import Uri from '../ThirdParty/Uri.js';
import when from '../ThirdParty/when.js';
import appendForwardSlash from './appendForwardSlash.js';
import Check from './Check.js';
import clone from './clone.js';
import combine from './combine.js';
import defaultValue from './defaultValue.js';
import defined from './defined.js';
import defineProperties from './defineProperties.js';
import DeveloperError from './DeveloperError.js';
import freezeObject from './freezeObject.js';
import getAbsoluteUri from './getAbsoluteUri.js';
import getBaseUri from './getBaseUri.js';
import getExtensionFromUri from './getExtensionFromUri.js';
import isBlobUri from './isBlobUri.js';
import isCrossOriginUrl from './isCrossOriginUrl.js';
import isDataUri from './isDataUri.js';
import loadAndExecuteScript from './loadAndExecuteScript.js';
import objectToQuery from './objectToQuery.js';
import queryToObject from './queryToObject.js';
import Request from './Request.js';
import RequestErrorEvent from './RequestErrorEvent.js';
import RequestScheduler from './RequestScheduler.js';
import RequestState from './RequestState.js';
import RuntimeError from './RuntimeError.js';
import TrustedServers from './TrustedServers.js';

    var xhrBlobSupported = (function() {
        try {
            var xhr = new XMLHttpRequest();
            xhr.open('GET', '#', true);
            xhr.responseType = 'blob';
            return xhr.responseType === 'blob';
        } catch (e) {
            return false;
        }
    })();

    /**
     * Parses a query string and returns the object equivalent.
     *
     * @param {Uri} uri The Uri with a query object.
     * @param {Resource} resource The Resource that will be assigned queryParameters.
     * @param {Boolean} merge If true, we'll merge with the resource's existing queryParameters. Otherwise they will be replaced.
     * @param {Boolean} preserveQueryParameters If true duplicate parameters will be concatenated into an array. If false, keys in uri will take precedence.
     *
     * @private
     */
    function parseQuery(uri, resource, merge, preserveQueryParameters) {
        var queryString = uri.query;
        if (!defined(queryString) || (queryString.length === 0)) {
            return {};
        }

        var query;
        // Special case we run into where the querystring is just a string, not key/value pairs
        if (queryString.indexOf('=') === -1) {
            var result = {};
            result[queryString] = undefined;
            query = result;
        } else {
            query = queryToObject(queryString);
        }

        if (merge) {
            resource._queryParameters = combineQueryParameters(query, resource._queryParameters, preserveQueryParameters);
        } else {
            resource._queryParameters = query;
        }
        uri.query = undefined;
    }

    /**
     * Converts a query object into a string.
     *
     * @param {Uri} uri The Uri object that will have the query object set.
     * @param {Resource} resource The resource that has queryParameters
     *
     * @private
     */
    function stringifyQuery(uri, resource) {
        var queryObject = resource._queryParameters;

        var keys = Object.keys(queryObject);

        // We have 1 key with an undefined value, so this is just a string, not key/value pairs
        if (keys.length === 1 && !defined(queryObject[keys[0]])) {
            uri.query = keys[0];
        } else {
            uri.query = objectToQuery(queryObject);
        }
    }

    /**
     * Clones a value if it is defined, otherwise returns the default value
     *
     * @param {*} [val] The value to clone.
     * @param {*} [defaultVal] The default value.
     *
     * @returns {*} A clone of val or the defaultVal.
     *
     * @private
     */
    function defaultClone(val, defaultVal) {
        if (!defined(val)) {
            return defaultVal;
        }

        return defined(val.clone) ? val.clone() : clone(val);
    }

    /**
     * Checks to make sure the Resource isn't already being requested.
     *
     * @param {Request} request The request to check.
     *
     * @private
     */
    function checkAndResetRequest(request) {
        if (request.state === RequestState.ISSUED || request.state === RequestState.ACTIVE) {
            throw new RuntimeError('The Resource is already being fetched.');
        }

        request.state = RequestState.UNISSUED;
        request.deferred = undefined;
    }

    /**
     * This combines a map of query parameters.
     *
     * @param {Object} q1 The first map of query parameters. Values in this map will take precedence if preserveQueryParameters is false.
     * @param {Object} q2 The second map of query parameters.
     * @param {Boolean} preserveQueryParameters If true duplicate parameters will be concatenated into an array. If false, keys in q1 will take precedence.
     *
     * @returns {Object} The combined map of query parameters.
     *
     * @example
     * var q1 = {
     *   a: 1,
     *   b: 2
     * };
     * var q2 = {
     *   a: 3,
     *   c: 4
     * };
     * var q3 = {
     *   b: [5, 6],
     *   d: 7
     * }
     *
     * // Returns
     * // {
     * //   a: [1, 3],
     * //   b: 2,
     * //   c: 4
     * // };
     * combineQueryParameters(q1, q2, true);
     *
     * // Returns
     * // {
     * //   a: 1,
     * //   b: 2,
     * //   c: 4
     * // };
     * combineQueryParameters(q1, q2, false);
     *
     * // Returns
     * // {
     * //   a: 1,
     * //   b: [2, 5, 6],
     * //   d: 7
     * // };
     * combineQueryParameters(q1, q3, true);
     *
     * // Returns
     * // {
     * //   a: 1,
     * //   b: 2,
     * //   d: 7
     * // };
     * combineQueryParameters(q1, q3, false);
     *
     * @private
     */
    function combineQueryParameters(q1, q2, preserveQueryParameters) {
        if (!preserveQueryParameters) {
            return combine(q1, q2);
        }

        var result = clone(q1, true);
        for (var param in q2) {
            if (q2.hasOwnProperty(param)) {
                var value = result[param];
                var q2Value = q2[param];
                if (defined(value)) {
                    if (!Array.isArray(value)) {
                        value = result[param] = [value];
                    }

                    result[param] = value.concat(q2Value);
                } else {
                    result[param] = Array.isArray(q2Value) ? q2Value.slice() : q2Value;
                }
            }
        }

        return result;
    }

    /**
     * A resource that includes the location and any other parameters we need to retrieve it or create derived resources. It also provides the ability to retry requests.
     *
     * @alias Resource
     * @constructor
     *
     * @param {String|Object} options A url or an object with the following properties
     * @param {String} options.url The url of the resource.
     * @param {Object} [options.queryParameters] An object containing query parameters that will be sent when retrieving the resource.
     * @param {Object} [options.templateValues] Key/Value pairs that are used to replace template values (eg. {x}).
     * @param {Object} [options.headers={}] Additional HTTP headers that will be sent.
     * @param {DefaultProxy} [options.proxy] A proxy to be used when loading the resource.
     * @param {Resource~RetryCallback} [options.retryCallback] The Function to call when a request for this resource fails. If it returns true, the request will be retried.
     * @param {Number} [options.retryAttempts=0] The number of times the retryCallback should be called before giving up.
     * @param {Request} [options.request] A Request object that will be used. Intended for internal use only.
     *
     * @example
     * function refreshTokenRetryCallback(resource, error) {
     *   if (error.statusCode === 403) {
     *     // 403 status code means a new token should be generated
     *     return getNewAccessToken()
     *       .then(function(token) {
     *         resource.queryParameters.access_token = token;
     *         return true;
     *       })
     *       .otherwise(function() {
     *         return false;
     *       });
     *   }
     *
     *   return false;
     * }
     *
     * var resource = new Resource({
     *    url: 'http://server.com/path/to/resource.json',
     *    proxy: new DefaultProxy('/proxy/'),
     *    headers: {
     *      'X-My-Header': 'valueOfHeader'
     *    },
     *    queryParameters: {
     *      'access_token': '123-435-456-000'
     *    },
     *    retryCallback: refreshTokenRetryCallback,
     *    retryAttempts: 1
     * });
     */
    function Resource(options) {
        options = defaultValue(options, defaultValue.EMPTY_OBJECT);
        if (typeof options === 'string') {
            options = {
                url: options
            };
        }

        //>>includeStart('debug', pragmas.debug);
        Check.typeOf.string('options.url', options.url);
        //>>includeEnd('debug');

        this._url = undefined;
        this._templateValues = defaultClone(options.templateValues, {});
        this._queryParameters = defaultClone(options.queryParameters, {});

        /**
         * Additional HTTP headers that will be sent with the request.
         *
         * @type {Object}
         */
        this.headers = defaultClone(options.headers, {});

        /**
         * A Request object that will be used. Intended for internal use only.
         *
         * @type {Request}
         */
        this.request = defaultValue(options.request, new Request());

        /**
         * A proxy to be used when loading the resource.
         *
         * @type {DefaultProxy}
         */
        this.proxy = options.proxy;

        /**
         * Function to call when a request for this resource fails. If it returns true or a Promise that resolves to true, the request will be retried.
         *
         * @type {Function}
         */
        this.retryCallback = options.retryCallback;

        /**
         * The number of times the retryCallback should be called before giving up.
         *
         * @type {Number}
         */
        this.retryAttempts = defaultValue(options.retryAttempts, 0);
        this._retryCount = 0;

        var uri = new Uri(options.url);
        parseQuery(uri, this, true, true);

