SGH / COMPONENTS

<!--
Copyright (c) 2014 The Polymer Project Authors. All rights reserved.
This code may only be used under the BSD style license found at https://polymer.github.io/LICENSE.txt
The complete set of authors may be found at https://polymer.github.io/AUTHORS.txt
The complete set of contributors may be found at https://polymer.github.io/CONTRIBUTORS.txt
Code distributed by Google as part of the polymer project is also
subject to an additional IP rights grant found at https://polymer.github.io/PATENTS.txt
-->

<link rel="import" href="../polymer/polymer.html">
<link rel="import" href="google-js-api.html">

<!--
Element for loading a specific client Google API with the JavaScript client library.

For loading `gapi.client` libraries

##### Example

    <google-client-loader id="shortener"
      name="urlshortener"
      version="v1"></google-client-loader>

    <script>
      var shortener = document.getElementById('shortener');
      shortener.addEventListener('google-api-load', function(event) {
        var request = shortener.api.url.get({
           shortUrl: 'http://goo.gl/fbsS'
        });
        request.execute(function(resp) {
          console.log(resp);
        });
      });
    </script>

@demo
-->
<dom-module id="google-client-loader">
  <template>
    <google-js-api on-js-api-load="_loadClient"></google-js-api>
  </template>
</dom-module>

<script>
  (function() {
    'use strict';

    // Stores whether the API client is done loading.
    var _clientLoaded = false;

    // Loaders and loading statuses for all APIs, indexed by API name.
    // This helps prevent multiple loading requests being fired at the same time
    // by multiple google-api-loader elements.
    var _statuses = {};
    var _loaders = {};

    Polymer({

      is: 'google-client-loader',

      /**
       * Fired when the requested API is loaded. Override this name
       * by setting `successEventName`.
       * @event google-api-load
       */

      /**
       * Fired if an error occurs while loading the requested API. Override this name
       * by setting `errorEventName`.
       * @event google-api-load-error
       */

      properties: {
        /**
         * Name of the API to load, e.g. 'urlshortener'.
         *
         * You can find the full list of APIs on the
         * <a href="https://developers.google.com/apis-explorer"> Google APIs
         * Explorer</a>.
         */
        name: String,

        /**
         * Version of the API to load, e.g. 'v1'.
         */
        version: String,

        /**
         * App Engine application ID for loading a Google Cloud Endpoints API.
         */
        appId: String,

        /**
         * Root URL where to load the API from, e.g. 'http://host/apis'.
         * For App Engine dev server this would be something like:
         * 'http://localhost:8080/_ah/api'.
         * Overrides 'appId' if both are specified.
         */
        apiRoot: String,

        /**
         * Name of the event fired when API library is loaded.
         */
        successEventName: {
          type: String,
          value: 'google-api-load'
        },

        /**
         * Name of the event fired when there is an error loading the library.
         */
        errorEventName: {
          type: String,
          value: 'google-api-load-error'
        }
      },

      // Used to fix events potentially being fired multiple times by
      // iron-jsonp-library.
      _waiting: false,

      /**
       * Returns the loaded API.
       * @type gapi.client
       */
      get api() {
        if (window.gapi && window.gapi.client &&
            window.gapi.client[this.name]) {
          return window.gapi.client[this.name];
        } else {
          return undefined;
        }
      },

      /**
       * Wrapper for `gapi.auth`.
       */
      get auth() {
        return gapi.auth;
      },

      _loadClient: function() {
        gapi.load('client', this._doneLoadingClient.bind(this));
      },

      _handleLoadResponse: function(response) {
        if (response && response.error) {
          _statuses[this.name] = 'error';
          this._fireError(response);
        } else {
          _statuses[this.name] = 'loaded';
          this._fireSuccess();
        }
      },

      _fireSuccess: function() {
        this.fire(this.successEventName,
            { 'name': this.name, 'version': this.version });
      },

      _fireError: function(response) {
        if (response && response.error) {
          this.fire(this.errorEventName, {
            'name': this.name,
            'version': this.version,
            'error': response.error });
        } else {
          this.fire(this.errorEventName, {
            'name': this.name,
            'version': this.version });
        }
      },

      _doneLoadingClient: function() {
        _clientLoaded = true;
        // Fix for API client load event being fired multiple times by
        // iron-jsonp-library.
        if (!this._waiting) {
          this._loadApi();
        }
      },

      _createSelfRemovingListener: function(eventName) {
        var handler = function () {
          _loaders[this.name].removeEventListener(eventName, handler);
          this._loadApi();
        }.bind(this);

        return handler;
      },

      _loadApi: function() {
        if (_clientLoaded && this.name && this.version) {
          this._waiting = false;
          // Is this API already loaded?
          if (_statuses[this.name] == 'loaded') {
            this._fireSuccess();
          // Is a different google-api-loader already loading this API?
          } else if (_statuses[this.name] == 'loading') {
            this._waiting = true;
            _loaders[this.name].addEventListener(this.successEventName,
                this._createSelfRemovingListener(this.successEventName));
            _loaders[this.name].addEventListener(this.errorEventName,
                this._createSelfRemovingListener(this.errorEventName));
          // Did we get an error when we tried to load this API before?
          } else if (_statuses[this.name] == 'error') {
            this._fireError();
          // Otherwise, looks like we're loading a new API.
          } else {
            var root;
            if (this.apiRoot) {
              root = this.apiRoot;
            } else if (this.appId) {
              root = 'https://' + this.appId + '.appspot.com/_ah/api';
            }
            _statuses[this.name] = 'loading';
            _loaders[this.name] = this;
            gapi.client.load(this.name, this.version,
                this._handleLoadResponse.bind(this), root);
          }
        }
      }
    });
  })();
</script>