<template>
  <view class="page-body">
    <canvas id="canvas" class="canvas"></canvas>
  </view>
</template>

<script setup>
  class Ball {
    private width : number
    private height : number
    public x : number
    public y : number
    public vx : number
    public vy : number
    public radius : number = 5

    constructor(w : number, h : number, x : number, y : number, vx : number, vy : number) {
      this.width = w
      this.height = h
      this.x = x
      this.y = y
      this.vx = vx
      this.vy = vy
    }

    move() {
      this.x += this.vx
      this.y += this.vy

      // 边框反弹
      if (this.x < this.radius) {
        this.vx = Math.abs(this.vx)
        return
      }
      if (this.x > this.width - this.radius) {
        this.vx = -Math.abs(this.vx)
      }
      if (this.y < this.radius) {
        this.vy = Math.abs(this.vy)
        return
      }
      if (this.y > this.width - this.radius) {
        this.vy = -Math.abs(this.vy)
      }
    }
  }

  class BallAnimation {
    private ctx : CanvasRenderingContext2D
    private ballList : Array<Ball> = []
    private speed = 3
    private layer = 3
    private ballInlayer = 20
    private interval : number = 0
    private runningFlag : boolean = false

    // #ifdef WEB
    private _bindAnimate: Function = null
    // #endif

    constructor(ctx : CanvasRenderingContext2D) {
      this.ctx = ctx
      this.initBall()
      this.ctx.fillStyle = '#007AFF'
      // #ifdef WEB
      this._bindAnimate = this.animate.bind(this)
      // #endif
    }

    private getDistance(x : number, y : number) : number {
      return Math.pow((Math.pow(x, 2) + Math.pow(y, 2)), 0.5)
    }

    private initBall() {
      const canvasWidth = this.ctx.canvas.offsetWidth;
      const canvasHeight = this.ctx.canvas.offsetHeight;
      for (let i = 0; i < this.layer; i++) {
        let radius = this.getDistance(canvasWidth / 2, canvasHeight / 2) / this.layer * i
        for (let j = 0; j < this.ballInlayer; j++) {
          let deg = j * 2 * Math.PI / this.ballInlayer,
            sin = Math.sin(deg),
            cos = Math.cos(deg),
            x = radius * cos + canvasWidth / 2,
            y = radius * sin + canvasHeight / 2,
            vx = this.speed * cos,
            vy = this.speed * sin
          this.ballList.push(new Ball(canvasWidth, canvasHeight, x, y, vx, vy))
        }
      }
    }

    public animate() {
      this.ctx.clearRect(0, 0, this.ctx.canvas.offsetWidth, this.ctx.canvas.offsetHeight)
      this.ballList.forEach((item) => {
        item.move()
        this.ctx.beginPath()
        this.ctx.arc(item.x, item.y, item.radius, 0, 2 * Math.PI)
        // this.ctx.ellipse(item.x, item.y, item.radius, item.radius, 0, 0, Math.PI * 2)
        this.ctx.fill()
      })
      // #ifdef APP
      this.ctx.draw()
      // #endif

      // #ifdef WEB
      if (!this.runningFlag) {
        return
      }
      requestAnimationFrame(this._bindAnimate)
      // #endif
    }

    start() {
      // #ifdef WEB
      cancelAnimationFrame(this._bindAnimate)
      this.runningFlag = true
      this.animate()
      // #endif

      // #ifdef APP
      //Todo.. requestAnimationFrame
      clearInterval(this.interval)
      this.interval = setInterval(() => {
        this.animate()
      }, 17)
      // #endif
    }

    stop() {
      // #ifdef WEB
      this.runningFlag = false
      cancelAnimationFrame(this._bindAnimate)
      // #endif

      // #ifdef APP
      //Todo.. requestAnimationFrame
      clearInterval(this.interval)
      // #endif
    }
  }

  let animation : BallAnimation | null = null
  onReady(() => {
    let canvas = uni.getElementById("canvas") as UniCanvasElement
    let canvasContext = canvas.getContext("2d");
    if (canvasContext != null) {
      const dpr = uni.getSystemInfoSync().pixelRatio
      canvas.width = canvas.offsetWidth * dpr
      canvas.height = canvas.offsetHeight * dpr
      canvasContext.scale(dpr, dpr)

      animation = new BallAnimation(canvasContext)
      animation?.start()
    } else {
      console.log("canvas.getContext error!!")
    }
  })

  onUnload(() => {
    animation?.stop()
    animation = null
  })

  onPageShow(() => {
    animation?.start()
  })

  onPageHide(() => {
    animation?.stop()
  })
</script>

<style>
  .page-body-wrapper {
    text-align: center;
  }

  .canvas {
    width: 300px;
    height: 300px;
    margin: auto;
    background-color: #fff;
  }
</style>