        // Remove the fragment as it's not sent with a request
        uri.fragment = undefined;

        this._url = uri.toString();
    }

    /**
     * A helper function to create a resource depending on whether we have a String or a Resource
     *
     * @param {Resource|String} resource A Resource or a String to use when creating a new Resource.
     *
     * @returns {Resource} If resource is a String, a Resource constructed with the url and options. Otherwise the resource parameter is returned.
     *
     * @private
     */
    Resource.createIfNeeded = function(resource) {
        if (resource instanceof Resource) {
            // Keep existing request object. This function is used internally to duplicate a Resource, so that it can't
            //  be modified outside of a class that holds it (eg. an imagery or terrain provider). Since the Request objects
            //  are managed outside of the providers, by the tile loading code, we want to keep the request property the same so if it is changed
            //  in the underlying tiling code the requests for this resource will use it.
            return  resource.getDerivedResource({
                request: resource.request
            });
        }

        if (typeof resource !== 'string') {
            return resource;
        }

        return new Resource({
            url: resource
        });
    };

    var supportsImageBitmapOptionsPromise;
    /**
     * A helper function to check whether createImageBitmap supports passing ImageBitmapOptions.
     *
     * @returns {Promise<Boolean>} A promise that resolves to true if this browser supports creating an ImageBitmap with options.
     *
     * @private
     */
    Resource.supportsImageBitmapOptions = function() {
        // Until the HTML folks figure out what to do about this, we need to actually try loading an image to
        // know if this browser supports passing options to the createImageBitmap function.
        // https://github.com/whatwg/html/pull/4248
        if (defined(supportsImageBitmapOptionsPromise)) {
            return supportsImageBitmapOptionsPromise;
        }

        if (typeof createImageBitmap !== 'function') {
            supportsImageBitmapOptionsPromise = when.resolve(false);
            return supportsImageBitmapOptionsPromise;
        }

        var imageDataUri = 'data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVQImWP4////fwAJ+wP9CNHoHgAAAABJRU5ErkJggg==';

        supportsImageBitmapOptionsPromise = Resource.fetchBlob({
            url : imageDataUri
        })
            .then(function(blob) {
                return createImageBitmap(blob, {
                    imageOrientation: 'flipY',
                    premultiplyAlpha: 'none'
                });
            })
            .then(function(imageBitmap) {
                return true;
            })
            .otherwise(function() {
                return false;
            });

        return supportsImageBitmapOptionsPromise;
    };

    defineProperties(Resource, {
        /**
         * Returns true if blobs are supported.
         *
         * @memberof Resource
         * @type {Boolean}
         *
         * @readonly
         */
        isBlobSupported : {
            get : function() {
                return xhrBlobSupported;
            }
        }
    });

    defineProperties(Resource.prototype, {
        /**
         * Query parameters appended to the url.
         *
         * @memberof Resource.prototype
         * @type {Object}
         *
         * @readonly
         */
        queryParameters: {
            get: function() {
                return this._queryParameters;
            }
        },

        /**
         * The key/value pairs used to replace template parameters in the url.
         *
         * @memberof Resource.prototype
         * @type {Object}
         *
         * @readonly
         */
        templateValues: {
            get: function() {
                return this._templateValues;
            }
        },

        /**
         * The url to the resource with template values replaced, query string appended and encoded by proxy if one was set.
         *
         * @memberof Resource.prototype
         * @type {String}
         */
        url: {
            get: function() {
                return this.getUrlComponent(true, true);
            },
            set: function(value) {
                var uri = new Uri(value);

                parseQuery(uri, this, false);

                // Remove the fragment as it's not sent with a request
                uri.fragment = undefined;

                this._url = uri.toString();
            }
        },

        /**
         * The file extension of the resource.
         *
         * @memberof Resource.prototype
         * @type {String}
         *
         * @readonly
         */
        extension: {
            get: function() {
                return getExtensionFromUri(this._url);
            }
        },

        /**
         * True if the Resource refers to a data URI.
         *
         * @memberof Resource.prototype
         * @type {Boolean}
         */
        isDataUri: {
            get: function() {
                return isDataUri(this._url);
            }
        },

        /**
         * True if the Resource refers to a blob URI.
         *
         * @memberof Resource.prototype
         * @type {Boolean}
         */
        isBlobUri: {
            get: function() {
                return isBlobUri(this._url);
            }
        },

        /**
         * True if the Resource refers to a cross origin URL.
         *
         * @memberof Resource.prototype
         * @type {Boolean}
         */
        isCrossOriginUrl: {
            get: function() {
                return isCrossOriginUrl(this._url);
            }
        },

        /**
         * True if the Resource has request headers. This is equivalent to checking if the headers property has any keys.
         *
         * @memberof Resource.prototype
         * @type {Boolean}
         */
        hasHeaders: {
            get: function() {
                return (Object.keys(this.headers).length > 0);
            }
        }
    });

    /**
     * Returns the url, optional with the query string and processed by a proxy.
     *
     * @param {Boolean} [query=false] If true, the query string is included.
     * @param {Boolean} [proxy=false] If true, the url is processed the proxy object if defined.
     *
     * @returns {String} The url with all the requested components.
     */
    Resource.prototype.getUrlComponent = function(query, proxy) {
        if(this.isDataUri) {
            return this._url;
        }

        var uri = new Uri(this._url);

        if (query) {
            stringifyQuery(uri, this);
        }

        // objectToQuery escapes the placeholders.  Undo that.
        var url = uri.toString().replace(/%7B/g, '{').replace(/%7D/g, '}');

        var templateValues = this._templateValues;
        url = url.replace(/{(.*?)}/g, function(match, key) {
            var replacement = templateValues[key];
            if (defined(replacement)) {
                // use the replacement value from templateValues if there is one...
                return encodeURIComponent(replacement);
            }
            // otherwise leave it unchanged
            return match;
        });

        if (proxy && defined(this.proxy)) {
            url = this.proxy.getURL(url);
        }
        return url;
    };

    /**
     * Combines the specified object and the existing query parameters. This allows you to add many parameters at once,
     *  as opposed to adding them one at a time to the queryParameters property. If a value is already set, it will be replaced with the new value.
     *
     * @param {Object} params The query parameters
     * @param {Boolean} [useAsDefault=false] If true the params will be used as the default values, so they will only be set if they are undefined.
     */
    Resource.prototype.setQueryParameters = function(params, useAsDefault) {
        if (useAsDefault) {
            this._queryParameters = combineQueryParameters(this._queryParameters, params, false);
        } else {
            this._queryParameters = combineQueryParameters(params, this._queryParameters, false);
        }
    };

    /**
     * Combines the specified object and the existing query parameters. This allows you to add many parameters at once,
     *  as opposed to adding them one at a time to the queryParameters property.
     *
     * @param {Object} params The query parameters
     */
    Resource.prototype.appendQueryParameters = function(params) {
        this._queryParameters = combineQueryParameters(params, this._queryParameters, true);
    };

    /**
     * Combines the specified object and the existing template values. This allows you to add many values at once,
     *  as opposed to adding them one at a time to the templateValues property. If a value is already set, it will become an array and the new value will be appended.
     *
     * @param {Object} template The template values
     * @param {Boolean} [useAsDefault=false] If true the values will be used as the default values, so they will only be set if they are undefined.
     */
    Resource.prototype.setTemplateValues = function(template, useAsDefault) {
        if (useAsDefault) {
            this._templateValues = combine(this._templateValues, template);
        } else {
            this._templateValues = combine(template, this._templateValues);
        }
    };

    /**
     * Returns a resource relative to the current instance. All properties remain the same as the current instance unless overridden in options.
     *
     * @param {Object} options An object with the following properties
     * @param {String} [options.url]  The url that will be resolved relative to the url of the current instance.
     * @param {Object} [options.queryParameters] An object containing query parameters that will be combined with those of the current instance.
     * @param {Object} [options.templateValues] Key/Value pairs that are used to replace template values (eg. {x}). These will be combined with those of the current instance.
     * @param {Object} [options.headers={}] Additional HTTP headers that will be sent.
     * @param {DefaultProxy} [options.proxy] A proxy to be used when loading the resource.
     * @param {Resource~RetryCallback} [options.retryCallback] The function to call when loading the resource fails.
     * @param {Number} [options.retryAttempts] The number of times the retryCallback should be called before giving up.
     * @param {Request} [options.request] A Request object that will be used. Intended for internal use only.
     * @param {Boolean} [options.preserveQueryParameters=false] If true, this will keep all query parameters from the current resource and derived resource. If false, derived parameters will replace those of the current resource.
     *
     * @returns {Resource} The resource derived from the current one.
     */
    Resource.prototype.getDerivedResource = function(options) {
        var resource = this.clone();
        resource._retryCount = 0;

        if (defined(options.url)) {
            var uri = new Uri(options.url);

            var preserveQueryParameters = defaultValue(options.preserveQueryParameters, false);
            parseQuery(uri, resource, true, preserveQueryParameters);

