const stars = (function(){
  var canvas = document.createElement("canvas"), ctx = canvas.getContext('2d')
  var s = Math.sin, c = Math.cos
  document.addEventListener("DOMContentLoaded", function(){
    document.body.appendChild(canvas)
    canvas.classList.add('stars')
    canvas.style.width="100%"
    canvas.style.height="100%"
    canvas.style.position="fixed"
    canvas.style.top="0px"
    canvas.style.left="0px"
    canvas.style.zIndex=-1
    document.body.addEventListener("resize", build)
    // document.body.parentNode.style.backgroundColor="black"
    ctx.strokeStyle="white"
    build()
  })
  function ri(n){ return Math.random() * n }
  function rr(a,b){ return (b-a) * Math.random() + a }
  function build(){
    var w = canvas.width = window.innerWidth * window.devicePixelRatio
    var h = canvas.height = window.innerHeight * window.devicePixelRatio
    ctx.clearRect(0,0,w,h)
    var n = Math.sqrt(w*h)|0
    while (n--) {
      var x = ri(w)
      var y = ri(h)
    	var r0 = rr(0, 1)
    	var r1 = rr(0, 1)
    	var r2 = rr(0, 1)
    	var t0 = ri(2*Math.PI)
    	var t1 = ri(2*Math.PI)
    	var t2 = ri(2*Math.PI)
      var x0 = x+c(t0)*r0
      var y0 = y+s(t0)*r0
      var x1 = x+c(t1)*r1
      var y1 = y+s(t1)*r1
      var x2 = x+c(t2)*r2
      var y2 = y+s(t2)*r2
    	ctx.beginPath()
    	ctx.moveTo(x,y)
    	ctx.bezierCurveTo(x0,y0,x1,y1,x2,y2)
    	var color = rr(0, 255)|0
      ctx.strokeStyle="rgb("+color+","+color+","+color+")"
    	ctx.stroke()
    }
  }
  let rebuilding = false
  function rebuild(){
    if (rebuilding) return
    rebuilding = true
    canvas.classList.add('fade')
    document.body.classList.add('fade')
    setTimeout(() => {
      // destroy()
      build()
      canvas.classList.remove('fade')
      document.body.classList.remove('fade')
      rebuilding = false
    }, 500)
  }
  return { rebuild: rebuild }
})()