'use strict';

/**
 * Parse headers into key value object
 *
 * @param {string} headers Raw headers as a string
 * @returns {Object} Parsed headers as key value object
 */
function parseHeaders(headers) {
  var parsed = {}, key, val, i;

  if (!headers) return parsed;

  forEach(headers.split('\n'), function(line) {
    i = line.indexOf(':');
    key = lowercase(trim(line.substr(0, i)));
    val = trim(line.substr(i + 1));

    if (key) {
      if (parsed[key]) {
        parsed[key] += ', ' + val;
      } else {
        parsed[key] = val;
      }
    }
  });

  return parsed;
}


/**
 * Returns a function that provides access to parsed headers.
 *
 * Headers are lazy parsed when first requested.
 * @see parseHeaders
 *
 * @param {(string|Object)} headers Headers to provide access to.
 * @returns {function(string=)} Returns a getter function which if called with:
 *
 *   - if called with single an argument returns a single header value or null
 *   - if called with no arguments returns an object containing all headers.
 */
function headersGetter(headers) {
  var headersObj = isObject(headers) ? headers : undefined;

  return function(name) {
    if (!headersObj) headersObj =  parseHeaders(headers);

    if (name) {
      return headersObj[lowercase(name)] || null;
    }

    return headersObj;
  };
}


/**
 * Chain all given functions
 *
 * This function is used for both request and response transforming
 *
 * @param {*} data Data to transform.
 * @param {function(string=)} headers Http headers getter fn.
 * @param {(function|Array.<function>)} fns Function or an array of functions.
 * @returns {*} Transformed data.
 */
function transformData(data, headers, fns) {
  if (isFunction(fns))
    return fns(data, headers);

  forEach(fns, function(fn) {
    data = fn(data, headers);
  });

  return data;
}


function isSuccess(status) {
  return 200 <= status && status < 300;
}


function $HttpProvider() {
  var JSON_START = /^\s*(\[|\{[^\{])/,
      JSON_END = /[\}\]]\s*$/,
      PROTECTION_PREFIX = /^\)\]\}',?\n/,
      CONTENT_TYPE_APPLICATION_JSON = {'Content-Type': 'application/json;charset=utf-8'};

  var defaults = this.defaults = {
    // transform incoming response data
    transformResponse: [function(data) {
      if (isString(data)) {
        // strip json vulnerability protection prefix
        data = data.replace(PROTECTION_PREFIX, '');
        if (JSON_START.test(data) && JSON_END.test(data))
          data = fromJson(data, true);
      }
      return data;
    }],

    // transform outgoing request data
    transformRequest: [function(d) {
      return isObject(d) && !isFile(d) ? toJson(d) : d;
    }],

    // default headers
    headers: {
      common: {
        'Accept': 'application/json, text/plain, */*'
      },
      post:   CONTENT_TYPE_APPLICATION_JSON,
      put:    CONTENT_TYPE_APPLICATION_JSON,
      patch:  CONTENT_TYPE_APPLICATION_JSON
    },

    xsrfCookieName: 'XSRF-TOKEN',
    xsrfHeaderName: 'X-XSRF-TOKEN'
  };

  /**
   * Are order by request. I.E. they are applied in the same order as
   * array on request, but revers order on response.
   */
  var interceptorFactories = this.interceptors = [];
  /**
   * For historical reasons, response interceptors ordered by the order in which
   * they are applied to response. (This is in revers to interceptorFactories)
   */
  var responseInterceptorFactories = this.responseInterceptors = [];

  this.$get = ['$httpBackend', '$browser', '$cacheFactory', '$rootScope', '$q', '$injector', '$$urlUtils',
      function($httpBackend, $browser, $cacheFactory, $rootScope, $q, $injector, $$urlUtils) {

    var defaultCache = $cacheFactory('$http');