            // Remove the fragment as it's not sent with a request
            uri.fragment = undefined;

            resource._url = uri.resolve(new Uri(getAbsoluteUri(this._url))).toString();
        }

        if (defined(options.queryParameters)) {
            resource._queryParameters = combine(options.queryParameters, resource._queryParameters);
        }
        if (defined(options.templateValues)) {
            resource._templateValues = combine(options.templateValues, resource.templateValues);
        }
        if (defined(options.headers)) {
            resource.headers = combine(options.headers, resource.headers);
        }
        if (defined(options.proxy)) {
            resource.proxy = options.proxy;
        }
        if (defined(options.request)) {
            resource.request = options.request;
        }
        if (defined(options.retryCallback)) {
            resource.retryCallback = options.retryCallback;
        }
        if (defined(options.retryAttempts)) {
            resource.retryAttempts = options.retryAttempts;
        }

        return resource;
    };

    /**
     * Called when a resource fails to load. This will call the retryCallback function if defined until retryAttempts is reached.
     *
     * @param {Error} [error] The error that was encountered.
     *
     * @returns {Promise<Boolean>} A promise to a boolean, that if true will cause the resource request to be retried.
     *
     * @private
     */
    Resource.prototype.retryOnError = function(error) {
        var retryCallback = this.retryCallback;
        if ((typeof retryCallback !== 'function') || (this._retryCount >= this.retryAttempts)) {
            return when(false);
        }

        var that = this;
        return when(retryCallback(this, error))
            .then(function(result) {
                ++that._retryCount;

                return result;
            });
    };

    /**
     * Duplicates a Resource instance.
     *
     * @param {Resource} [result] The object onto which to store the result.
     *
     * @returns {Resource} The modified result parameter or a new Resource instance if one was not provided.
     */
    Resource.prototype.clone = function(result) {
        if (!defined(result)) {
            result = new Resource({
                url : this._url
            });
        }

        result._url = this._url;
        result._queryParameters = clone(this._queryParameters);
        result._templateValues = clone(this._templateValues);
        result.headers = clone(this.headers);
        result.proxy = this.proxy;
        result.retryCallback = this.retryCallback;
        result.retryAttempts = this.retryAttempts;
        result._retryCount = 0;
        result.request = this.request.clone();

        return result;
    };

    /**
     * Returns the base path of the Resource.
     *
     * @param {Boolean} [includeQuery = false] Whether or not to include the query string and fragment form the uri
     *
     * @returns {String} The base URI of the resource
     */
    Resource.prototype.getBaseUri = function(includeQuery) {
        return getBaseUri(this.getUrlComponent(includeQuery), includeQuery);
    };

    /**
     * Appends a forward slash to the URL.
     */
    Resource.prototype.appendForwardSlash = function() {
        this._url = appendForwardSlash(this._url);
    };

    /**
     * Asynchronously loads the resource as raw binary data.  Returns a promise that will resolve to
     * an ArrayBuffer once loaded, or reject if the resource failed to load.  The data is loaded
     * using XMLHttpRequest, which means that in order to make requests to another origin,
     * the server must have Cross-Origin Resource Sharing (CORS) headers enabled.
     *
     * @returns {Promise.<ArrayBuffer>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     *
     * @example
     * // load a single URL asynchronously
     * resource.fetchArrayBuffer().then(function(arrayBuffer) {
     *     // use the data
     * }).otherwise(function(error) {
     *     // an error occurred
     * });
     *
     * @see {@link http://www.w3.org/TR/cors/|Cross-Origin Resource Sharing}
     * @see {@link http://wiki.commonjs.org/wiki/Promises/A|CommonJS Promises/A}
     */
    Resource.prototype.fetchArrayBuffer = function () {
        return this.fetch({
            responseType : 'arraybuffer'
        });
    };

    /**
     * Creates a Resource and calls fetchArrayBuffer() on it.
     *
     * @param {String|Object} options A url or an object with the following properties
     * @param {String} options.url The url of the resource.
     * @param {Object} [options.queryParameters] An object containing query parameters that will be sent when retrieving the resource.
     * @param {Object} [options.templateValues] Key/Value pairs that are used to replace template values (eg. {x}).
     * @param {Object} [options.headers={}] Additional HTTP headers that will be sent.
     * @param {DefaultProxy} [options.proxy] A proxy to be used when loading the resource.
     * @param {Resource~RetryCallback} [options.retryCallback] The Function to call when a request for this resource fails. If it returns true, the request will be retried.
     * @param {Number} [options.retryAttempts=0] The number of times the retryCallback should be called before giving up.
     * @param {Request} [options.request] A Request object that will be used. Intended for internal use only.
     * @returns {Promise.<ArrayBuffer>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     */
    Resource.fetchArrayBuffer = function (options) {
        var resource = new Resource(options);
        return resource.fetchArrayBuffer();
    };

    /**
     * Asynchronously loads the given resource as a blob.  Returns a promise that will resolve to
     * a Blob once loaded, or reject if the resource failed to load.  The data is loaded
     * using XMLHttpRequest, which means that in order to make requests to another origin,
     * the server must have Cross-Origin Resource Sharing (CORS) headers enabled.
     *
     * @returns {Promise.<Blob>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     *
     * @example
     * // load a single URL asynchronously
     * resource.fetchBlob().then(function(blob) {
     *     // use the data
     * }).otherwise(function(error) {
     *     // an error occurred
     * });
     *
     * @see {@link http://www.w3.org/TR/cors/|Cross-Origin Resource Sharing}
     * @see {@link http://wiki.commonjs.org/wiki/Promises/A|CommonJS Promises/A}
     */
    Resource.prototype.fetchBlob = function () {
        return this.fetch({
            responseType : 'blob'
        });
    };

    /**
     * Creates a Resource and calls fetchBlob() on it.
     *
     * @param {String|Object} options A url or an object with the following properties
     * @param {String} options.url The url of the resource.
     * @param {Object} [options.queryParameters] An object containing query parameters that will be sent when retrieving the resource.
     * @param {Object} [options.templateValues] Key/Value pairs that are used to replace template values (eg. {x}).
     * @param {Object} [options.headers={}] Additional HTTP headers that will be sent.
     * @param {DefaultProxy} [options.proxy] A proxy to be used when loading the resource.
     * @param {Resource~RetryCallback} [options.retryCallback] The Function to call when a request for this resource fails. If it returns true, the request will be retried.
     * @param {Number} [options.retryAttempts=0] The number of times the retryCallback should be called before giving up.
     * @param {Request} [options.request] A Request object that will be used. Intended for internal use only.
     * @returns {Promise.<Blob>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     */
    Resource.fetchBlob = function (options) {
        var resource = new Resource(options);
        return resource.fetchBlob();
    };

    /**
     * Asynchronously loads the given image resource.  Returns a promise that will resolve to
     * an {@link https://developer.mozilla.org/en-US/docs/Web/API/ImageBitmap|ImageBitmap} if <code>preferImageBitmap</code> is true and the browser supports <code>createImageBitmap</code> or otherwise an
     * {@link https://developer.mozilla.org/en-US/docs/Web/API/HTMLImageElement|Image} once loaded, or reject if the image failed to load.
     *
     * @param {Object} [options] An object with the following properties.
     * @param {Boolean} [options.preferBlob=false] If true, we will load the image via a blob.
     * @param {Boolean} [options.preferImageBitmap=false] If true, image will be decoded during fetch and an <code>ImageBitmap</code> is returned.
     * @param {Boolean} [options.flipY=false] If true, image will be vertically flipped during decode. Only applies if the browser supports <code>createImageBitmap</code>.
     * @returns {Promise.<ImageBitmap>|Promise.<Image>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     *
     *
     * @example
     * // load a single image asynchronously
     * resource.fetchImage().then(function(image) {
     *     // use the loaded image
     * }).otherwise(function(error) {
     *     // an error occurred
     * });
     *
     * // load several images in parallel
     * when.all([resource1.fetchImage(), resource2.fetchImage()]).then(function(images) {
     *     // images is an array containing all the loaded images
     * });
     *
     * @see {@link http://www.w3.org/TR/cors/|Cross-Origin Resource Sharing}
     * @see {@link http://wiki.commonjs.org/wiki/Promises/A|CommonJS Promises/A}
     */
    Resource.prototype.fetchImage = function (options) {
        options = defaultValue(options, defaultValue.EMPTY_OBJECT);
        var preferImageBitmap = defaultValue(options.preferImageBitmap, false);
        var preferBlob = defaultValue(options.preferBlob, false);
        var flipY = defaultValue(options.flipY, false);

        checkAndResetRequest(this.request);

