SGH / COMPONENTS

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<link rel="import" href="../polymer/polymer.html">
<link rel="import" href="../promise-polyfill/promise-polyfill-lite.html">

<!--
iron-request can be used to perform XMLHttpRequests.

    <iron-request id="xhr"></iron-request>
    ...
    this.$.xhr.send({url: url, params: params});
-->
<script>
  'use strict'

  Polymer({
    is: 'iron-request',

    hostAttributes: {
      hidden: true
    },

    properties: {

      /**
       * A reference to the XMLHttpRequest instance used to generate the
       * network request.
       *
       * @type {XMLHttpRequest}
       */
      xhr: {
        type: Object,
        notify: true,
        readOnly: true,
        value: function() {
          return new XMLHttpRequest();
        }
      },

      /**
       * A reference to the parsed response body, if the `xhr` has completely
       * resolved.
       *
       * @type {*}
       * @default null
       */
      response: {
        type: Object,
        notify: true,
        readOnly: true,
        value: function() {
         return null;
        }
      },

      /**
       * A reference to the status code, if the `xhr` has completely resolved.
       */
      status: {
        type: Number,
        notify: true,
        readOnly: true,
        value: 0
      },

      /**
       * A reference to the status text, if the `xhr` has completely resolved.
       */
      statusText: {
        type: String,
        notify: true,
        readOnly: true,
        value: ''
      },

      /**
       * A promise that resolves when the `xhr` response comes back, or rejects
       * if there is an error before the `xhr` completes.
       *
       * @type {Promise}
       */
      completes: {
        type: Object,
        readOnly: true,
        notify: true,
        value: function() {
          return new Promise(function (resolve, reject) {
            this.resolveCompletes = resolve;
            this.rejectCompletes = reject;
          }.bind(this));
        }
      },

      /**
       * An object that contains progress information emitted by the XHR if
       * available.
       *
       * @default {}
       */
      progress: {
        type: Object,
        notify: true,
        readOnly: true,
        value: function() {
          return {};
        }
      },

      /**
       * Aborted will be true if an abort of the request is attempted.
       */
      aborted: {
        type: Boolean,
        notify: true,
        readOnly: true,
        value: false,
      },

      /**
       * Errored will be true if the browser fired an error event from the
       * XHR object (mainly network errors).
       */
      errored: {
        type: Boolean,
        notify: true,
        readOnly: true,
        value: false
      },

      /**
       * TimedOut will be true if the XHR threw a timeout event.
       */
      timedOut: {
        type: Boolean,
        notify: true,
        readOnly: true,
        value: false
      }
    },

    /**
     * Succeeded is true if the request succeeded. The request succeeded if it
     * loaded without error, wasn't aborted, and the status code is ≥ 200, and
     * < 300, or if the status code is 0.
     *
     * The status code 0 is accepted as a success because some schemes - e.g.
     * file:// - don't provide status codes.
     *
     * @return {boolean}
     */
    get succeeded() {
      if (this.errored || this.aborted || this.timedOut) {
        return false;
      }
      var status = this.xhr.status || 0;

      // Note: if we are using the file:// protocol, the status code will be 0
      // for all outcomes (successful or otherwise).
      return status === 0 ||
        (status >= 200 && status < 300);
    },

    /**
     * Sends an HTTP request to the server and returns the XHR object.
     *
     * @param {{
     *   url: string,
     *   method: (string|undefined),
     *   async: (boolean|undefined),
     *   body: (ArrayBuffer|ArrayBufferView|Blob|Document|FormData|null|string|undefined|Object),
     *   headers: (Object|undefined),
     *   handleAs: (string|undefined),
     *   withCredentials: (boolean|undefined)}} options -
     *     url The url to which the request is sent.
     *     method The HTTP method to use, default is GET.
     *     async By default, all requests are sent asynchronously. To send synchronous requests,
     *         set to true.
     *     body The content for the request body for POST method.
     *     headers HTTP request headers. All keys must be lower case.
     *     handleAs The response type. Default is 'text'.
     *     withCredentials Whether or not to send credentials on the request. Default is false.
     *   timeout: (Number|undefined)
     * @return {Promise}
     */
    send: function (options) {
      var xhr = this.xhr;

      if (xhr.readyState > 0) {
        return null;
      }

      xhr.addEventListener('progress', function (progress) {
        this._setProgress({
          lengthComputable: progress.lengthComputable,
          loaded: progress.loaded,
          total: progress.total
        });
      }.bind(this))

      xhr.addEventListener('error', function (error) {
        this._setErrored(true);
        this._updateStatus();
        this.rejectCompletes(error);
      }.bind(this));

      xhr.addEventListener('timeout', function (error) {
        this._setTimedOut(true);
        this._updateStatus();
        this.rejectCompletes(error);
      }.bind(this));

      xhr.addEventListener('abort', function () {
        this._updateStatus();
        this.rejectCompletes(new Error('Request aborted.'));
      }.bind(this));

