<script>
 class Map{ //地图
  constructor(){
   this.mapEle = document.getElementById("map");
   this.w = this.mapEle.offsetWidth;
   this.h = this.mapEle.offsetHeight;
  }
 }
 class Food{ //食物
  constructor(){
   this.w = 20;
   this.h = 20;
   this.x = 0;
   this.y = 0;
   this.c = "orange";
   this.createEle();
  } 
  createEle(){
   this.foodEle = document.createElement("div");
   this.foodEle.style.cssText = `width:${this.w}px;height:${this.h}px;background:${this.c};position:absolute;left:${this.x * this.w}px;top:${this.y * this.h}px;border-radius: 40%;`;
   m.mapEle.appendChild(this.foodEle);
  }
  randomPos(){
   this.x = random(0,(m.w-this.w) / this.w);
   this.y = random(0,(m.h-this.h) / this.h);
   this.foodEle.style.left = this.x * this.w + "px";
   this.foodEle.style.top = this.y * this.h + "px";
  }
 }
 class Snake{ //身体
  constructor(){
   this.w = 20;
   this.h = 20;
   this.body = [{
     ele:null,x:4,y:3,c:randomColor()
   },{
    ele:null,x:3,y:3,c:randomColor()
   },{
    ele:null,x:2,y:3,c:randomColor()
   }];
   this.d = "right"; //设置默认行走方向
   this.createEle();
  }
  createEle(){
   for(var i=0;i<this.body.length;i++){
    if(!this.body[i].ele){
     this.body[i].ele = document.createElement("div");
     m.mapEle.appendChild(this.body[i].ele);
    }
    this.body[i].ele.style.cssText = `width:${this.w}px;height:${this.h}px;background:${this.body[i].c};position:absolute;left:${this.body[i].x * this.w}px;top:${this.body[i].y * this.h}px;color:#fff;border-radius: 40%;`;
   }
   this.body[0].ele.innerHTML = "00"
   setTimeout(()=>{this.move()},300);
  }
  move(){
   for(var i=this.body.length-1;i>0;i--){
    this.body[i].x = this.body[i-1].x;
    this.body[i].y = this.body[i-1].y;
   }
   switch(this.d){
    case "left":this.body[0].x -= 1;break;
    case "right":this.body[0].x += 1;break;
    case "top":this.body[0].y -= 1;break;
    case "bottom":this.body[0].y += 1;break;
   }
   if(this.body[0].x < 0 || this.body[0].y < 0 || this.body[0].x > ((m.w-this.w) / this.w) || this.body[0].y > ((m.h-this.h) / this.h)){
    alert("撞墙了");
    return;
   }
   if(this.body[0].x === f.x && this.body[0].y === f.y){
    this.body.push({ele:null,x:this.body[this.body.length-1].x,y:this.body[this.body.length-1].y,c:randomColor()});
    f.randomPos();
   }
   for(var i=1;i<this.body.length;i++){
    if(this.body[0].x == this.body[i].x && this.body[0].y == this.body[i].y){
     alert("撞到自己了");
     return;
    }
   }
   this.createEle();
  }
  direct(type){
   switch(type){
    case 37:
     if(this.d === "right") break;
     this.d = "left";break;
    case 38:
     if(this.d === "bottom") break;
     this.d = "top";break;
    case 39:
     if(this.d === "left") break;
     this.d = "right";break;
    case 40:
     if(this.d === "top") break;
     this.d = "bottom";break;
   }
  }
 }
 function random(a,b){
  return Math.round(Math.random()*(a-b)+b);
 }
 function randomColor(){
  return `rgb(${random(0,255)},${random(0,255)},${random(0,255)})`;
 }
 
 var m = new Map();
 
 var f = new Food();
 f.randomPos();
 
 var s = new Snake();
 document.onkeydown = function(eve){
  var e = eve || window.event;
  var code = e.keyCode || e.which;
  s.direct(code);
 }
</script>