        // We try to load the image normally if
        // 1. Blobs aren't supported
        // 2. It's a data URI
        // 3. It's a blob URI
        // 4. It doesn't have request headers and we preferBlob is false
        if (!xhrBlobSupported || this.isDataUri || this.isBlobUri || (!this.hasHeaders && !preferBlob)) {
            return fetchImage({
                resource: this,
                flipY: flipY,
                preferImageBitmap: preferImageBitmap
            });
        }

        var blobPromise = this.fetchBlob();
        if (!defined(blobPromise)) {
            return;
        }

        var supportsImageBitmap;
        var useImageBitmap;
        var generatedBlobResource;
        var generatedBlob;
        return Resource.supportsImageBitmapOptions()
            .then(function(result) {
                supportsImageBitmap = result;
                useImageBitmap = supportsImageBitmap && preferImageBitmap;
                return blobPromise;
            })
            .then(function(blob) {
                if (!defined(blob)) {
                    return;
                }
                generatedBlob = blob;
                if (useImageBitmap) {
                    return Resource.createImageBitmapFromBlob(blob, {
                        flipY: flipY,
                        premultiplyAlpha: false
                    });
                }
                var blobUrl = window.URL.createObjectURL(blob);
                generatedBlobResource = new Resource({
                    url: blobUrl
                });

                return fetchImage({
                    resource: generatedBlobResource,
                    flipY: flipY,
                    preferImageBitmap: false
                });
            })
            .then(function(image) {
                if (!defined(image)) {
                    return;
                }

                // The blob object may be needed for use by a TileDiscardPolicy,
                // so attach it to the image.
                image.blob = generatedBlob;

                if (useImageBitmap) {
                    return image;
                }

                window.URL.revokeObjectURL(generatedBlobResource.url);
                return image;
            })
            .otherwise(function(error) {
                if (defined(generatedBlobResource)) {
                    window.URL.revokeObjectURL(generatedBlobResource.url);
                }

                // If the blob load succeeded but the image decode failed, attach the blob
                // to the error object for use by a TileDiscardPolicy.
                // In particular, BingMapsImageryProvider uses this to detect the
                // zero-length response that is returned when a tile is not available.
                error.blob = generatedBlob;

                return when.reject(error);
            });
    };

    /**
     * Fetches an image and returns a promise to it.
     *
     * @param {Object} [options] An object with the following properties.
     * @param {Resource} [options.resource] Resource object that points to an image to fetch.
     * @param {Boolean} [options.preferImageBitmap] If true, image will be decoded during fetch and an <code>ImageBitmap</code> is returned.
     * @param {Boolean} [options.flipY] If true, image will be vertically flipped during decode. Only applies if the browser supports <code>createImageBitmap</code>.
     *
     * @private
     */
    function fetchImage(options) {
        var resource = options.resource;
        var flipY = options.flipY;
        var preferImageBitmap = options.preferImageBitmap;

        var request = resource.request;
        request.url = resource.url;
        request.requestFunction = function() {
            var url = resource.url;
            var crossOrigin = false;

            // data URIs can't have crossorigin set.
            if (!resource.isDataUri && !resource.isBlobUri) {
                crossOrigin = resource.isCrossOriginUrl;
            }

            var deferred = when.defer();
            Resource._Implementations.createImage(url, crossOrigin, deferred, flipY, preferImageBitmap);

            return deferred.promise;
        };

        var promise = RequestScheduler.request(request);
        if (!defined(promise)) {
            return;
        }

        return promise
            .otherwise(function(e) {
                // Don't retry cancelled or otherwise aborted requests
                if (request.state !== RequestState.FAILED) {
                    return when.reject(e);
                }

                return resource.retryOnError(e)
                    .then(function(retry) {
                        if (retry) {
                            // Reset request so it can try again
                            request.state = RequestState.UNISSUED;
                            request.deferred = undefined;

                            return fetchImage({
                                resource: resource,
                                flipY: flipY,
                                preferImageBitmap: preferImageBitmap
                            });
                        }

                        return when.reject(e);
                    });
            });
    }

    /**
     * Creates a Resource and calls fetchImage() on it.
     *
     * @param {String|Object} options A url or an object with the following properties
     * @param {String} options.url The url of the resource.
     * @param {Object} [options.queryParameters] An object containing query parameters that will be sent when retrieving the resource.
     * @param {Object} [options.templateValues] Key/Value pairs that are used to replace template values (eg. {x}).
     * @param {Object} [options.headers={}] Additional HTTP headers that will be sent.
     * @param {DefaultProxy} [options.proxy] A proxy to be used when loading the resource.
     * @param {Boolean} [options.flipY=false] Whether to vertically flip the image during fetch and decode. Only applies when requesting an image and the browser supports <code>createImageBitmap</code>.
     * @param {Resource~RetryCallback} [options.retryCallback] The Function to call when a request for this resource fails. If it returns true, the request will be retried.
     * @param {Number} [options.retryAttempts=0] The number of times the retryCallback should be called before giving up.
     * @param {Request} [options.request] A Request object that will be used. Intended for internal use only.
     * @param {Boolean} [options.preferBlob=false]  If true, we will load the image via a blob.
     * @param {Boolean} [options.preferImageBitmap=false] If true, image will be decoded during fetch and an <code>ImageBitmap</code> is returned.
     * @returns {Promise.<ImageBitmap>|Promise.<Image>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     */
    Resource.fetchImage = function (options) {
        var resource = new Resource(options);
        return resource.fetchImage({
            flipY: options.flipY,
            preferBlob: options.preferBlob,
            preferImageBitmap: options.preferImageBitmap
        });
    };

    /**
     * Asynchronously loads the given resource as text.  Returns a promise that will resolve to
     * a String once loaded, or reject if the resource failed to load.  The data is loaded
     * using XMLHttpRequest, which means that in order to make requests to another origin,
     * the server must have Cross-Origin Resource Sharing (CORS) headers enabled.
     *
     * @returns {Promise.<String>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     *
     * @example
     * // load text from a URL, setting a custom header
     * var resource = new Resource({
     *   url: 'http://someUrl.com/someJson.txt',
     *   headers: {
     *     'X-Custom-Header' : 'some value'
     *   }
     * });
     * resource.fetchText().then(function(text) {
     *     // Do something with the text
     * }).otherwise(function(error) {
     *     // an error occurred
     * });
     *
     * @see {@link https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest|XMLHttpRequest}
     * @see {@link http://www.w3.org/TR/cors/|Cross-Origin Resource Sharing}
     * @see {@link http://wiki.commonjs.org/wiki/Promises/A|CommonJS Promises/A}
     */
    Resource.prototype.fetchText = function() {
        return this.fetch({
            responseType : 'text'
        });
    };

    /**
     * Creates a Resource and calls fetchText() on it.
     *
     * @param {String|Object} options A url or an object with the following properties
     * @param {String} options.url The url of the resource.
     * @param {Object} [options.queryParameters] An object containing query parameters that will be sent when retrieving the resource.
     * @param {Object} [options.templateValues] Key/Value pairs that are used to replace template values (eg. {x}).
     * @param {Object} [options.headers={}] Additional HTTP headers that will be sent.
     * @param {DefaultProxy} [options.proxy] A proxy to be used when loading the resource.
     * @param {Resource~RetryCallback} [options.retryCallback] The Function to call when a request for this resource fails. If it returns true, the request will be retried.
     * @param {Number} [options.retryAttempts=0] The number of times the retryCallback should be called before giving up.
     * @param {Request} [options.request] A Request object that will be used. Intended for internal use only.
     * @returns {Promise.<String>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     */
    Resource.fetchText = function (options) {
        var resource = new Resource(options);
        return resource.fetchText();
    };

    // note: &#42;&#47;&#42; below is */* but that ends the comment block early
    /**
     * Asynchronously loads the given resource as JSON.  Returns a promise that will resolve to
     * a JSON object once loaded, or reject if the resource failed to load.  The data is loaded
     * using XMLHttpRequest, which means that in order to make requests to another origin,
     * the server must have Cross-Origin Resource Sharing (CORS) headers enabled. This function
     * adds 'Accept: application/json,&#42;&#47;&#42;;q=0.01' to the request headers, if not
     * already specified.
     *
     * @returns {Promise.<Object>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     *
     *
     * @example
     * resource.fetchJson().then(function(jsonData) {
     *     // Do something with the JSON object
     * }).otherwise(function(error) {
     *     // an error occurred
     * });
     *
     * @see {@link http://www.w3.org/TR/cors/|Cross-Origin Resource Sharing}
     * @see {@link http://wiki.commonjs.org/wiki/Promises/A|CommonJS Promises/A}
     */
    Resource.prototype.fetchJson = function() {
        var promise = this.fetch({
            responseType : 'text',
            headers: {
                Accept : 'application/json,*/*;q=0.01'
            }
        });

        if (!defined(promise)) {
            return undefined;
        }

        return promise
            .then(function(value) {
                if (!defined(value)) {
                    return;
                }
                return JSON.parse(value);
            });
    };

