// Copyright 2011 The Closure Library Authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS-IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.


/**
 * @fileoverview Offered as an alternative to XhrIo as a way for making requests
 * via XMLHttpRequest.  Instead of mirroring the XHR interface and exposing
 * events, results are used as a way to pass a "promise" of the response to
 * interested parties.
 *
 */

goog.provide('goog.labs.net.xhr');
goog.provide('goog.labs.net.xhr.Error');
goog.provide('goog.labs.net.xhr.HttpError');
goog.provide('goog.labs.net.xhr.TimeoutError');

goog.require('goog.debug.Error');
goog.require('goog.json');
goog.require('goog.labs.result');
goog.require('goog.net.HttpStatus');
goog.require('goog.net.XmlHttp');
goog.require('goog.string');
goog.require('goog.uri.utils');



goog.scope(function() {
var _ = goog.labs.net.xhr;
var Result = goog.labs.result.Result;
var SimpleResult = goog.labs.result.SimpleResult;
var Wait = goog.labs.result.wait;
var HttpStatus = goog.net.HttpStatus;


/**
 * Configuration options for an XMLHttpRequest.
 * - headers: map of header key/value pairs.
 * - timeoutMs: number of milliseconds after which the request will be timed
 *      out by the client. Default is to allow the browser to handle timeouts.
 * - withCredentials: whether user credentials are to be included in a
 *      cross-origin request.  See:
 *      http://dev.w3.org/2006/webapi/XMLHttpRequest-2/#the-withcredentials-attribute
 * - mimeType: allows the caller to override the content-type and charset for
 *      the request, which is useful when requesting binary data.  See:
 *      http://dev.w3.org/2006/webapi/XMLHttpRequest-2/#dom-xmlhttprequest-overridemimetype
 * - xssiPrefix: Prefix used for protecting against XSSI attacks, which should
 *      be removed before parsing the response as JSON.
 *
 * @typedef {{
 *   headers: (Object.<string>|undefined),
 *   timeoutMs: (number|undefined),
 *   withCredentials: (boolean|undefined),
 *   mimeType: (string|undefined),
 *   xssiPrefix: (string|undefined)
 * }}
 */
_.Options;


/**
 * Defines the types that are allowed as post data.
 * @typedef {(ArrayBuffer|Blob|Document|FormData|null|string|undefined)}
 */
_.PostData;


/**
 * The Content-Type HTTP header name.
 * @type {string}
 */
_.CONTENT_TYPE_HEADER = 'Content-Type';


/**
 * The Content-Type HTTP header value for a url-encoded form.
 * @type {string}
 */
_.FORM_CONTENT_TYPE = 'application/x-www-form-urlencoded;charset=utf-8';


/**
 * Sends a get request, returning a transformed result which will be resolved
 * with the response text once the request completes.
 *
 * @param {string} url The URL to request.
 * @param {_.Options=} opt_options Configuration options for the request.
 * @return {!Result} A result object that will be resolved
 *     with the response text once the request finishes.
 */
_.get = function(url, opt_options) {
  var result = _.send('GET', url, null, opt_options);
  var transformedResult = goog.labs.result.transform(result,
                                                     _.getResponseText_);
  return transformedResult;
};


/**
 * Sends a post request, returning a transformed result which will be resolved
 * with the response text once the request completes.
 *
 * @param {string} url The URL to request.
 * @param {_.PostData} data The body of the post request.
 * @param {_.Options=} opt_options Configuration options for the request.
 * @return {!Result} A result object that will be resolved
 *     with the response text once the request finishes.
 */
_.post = function(url, data, opt_options) {
  var result = _.send('POST', url, data, opt_options);
  var transformedResult = goog.labs.result.transform(result,
                                                     _.getResponseText_);
  return transformedResult;
};


/**
 * Sends a get request, returning a result which will be resolved with
 * the parsed response text once the request completes.
 *
 * @param {string} url The URL to request.
 * @param {_.Options=} opt_options Configuration options for the request.
 * @return {!Result} A result object that will be resolved
 *     with the response JSON once the request finishes.
 */
_.getJson = function(url, opt_options) {
  var result = _.send('GET', url, null, opt_options);
  var transformedResult = _.addJsonParsingCallbacks_(result, opt_options);
  return transformedResult;
};


/**
 * Sends a post request, returning a result which will be resolved with
 * the parsed response text once the request completes.
 *
 * @param {string} url The URL to request.
 * @param {_.PostData} data The body of the post request.
 * @param {_.Options=} opt_options Configuration options for the request.
 * @return {!Result} A result object that will be resolved
 *     with the response JSON once the request finishes.
 */
_.postJson = function(url, data, opt_options) {
  var result = _.send('POST', url, data, opt_options);
  var transformedResult = _.addJsonParsingCallbacks_(result, opt_options);
  return transformedResult;
};


