood() {
 var x = null, y = null;
 var include = true; //表示食物的位置是否在蛇身上
 var random = function(max, min) { //产生一个随机数
 return Math.floor(Math.random()*(max - min + 1))
 };
 while(include) {
 x = random(config.tr - 1, 0);
 y = random(config.td - 1, 0);

 snake.pos.forEach(function(val) {
 if(x != val[0] && y != val[1]) {
 include = false;
 }
 });
 }

 //生成食物
 food = new Square(x, y, "food");
 food.pos = [x, y]; //记录食物坐标
 food.create();
}

//游戏逻辑
function Game() {
 this.score = 0; //分数
 this.timer = null; //计时器
}
Game.prototype.init = function() {
 snake.init();
 // snake.getNextPos(); //获取下一个点坐标
 createFood();

 document.onkeydown = function(event) {
 if(event.which == 37 && snake.direction != snake.directionKey.right) { 
  //鼠标左键,蛇不能是正在往右走
 snake.direction = snake.directionKey.left;
 } else if (event.which == 38 && snake.direction != snake.directionKey.down) { 
 //鼠标上键
 snake.direction = snake.directionKey.up;
 } else if (event.which == 39 && snake.direction != snake.directionKey.left) { 
 //鼠标右键
 snake.direction = snake.directionKey.right;
 } else if (event.which == 40 && snake.direction != snake.directionKey.up) { 
 //鼠标下键
 snake.direction = snake.directionKey.down;
 }
 }
 this.start();
};
game = new Game();
//开始游戏
Game.prototype.start = function() {
 this.timer = setInterval(function() {
 snake.getNextPos(); //获取下一个坐标点，做下一步动作
 }, 200);
};
//游戏结束
Game.prototype.gameOver = function() {
 console.log("gameOver");
 clearInterval(this.timer);
 var gameOver = document.querySelector('.gameOver');
 var gameScore = document.querySelector('.gameOver .score');
 gameOver.style.display = 'block'; //显示游戏结束界面
 gameScore.innerHTML = `${this.score}`; //将分数记入该界面
};

//开启游戏
function startGame() {
 var startBtn = document.querySelector('.btn button');
 var snakeWrap = document.querySelector('.snakeWrap');
 startBtn.onclick = function() {
 startBtn.parentNode.style.display = 'none'; //隐藏开始游戏界面
  snakeWrap.style.display = 'block'; //显示进入游戏的界面
  game.init();

 }
}
startGame();