    /**
     * Interceptors stored in reverse order. Inner interceptors before outer interceptors.
     * The reversal is needed so that we can build up the interception chain around the
     * server request.
     */
    var reversedInterceptors = [];

    forEach(interceptorFactories, function(interceptorFactory) {
      reversedInterceptors.unshift(isString(interceptorFactory)
          ? $injector.get(interceptorFactory) : $injector.invoke(interceptorFactory));
    });

    forEach(responseInterceptorFactories, function(interceptorFactory, index) {
      var responseFn = isString(interceptorFactory)
          ? $injector.get(interceptorFactory)
          : $injector.invoke(interceptorFactory);

      /**
       * Response interceptors go before "around" interceptors (no real reason, just
       * had to pick one.) But they are already reversed, so we can't use unshift, hence
       * the splice.
       */
      reversedInterceptors.splice(index, 0, {
        response: function(response) {
          return responseFn($q.when(response));
        },
        responseError: function(response) {
          return responseFn($q.reject(response));
        }
      });
    });


    /**
     * @ngdoc function
     * @name ng.$http
     * @requires $httpBackend
     * @requires $browser
     * @requires $cacheFactory
     * @requires $rootScope
     * @requires $q
     * @requires $injector
     *
     * @description
     * The `$http` service is a core Angular service that facilitates communication with the remote
     * HTTP servers via the browser's {@link https://developer.mozilla.org/en/xmlhttprequest
     * XMLHttpRequest} object or via {@link http://en.wikipedia.org/wiki/JSONP JSONP}.
     *
     * For unit testing applications that use `$http` service, see
     * {@link ngMock.$httpBackend $httpBackend mock}.
     *
     * For a higher level of abstraction, please check out the {@link ngResource.$resource
     * $resource} service.
     *
     * The $http API is based on the {@link ng.$q deferred/promise APIs} exposed by
     * the $q service. While for simple usage patterns this doesn't matter much, for advanced usage
     * it is important to familiarize yourself with these APIs and the guarantees they provide.
     *
     *
     * # General usage
     * The `$http` service is a function which takes a single argument — a configuration object —
     * that is used to generate an HTTP request and returns  a {@link ng.$q promise}
     * with two $http specific methods: `success` and `error`.
     *
     * <pre>
     *   $http({method: 'GET', url: '/someUrl'}).
     *     success(function(data, status, headers, config) {
     *       // this callback will be called asynchronously
     *       // when the response is available
     *     }).
     *     error(function(data, status, headers, config) {
     *       // called asynchronously if an error occurs
     *       // or server returns response with an error status.
     *     });
     * </pre>
     *
     * Since the returned value of calling the $http function is a `promise`, you can also use
     * the `then` method to register callbacks, and these callbacks will receive a single argument –
     * an object representing the response. See the API signature and type info below for more
     * details.
     *
     * A response status code between 200 and 299 is considered a success status and
     * will result in the success callback being called. Note that if the response is a redirect,
     * XMLHttpRequest will transparently follow it, meaning that the error callback will not be
     * called for such responses.
     *
     * # Shortcut methods
     *
     * Since all invocations of the $http service require passing in an HTTP method and URL, and
     * POST/PUT requests require request data to be provided as well, shortcut methods
     * were created:
     *
     * <pre>
     *   $http.get('/someUrl').success(successCallback);
     *   $http.post('/someUrl', data).success(successCallback);
     * </pre>
     *
     * Complete list of shortcut methods:
     *
     * - {@link ng.$http#get $http.get}
     * - {@link ng.$http#head $http.head}
     * - {@link ng.$http#post $http.post}
     * - {@link ng.$http#put $http.put}
     * - {@link ng.$http#delete $http.delete}
     * - {@link ng.$http#jsonp $http.jsonp}
     *
     *
     * # Setting HTTP Headers
     *
     * The $http service will automatically add certain HTTP headers to all requests. These defaults
     * can be fully configured by accessing the `$httpProvider.defaults.headers` configuration
     * object, which currently contains this default configuration:
     *
     * - `$httpProvider.defaults.headers.common` (headers that are common for all requests):
     *   - `Accept: application/json, text/plain, * / *`
     * - `$httpProvider.defaults.headers.post`: (header defaults for POST requests)
     *   - `Content-Type: application/json`
     * - `$httpProvider.defaults.headers.put` (header defaults for PUT requests)
     *   - `Content-Type: application/json`
     *
     * To add or overwrite these defaults, simply add or remove a property from these configuration
