text: define([
          '../Core/Credit',
          '../Core/defaultValue',
          '../Core/defined',
          '../Core/defineProperties',
          '../Core/DeveloperError',
          '../Core/MapboxApi',
          '../Core/Resource',
          './UrlTemplateImageryProvider'
      ], function(
          Credit,
          defaultValue,
          defined,
          defineProperties,
          DeveloperError,
          MapboxApi,
          Resource,
          UrlTemplateImageryProvider) {
      'use strict';
  
      var trailingSlashRegex = /\/$/;
      var defaultCredit = new Credit('&copy; <a href="https://www.mapbox.com/about/maps/">Mapbox</a> &copy; <a href="http://www.openstreetmap.org/copyright">OpenStreetMap</a> <strong><a href="https://www.mapbox.com/map-feedback/">Improve this map</a></strong>');
  
      /**
       * Provides tiled imagery hosted by Mapbox.
       *
       * @alias MapboxImageryProvider
       * @constructor
       *
       * @param {Object} [options] Object with the following properties:
       * @param {String} [options.url='https://api.mapbox.com/v4/'] The Mapbox server url.
       * @param {String} options.mapId The Mapbox Map ID.
       * @param {String} [options.accessToken] The public access token for the imagery.
       * @param {String} [options.format='png'] The format of the image request.
       * @param {Ellipsoid} [options.ellipsoid] The ellipsoid.  If not specified, the WGS84 ellipsoid is used.
       * @param {Number} [options.minimumLevel=0] The minimum level-of-detail supported by the imagery provider.  Take care when specifying
       *                 this that the number of tiles at the minimum level is small, such as four or less.  A larger number is likely
       *                 to result in rendering problems.
       * @param {Number} [options.maximumLevel] The maximum level-of-detail supported by the imagery provider, or undefined if there is no limit.
       * @param {Rectangle} [options.rectangle=Rectangle.MAX_VALUE] The rectangle, in radians, covered by the image.
       * @param {Credit|String} [options.credit] A credit for the data source, which is displayed on the canvas.
       *
       *
       * @example
       * // Mapbox tile provider
       * var mapbox = new Cesium.MapboxImageryProvider({
       *     mapId: 'mapbox.streets',
       *     accessToken: 'thisIsMyAccessToken'
       * });
       *
       * @see {@link https://www.mapbox.com/developers/api/maps/#tiles}
       * @see {@link https://www.mapbox.com/developers/api/#access-tokens}
       */
      function MapboxImageryProvider(options) {
          options = defaultValue(options, defaultValue.EMPTY_OBJECT);
          var mapId = options.mapId;
          //>>includeStart('debug', pragmas.debug);
          if (!defined(mapId)) {
              throw new DeveloperError('options.mapId is required.');
          }
          //>>includeEnd('debug');
  
          var url = options.url;
          if (!defined(url)) {
              url = 'https://{s}.tiles.mapbox.com/v4/';
          }
          this._url = url;
  
          var resource = Resource.createIfNeeded(url);
  
          var accessToken = MapboxApi.getAccessToken(options.accessToken);
          this._mapId = mapId;
          this._accessToken = accessToken;
  
          this._accessTokenErrorCredit = Credit.clone(MapboxApi.getErrorCredit(options.accessToken));
          var format = defaultValue(options.format, 'png');
          if (!/\./.test(format)) {
              format = '.' + format;
          }
          this._format = format;
  
          var templateUrl = resource.getUrlComponent();
          if (!trailingSlashRegex.test(templateUrl)) {
              templateUrl += '/';
          }
          templateUrl += mapId + '/{z}/{x}/{y}' + this._format;
          resource.url = templateUrl;
  
          resource.setQueryParameters({
              access_token: accessToken
          });
  
          var credit;
          if (defined(options.credit)) {
              credit = options.credit;
              if (typeof credit === 'string') {
                  credit = new Credit(credit);
              }
          } else {
              credit = defaultCredit;
          }
  
          this._resource = resource;
          this._imageryProvider = new UrlTemplateImageryProvider({
              url: resource,
              credit: credit,
              ellipsoid: options.ellipsoid,
              minimumLevel: options.minimumLevel,
              maximumLevel: options.maximumLevel,
              rectangle: options.rectangle
          });
      }
  
      defineProperties(MapboxImageryProvider.prototype, {
          /**
           * Gets the URL of the Mapbox server.
           * @memberof MapboxImageryProvider.prototype
           * @type {String}
           * @readonly
           */
          url : {
              get : function() {
                  return this._url;
              }
          },
  