/**
 * Sends a request using XMLHttpRequest and returns a result.
 *
 * @param {string} method The HTTP method for the request.
 * @param {string} url The URL to request.
 * @param {_.PostData} data The body of the post request.
 * @param {_.Options=} opt_options Configuration options for the request.
 * @return {!Result} A result object that will be resolved
 *     with the XHR object as it's value when the request finishes.
 */
_.send = function(method, url, data, opt_options) {

  var result = new SimpleResult();

  // When the deferred is cancelled, we abort the XHR.  We want to make sure
  // the readystatechange event still fires, so it can do the timeout
  // cleanup, however we don't want the callback or errback to be called
  // again.  Thus the slight ugliness here.  If results were pushed into
  // makeRequest, this could become a lot cleaner but we want an option for
  // people not to include goog.labs.result.Result.
  goog.labs.result.waitOnError(result, function(result) {
    if (result.isCanceled()) {
      xhr.abort();
      xhr.onreadystatechange = goog.nullFunction;
    }
  });

  function callback(data) {
    result.setValue(data);
  }

  function errback(err) {
    result.setError(err);
  }

  var xhr = _.makeRequest(method, url, data, opt_options, callback, errback);

  return result;
};


/**
 * Creates a new XMLHttpRequest and initiates a request.
 *
 * @param {string} method The HTTP method for the request.
 * @param {string} url The URL to request.
 * @param {_.PostData} data The body of the post request, unless the content
 *    type is explicitly set in the Options, then it will default to form
 *    urlencoded.
 * @param {_.Options=} opt_options Configuration options for the request.
 * @param {function(XMLHttpRequest)=} opt_callback Optional callback to call
 *     when the request completes.
 * @param {function(Error)=} opt_errback Optional callback to call
 *     when there is an error.
 * @return {!XMLHttpRequest} The new XMLHttpRequest.
 */
_.makeRequest = function(
    method, url, data, opt_options, opt_callback, opt_errback) {
  var options = opt_options || {};
  var callback = opt_callback || goog.nullFunction;
  var errback = opt_errback || goog.nullFunction;
  var timer;

  var xhr = /** @type {!XMLHttpRequest} */ (goog.net.XmlHttp());
  try {
    xhr.open(method, url, true);
  } catch (e) {
    // XMLHttpRequest.open may throw when 'open' is called, for example, IE7
    // throws "Access Denied" for cross-origin requests.
    errback(new _.Error('Error opening XHR: ' + e.message, url, xhr));
    return xhr;
  }

  // So sad that IE doesn't support onload and onerror.
  xhr.onreadystatechange = function() {
    if (xhr.readyState == goog.net.XmlHttp.ReadyState.COMPLETE) {
      window.clearTimeout(timer);
      if (HttpStatus.isSuccess(xhr.status) ||
          xhr.status === 0 && !_.isEffectiveSchemeHttp_(url)) {
        callback(xhr);
      } else {
        errback(new _.HttpError(xhr.status, url, xhr));
      }
    }
  };

  // Set the headers.
  var contentTypeIsSet = false;
  if (options.headers) {
    for (var key in options.headers) {
      xhr.setRequestHeader(key, options.headers[key]);
    }
    contentTypeIsSet = _.CONTENT_TYPE_HEADER in options.headers;
  }

  // If a content type hasn't been set, default to form-urlencoded/UTF8 for
  // POSTs.  This is because some proxies have been known to reject posts
  // without a content-type.
  if (method == 'POST' && !contentTypeIsSet) {
    xhr.setRequestHeader(_.CONTENT_TYPE_HEADER, _.FORM_CONTENT_TYPE);
  }

  // Set whether to pass cookies on cross-domain requests (if applicable).
  // @see http://dev.w3.org/2006/webapi/XMLHttpRequest-2/#the-withcredentials-attribute
  if (options.withCredentials) {
    xhr.withCredentials = options.withCredentials;
  }

  // Allow the request to override the mime type, useful for getting binary
  // data from the server.  e.g. 'text/plain; charset=x-user-defined'.
  // @see http://dev.w3.org/2006/webapi/XMLHttpRequest-2/#dom-xmlhttprequest-overridemimetype
  if (options.mimeType) {
    xhr.overrideMimeType(options.mimeType);
  }