     * objects. To add headers for an HTTP method other than POST or PUT, simply add a new object
     * with the lowercased HTTP method name as the key, e.g.
     * `$httpProvider.defaults.headers.get['My-Header']='value'`.
     *
     * Additionally, the defaults can be set at runtime via the `$http.defaults` object in the same
     * fashion.
     *
     *
     * # Transforming Requests and Responses
     *
     * Both requests and responses can be transformed using transform functions. By default, Angular
     * applies these transformations:
     *
     * Request transformations:
     *
     * - If the `data` property of the request configuration object contains an object, serialize it into
     *   JSON format.
     *
     * Response transformations:
     *
     *  - If XSRF prefix is detected, strip it (see Security Considerations section below).
     *  - If JSON response is detected, deserialize it using a JSON parser.
     *
     * To globally augment or override the default transforms, modify the `$httpProvider.defaults.transformRequest` and
     * `$httpProvider.defaults.transformResponse` properties. These properties are by default an
     * array of transform functions, which allows you to `push` or `unshift` a new transformation function into the
     * transformation chain. You can also decide to completely override any default transformations by assigning your
     * transformation functions to these properties directly without the array wrapper.
     *
     * Similarly, to locally override the request/response transforms, augment the `transformRequest` and/or
     * `transformResponse` properties of the configuration object passed into `$http`.
     *
     *
     * # Caching
     *
     * To enable caching, set the configuration property `cache` to `true`. When the cache is
     * enabled, `$http` stores the response from the server in local cache. Next time the
     * response is served from the cache without sending a request to the server.
     *
     * Note that even if the response is served from cache, delivery of the data is asynchronous in
     * the same way that real requests are.
     *
     * If there are multiple GET requests for the same URL that should be cached using the same
     * cache, but the cache is not populated yet, only one request to the server will be made and
     * the remaining requests will be fulfilled using the response from the first request.
     *
     * A custom default cache built with $cacheFactory can be provided in $http.defaults.cache.
     * To skip it, set configuration property `cache` to `false`.
     *
     *
     * # Interceptors
     *
     * Before you start creating interceptors, be sure to understand the
     * {@link ng.$q $q and deferred/promise APIs}.
     *
     * For purposes of global error handling, authentication, or any kind of synchronous or
     * asynchronous pre-processing of request or postprocessing of responses, it is desirable to be
     * able to intercept requests before they are handed to the server and
     * responses before they are handed over to the application code that
     * initiated these requests. The interceptors leverage the {@link ng.$q
     * promise APIs} to fulfill this need for both synchronous and asynchronous pre-processing.
     *
     * The interceptors are service factories that are registered with the `$httpProvider` by
     * adding them to the `$httpProvider.interceptors` array. The factory is called and
     * injected with dependencies (if specified) and returns the interceptor.
     *
     * There are two kinds of interceptors (and two kinds of rejection interceptors):
     *
     *   * `request`: interceptors get called with http `config` object. The function is free to modify
     *     the `config` or create a new one. The function needs to return the `config` directly or as a
     *     promise.
     *   * `requestError`: interceptor gets called when a previous interceptor threw an error or resolved
     *      with a rejection.
     *   * `response`: interceptors get called with http `response` object. The function is free to modify
     *     the `response` or create a new one. The function needs to return the `response` directly or as a
     *     promise.
     *   * `responseError`: interceptor gets called when a previous interceptor threw an error or resolved
     *      with a rejection.
     *
     *
     * <pre>
     *   // register the interceptor as a service
     *   $provide.factory('myHttpInterceptor', function($q, dependency1, dependency2) {
     *     return {
     *       // optional method
     *       'request': function(config) {
     *         // do something on success
     *         return config || $q.when(config);
     *       },
     *
     *       // optional method
     *      'requestError': function(rejection) {
     *         // do something on error
     *         if (canRecover(rejection)) {
     *           return responseOrNewPromise
     *         }
     *         return $q.reject(rejection);
     *       },
     *
     *
     *
     *       // optional method
     *       'response': function(response) {
     *         // do something on success
     *         return response || $q.when(response);
     *       },
