michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: "use strict";
michael@0: 
michael@0: module.metadata = {
michael@0:   "stability": "unstable"
michael@0: };
michael@0: 
michael@0: const { Cc, Ci, Cr } = require("chrome");
michael@0: const { emit, on, off } = require("./core");
michael@0: const { addObserver } = Cc['@mozilla.org/observer-service;1'].
michael@0:                         getService(Ci.nsIObserverService);
michael@0: 
michael@0: // Simple class that can be used to instantiate event channel that
michael@0: // implements `nsIObserver` interface. It's will is used by `observe`
michael@0: // function as observer + event target. It basically proxies observer
michael@0: // notifications as to it's registered listeners.
michael@0: function ObserverChannel() {}
michael@0: Object.freeze(Object.defineProperties(ObserverChannel.prototype, {
michael@0:   QueryInterface: {
michael@0:     value: function(iid) {
michael@0:       if (!iid.equals(Ci.nsIObserver) &&
michael@0:           !iid.equals(Ci.nsISupportsWeakReference) &&
michael@0:           !iid.equals(Ci.nsISupports))
michael@0:         throw Cr.NS_ERROR_NO_INTERFACE;
michael@0:       return this;
michael@0:     }
michael@0:   },
michael@0:   observe: {
michael@0:     value: function(subject, topic, data) {
michael@0:       emit(this, "data", {
michael@0:         type: topic,
michael@0:         target: subject,
michael@0:         data: data
michael@0:       });
michael@0:     }
michael@0:   }
michael@0: }));
michael@0: 
michael@0: function observe(topic) {
michael@0:   let observerChannel = new ObserverChannel();
michael@0: 
michael@0:   // Note: `nsIObserverService` will not hold a weak reference to a
michael@0:   // observerChannel (since third argument is `true`). There for if it
michael@0:   // will be GC-ed with all it's event listeners once no other references
michael@0:   // will be held.
michael@0:   addObserver(observerChannel, topic, true);
michael@0: 
michael@0:   return observerChannel;
michael@0: }
michael@0: 
michael@0: exports.observe = observe;