<!--
// 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.
-->
<import src="sky-element.sky" />
<import src="sky-scrollable.sky" />

<sky-element>
<template>
  <style>
    #mask {
      background-color: black;
      will-change: opacity;
      position: absolute;
      top: 0;
      left: 0;
      bottom: 0;
      right: 0;
    }
    #content {
      background-color: white;
      will-change: transform;
      position: absolute;
      width: 256px;
      top: 0;
      left: 0;
      bottom: 0;
    }
  </style>
  <div id="mask" />
  <div id="content">
    <content/>
  </div>
</template>
<script>
import "animation/controller.dart";
import "animation/curves.dart";
import "animation/timer.dart";
import "dart:math" as math;
import "dart:sky";

const double _kWidth = 256.0;
const double _kMinFlingVelocity = 0.4;
const double _kMinAnimationDurationMS = 246.0;
const double _kMaxAnimationDurationMS = 600.0;
const Cubic _kAnimationCurve = easeOut;

@Tagname('sky-drawer')
class SkyDrawer extends SkyElement implements AnimationDelegate {
  Element _mask;
  Element _content;
  double _position = 0.0;
  AnimationController _animation;

  SkyDrawer() {
    _animation = new AnimationController(this);

    addEventListener('pointerdown', _handlePointerDown);
    addEventListener('pointermove', _handlePointerMove);
    addEventListener('pointerup', _handlePointerUp);
    addEventListener('pointercancel', _handlePointerCancel);
  }

  void shadowRootReady() {
    _mask = shadowRoot.getElementById('mask');
    _mask.addEventListener('gesturetap', _handleMaskTap);
    _content = shadowRoot.getElementById('content');
    _content.addEventListener('gestureflingstart', _handleFlingStart);
    position = -_kWidth;
  }

  void toggle() {
    if (isMostlyClosed)
      open();
    else
      close();
  }

  void open() {
    _animateToPosition(0.0);
  }

  void close() {
    _animateToPosition(-_kWidth);
  }

  bool get isClosed => _position <= -_kWidth;
  bool get isMostlyClosed => _position <= -_kWidth / 2;
  double get position => _position;

  set position(double value) {
    double newPosition = math.min(0.0, math.max(value, -_kWidth));
    _position = newPosition;
    _content.style['transform'] = 'translateX(${newPosition}px)';
    _mask.style['opacity'] = '${(newPosition / _kWidth + 1) * 0.25}';
    style['display'] = isClosed ? 'none' : '';
  }

  void _settle() {
    if (isMostlyClosed)
      close();
    else
      open();
  }

  void _animateToPosition(double targetPosition) {
    double currentPosition = _position;
    double distance = (targetPosition - currentPosition).abs();
    double duration = _kMaxAnimationDurationMS * distance / _kWidth;
    _animation.start(
      begin: currentPosition,
      end: targetPosition,
      duration: math.max(_kMinAnimationDurationMS, duration),
      curve: _kAnimationCurve);
  }

  void updateAnimation(double p) {
    position = p;
  }

  void _handleMaskTap(_) {
    close();
  }

  void _handlePointerDown(_) {
    _animation.stop();
  }

  void _handlePointerMove(PointerEvent event) {
    position += event.dx;
  }

  void _handlePointerUp(_) {
    if (!_animation.isAnimating)
      _settle();
  }

  void _handlePointerCancel(_) {
    if (!_animation.isAnimating)
      _settle();
  }

  void _handleFlingStart(event) {
    double direction = event.velocityX.sign();
    double velocityX = event.velocityX.abs() / 1000;
    if (velocityX < _kMinFlingVelocity)
      return;
    double targetPosition = direction < 0.0 ? -kWidth : 0.0;
    double currentPosition = _position;
    double distance = (targetPosition - currentPosition).abs();
    double duration = distance / velocityX;
    _animation.start(
      begin: currentPosition,
      end: targetPosition,
      duration: duration,
      curve: linear);
  }
}

_init(script) => register(script, SkyDrawer);
</script>
</sky-element>