     *
     *       // optional method
     *      'responseError': function(rejection) {
     *         // do something on error
     *         if (canRecover(rejection)) {
     *           return responseOrNewPromise
     *         }
     *         return $q.reject(rejection);
     *       };
     *     }
     *   });
     *
     *   $httpProvider.interceptors.push('myHttpInterceptor');
     *
     *
     *   // register the interceptor via an anonymous factory
     *   $httpProvider.interceptors.push(function($q, dependency1, dependency2) {
     *     return {
     *      'request': function(config) {
     *          // same as above
     *       },
     *       'response': function(response) {
     *          // same as above
     *       }
     *   });
     * </pre>
     *
     * # Response interceptors (DEPRECATED)
     *
     * Before you start creating interceptors, be sure to understand the
     * {@link ng.$q $q and deferred/promise APIs}.
     *
     * For purposes of global error handling, authentication or any kind of synchronous or
     * asynchronous preprocessing of received responses, it is desirable to be able to intercept
     * responses for http requests before they are handed over to the application code that
     * initiated these requests. The response interceptors leverage the {@link ng.$q
     * promise apis} to fulfil this need for both synchronous and asynchronous preprocessing.
     *
     * The interceptors are service factories that are registered with the $httpProvider by
     * adding them to the `$httpProvider.responseInterceptors` array. The factory is called and
     * injected with dependencies (if specified) and returns the interceptor  — a function that
     * takes a {@link ng.$q promise} and returns the original or a new promise.
     *
     * <pre>
     *   // register the interceptor as a service
     *   $provide.factory('myHttpInterceptor', function($q, dependency1, dependency2) {
     *     return function(promise) {
     *       return promise.then(function(response) {
     *         // do something on success
     *       }, function(response) {
     *         // do something on error
     *         if (canRecover(response)) {
     *           return responseOrNewPromise
     *         }
     *         return $q.reject(response);
     *       });
     *     }
     *   });
     *
     *   $httpProvider.responseInterceptors.push('myHttpInterceptor');
     *
     *
     *   // register the interceptor via an anonymous factory
     *   $httpProvider.responseInterceptors.push(function($q, dependency1, dependency2) {
     *     return function(promise) {
     *       // same as above
     *     }
     *   });
     * </pre>
     *
     *
     * # Security Considerations
     *
     * When designing web applications, consider security threats from:
     *
     * - {@link http://haacked.com/archive/2008/11/20/anatomy-of-a-subtle-json-vulnerability.aspx
     *   JSON vulnerability}
     * - {@link http://en.wikipedia.org/wiki/Cross-site_request_forgery XSRF}
     *
     * Both server and the client must cooperate in order to eliminate these threats. Angular comes
     * pre-configured with strategies that address these issues, but for this to work backend server
     * cooperation is required.
     *
     * ## JSON Vulnerability Protection
     *
     * A {@link http://haacked.com/archive/2008/11/20/anatomy-of-a-subtle-json-vulnerability.aspx
     * JSON vulnerability} allows third party website to turn your JSON resource URL into
     * {@link http://en.wikipedia.org/wiki/JSONP JSONP} request under some conditions. To
     * counter this your server can prefix all JSON requests with following string `")]}',\n"`.
     * Angular will automatically strip the prefix before processing it as JSON.
     *
     * For example if your server needs to return:
     * <pre>
     * ['one','two']
     * </pre>
     *
     * which is vulnerable to attack, your server can return:
     * <pre>
     * )]}',
     * ['one','two']
     * </pre>
     *
     * Angular will strip the prefix, before processing the JSON.
     *
     *
     * ## Cross Site Request Forgery (XSRF) Protection
     *
     * {@link http://en.wikipedia.org/wiki/Cross-site_request_forgery XSRF} is a technique by which
     * an unauthorized site can gain your user's private data. Angular provides a mechanism
     * to counter XSRF. When performing XHR requests, the $http service reads a token from a cookie
     * (by default, `XSRF-TOKEN`) and sets it as an HTTP header (`X-XSRF-TOKEN`). Since only
     * JavaScript that runs on your domain could read the cookie, your server can be assured that
     * the XHR came from JavaScript running on your domain. The header will not be set for
     * cross-domain requests.
     *
     * To take advantage of this, your server needs to set a token in a JavaScript readable session
     * cookie called `XSRF-TOKEN` on the first HTTP GET request. On subsequent XHR requests the
     * server can verify that the cookie matches `X-XSRF-TOKEN` HTTP header, and therefore be sure
     * that only JavaScript running on your domain could have sent the request. The token must be
