var Ease = use('ease')
var time = use('time')

var rate = 1/240

var TweenEngine = {
  tweens: [],
  add(tween) {
    this.tweens.push(tween)
  },
  remove(tween) {
    this.tweens = this.tweens.filter(t => t != tween)
  },
  update(dt) {
    var now = time.number()
    for (var tween of this.tweens.slice()) {
      tween._update(now)
    }
    
    $_.delay(_ => TweenEngine.update(), rate)
  }
}

function Tween(obj) {
  this.obj = obj
  this.startVals = {}
  this.endVals = {}
  this.duration = 0
  this.easing = Ease.linear
  this.startTime = 0
  this.onCompleteCallback = function() {}
}

Tween.prototype.to = function(props, duration) {
  for (var key in props) {
    this.startVals[key] = this.obj[key]
    this.endVals[key] = props[key]
  }
  this.duration = duration
  this.startTime = time.number()

  TweenEngine.add(this)
  return this
}

Tween.prototype.ease = function(easingFn) {
  this.easing = easingFn
  return this
}

Tween.prototype.onComplete = function(callback) {
  this.onCompleteCallback = callback
  return this
}

Tween.prototype.onUpdate = function(cb) {
  this.onUpdateCallback = cb
  return this
}

Tween.prototype._update = function(now) {
  var elapsed = now - this.startTime
  var t = Math.min(elapsed / this.duration, 1)
  var eased = this.easing(t)

  for (var key in this.endVals) {
    var start = this.startVals[key]
    var end = this.endVals[key]
    this.obj[key] = start + (end - start) * eased
    this.onUpdateCallback?.()
  }

  if (t == 1) {
    this.onCompleteCallback()
    TweenEngine.remove(this)
  }
}

function tween(obj) {
  return new Tween(obj)
}

$_.delay(_ => TweenEngine.update(), rate)

return tween