  // Handle timeouts, if requested.
  if (options.timeoutMs > 0) {
    timer = window.setTimeout(function() {
      // Clear event listener before aborting so the errback will not be
      // called twice.
      xhr.onreadystatechange = goog.nullFunction;
      xhr.abort();
      errback(new _.TimeoutError(url, xhr));
    }, options.timeoutMs);
  }

  // Trigger the send.
  try {
    xhr.send(data);
  } catch (e) {
    // XMLHttpRequest.send is known to throw on some versions of FF, for example
    // if a cross-origin request is disallowed.
    errback(new _.Error('Error sending XHR: ' + e.message, url, xhr));
  }

  return xhr;
};


/**
 * @param {string} url The URL to test.
 * @return {boolean} Whether the effective scheme is HTTP or HTTPs.
 * @private
 */
_.isEffectiveSchemeHttp_ = function(url) {
  var scheme = goog.uri.utils.getEffectiveScheme(url);
  // NOTE(user): Empty-string is for the case under FF3.5 when the location
  // is not defined inside a web worker.
  return scheme == 'http' || scheme == 'https' || scheme == '';
};


/**
 * Returns the response text of an XHR object.  Intended to be called when
 * the result resolves.
 *
 * @param {!XMLHttpRequest} xhr The XHR object.
 * @return {string} The response text.
 * @private
 */
_.getResponseText_ = function(xhr) {
  return xhr.responseText;
};


/**
 * Transforms a result, parsing the JSON in the original result value's
 * responseText. The transformed result's value is a javascript object.
 * Parse errors resolve the transformed result in an error.
 *
 * @param {!Result} result The result to wait on.
 * @param {_.Options|undefined} options The options object.
 *
 * @return {!Result} The transformed result.
 * @private
 */
_.addJsonParsingCallbacks_ = function(result, options) {
  var resultWithResponseText = goog.labs.result.transform(result,
                                                          _.getResponseText_);
  var prefixStrippedResult = resultWithResponseText;
  if (options && options.xssiPrefix) {
    prefixStrippedResult = goog.labs.result.transform(resultWithResponseText,
        goog.partial(_.stripXssiPrefix_, options.xssiPrefix));
  }

  var jsonParsedResult = goog.labs.result.transform(prefixStrippedResult,
                                                    goog.json.parse);
  return jsonParsedResult;
};


/**
 * Strips the XSSI prefix from the input string.
 *
 * @param {string} prefix The XSSI prefix.
 * @param {string} string The string to strip the prefix from.
 * @return {string} The input string without the prefix.
 * @private
 */
_.stripXssiPrefix_ = function(prefix, string) {
  if (goog.string.startsWith(string, prefix)) {
    string = string.substring(prefix.length);
  }
  return string;
};



/**
 * Generic error that may occur during a request.
 *
 * @param {string} message The error message.
 * @param {string} url The URL that was being requested.
 * @param {!XMLHttpRequest} xhr The XMLHttpRequest that failed.
 * @extends {goog.debug.Error}
 * @constructor
 */
_.Error = function(message, url, xhr) {
  goog.base(this, message + ', url=' + url);

  /**
   * The URL that was requested.
   * @type {string}
   */
  this.url = url;

  /**
   * The XMLHttpRequest corresponding with the failed request.
   * @type {!XMLHttpRequest}
   */
  this.xhr = xhr;
};
goog.inherits(_.Error, goog.debug.Error);


/** @override */
_.Error.prototype.name = 'XhrError';



/**
 * Class for HTTP errors.
 *
 * @param {number} status The HTTP status code of the response.
 * @param {string} url The URL that was being requested.
 * @param {!XMLHttpRequest} xhr The XMLHttpRequest that failed.
 * @extends {_.Error}
 * @constructor
 */
_.HttpError = function(status, url, xhr) {
  goog.base(this, 'Request Failed, status=' + status, url, xhr);

  /**
   * The HTTP status code for the error.
   * @type {number}
   */
  this.status = status;
};
goog.inherits(_.HttpError, _.Error);


/** @override */
_.HttpError.prototype.name = 'XhrHttpError';



/**
 * Class for Timeout errors.
 *
 * @param {string} url The URL that timed out.
 * @param {!XMLHttpRequest} xhr The XMLHttpRequest that failed.
 * @extends {_.Error}
 * @constructor
 */
_.TimeoutError = function(url, xhr) {
  goog.base(this, 'Request timed out', url, xhr);
};
goog.inherits(_.TimeoutError, _.Error);


/** @override */
_.TimeoutError.prototype.name = 'XhrTimeoutError';

});  // goog.scope
