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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership. The ASF licenses this file
 * to you 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.
 */

gadgets.rpctx = gadgets.rpctx || {};

/*
 * For all others, we have a fallback mechanism known as "ifpc". IFPC
 * exploits the fact that while same-origin policy prohibits a frame from
 * accessing members on a window not in the same domain, that frame can,
 * however, navigate the window heirarchy (via parent). This is exploited by
 * having a page on domain A that wants to talk to domain B create an iframe
 * on domain B pointing to a special relay file and with a message encoded
 * after the hash (#). This relay, in turn, finds the page on domain B, and
 * can call a receipt function with the message given to it. The relay URL
 * used by each caller is set via the gadgets.rpc.setRelayUrl(..) and
 * *must* be called before the call method is used.
 *
 *   ifpc: Iframe-based method, utilizing a relay page, to send a message.
 *      - No known major browsers still use this method, but it remains
 *        useful as a catch-all fallback for the time being.
 */
if (!gadgets.rpctx.ifpc) {  // make lib resilient to double-inclusion

gadgets.rpctx.ifpc = function() {
  var iframePool = [];
  var callId = 0;
  var ready;

  /**
   * Encodes arguments for the legacy IFPC wire format.
   *
   * @param {Object} args
   * @return {string} the encoded args
   */
  function encodeLegacyData(args) {
    var argsEscaped = [];
    for(var i = 0, j = args.length; i < j; ++i) {
      argsEscaped.push(encodeURIComponent(gadgets.json.stringify(args[i])));
    }
    return argsEscaped.join('&');
  }

  /**
   * Helper function to emit an invisible IFrame.
   * @param {string} src SRC attribute of the IFrame to emit.
   * @private
   */
  function emitInvisibleIframe(src) {
    var iframe;
    // Recycle IFrames
    for (var i = iframePool.length - 1; i >=0; --i) {
      var ifr = iframePool[i];
      try {
        if (ifr && (ifr.recyclable || ifr.readyState === 'complete')) {
          ifr.parentNode.removeChild(ifr);
          if (window.ActiveXObject) {
            // For MSIE, delete any iframes that are no longer being used. MSIE
            // cannot reuse the IFRAME because a navigational click sound will
            // be triggered when we set the SRC attribute.
            // Other browsers scan the pool for a free iframe to reuse.
            iframePool[i] = ifr = null;
            iframePool.splice(i, 1);
          } else {
            ifr.recyclable = false;
            iframe = ifr;
            break;
          }
        }
      } catch (e) {
        // Ignore; IE7 throws an exception when trying to read readyState and
        // readyState isn't set.
      }
    }
    // Create IFrame if necessary
    if (!iframe) {
      iframe = document.createElement('iframe');
      iframe.style.border = iframe.style.width = iframe.style.height = '0px';
      iframe.style.visibility = 'hidden';
      iframe.style.position = 'absolute';
      iframe.onload = function() { this.recyclable = true; };
      iframePool.push(iframe);
    }
    iframe.src = src;
    window.setTimeout(function() { document.body.appendChild(iframe); }, 0);
  }

  return {
    getCode: function() {
      return 'ifpc';
    },

    isParentVerifiable: function() {
      return true;
    },

    init: function(processFn, readyFn) {
      // No global setup.
      ready = readyFn;
      ready('..', true);  // Ready immediately.
      return true;
    },

    setup: function(receiverId, token) {
      // Indicate readiness to send to receiver.
      ready(receiverId, true);
      return true;
    },

    call: function(targetId, from, rpc) {
      // Retrieve the relay file used by IFPC. Note that
      // this must be set before the call, and so we conduct
      // an extra check to ensure it is not blank.
      var relay = gadgets.rpc.getRelayUrl(targetId);
      ++callId;

      if (!relay) {
        gadgets.warn('No relay file assigned for IFPC');
        return false;
      }

      // The RPC mechanism supports two formats for IFPC (legacy and current).
      var src = null;
      if (rpc.l) {
        // Use legacy protocol.
        // Format: #iframe_id&callId&num_packets&packet_num&block_of_data
        var callArgs = rpc.a;
        src = [relay, '#', encodeLegacyData([from, callId, 1, 0,
               encodeLegacyData([from, rpc.s, '', '', from].concat(
                 callArgs))])].join('');
      } else {
        // Format: #targetId & sourceId@callId & packetNum & packetId & packetData
        src = [relay, '#', targetId, '&', from, '@', callId,
               '&1&0&', encodeURIComponent(gadgets.json.stringify(rpc))].join('');
      }

      // Conduct the IFPC call by creating the Iframe with
      // the relay URL and appended message.
      emitInvisibleIframe(src);
      return true;
    }
  };
}();

} // !end of double inclusion guard