    /**
     * Creates a Resource and calls fetchJson() on it.
     *
     * @param {String|Object} options A url or an object with the following properties
     * @param {String} options.url The url of the resource.
     * @param {Object} [options.queryParameters] An object containing query parameters that will be sent when retrieving the resource.
     * @param {Object} [options.templateValues] Key/Value pairs that are used to replace template values (eg. {x}).
     * @param {Object} [options.headers={}] Additional HTTP headers that will be sent.
     * @param {DefaultProxy} [options.proxy] A proxy to be used when loading the resource.
     * @param {Resource~RetryCallback} [options.retryCallback] The Function to call when a request for this resource fails. If it returns true, the request will be retried.
     * @param {Number} [options.retryAttempts=0] The number of times the retryCallback should be called before giving up.
     * @param {Request} [options.request] A Request object that will be used. Intended for internal use only.
     * @returns {Promise.<Object>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     */
    Resource.fetchJson = function (options) {
        var resource = new Resource(options);
        return resource.fetchJson();
    };

    /**
     * Asynchronously loads the given resource as XML.  Returns a promise that will resolve to
     * an XML Document once loaded, or reject if the resource failed to load.  The data is loaded
     * using XMLHttpRequest, which means that in order to make requests to another origin,
     * the server must have Cross-Origin Resource Sharing (CORS) headers enabled.
     *
     * @returns {Promise.<XMLDocument>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     *
     *
     * @example
     * // load XML from a URL, setting a custom header
     * Cesium.loadXML('http://someUrl.com/someXML.xml', {
     *   'X-Custom-Header' : 'some value'
     * }).then(function(document) {
     *     // Do something with the document
     * }).otherwise(function(error) {
     *     // an error occurred
     * });
     *
     * @see {@link https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest|XMLHttpRequest}
     * @see {@link http://www.w3.org/TR/cors/|Cross-Origin Resource Sharing}
     * @see {@link http://wiki.commonjs.org/wiki/Promises/A|CommonJS Promises/A}
     */
    Resource.prototype.fetchXML = function() {
        return this.fetch({
            responseType : 'document',
            overrideMimeType : 'text/xml'
        });
    };

    /**
     * Creates a Resource and calls fetchXML() on it.
     *
     * @param {String|Object} options A url or an object with the following properties
     * @param {String} options.url The url of the resource.
     * @param {Object} [options.queryParameters] An object containing query parameters that will be sent when retrieving the resource.
     * @param {Object} [options.templateValues] Key/Value pairs that are used to replace template values (eg. {x}).
     * @param {Object} [options.headers={}] Additional HTTP headers that will be sent.
     * @param {DefaultProxy} [options.proxy] A proxy to be used when loading the resource.
     * @param {Resource~RetryCallback} [options.retryCallback] The Function to call when a request for this resource fails. If it returns true, the request will be retried.
     * @param {Number} [options.retryAttempts=0] The number of times the retryCallback should be called before giving up.
     * @param {Request} [options.request] A Request object that will be used. Intended for internal use only.
     * @returns {Promise.<XMLDocument>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     */
    Resource.fetchXML = function (options) {
        var resource = new Resource(options);
        return resource.fetchXML();
    };

    /**
     * Requests a resource using JSONP.
     *
     * @param {String} [callbackParameterName='callback'] The callback parameter name that the server expects.
     * @returns {Promise.<Object>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     *
     *
     * @example
     * // load a data asynchronously
     * resource.fetchJsonp().then(function(data) {
     *     // use the loaded data
     * }).otherwise(function(error) {
     *     // an error occurred
     * });
     *
     * @see {@link http://wiki.commonjs.org/wiki/Promises/A|CommonJS Promises/A}
     */
    Resource.prototype.fetchJsonp = function(callbackParameterName) {
        callbackParameterName = defaultValue(callbackParameterName, 'callback');

        checkAndResetRequest(this.request);

        //generate a unique function name
        var functionName;
        do {
            functionName = 'loadJsonp' + Math.random().toString().substring(2, 8);
        } while (defined(window[functionName]));

        return fetchJsonp(this, callbackParameterName, functionName);
    };

    function fetchJsonp(resource, callbackParameterName, functionName) {
        var callbackQuery = {};
        callbackQuery[callbackParameterName] = functionName;
        resource.setQueryParameters(callbackQuery);

        var request = resource.request;
        request.url = resource.url;
        request.requestFunction = function() {
            var deferred = when.defer();

            //assign a function with that name in the global scope
            window[functionName] = function(data) {
                deferred.resolve(data);

                try {
                    delete window[functionName];
                } catch (e) {
                    window[functionName] = undefined;
                }
            };

            Resource._Implementations.loadAndExecuteScript(resource.url, functionName, deferred);
            return deferred.promise;
        };

        var promise = RequestScheduler.request(request);
        if (!defined(promise)) {
            return;
        }

        return promise
            .otherwise(function(e) {
                if (request.state !== RequestState.FAILED) {
                    return when.reject(e);
                }

                return resource.retryOnError(e)
                    .then(function(retry) {
                        if (retry) {
                            // Reset request so it can try again
                            request.state = RequestState.UNISSUED;
                            request.deferred = undefined;

                            return fetchJsonp(resource, callbackParameterName, functionName);
                        }

                        return when.reject(e);
                    });
            });
    }

    /**
     * Creates a Resource from a URL and calls fetchJsonp() on it.
     *
     * @param {String|Object} options A url or an object with the following properties
     * @param {String} options.url The url of the resource.
     * @param {Object} [options.queryParameters] An object containing query parameters that will be sent when retrieving the resource.
     * @param {Object} [options.templateValues] Key/Value pairs that are used to replace template values (eg. {x}).
     * @param {Object} [options.headers={}] Additional HTTP headers that will be sent.
     * @param {DefaultProxy} [options.proxy] A proxy to be used when loading the resource.
     * @param {Resource~RetryCallback} [options.retryCallback] The Function to call when a request for this resource fails. If it returns true, the request will be retried.
     * @param {Number} [options.retryAttempts=0] The number of times the retryCallback should be called before giving up.
     * @param {Request} [options.request] A Request object that will be used. Intended for internal use only.
     * @param {String} [options.callbackParameterName='callback'] The callback parameter name that the server expects.
     * @returns {Promise.<Object>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     */
    Resource.fetchJsonp = function (options) {
        var resource = new Resource(options);
        return resource.fetchJsonp(options.callbackParameterName);
    };

    /**
     * @private
     */
    Resource.prototype._makeRequest = function(options) {
        var resource = this;
        checkAndResetRequest(resource.request);

        var request = resource.request;
        request.url = resource.url;

        request.requestFunction = function() {
            var responseType = options.responseType;
            var headers = combine(options.headers, resource.headers);
            var overrideMimeType = options.overrideMimeType;
            var method = options.method;
            var data = options.data;
            var deferred = when.defer();
            var xhr = Resource._Implementations.loadWithXhr(resource.url, responseType, method, data, headers, deferred, overrideMimeType);
            if (defined(xhr) && defined(xhr.abort)) {
                request.cancelFunction = function() {
                    xhr.abort();
                };
            }
            return deferred.promise;
        };

        var promise = RequestScheduler.request(request);
        if (!defined(promise)) {
            return;
        }

        return promise
            .then(function(data) {
                return data;
            })
            .otherwise(function(e) {
                if (request.state !== RequestState.FAILED) {
                    return when.reject(e);
                }

                return resource.retryOnError(e)
                    .then(function(retry) {
                        if (retry) {
                            // Reset request so it can try again
                            request.state = RequestState.UNISSUED;
                            request.deferred = undefined;

                            return resource.fetch(options);
                        }

                        return when.reject(e);
                    });
            });
    };

    var dataUriRegex = /^data:(.*?)(;base64)?,(.*)$/;

    function decodeDataUriText(isBase64, data) {
        var result = decodeURIComponent(data);
        if (isBase64) {
            return atob(result);
        }
        return result;
    }

    function decodeDataUriArrayBuffer(isBase64, data) {
        var byteString = decodeDataUriText(isBase64, data);
        var buffer = new ArrayBuffer(byteString.length);
        var view = new Uint8Array(buffer);
        for (var i = 0; i < byteString.length; i++) {
            view[i] = byteString.charCodeAt(i);
        }
        return buffer;
    }

    function decodeDataUri(dataUriRegexResult, responseType) {
        responseType = defaultValue(responseType, '');
        var mimeType = dataUriRegexResult[1];
        var isBase64 = !!dataUriRegexResult[2];
        var data = dataUriRegexResult[3];

        switch (responseType) {
            case '':
            case 'text':
                return decodeDataUriText(isBase64, data);
            case 'arraybuffer':
                return decodeDataUriArrayBuffer(isBase64, data);
            case 'blob':
                var buffer = decodeDataUriArrayBuffer(isBase64, data);
                return new Blob([buffer], {
                    type : mimeType
                });
            case 'document':
                var parser = new DOMParser();
                return parser.parseFromString(decodeDataUriText(isBase64, data), mimeType);
            case 'json':
                return JSON.parse(decodeDataUriText(isBase64, data));
            default:
                //>>includeStart('debug', pragmas.debug);
                throw new DeveloperError('Unhandled responseType: ' + responseType);
            //>>includeEnd('debug');
        }
    }

