/*

File: transitions.js

Abstract: JavaScript file for the Transitions class, which is used to

  manage and run basic inter-image transitions.

Version: 1.1

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*/

const cDefaultDuration = 1000;

// This Transition class manages a transition between one asset and the next.

// It's not directly related to a CSS Transition (though it may use one).

function Transition(type, transitionContainer, duration)

{

  this.init(type, transitionContainer, duration);

};

Transition.prototype.init = function(type, transitionContainer, duration)

{

  this.transitionType = type;

  this.transitionContainer = transitionContainer;

  // Store the duration, as milliseconds.

  this.duration = (typeof duration == "undefined") ? cDefaultDuration : duration;

}

// Start doing work to make the transition happen (e.g. load the image)

Transition.prototype.initiateTransition = function(oldContents, newContent, slowMode)

{

  this.transitionContainer.addClassName(this.transitionType);

  this.slowMode = slowMode;

  if (this.slowMode)

    this.transitionContainer.addClassName("slowmode");

  this.oldContents = oldContents;

  this.contents = newContent;

}

Transition.prototype.initiateElementTransition = function(element, slowMode)

{

  this.transitionContainer.addClassName(this.transitionType);

  this.slowMode = slowMode;

  if (this.slowMode)

    this.transitionContainer.addClassName("slowmode");

  this.contents = element;

  var _self = this;

  setTimeout(function() {

    _self.startTransition();

  }, 0);

}

// This tells us that the image or video have loaded, and we're ready to run the transition.

Transition.prototype.contentsReady = function()

{

  var videos = this.contents.querySelectorAll('video');

  if (videos.length)

    videos[0].play();

  this.startTransition();

}

Transition.prototype.startTransition = function()

{

  this.isPlaying = true;

  // Set up the CSS classnames to describe the initial state.

  this.transitionContainer.addClassName('initial');

  this.newContents = this.prepareIncomingContents(this.contents);

  this.newContents.addClassName('incoming');

  this.transitionContainer.appendChild(this.newContents);

  var outgoingContents = this.prepareOutgoingContents(this.oldContents);

  if (outgoingContents != this.oldContents)

    this.transitionContainer.replaceChild(outgoingContents, this.oldContents);

  outgoingContents.addClassName('outgoing');

  var _self = this;

  // This short timer gives the browser chance to render the initial style, and

  // therefore to subsequently show the CSS transition.

  window.setTimeout(function() {

    _self.transitionContainer.addClassName('final');

    var duration = _self.duration;

    if (_self.slowMode)

      duration *= 5;

    // We have effects that use both CSS transitions and keyframe animations. To avoid

    // having to register listeners for both, we'll just use a JS timer to know when

    // the effect is complete.

    window.setTimeout(function() {

      _self.transitionDone();

    }, duration);

  }, 100);

}

Transition.prototype.prepareIncomingContents = function(incomingContents)

{

  // For subclassers to override.

  return incomingContents;

}

Transition.prototype.prepareOutgoingContents = function(outgoingContents)

{

  // For subclassers to override.

  return outgoingContents;

}

// Called when the transition is done.

Transition.prototype.transitionDone = function()

{

  this.isPlaying = false;

  var oldContents = this.transitionContainer.firstChild;

  this.transitionContainer.removeChild(oldContents);

  this.newContents.removeClassName('incoming');

  this.transitionContainer.removeClassName('final');

  this.transitionContainer.removeClassName(this.transitionType);

  if (this.slowMode)

    this.transitionContainer.removeClassName("slowmode");

}

Transition.prototype.playing = function()

{

  return this.isPlaying;

}