      // Called after all of the above.
      xhr.addEventListener('loadend', function () {
        this._updateStatus();

        if (!this.succeeded) {
          this.rejectCompletes(new Error('The request failed with status code: ' + this.xhr.status));
          return;
        }

        this._setResponse(this.parseResponse());
        this.resolveCompletes(this);
      }.bind(this));

      this.url = options.url;
      xhr.open(
        options.method || 'GET',
        options.url,
        options.async !== false
      );

      var acceptType = {
        'json': 'application/json',
        'text': 'text/plain',
        'html': 'text/html',
        'xml': 'application/xml',
        'arraybuffer': 'application/octet-stream'
      }[options.handleAs];
      var headers = options.headers || {};
      if (acceptType && !headers['accept']) {
        headers['accept'] = acceptType;
      }
      Object.keys(headers).forEach(function (requestHeader) {
        if (/[A-Z]/.test(requestHeader)) {
          console.error('Headers must be lower case, got', requestHeader);
        }
        xhr.setRequestHeader(
          requestHeader,
          headers[requestHeader]
        );
      }, this);

      var body = this._encodeBodyObject(options.body, headers['content-type']);

      // In IE, `xhr.responseType` is an empty string when the response
      // returns. Hence, caching it as `xhr._responseType`.
      if (options.async !== false) {
        xhr.responseType = xhr._responseType = (options.handleAs || 'text');
      }
      xhr.withCredentials = !!options.withCredentials;
      xhr.timeout = options.timeout;



      xhr.send(
        /** @type {ArrayBuffer|ArrayBufferView|Blob|Document|FormData|
                   null|string|undefined} */
        (body));

      return this.completes;
    },

    /**
     * Attempts to parse the response body of the XHR. If parsing succeeds,
     * the value returned will be deserialized based on the `responseType`
     * set on the XHR.
     *
     * @return {*} The parsed response,
     * or undefined if there was an empty response or parsing failed.
     */
    parseResponse: function () {
      var xhr = this.xhr;
      var responseType = xhr.responseType || xhr._responseType;
      var preferResponseText = !this.xhr.responseType;

      try {
        switch (responseType) {
          case 'json':
            // If the xhr object doesn't have a natural `xhr.responseType`,
            // we can assume that the browser hasn't parsed the response for us,
            // and so parsing is our responsibility. Likewise if response is
            // undefined, as there's no way to encode undefined in JSON.
            if (preferResponseText || xhr.response === undefined) {
              // Try to emulate the JSON section of the response body section of
              // the spec: https://xhr.spec.whatwg.org/#response-body
              // That is to say, we try to parse as JSON, but if anything goes
              // wrong return null.
              try {
                return JSON.parse(xhr.responseText);;
              } catch (_) {
                return null;
              }
            }

            return xhr.response;
          case 'xml':
            return xhr.responseXML;
          case 'blob':
          case 'document':
          case 'arraybuffer':
            return xhr.response;
          case 'text':
          default:
            return xhr.responseText;
        }
      } catch (e) {
        this.rejectCompletes(new Error('Could not parse response. ' + e.message));
      }
    },

    /**
     * Aborts the request.
     */
    abort: function () {
      this._setAborted(true);
      this.xhr.abort();
    },

    /**
     * @param {*} body The given body of the request to try and encode.
     * @param {?string} contentType The given content type, to infer an encoding
     *     from.
     * @return {*} Either the encoded body as a string, if successful,
     *     or the unaltered body object if no encoding could be inferred.
     */
    _encodeBodyObject: function(body, contentType) {
      if (typeof body == 'string') {
        return body;  // Already encoded.
      }
      var bodyObj = /** @type {Object} */ (body);
      switch(contentType) {
        case('application/json'):
          return JSON.stringify(bodyObj);
        case('application/x-www-form-urlencoded'):
          return this._wwwFormUrlEncode(bodyObj);
      }
      return body;
    },

    /**
     * @param {Object} object The object to encode as x-www-form-urlencoded.
     * @return {string} .
     */
    _wwwFormUrlEncode: function(object) {
      if (!object) {
        return '';
      }
      var pieces = [];
      Object.keys(object).forEach(function(key) {
        // TODO(rictic): handle array values here, in a consistent way with
        //   iron-ajax params.
        pieces.push(
            this._wwwFormUrlEncodePiece(key) + '=' +
            this._wwwFormUrlEncodePiece(object[key]));
      }, this);
      return pieces.join('&');
    },

    /**
     * @param {*} str A key or value to encode as x-www-form-urlencoded.
     * @return {string} .
     */
    _wwwFormUrlEncodePiece: function(str) {
      // Spec says to normalize newlines to \r\n and replace %20 spaces with +.
      // jQuery does this as well, so this is likely to be widely compatible.
      return encodeURIComponent(str.toString().replace(/\r?\n/g, '\r\n'))
          .replace(/%20/g, '+');
    },

    /**
     * Updates the status code and status text.
     */
    _updateStatus: function() {
      this._setStatus(this.xhr.status);
      this._setStatusText((this.xhr.statusText === undefined) ? '' : this.xhr.statusText);
    }
  });
</script>