    /**
     * Asynchronously loads the given resource.  Returns a promise that will resolve to
     * the result once loaded, or reject if the resource failed to load.  The data is loaded
     * using XMLHttpRequest, which means that in order to make requests to another origin,
     * the server must have Cross-Origin Resource Sharing (CORS) headers enabled. It's recommended that you use
     * the more specific functions eg. fetchJson, fetchBlob, etc.
     *
     * @param {Object} [options] Object with the following properties:
     * @param {String} [options.responseType] The type of response.  This controls the type of item returned.
     * @param {Object} [options.headers] Additional HTTP headers to send with the request, if any.
     * @param {String} [options.overrideMimeType] Overrides the MIME type returned by the server.
     * @returns {Promise.<Object>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     *
     *
     * @example
     * resource.fetch()
     *   .then(function(body) {
     *       // use the data
     *   }).otherwise(function(error) {
     *       // an error occurred
     *   });
     *
     * @see {@link http://www.w3.org/TR/cors/|Cross-Origin Resource Sharing}
     * @see {@link http://wiki.commonjs.org/wiki/Promises/A|CommonJS Promises/A}
     */
    Resource.prototype.fetch = function(options) {
        options = defaultClone(options, {});
        options.method = 'GET';

        return this._makeRequest(options);
    };

    /**
     * Creates a Resource from a URL and calls fetch() on it.
     *
     * @param {String|Object} options A url or an object with the following properties
     * @param {String} options.url The url of the resource.
     * @param {Object} [options.queryParameters] An object containing query parameters that will be sent when retrieving the resource.
     * @param {Object} [options.templateValues] Key/Value pairs that are used to replace template values (eg. {x}).
     * @param {Object} [options.headers={}] Additional HTTP headers that will be sent.
     * @param {DefaultProxy} [options.proxy] A proxy to be used when loading the resource.
     * @param {Resource~RetryCallback} [options.retryCallback] The Function to call when a request for this resource fails. If it returns true, the request will be retried.
     * @param {Number} [options.retryAttempts=0] The number of times the retryCallback should be called before giving up.
     * @param {Request} [options.request] A Request object that will be used. Intended for internal use only.
     * @param {String} [options.responseType] The type of response.  This controls the type of item returned.
     * @param {String} [options.overrideMimeType] Overrides the MIME type returned by the server.
     * @returns {Promise.<Object>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     */
    Resource.fetch = function (options) {
        var resource = new Resource(options);
        return resource.fetch({
            // Make copy of just the needed fields because headers can be passed to both the constructor and to fetch
            responseType: options.responseType,
            overrideMimeType: options.overrideMimeType
        });
    };

    /**
     * Asynchronously deletes the given resource.  Returns a promise that will resolve to
     * the result once loaded, or reject if the resource failed to load.  The data is loaded
     * using XMLHttpRequest, which means that in order to make requests to another origin,
     * the server must have Cross-Origin Resource Sharing (CORS) headers enabled.
     *
     * @param {Object} [options] Object with the following properties:
     * @param {String} [options.responseType] The type of response.  This controls the type of item returned.
     * @param {Object} [options.headers] Additional HTTP headers to send with the request, if any.
     * @param {String} [options.overrideMimeType] Overrides the MIME type returned by the server.
     * @returns {Promise.<Object>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     *
     *
     * @example
     * resource.delete()
     *   .then(function(body) {
     *       // use the data
     *   }).otherwise(function(error) {
     *       // an error occurred
     *   });
     *
     * @see {@link http://www.w3.org/TR/cors/|Cross-Origin Resource Sharing}
     * @see {@link http://wiki.commonjs.org/wiki/Promises/A|CommonJS Promises/A}
     */
    Resource.prototype.delete = function(options) {
        options = defaultClone(options, {});
        options.method = 'DELETE';

        return this._makeRequest(options);
    };

    /**
     * Creates a Resource from a URL and calls delete() on it.
     *
     * @param {String|Object} options A url or an object with the following properties
     * @param {String} options.url The url of the resource.
     * @param {Object} [options.data] Data that is posted with the resource.
     * @param {Object} [options.queryParameters] An object containing query parameters that will be sent when retrieving the resource.
     * @param {Object} [options.templateValues] Key/Value pairs that are used to replace template values (eg. {x}).
     * @param {Object} [options.headers={}] Additional HTTP headers that will be sent.
     * @param {DefaultProxy} [options.proxy] A proxy to be used when loading the resource.
     * @param {Resource~RetryCallback} [options.retryCallback] The Function to call when a request for this resource fails. If it returns true, the request will be retried.
     * @param {Number} [options.retryAttempts=0] The number of times the retryCallback should be called before giving up.
     * @param {Request} [options.request] A Request object that will be used. Intended for internal use only.
     * @param {String} [options.responseType] The type of response.  This controls the type of item returned.
     * @param {String} [options.overrideMimeType] Overrides the MIME type returned by the server.
     * @returns {Promise.<Object>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     */
    Resource.delete = function (options) {
        var resource = new Resource(options);
        return resource.delete({
            // Make copy of just the needed fields because headers can be passed to both the constructor and to fetch
            responseType: options.responseType,
            overrideMimeType: options.overrideMimeType,
            data: options.data
        });
    };

    /**
     * Asynchronously gets headers the given resource.  Returns a promise that will resolve to
     * the result once loaded, or reject if the resource failed to load.  The data is loaded
     * using XMLHttpRequest, which means that in order to make requests to another origin,
     * the server must have Cross-Origin Resource Sharing (CORS) headers enabled.
     *
     * @param {Object} [options] Object with the following properties:
     * @param {String} [options.responseType] The type of response.  This controls the type of item returned.
     * @param {Object} [options.headers] Additional HTTP headers to send with the request, if any.
     * @param {String} [options.overrideMimeType] Overrides the MIME type returned by the server.
     * @returns {Promise.<Object>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     *
     *
     * @example
     * resource.head()
     *   .then(function(headers) {
     *       // use the data
     *   }).otherwise(function(error) {
     *       // an error occurred
     *   });
     *
     * @see {@link http://www.w3.org/TR/cors/|Cross-Origin Resource Sharing}
     * @see {@link http://wiki.commonjs.org/wiki/Promises/A|CommonJS Promises/A}
     */
    Resource.prototype.head = function(options) {
        options = defaultClone(options, {});
        options.method = 'HEAD';

        return this._makeRequest(options);
    };

    /**
     * Creates a Resource from a URL and calls head() on it.
     *
     * @param {String|Object} options A url or an object with the following properties
     * @param {String} options.url The url of the resource.
     * @param {Object} [options.queryParameters] An object containing query parameters that will be sent when retrieving the resource.
     * @param {Object} [options.templateValues] Key/Value pairs that are used to replace template values (eg. {x}).
     * @param {Object} [options.headers={}] Additional HTTP headers that will be sent.
     * @param {DefaultProxy} [options.proxy] A proxy to be used when loading the resource.
     * @param {Resource~RetryCallback} [options.retryCallback] The Function to call when a request for this resource fails. If it returns true, the request will be retried.
     * @param {Number} [options.retryAttempts=0] The number of times the retryCallback should be called before giving up.
     * @param {Request} [options.request] A Request object that will be used. Intended for internal use only.
     * @param {String} [options.responseType] The type of response.  This controls the type of item returned.
     * @param {String} [options.overrideMimeType] Overrides the MIME type returned by the server.
     * @returns {Promise.<Object>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     */
    Resource.head = function (options) {
        var resource = new Resource(options);
        return resource.head({
            // Make copy of just the needed fields because headers can be passed to both the constructor and to fetch
            responseType: options.responseType,
            overrideMimeType: options.overrideMimeType
        });
    };

    /**
     * Asynchronously gets options the given resource.  Returns a promise that will resolve to
     * the result once loaded, or reject if the resource failed to load.  The data is loaded
     * using XMLHttpRequest, which means that in order to make requests to another origin,
     * the server must have Cross-Origin Resource Sharing (CORS) headers enabled.
     *
     * @param {Object} [options] Object with the following properties:
     * @param {String} [options.responseType] The type of response.  This controls the type of item returned.
     * @param {Object} [options.headers] Additional HTTP headers to send with the request, if any.
     * @param {String} [options.overrideMimeType] Overrides the MIME type returned by the server.
     * @returns {Promise.<Object>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     *
     *
     * @example
     * resource.options()
     *   .then(function(headers) {
     *       // use the data
     *   }).otherwise(function(error) {
     *       // an error occurred
     *   });
     *
     * @see {@link http://www.w3.org/TR/cors/|Cross-Origin Resource Sharing}
     * @see {@link http://wiki.commonjs.org/wiki/Promises/A|CommonJS Promises/A}
     */
    Resource.prototype.options = function(options) {
        options = defaultClone(options, {});
        options.method = 'OPTIONS';

        return this._makeRequest(options);
    };