     * unique for each user and must be verifiable by the server (to prevent the JavaScript from making
     * up its own tokens). We recommend that the token is a digest of your site's authentication
     * cookie with a {@link https://en.wikipedia.org/wiki/Salt_(cryptography) salt} for added security.
     *
     * The name of the headers can be specified using the xsrfHeaderName and xsrfCookieName
     * properties of either $httpProvider.defaults, or the per-request config object.
     *
     *
     * @param {object} config Object describing the request to be made and how it should be
     *    processed. The object has following properties:
     *
     *    - **method** – `{string}` – HTTP method (e.g. 'GET', 'POST', etc)
     *    - **url** – `{string}` – Absolute or relative URL of the resource that is being requested.
     *    - **params** – `{Object.<string|Object>}` – Map of strings or objects which will be turned to
     *      `?key1=value1&key2=value2` after the url. If the value is not a string, it will be JSONified.
     *    - **data** – `{string|Object}` – Data to be sent as the request message data.
     *    - **headers** – `{Object}` – Map of strings or functions which return strings representing
     *      HTTP headers to send to the server. If the return value of a function is null, the header will
     *      not be sent.
     *    - **xsrfHeaderName** – `{string}` – Name of HTTP header to populate with the XSRF token.
     *    - **xsrfCookieName** – `{string}` – Name of cookie containing the XSRF token.
     *    - **transformRequest** – `{function(data, headersGetter)|Array.<function(data, headersGetter)>}` –
     *      transform function or an array of such functions. The transform function takes the http
     *      request body and headers and returns its transformed (typically serialized) version.
     *    - **transformResponse** – `{function(data, headersGetter)|Array.<function(data, headersGetter)>}` –
     *      transform function or an array of such functions. The transform function takes the http
     *      response body and headers and returns its transformed (typically deserialized) version.
     *    - **cache** – `{boolean|Cache}` – If true, a default $http cache will be used to cache the
     *      GET request, otherwise if a cache instance built with
     *      {@link ng.$cacheFactory $cacheFactory}, this cache will be used for
     *      caching.
     *    - **timeout** – `{number|Promise}` – timeout in milliseconds, or {@link ng.$q promise}
     *      that should abort the request when resolved.
     *    - **withCredentials** - `{boolean}` - whether to to set the `withCredentials` flag on the
     *      XHR object. See {@link https://developer.mozilla.org/en/http_access_control#section_5
     *      requests with credentials} for more information.
     *    - **responseType** - `{string}` - see {@link
     *      https://developer.mozilla.org/en-US/docs/DOM/XMLHttpRequest#responseType requestType}.
     *
     * @returns {HttpPromise} Returns a {@link ng.$q promise} object with the
     *   standard `then` method and two http specific methods: `success` and `error`. The `then`
     *   method takes two arguments a success and an error callback which will be called with a
     *   response object. The `success` and `error` methods take a single argument - a function that
     *   will be called when the request succeeds or fails respectively. The arguments passed into
     *   these functions are destructured representation of the response object passed into the
     *   `then` method. The response object has these properties:
     *
     *   - **data** – `{string|Object}` – The response body transformed with the transform functions.
     *   - **status** – `{number}` – HTTP status code of the response.
     *   - **headers** – `{function([headerName])}` – Header getter function.
     *   - **config** – `{Object}` – The configuration object that was used to generate the request.
     *
     * @property {Array.<Object>} pendingRequests Array of config objects for currently pending
     *   requests. This is primarily meant to be used for debugging purposes.
     *
     *
     * @example
      <example>
        <file name="index.html">
          <div ng-controller="FetchCtrl">
            <select ng-model="method">
              <option>GET</option>
              <option>JSONP</option>
            </select>
            <input type="text" ng-model="url" size="80"/>
            <button ng-click="fetch()">fetch</button><br>
            <button ng-click="updateModel('GET', 'http-hello.html')">Sample GET</button>
            <button ng-click="updateModel('JSONP', 'http://angularjs.org/greet.php?callback=JSON_CALLBACK&name=Super%20Hero')">Sample JSONP</button>
            <button ng-click="updateModel('JSONP', 'http://angularjs.org/doesntexist&callback=JSON_CALLBACK')">Invalid JSONP</button>
            <pre>http status code: {{status}}</pre>
            <pre>http response data: {{data}}</pre>
          </div>
        </file>
        <file name="script.js">
          function FetchCtrl($scope, $http, $templateCache) {
            $scope.method = 'GET';
            $scope.url = 'http-hello.html';

