// Documentation of methods used here are at:
// https://developer.mozilla.org/en-US/Add-ons/Code_snippets/Interaction_between_privileged_and_non-privileged_pages

var pktPanelMessaging = (function() {

 function panelIdFromURL(url) {
   var panelId = url.match(/panelId=([\w|\d|\.]*)&?/);
        if (panelId && panelId.length > 1) {
            return panelId[1];
        }

        return 0;
 }

 function prefixedMessageId(messageId) {
   return "PKT_" + messageId;
 }

 function panelPrefixedMessageId(panelId, messageId) {
   return prefixedMessageId(panelId + "_" + messageId);
 }

 function addMessageListener(panelId, messageId, callback) {
   document.addEventListener(panelPrefixedMessageId(panelId, messageId), function(e) {

    callback(JSON.parse(e.target.getAttribute("payload"))[0]);

    // TODO: Figure out why e.target.parentNode is null
    // e.target.parentNode.removeChild(e.target);

    });

  }

  function removeMessageListener(panelId, messageId, callback) {
   document.removeEventListener(panelPrefixedMessageId(panelId, messageId), callback);
  }

 function sendMessage(panelId, messageId, payload, callback) {
   // Payload needs to be an object in format:
   // { panelId: panelId, data: {} }
   var messagePayload = {
     panelId,
     data: (payload || {})
   };

    // Create a callback to listen for a response
    if (callback) {
      var messageResponseId = messageId + "Response";
      var responseListener = function(responsePayload) {
        callback(responsePayload);
        removeMessageListener(panelId, messageResponseId, responseListener);
      };

      addMessageListener(panelId, messageResponseId, responseListener);
    }

      // Send message
    var element = document.createElement("PKTMessageFromPanelElement");
    element.setAttribute("payload", JSON.stringify([messagePayload]));
    document.documentElement.appendChild(element);

    var evt = document.createEvent("Events");
    evt.initEvent(prefixedMessageId(messageId), true, false);
    element.dispatchEvent(evt);
  }


    /**
     * Public functions
     */
    return {
      panelIdFromURL,
        addMessageListener,
        removeMessageListener,
        sendMessage
    };
}());