    /**
     * Creates a Resource from a URL and calls options() on it.
     *
     * @param {String|Object} options A url or an object with the following properties
     * @param {String} options.url The url of the resource.
     * @param {Object} [options.queryParameters] An object containing query parameters that will be sent when retrieving the resource.
     * @param {Object} [options.templateValues] Key/Value pairs that are used to replace template values (eg. {x}).
     * @param {Object} [options.headers={}] Additional HTTP headers that will be sent.
     * @param {DefaultProxy} [options.proxy] A proxy to be used when loading the resource.
     * @param {Resource~RetryCallback} [options.retryCallback] The Function to call when a request for this resource fails. If it returns true, the request will be retried.
     * @param {Number} [options.retryAttempts=0] The number of times the retryCallback should be called before giving up.
     * @param {Request} [options.request] A Request object that will be used. Intended for internal use only.
     * @param {String} [options.responseType] The type of response.  This controls the type of item returned.
     * @param {String} [options.overrideMimeType] Overrides the MIME type returned by the server.
     * @returns {Promise.<Object>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     */
    Resource.options = function (options) {
        var resource = new Resource(options);
        return resource.options({
            // Make copy of just the needed fields because headers can be passed to both the constructor and to fetch
            responseType: options.responseType,
            overrideMimeType: options.overrideMimeType
        });
    };

    /**
     * Asynchronously posts data to the given resource.  Returns a promise that will resolve to
     * the result once loaded, or reject if the resource failed to load.  The data is loaded
     * using XMLHttpRequest, which means that in order to make requests to another origin,
     * the server must have Cross-Origin Resource Sharing (CORS) headers enabled.
     *
     * @param {Object} data Data that is posted with the resource.
     * @param {Object} [options] Object with the following properties:
     * @param {Object} [options.data] Data that is posted with the resource.
     * @param {String} [options.responseType] The type of response.  This controls the type of item returned.
     * @param {Object} [options.headers] Additional HTTP headers to send with the request, if any.
     * @param {String} [options.overrideMimeType] Overrides the MIME type returned by the server.
     * @returns {Promise.<Object>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     *
     *
     * @example
     * resource.post(data)
     *   .then(function(result) {
     *       // use the result
     *   }).otherwise(function(error) {
     *       // an error occurred
     *   });
     *
     * @see {@link http://www.w3.org/TR/cors/|Cross-Origin Resource Sharing}
     * @see {@link http://wiki.commonjs.org/wiki/Promises/A|CommonJS Promises/A}
     */
    Resource.prototype.post = function(data, options) {
        Check.defined('data', data);

        options = defaultClone(options, {});
        options.method = 'POST';
        options.data = data;

        return this._makeRequest(options);
    };

    /**
     * Creates a Resource from a URL and calls post() on it.
     *
     * @param {Object} options A url or an object with the following properties
     * @param {String} options.url The url of the resource.
     * @param {Object} options.data Data that is posted with the resource.
     * @param {Object} [options.queryParameters] An object containing query parameters that will be sent when retrieving the resource.
     * @param {Object} [options.templateValues] Key/Value pairs that are used to replace template values (eg. {x}).
     * @param {Object} [options.headers={}] Additional HTTP headers that will be sent.
     * @param {DefaultProxy} [options.proxy] A proxy to be used when loading the resource.
     * @param {Resource~RetryCallback} [options.retryCallback] The Function to call when a request for this resource fails. If it returns true, the request will be retried.
     * @param {Number} [options.retryAttempts=0] The number of times the retryCallback should be called before giving up.
     * @param {Request} [options.request] A Request object that will be used. Intended for internal use only.
     * @param {String} [options.responseType] The type of response.  This controls the type of item returned.
     * @param {String} [options.overrideMimeType] Overrides the MIME type returned by the server.
     * @returns {Promise.<Object>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     */
    Resource.post = function (options) {
        var resource = new Resource(options);
        return resource.post(options.data, {
            // Make copy of just the needed fields because headers can be passed to both the constructor and to post
            responseType: options.responseType,
            overrideMimeType: options.overrideMimeType
        });
    };

    /**
     * Asynchronously puts data to the given resource.  Returns a promise that will resolve to
     * the result once loaded, or reject if the resource failed to load.  The data is loaded
     * using XMLHttpRequest, which means that in order to make requests to another origin,
     * the server must have Cross-Origin Resource Sharing (CORS) headers enabled.
     *
     * @param {Object} data Data that is posted with the resource.
     * @param {Object} [options] Object with the following properties:
     * @param {String} [options.responseType] The type of response.  This controls the type of item returned.
     * @param {Object} [options.headers] Additional HTTP headers to send with the request, if any.
     * @param {String} [options.overrideMimeType] Overrides the MIME type returned by the server.
     * @returns {Promise.<Object>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     *
     *
     * @example
     * resource.put(data)
     *   .then(function(result) {
     *       // use the result
     *   }).otherwise(function(error) {
     *       // an error occurred
     *   });
     *
     * @see {@link http://www.w3.org/TR/cors/|Cross-Origin Resource Sharing}
     * @see {@link http://wiki.commonjs.org/wiki/Promises/A|CommonJS Promises/A}
     */
    Resource.prototype.put = function(data, options) {
        Check.defined('data', data);

        options = defaultClone(options, {});
        options.method = 'PUT';
        options.data = data;

        return this._makeRequest(options);
    };

    /**
     * Creates a Resource from a URL and calls put() on it.
     *
     * @param {Object} options A url or an object with the following properties
     * @param {String} options.url The url of the resource.
     * @param {Object} options.data Data that is posted with the resource.
     * @param {Object} [options.queryParameters] An object containing query parameters that will be sent when retrieving the resource.
     * @param {Object} [options.templateValues] Key/Value pairs that are used to replace template values (eg. {x}).
     * @param {Object} [options.headers={}] Additional HTTP headers that will be sent.
     * @param {DefaultProxy} [options.proxy] A proxy to be used when loading the resource.
     * @param {Resource~RetryCallback} [options.retryCallback] The Function to call when a request for this resource fails. If it returns true, the request will be retried.
     * @param {Number} [options.retryAttempts=0] The number of times the retryCallback should be called before giving up.
     * @param {Request} [options.request] A Request object that will be used. Intended for internal use only.
     * @param {String} [options.responseType] The type of response.  This controls the type of item returned.
     * @param {String} [options.overrideMimeType] Overrides the MIME type returned by the server.
     * @returns {Promise.<Object>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     */
    Resource.put = function (options) {
        var resource = new Resource(options);
        return resource.put(options.data, {
            // Make copy of just the needed fields because headers can be passed to both the constructor and to post
            responseType: options.responseType,
            overrideMimeType: options.overrideMimeType
        });
    };

    /**
     * Asynchronously patches data to the given resource.  Returns a promise that will resolve to
     * the result once loaded, or reject if the resource failed to load.  The data is loaded
     * using XMLHttpRequest, which means that in order to make requests to another origin,
     * the server must have Cross-Origin Resource Sharing (CORS) headers enabled.
     *
     * @param {Object} data Data that is posted with the resource.
     * @param {Object} [options] Object with the following properties:
     * @param {String} [options.responseType] The type of response.  This controls the type of item returned.
     * @param {Object} [options.headers] Additional HTTP headers to send with the request, if any.
     * @param {String} [options.overrideMimeType] Overrides the MIME type returned by the server.
     * @returns {Promise.<Object>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     *
     *
     * @example
     * resource.patch(data)
     *   .then(function(result) {
     *       // use the result
     *   }).otherwise(function(error) {
     *       // an error occurred
     *   });
     *
     * @see {@link http://www.w3.org/TR/cors/|Cross-Origin Resource Sharing}
     * @see {@link http://wiki.commonjs.org/wiki/Promises/A|CommonJS Promises/A}
     */
    Resource.prototype.patch = function(data, options) {
        Check.defined('data', data);

        options = defaultClone(options, {});
        options.method = 'PATCH';
        options.data = data;

        return this._makeRequest(options);
    };

    /**
     * Creates a Resource from a URL and calls patch() on it.
     *
     * @param {Object} options A url or an object with the following properties
     * @param {String} options.url The url of the resource.
     * @param {Object} options.data Data that is posted with the resource.
     * @param {Object} [options.queryParameters] An object containing query parameters that will be sent when retrieving the resource.
     * @param {Object} [options.templateValues] Key/Value pairs that are used to replace template values (eg. {x}).
     * @param {Object} [options.headers={}] Additional HTTP headers that will be sent.
     * @param {DefaultProxy} [options.proxy] A proxy to be used when loading the resource.
     * @param {Resource~RetryCallback} [options.retryCallback] The Function to call when a request for this resource fails. If it returns true, the request will be retried.
     * @param {Number} [options.retryAttempts=0] The number of times the retryCallback should be called before giving up.
     * @param {Request} [options.request] A Request object that will be used. Intended for internal use only.
     * @param {String} [options.responseType] The type of response.  This controls the type of item returned.
     * @param {String} [options.overrideMimeType] Overrides the MIME type returned by the server.
     * @returns {Promise.<Object>|undefined} a promise that will resolve to the requested data when loaded. Returns undefined if <code>request.throttle</code> is true and the request does not have high enough priority.
     */
    Resource.patch = function (options) {
        var resource = new Resource(options);
        return resource.patch(options.data, {
            // Make copy of just the needed fields because headers can be passed to both the constructor and to post
            responseType: options.responseType,
            overrideMimeType: options.overrideMimeType
        });
    };