            $scope.fetch = function() {
              $scope.code = null;
              $scope.response = null;

              $http({method: $scope.method, url: $scope.url, cache: $templateCache}).
                success(function(data, status) {
                  $scope.status = status;
                  $scope.data = data;
                }).
                error(function(data, status) {
                  $scope.data = data || "Request failed";
                  $scope.status = status;
              });
            };

            $scope.updateModel = function(method, url) {
              $scope.method = method;
              $scope.url = url;
            };
          }
        </file>
        <file name="http-hello.html">
          Hello, $http!
        </file>
        <file name="scenario.js">
          it('should make an xhr GET request', function() {
            element(':button:contains("Sample GET")').click();
            element(':button:contains("fetch")').click();
            expect(binding('status')).toBe('200');
            expect(binding('data')).toMatch(/Hello, \$http!/);
          });

          it('should make a JSONP request to angularjs.org', function() {
            element(':button:contains("Sample JSONP")').click();
            element(':button:contains("fetch")').click();
            expect(binding('status')).toBe('200');
            expect(binding('data')).toMatch(/Super Hero!/);
          });

          it('should make JSONP request to invalid URL and invoke the error handler',
              function() {
            element(':button:contains("Invalid JSONP")').click();
            element(':button:contains("fetch")').click();
            expect(binding('status')).toBe('0');
            expect(binding('data')).toBe('Request failed');
          });
        </file>
      </example>
     */
    function $http(requestConfig) {
      var config = {
        transformRequest: defaults.transformRequest,
        transformResponse: defaults.transformResponse
      };
      var headers = mergeHeaders(requestConfig);

      extend(config, requestConfig);
      config.headers = headers;
      config.method = uppercase(config.method);

      var xsrfValue = $$urlUtils.isSameOrigin(config.url)
          ? $browser.cookies()[config.xsrfCookieName || defaults.xsrfCookieName]
          : undefined;
      if (xsrfValue) {
        headers[(config.xsrfHeaderName || defaults.xsrfHeaderName)] = xsrfValue;
      }


      var serverRequest = function(config) {
        headers = config.headers;
        var reqData = transformData(config.data, headersGetter(headers), config.transformRequest);

        // strip content-type if data is undefined
        if (isUndefined(config.data)) {
          forEach(headers, function(value, header) {
            if (lowercase(header) === 'content-type') {
                delete headers[header];
            }
          });
        }

        if (isUndefined(config.withCredentials) && !isUndefined(defaults.withCredentials)) {
          config.withCredentials = defaults.withCredentials;
        }

        // send request
        return sendReq(config, reqData, headers).then(transformResponse, transformResponse);
      };

      var chain = [serverRequest, undefined];
      var promise = $q.when(config);

