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// Copyright 2012 The Closure Library Authors. All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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//      http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS-IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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/**
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 * @fileoverview Simple image loader, used for preloading.
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 * @author [email protected] (Nathan Naze)
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 */
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goog.provide('goog.labs.net.image');
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goog.require('goog.Promise');
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goog.require('goog.events.EventHandler');
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goog.require('goog.events.EventType');
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goog.require('goog.net.EventType');
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goog.require('goog.userAgent');
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/**
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 * Loads a single image.  Useful for preloading images.
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 *
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 * @param {string} uri URI of the image.
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 * @param {(!Image|function(): !Image)=} opt_image If present, instead of
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 *     creating a new Image instance the function will use the passed Image
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 *     instance or the result of calling the Image factory respectively. This
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 *     can be used to control exactly how Image instances are created, for
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 *     example if they should be created in a particular document element, or
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 *     have fields that will trigger CORS image fetches.
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 * @return {!goog.Promise<!Image>} A Promise that will be resolved with the
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 *     given image if the image successfully loads.
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 */
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goog.labs.net.image.load = function(uri, opt_image) {
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  return new goog.Promise(function(resolve, reject) {
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    var image;
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    if (!goog.isDef(opt_image)) {
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      image = new Image();
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    } else if (goog.isFunction(opt_image)) {
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      image = opt_image();
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    } else {
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      image = opt_image;
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    }
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    // IE's load event on images can be buggy.  For older browsers, wait for
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    // readystatechange events and check if readyState is 'complete'.
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    // See:
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    // http://msdn.microsoft.com/en-us/library/ie/ms536957(v=vs.85).aspx
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    // http://msdn.microsoft.com/en-us/library/ie/ms534359(v=vs.85).aspx
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    //
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    // Starting with IE11, start using standard 'load' events.
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    // See:
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    // http://msdn.microsoft.com/en-us/library/ie/dn467845(v=vs.85).aspx
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    var loadEvent = (goog.userAgent.IE && goog.userAgent.VERSION < 11) ?
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        goog.net.EventType.READY_STATE_CHANGE :
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        goog.events.EventType.LOAD;
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    var handler = new goog.events.EventHandler();
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    handler.listen(
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        image, [loadEvent, goog.net.EventType.ABORT, goog.net.EventType.ERROR],
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        function(e) {
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          // We only registered listeners for READY_STATE_CHANGE for IE.
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          // If readyState is now COMPLETE, the image has loaded.
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          // See related comment above.
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          if (e.type == goog.net.EventType.READY_STATE_CHANGE &&
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              image.readyState != goog.net.EventType.COMPLETE) {
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            return;
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          }
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          // At this point, we know whether the image load was successful
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          // and no longer care about image events.
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          goog.dispose(handler);
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          // Whether the image successfully loaded.
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          if (e.type == loadEvent) {
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            resolve(image);
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          } else {
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            reject(null);
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          }
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        });
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    // Initiate the image request.
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    image.src = uri;
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  });
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};
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