    /**
     * Contains implementations of functions that can be replaced for testing
     *
     * @private
     */
    Resource._Implementations = {};

    function loadImageElement(url, crossOrigin, deferred) {
        var image = new Image();

        image.onload = function() {
            deferred.resolve(image);
        };

        image.onerror = function(e) {
            deferred.reject(e);
        };

        if (crossOrigin) {
            if (TrustedServers.contains(url)) {
                image.crossOrigin = 'use-credentials';
            } else {
                image.crossOrigin = '';
            }
        }

        image.src = url;
    }

    Resource._Implementations.createImage = function(url, crossOrigin, deferred, flipY, preferImageBitmap) {
        // Passing an Image to createImageBitmap will force it to run on the main thread
        // since DOM elements don't exist on workers. We convert it to a blob so it's non-blocking.
        // See:
        //    https://bugzilla.mozilla.org/show_bug.cgi?id=1044102#c38
        //    https://bugs.chromium.org/p/chromium/issues/detail?id=580202#c10
        Resource.supportsImageBitmapOptions()
            .then(function(supportsImageBitmap) {
                // We can only use ImageBitmap if we can flip on decode.
                // See: https://github.com/AnalyticalGraphicsInc/cesium/pull/7579#issuecomment-466146898
                if (!(supportsImageBitmap && preferImageBitmap)) {
                    loadImageElement(url, crossOrigin, deferred);
                    return;
                }

                return Resource.fetchBlob({
                    url: url
                })
                .then(function(blob) {
                    if (!defined(blob)) {
                        deferred.reject(new RuntimeError('Successfully retrieved ' + url + ' but it contained no content.'));
                        return;
                    }

                    return Resource.createImageBitmapFromBlob(blob, {
                        flipY: flipY,
                        premultiplyAlpha: false
                    });
                }).then(deferred.resolve);
            })
            .otherwise(deferred.reject);
    };

    /**
     * Wrapper for createImageBitmap
     *
     * @private
     */
    Resource.createImageBitmapFromBlob = function(blob, options) {
        Check.defined('options', options);
        Check.typeOf.bool('options.flipY', options.flipY);
        Check.typeOf.bool('options.premultiplyAlpha', options.premultiplyAlpha);

        return createImageBitmap(blob, {
            imageOrientation: options.flipY ? 'flipY' : 'none',
            premultiplyAlpha: options.premultiplyAlpha ? 'premultiply' : 'none'
        });
    };

    function decodeResponse(loadWithHttpResponse, responseType) {
        switch (responseType) {
          case 'text':
              return loadWithHttpResponse.toString('utf8');
          case 'json':
              return JSON.parse(loadWithHttpResponse.toString('utf8'));
          default:
              return new Uint8Array(loadWithHttpResponse).buffer;
        }
    }

    function loadWithHttpRequest(url, responseType, method, data, headers, deferred, overrideMimeType) {

        // Specifically use the Node version of require to avoid conflicts with the global
        // require defined in the built version of Cesium.
        var nodeRequire = global.require; // eslint-disable-line

        // Note: only the 'json' and 'text' responseTypes transforms the loaded buffer
        var URL = nodeRequire('url').parse(url);
        var http = URL.protocol === 'https:' ? nodeRequire('https') : nodeRequire('http');
        var zlib = nodeRequire('zlib');
        var options = {
            protocol : URL.protocol,
            hostname : URL.hostname,
            port : URL.port,
            path : URL.path,
            query : URL.query,
            method : method,
            headers : headers
        };

        http.request(options)
            .on('response', function(res) {
                if (res.statusCode < 200 || res.statusCode >= 300) {
                    deferred.reject(new RequestErrorEvent(res.statusCode, res, res.headers));
                    return;
                }

                var chunkArray = [];
                res.on('data', function(chunk) {
                    chunkArray.push(chunk);
                });

                res.on('end', function() {
                    var result = Buffer.concat(chunkArray); // eslint-disable-line
                    if (res.headers['content-encoding'] === 'gzip') {
                        zlib.gunzip(result, function(error, resultUnzipped) {
                            if (error) {
                                deferred.reject(new RuntimeError('Error decompressing response.'));
                            } else {
                                deferred.resolve(decodeResponse(resultUnzipped, responseType));
                            }
                        });
                    } else {
                        deferred.resolve(decodeResponse(result, responseType));
                    }
                });
            }).on('error', function(e) {
                deferred.reject(new RequestErrorEvent());
            }).end();
    }

    var noXMLHttpRequest = typeof XMLHttpRequest === 'undefined';
    Resource._Implementations.loadWithXhr = function(url, responseType, method, data, headers, deferred, overrideMimeType) {
        var dataUriRegexResult = dataUriRegex.exec(url);
        if (dataUriRegexResult !== null) {
            deferred.resolve(decodeDataUri(dataUriRegexResult, responseType));
            return;
        }

        if (noXMLHttpRequest) {
            loadWithHttpRequest(url, responseType, method, data, headers, deferred, overrideMimeType);
            return;
        }

        var xhr = new XMLHttpRequest();

        if (TrustedServers.contains(url)) {
            xhr.withCredentials = true;
        }

        xhr.open(method, url, true);

        if (defined(overrideMimeType) && defined(xhr.overrideMimeType)) {
            xhr.overrideMimeType(overrideMimeType);
        }

        if (defined(headers)) {
            for (var key in headers) {
                if (headers.hasOwnProperty(key)) {
                    xhr.setRequestHeader(key, headers[key]);
                }
            }
        }

        if (defined(responseType)) {
            xhr.responseType = responseType;
        }

        // While non-standard, file protocol always returns a status of 0 on success
        var localFile = false;
        if (typeof url === 'string') {
            localFile = (url.indexOf('file://') === 0) || (typeof window !== 'undefined' && window.location.origin === 'file://');
        }

        xhr.onload = function() {
            if ((xhr.status < 200 || xhr.status >= 300) && !(localFile && xhr.status === 0)) {
                deferred.reject(new RequestErrorEvent(xhr.status, xhr.response, xhr.getAllResponseHeaders()));
                return;
            }

            var response = xhr.response;
            var browserResponseType = xhr.responseType;

            if (method === 'HEAD' || method === 'OPTIONS') {
                var responseHeaderString = xhr.getAllResponseHeaders();
                var splitHeaders = responseHeaderString.trim().split(/[\r\n]+/);

                var responseHeaders = {};
                splitHeaders.forEach(function (line) {
                    var parts = line.split(': ');
                    var header = parts.shift();
                    responseHeaders[header] = parts.join(': ');
                });

                deferred.resolve(responseHeaders);
                return;
            }

            //All modern browsers will go into either the first or second if block or last else block.
            //Other code paths support older browsers that either do not support the supplied responseType
            //or do not support the xhr.response property.
            if (xhr.status === 204) {
                // accept no content
                deferred.resolve();
            } else if (defined(response) && (!defined(responseType) || (browserResponseType === responseType))) {
                deferred.resolve(response);
            } else if ((responseType === 'json') && typeof response === 'string') {
                try {
                    deferred.resolve(JSON.parse(response));
                } catch (e) {
                    deferred.reject(e);
                }
            } else if ((browserResponseType === '' || browserResponseType === 'document') && defined(xhr.responseXML) && xhr.responseXML.hasChildNodes()) {
                deferred.resolve(xhr.responseXML);
            } else if ((browserResponseType === '' || browserResponseType === 'text') && defined(xhr.responseText)) {
                deferred.resolve(xhr.responseText);
            } else {
                deferred.reject(new RuntimeError('Invalid XMLHttpRequest response type.'));
            }
        };

        xhr.onerror = function(e) {
            deferred.reject(new RequestErrorEvent());
        };

        xhr.send(data);

        return xhr;
    };

    Resource._Implementations.loadAndExecuteScript = function(url, functionName, deferred) {
        return loadAndExecuteScript(url, functionName).otherwise(deferred.reject);
    };

    /**
     * The default implementations
     *
     * @private
     */
    Resource._DefaultImplementations = {};
    Resource._DefaultImplementations.createImage = Resource._Implementations.createImage;
    Resource._DefaultImplementations.loadWithXhr = Resource._Implementations.loadWithXhr;
    Resource._DefaultImplementations.loadAndExecuteScript = Resource._Implementations.loadAndExecuteScript;

    /**
     * A resource instance initialized to the current browser location
     *
     * @type {Resource}
     * @constant
     */
    Resource.DEFAULT = freezeObject(new Resource({
        url: (typeof document === 'undefined') ? '' : document.location.href.split('?')[0]
    }));

    /**
     * A function that returns the value of the property.
     * @callback Resource~RetryCallback
     *
     * @param {Resource} [resource] The resource that failed to load.
     * @param {Error} [error] The error that occurred during the loading of the resource.
     * @returns {Boolean|Promise<Boolean>} If true or a promise that resolved to true, the resource will be retried. Otherwise the failure will be returned.
     */
export default Resource;