/* Copyright (c) 2012 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.
 */

/**
 * @fileoverview
 * A class that loads a WCS IQ client and constructs remoting.wcs as a
 * wrapper for it.
 */

'use strict';

/** @suppress {duplicate} */
var remoting = remoting || {};

/** @type {remoting.WcsLoader} */
remoting.wcsLoader = null;

/**
 * @constructor
 * @private
 */
remoting.WcsLoader = function() {
  /**
   * The WCS client that will be downloaded. This variable is initialized (via
   * remoting.wcsLoader) by the downloaded Javascript.
   * @type {remoting.WcsIqClient}
   */
  this.wcsIqClient = null;
};

/**
 * Load WCS if necessary, then invoke the callback with an access token.
 *
 * @param {function(string?): void} onReady The callback function, called with
 *     an OAuth2 access token when WCS has been loaded, or with null on error.
 * @return {void} Nothing.
 */
remoting.WcsLoader.load = function(onReady) {
  if (!remoting.wcsLoader) {
    remoting.wcsLoader = new remoting.WcsLoader();
  }
  /** @param {string?} token The OAuth2 access token. */
  var start = function(token) {
    if (token) {
      remoting.wcsLoader.start_(token, onReady);
    } else {
      console.error('WcsLoader: Authentication failed.');
      onReady(null);
    }
  };
  remoting.oauth2.callWithToken(start);
};

/**
 * The URL of the GTalk gadget.
 * @type {string}
 * @private
 */
remoting.WcsLoader.prototype.TALK_GADGET_URL_ =
    'https://talkgadget.google.com/talkgadget/';

/**
 * The id of the script node.
 * @type {string}
 * @private
 */
remoting.WcsLoader.prototype.SCRIPT_NODE_ID_ = 'wcs-script-node';

/**
 * The attribute name indicating that the WCS has finished loading.
 * @type {string}
 * @private
 */
remoting.WcsLoader.prototype.SCRIPT_NODE_LOADED_FLAG_ = 'wcs-script-loaded';

/**
 * Starts loading the WCS IQ client.
 *
 * When it's loaded, construct remoting.wcs as a wrapper for it.
 * When the WCS connection is ready, or on error, call |onReady|.
 *
 * @param {string} token An OAuth2 access token.
 * @param {function(string?): void} onReady The callback function, called with
 *     an OAuth2 access token when WCS has been loaded, or with null on error.
 * @return {void} Nothing.
 * @private
 */
remoting.WcsLoader.prototype.start_ = function(token, onReady) {
  var node = document.getElementById(this.SCRIPT_NODE_ID_);
  if (!node) {
    // The first time, there will be no script node, so create one.
    node = document.createElement('script');
    node.id = this.SCRIPT_NODE_ID_;
    node.src = this.TALK_GADGET_URL_ + 'iq?access_token=' + token;
    node.type = 'text/javascript';
    document.body.insertBefore(node, document.body.firstChild);
  } else if (node.hasAttribute(this.SCRIPT_NODE_LOADED_FLAG_)) {
    // Subsequently, explicitly invoke onReady if onload has already fired.
    // TODO(jamiewalch): It's possible that the WCS client has not finished
    // initializing. Add support for multiple callbacks to the remoting.Wcs
    // class to address this.
    onReady(token);
    return;
  }
  /** @type {remoting.WcsLoader} */
  var that = this;
  var onLoad = function() {
    var typedNode = /** @type {Element} */ (node);
    typedNode.setAttribute(that.SCRIPT_NODE_LOADED_FLAG_, true);
    that.constructWcs_(token, onReady);
  };
  var onError = function() {
    var typedNode = /** @type {Element} */ (node);
    typedNode.parentNode.removeChild(node);
    onReady(null);
  };
  node.addEventListener('load', onLoad, false);
  node.addEventListener('error', onError, false);
};

/**
 * Constructs the remoting.wcs object.
 *
 * @param {string} token An OAuth2 access token.
 * @param {function(string?): void} onReady The callback function, called with
 *     an OAuth2 access token when WCS has been loaded, or with null on error.
 * @return {void} Nothing.
 * @private
 */
remoting.WcsLoader.prototype.constructWcs_ = function(token, onReady) {
  remoting.wcs = new remoting.Wcs(
      remoting.wcsLoader.wcsIqClient,
      token,
      function() { onReady(token); });
};