          /**
           * Gets a value indicating whether or not the provider is ready for use.
           * @memberof MapboxImageryProvider.prototype
           * @type {Boolean}
           * @readonly
           */
          ready : {
              get : function() {
                  return this._imageryProvider.ready;
              }
          },
  
          /**
           * Gets a promise that resolves to true when the provider is ready for use.
           * @memberof MapboxImageryProvider.prototype
           * @type {Promise.<Boolean>}
           * @readonly
           */
          readyPromise : {
              get : function() {
                  return this._imageryProvider.readyPromise;
              }
          },
  
          /**
           * Gets the rectangle, in radians, of the imagery provided by the instance.  This function should
           * not be called before {@link MapboxImageryProvider#ready} returns true.
           * @memberof MapboxImageryProvider.prototype
           * @type {Rectangle}
           * @readonly
           */
          rectangle: {
              get : function() {
                  return this._imageryProvider.rectangle;
              }
          },
  
          /**
           * Gets the width of each tile, in pixels.  This function should
           * not be called before {@link MapboxImageryProvider#ready} returns true.
           * @memberof MapboxImageryProvider.prototype
           * @type {Number}
           * @readonly
           */
          tileWidth : {
              get : function() {
                  return this._imageryProvider.tileWidth;
              }
          },
  
          /**
           * Gets the height of each tile, in pixels.  This function should
           * not be called before {@link MapboxImageryProvider#ready} returns true.
           * @memberof MapboxImageryProvider.prototype
           * @type {Number}
           * @readonly
           */
          tileHeight : {
              get : function() {
                  return this._imageryProvider.tileHeight;
              }
          },
  
          /**
           * Gets the maximum level-of-detail that can be requested.  This function should
           * not be called before {@link MapboxImageryProvider#ready} returns true.
           * @memberof MapboxImageryProvider.prototype
           * @type {Number}
           * @readonly
           */
          maximumLevel : {
              get : function() {
                  return this._imageryProvider.maximumLevel;
              }
          },
  
          /**
           * Gets the minimum level-of-detail that can be requested.  This function should
           * not be called before {@link MapboxImageryProvider#ready} returns true. Generally,
           * a minimum level should only be used when the rectangle of the imagery is small
           * enough that the number of tiles at the minimum level is small.  An imagery
           * provider with more than a few tiles at the minimum level will lead to
           * rendering problems.
           * @memberof MapboxImageryProvider.prototype
           * @type {Number}
           * @readonly
           */
          minimumLevel : {
              get : function() {
                  return this._imageryProvider.minimumLevel;
              }
          },
  
          /**
           * Gets the tiling scheme used by the provider.  This function should
           * not be called before {@link MapboxImageryProvider#ready} returns true.
           * @memberof MapboxImageryProvider.prototype
           * @type {TilingScheme}
           * @readonly
           */
          tilingScheme : {
              get : function() {
                  return this._imageryProvider.tilingScheme;
              }
          },
  
          /**
           * Gets the tile discard policy.  If not undefined, the discard policy is responsible
           * for filtering out "missing" tiles via its shouldDiscardImage function.  If this function
           * returns undefined, no tiles are filtered.  This function should
           * not be called before {@link MapboxImageryProvider#ready} returns true.
           * @memberof MapboxImageryProvider.prototype
           * @type {TileDiscardPolicy}
           * @readonly
           */
          tileDiscardPolicy : {
              get : function() {
                  return this._imageryProvider.tileDiscardPolicy;
              }
          },
  
          /**
           * Gets an event that is raised when the imagery provider encounters an asynchronous error..  By subscribing
           * to the event, you will be notified of the error and can potentially recover from it.  Event listeners
           * are passed an instance of {@link TileProviderError}.
           * @memberof MapboxImageryProvider.prototype
           * @type {Event}
           * @readonly
           */
          errorEvent : {
              get : function() {
                  return this._imageryProvider.errorEvent;
              }
          },
  