      // apply interceptors
      forEach(reversedInterceptors, function(interceptor) {
        if (interceptor.request || interceptor.requestError) {
          chain.unshift(interceptor.request, interceptor.requestError);
        }
        if (interceptor.response || interceptor.responseError) {
          chain.push(interceptor.response, interceptor.responseError);
        }
      });

      while(chain.length) {
        var thenFn = chain.shift();
        var rejectFn = chain.shift();

        promise = promise.then(thenFn, rejectFn);
      }

      promise.success = function(fn) {
        promise.then(function(response) {
          fn(response.data, response.status, response.headers, config);
        });
        return promise;
      };

      promise.error = function(fn) {
        promise.then(null, function(response) {
          fn(response.data, response.status, response.headers, config);
        });
        return promise;
      };

      return promise;

      function transformResponse(response) {
        // make a copy since the response must be cacheable
        var resp = extend({}, response, {
          data: transformData(response.data, response.headers, config.transformResponse)
        });
        return (isSuccess(response.status))
          ? resp
          : $q.reject(resp);
      }

      function mergeHeaders(config) {
        var defHeaders = defaults.headers,
            reqHeaders = extend({}, config.headers),
            defHeaderName, lowercaseDefHeaderName, reqHeaderName;

        defHeaders = extend({}, defHeaders.common, defHeaders[lowercase(config.method)]);

        // execute if header value is function
        execHeaders(defHeaders);
        execHeaders(reqHeaders);

        // using for-in instead of forEach to avoid unecessary iteration after header has been found
        defaultHeadersIteration:
        for (defHeaderName in defHeaders) {
          lowercaseDefHeaderName = lowercase(defHeaderName);

          for (reqHeaderName in reqHeaders) {
            if (lowercase(reqHeaderName) === lowercaseDefHeaderName) {
              continue defaultHeadersIteration;
            }
          }

          reqHeaders[defHeaderName] = defHeaders[defHeaderName];
        }

        return reqHeaders;

        function execHeaders(headers) {
          var headerContent;

          forEach(headers, function(headerFn, header) {
            if (isFunction(headerFn)) {
              headerContent = headerFn();
              if (headerContent != null) {
                headers[header] = headerContent;
              } else {
                delete headers[header];
              }
            }
          });
        }
      }
    }

    $http.pendingRequests = [];

    /**
     * @ngdoc method
     * @name ng.$http#get
     * @methodOf ng.$http
     *
     * @description
     * Shortcut method to perform `GET` request.
     *
     * @param {string} url Relative or absolute URL specifying the destination of the request
     * @param {Object=} config Optional configuration object
     * @returns {HttpPromise} Future object
     */

    /**
     * @ngdoc method
     * @name ng.$http#delete
     * @methodOf ng.$http
     *
     * @description
     * Shortcut method to perform `DELETE` request.
     *
     * @param {string} url Relative or absolute URL specifying the destination of the request
     * @param {Object=} config Optional configuration object
     * @returns {HttpPromise} Future object
     */

    /**
     * @ngdoc method
     * @name ng.$http#head
     * @methodOf ng.$http
     *
     * @description
     * Shortcut method to perform `HEAD` request.
     *
     * @param {string} url Relative or absolute URL specifying the destination of the request
     * @param {Object=} config Optional configuration object
     * @returns {HttpPromise} Future object
     */

    /**
     * @ngdoc method
     * @name ng.$http#jsonp
     * @methodOf ng.$http
     *
     * @description
     * Shortcut method to perform `JSONP` request.
     *
     * @param {string} url Relative or absolute URL specifying the destination of the request.
     *                     Should contain `JSON_CALLBACK` string.
     * @param {Object=} config Optional configuration object
     * @returns {HttpPromise} Future object
     */
    createShortMethods('get', 'delete', 'head', 'jsonp');

    /**
     * @ngdoc method
     * @name ng.$http#post
     * @methodOf ng.$http
     *
     * @description
     * Shortcut method to perform `POST` request.
     *
     * @param {string} url Relative or absolute URL specifying the destination of the request
     * @param {*} data Request content
     * @param {Object=} config Optional configuration object
     * @returns {HttpPromise} Future object
     */

    /**
     * @ngdoc method
     * @name ng.$http#put
     * @methodOf ng.$http
     *
     * @description
     * Shortcut method to perform `PUT` request.
     *
     * @param {string} url Relative or absolute URL specifying the destination of the request
     * @param {*} data Request content
     * @param {Object=} config Optional configuration object
     * @returns {HttpPromise} Future object
     */
    createShortMethodsWithData('post', 'put');

