<!--
// Copyright 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
-->
<script>
module.exports = class AnimationTimer {
  constructor(delegate) {
    this.delegate_ = delegate;
    this.startTime_ = 0;
    this.duration_ = 0;
    this.animationId_ = 0;
    Object.preventExtensions(this);
  }

  start(duration) {
    if (this.animationId_)
      this.stop();
    this.duration_ = duration;
    this.scheduleTick_();
  }

  stop() {
    cancelAnimationFrame(this.animationId_);
    this.startTime_ = 0;
    this.duration_ = 0;
    this.animationId_ = 0;
  }

  scheduleTick_() {
    if (this.animationId_)
      throw new Error("Tick already scheduled.");
    this.animationId_ = requestAnimationFrame(this.tick_.bind(this));
  }

  tick_(timeStamp) {
    this.animationId_ = 0;
    if (!this.startTime_)
      this.startTime_ = timeStamp;
    var elapsedTime = timeStamp - this.startTime_;
    var t = Math.max(0, Math.min(1, elapsedTime / this.duration_));
    if (t < 1)
      this.scheduleTick_();
    else
      this.stop();
    this.delegate_.updateAnimation(t);
  }
};
</script>