var EXPORTED_SYMBOLS = ["init"];

const Cc = Components.classes;
const Ci = Components.interfaces;
const Cu = Components.utils;

Components.utils.import("resource://gre/modules/XPCOMUtils.jsm");

function buildRequestor(window) {
  return function request(caps, callback) {
    if (!(typeof(caps) == "object" ||
          typeof(caps) == "string"))
      throw new Error("Must provide capabilities as first parameter.");

    if (typeof(callback) != "function")
      throw new Error("Must provide callback as second parameter");

    if (typeof(caps) == "object")
      caps = new XPCSafeJSObjectWrapper(caps);
    callback = new XPCSafeJSObjectWrapper(callback);

    // TODO: Present UI to user and inject requested capabilities.
  };
}

var listener = {
  QueryInterface : XPCOMUtils.generateQI([Ci.nsIWebProgressListener,
                                          Ci.nsISupportsWeakReference]),

  onStateChange : function (aWebProgress, aRequest,
                            aStateFlags,  aStatus) {
    // STATE_START is too early, doc is still the old page.
    // STATE_STOP is inconviently late (it's onload)
    if (!(aStateFlags & Ci.nsIWebProgressListener.STATE_TRANSFERRING))
      return;

    var window = aWebProgress.DOMWindow;

    if (window.wrappedJSObject) {
      var sandbox = Cu.Sandbox(window);
      sandbox.importFunction(buildRequestor(window));
      sandbox.window = window.wrappedJSObject;

      function setupPowerbox() {
        window.powerbox = {request: request};
      }

      Cu.evalInSandbox("(" + setupPowerbox.toString() + ")();", sandbox);
    }
  },

  // stubs for the nsIWebProgressListener interfaces which we don't use.
  onProgressChange : function() { },
  onLocationChange : function() { },
  onStatusChange   : function() { },
  onSecurityChange : function() { }
};

function init() {
  // WebProgressListener for getting notification of new doc loads.
  // XXX Ugh. Since we're a chrome overlay, it would be nice to just
  // use gBrowser.addProgressListener(). But that isn't sending
  // STATE_TRANSFERRING, and the earliest we can get at the page is
  // STATE_STOP (which is onload, and is inconviently late).
  // We'll use the docloader service instead, but that means we need to
  // filter out loads for other windows.
  var docsvc = Cc["@mozilla.org/docloaderservice;1"].
               getService(Ci.nsIWebProgress);

  docsvc.addProgressListener(listener,
                             Ci.nsIWebProgress.NOTIFY_STATE_DOCUMENT);
}