        /**
         * @ngdoc property
         * @name ng.$http#defaults
         * @propertyOf ng.$http
         *
         * @description
         * Runtime equivalent of the `$httpProvider.defaults` property. Allows configuration of
         * default headers, withCredentials as well as request and response transformations.
         *
         * See "Setting HTTP Headers" and "Transforming Requests and Responses" sections above.
         */
    $http.defaults = defaults;


    return $http;


    function createShortMethods(names) {
      forEach(arguments, function(name) {
        $http[name] = function(url, config) {
          return $http(extend(config || {}, {
            method: name,
            url: url
          }));
        };
      });
    }


    function createShortMethodsWithData(name) {
      forEach(arguments, function(name) {
        $http[name] = function(url, data, config) {
          return $http(extend(config || {}, {
            method: name,
            url: url,
            data: data
          }));
        };
      });
    }


    /**
     * Makes the request.
     *
     * !!! ACCESSES CLOSURE VARS:
     * $httpBackend, defaults, $log, $rootScope, defaultCache, $http.pendingRequests
     */
    function sendReq(config, reqData, reqHeaders) {
      var deferred = $q.defer(),
          promise = deferred.promise,
          cache,
          cachedResp,
          url = buildUrl(config.url, config.params);

      $http.pendingRequests.push(config);
      promise.then(removePendingReq, removePendingReq);


      if ((config.cache || defaults.cache) && config.cache !== false && config.method == 'GET') {
        cache = isObject(config.cache) ? config.cache
              : isObject(defaults.cache) ? defaults.cache
              : defaultCache;
      }

      if (cache) {
        cachedResp = cache.get(url);
        if (cachedResp) {
          if (cachedResp.then) {
            // cached request has already been sent, but there is no response yet
            cachedResp.then(removePendingReq, removePendingReq);
            return cachedResp;
          } else {
            // serving from cache
            if (isArray(cachedResp)) {
              resolvePromise(cachedResp[1], cachedResp[0], copy(cachedResp[2]));
            } else {
              resolvePromise(cachedResp, 200, {});
            }
          }
        } else {
          // put the promise for the non-transformed response into cache as a placeholder
          cache.put(url, promise);
        }
      }

      // if we won't have the response in cache, send the request to the backend
      if (!cachedResp) {
        $httpBackend(config.method, url, reqData, done, reqHeaders, config.timeout,
            config.withCredentials, config.responseType);
      }

      return promise;


      /**
       * Callback registered to $httpBackend():
       *  - caches the response if desired
       *  - resolves the raw $http promise
       *  - calls $apply
       */
      function done(status, response, headersString) {
        if (cache) {
          if (isSuccess(status)) {
            cache.put(url, [status, response, parseHeaders(headersString)]);
          } else {
            // remove promise from the cache
            cache.remove(url);
          }
        }

        resolvePromise(response, status, headersString);
        if (!$rootScope.$$phase) $rootScope.$apply();
      }


      /**
       * Resolves the raw $http promise.
       */
      function resolvePromise(response, status, headers) {
        // normalize internal statuses to 0
        status = Math.max(status, 0);

        (isSuccess(status) ? deferred.resolve : deferred.reject)({
          data: response,
          status: status,
          headers: headersGetter(headers),
          config: config
        });
      }


      function removePendingReq() {
        var idx = indexOf($http.pendingRequests, config);
        if (idx !== -1) $http.pendingRequests.splice(idx, 1);
      }
    }


    function buildUrl(url, params) {
          if (!params) return url;
          var parts = [];
          forEachSorted(params, function(value, key) {
            if (value == null || value == undefined) return;
            if (!isArray(value)) value = [value];

            forEach(value, function(v) {
              if (isObject(v)) {
                v = toJson(v);
              }
              parts.push(encodeUriQuery(key) + '=' +
                         encodeUriQuery(v));
            });
          });
          return url + ((url.indexOf('?') == -1) ? '?' : '&') + parts.join('&');
        }


  }];
}