          /**
           * Gets the credit to display when this imagery provider is active.  Typically this is used to credit
           * the source of the imagery. This function should
           * not be called before {@link MapboxImageryProvider#ready} returns true.
           * @memberof MapboxImageryProvider.prototype
           * @type {Credit}
           * @readonly
           */
          credit : {
              get : function() {
                  return this._imageryProvider.credit;
              }
          },
  
          /**
           * Gets the proxy used by this provider.
           * @memberof MapboxImageryProvider.prototype
           * @type {Proxy}
           * @readonly
           */
          proxy : {
              get : function() {
                  return this._imageryProvider.proxy;
              }
          },
  
          /**
           * Gets a value indicating whether or not the images provided by this imagery provider
           * include an alpha channel.  If this property is false, an alpha channel, if present, will
           * be ignored.  If this property is true, any images without an alpha channel will be treated
           * as if their alpha is 1.0 everywhere.  When this property is false, memory usage
           * and texture upload time are reduced.
           * @memberof MapboxImageryProvider.prototype
           * @type {Boolean}
           * @readonly
           */
          hasAlphaChannel : {
              get : function() {
                  return this._imageryProvider.hasAlphaChannel;
              }
          }
      });
  
      /**
       * Gets the credits to be displayed when a given tile is displayed.
       *
       * @param {Number} x The tile X coordinate.
       * @param {Number} y The tile Y coordinate.
       * @param {Number} level The tile level;
       * @returns {Credit[]} The credits to be displayed when the tile is displayed.
       *
       * @exception {DeveloperError} <code>getTileCredits</code> must not be called before the imagery provider is ready.
       */
      MapboxImageryProvider.prototype.getTileCredits = function(x, y, level) {
          if (defined(this._accessTokenErrorCredit)) {
              return [this._accessTokenErrorCredit];
          }
      };
  
      /**
       * Requests the image for a given tile.  This function should
       * not be called before {@link MapboxImageryProvider#ready} returns true.
       *
       * @param {Number} x The tile X coordinate.
       * @param {Number} y The tile Y coordinate.
       * @param {Number} level The tile level.
       * @param {Request} [request] The request object. Intended for internal use only.
       * @returns {Promise.<Image|Canvas>|undefined} A promise for the image that will resolve when the image is available, or
       *          undefined if there are too many active requests to the server, and the request
       *          should be retried later.  The resolved image may be either an
       *          Image or a Canvas DOM object.
       *
       * @exception {DeveloperError} <code>requestImage</code> must not be called before the imagery provider is ready.
       */
      MapboxImageryProvider.prototype.requestImage = function(x, y, level, request) {
          return this._imageryProvider.requestImage(x, y, level, request);
      };
  
      /**
       * Asynchronously determines what features, if any, are located at a given longitude and latitude within
       * a tile.  This function should not be called before {@link MapboxImageryProvider#ready} returns true.
       * This function is optional, so it may not exist on all ImageryProviders.
       *
       *
       * @param {Number} x The tile X coordinate.
       * @param {Number} y The tile Y coordinate.
       * @param {Number} level The tile level.
       * @param {Number} longitude The longitude at which to pick features.
       * @param {Number} latitude  The latitude at which to pick features.
       * @return {Promise.<ImageryLayerFeatureInfo[]>|undefined} A promise for the picked features that will resolve when the asynchronous
       *                   picking completes.  The resolved value is an array of {@link ImageryLayerFeatureInfo}
       *                   instances.  The array may be empty if no features are found at the given location.
       *                   It may also be undefined if picking is not supported.
       *
       * @exception {DeveloperError} <code>pickFeatures</code> must not be called before the imagery provider is ready.
       */
      MapboxImageryProvider.prototype.pickFeatures = function(x, y, level, longitude, latitude) {
          return this._imageryProvider.pickFeatures(x, y, level, longitude, latitude);
      };
  
      // Exposed for tests
      MapboxImageryProvider._defaultCredit = defaultCredit;
  
      return MapboxImageryProvider;
  });
  