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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
"use strict";
const { Cc, Ci } = require("chrome");
const { Unknown } = require("./xpcom");
const { when: unload } = require("./unload");
const memory = require("./memory");
/**
* A service for adding, removing and notifying observers of notifications.
* Wraps the nsIObserverService interface.
*
* @version 0.2
*/
var service = Cc["@mozilla.org/observer-service;1"].
getService(Ci.nsIObserverService);
/**
* A cache of observers that have been added.
*
* We use this to remove observers when a caller calls |Observers.remove|.
*/
var cache = [];
/**
* Topics specifically available to Jetpack-generated extensions.
*
* Using these predefined consts instead of the platform strings is good:
* - allows us to scope topics specifically for Jetpacks
* - addons aren't dependent on strings nor behavior of core platform topics
* - the core platform topics are not clearly named
*
*/
exports.topics = {
/**
* A topic indicating that the application is in a state usable
* by add-ons.
*/
get APPLICATION_READY() packaging.jetpackID + "_APPLICATION_READY"
};
/**
* Register the given callback as an observer of the given topic.
*
* @param topic {String}
* the topic to observe
*
* @param callback {Object}
* the callback; an Object that implements nsIObserver or a Function
* that gets called when the notification occurs
*
* @param target {Object} [optional]
* the object to use as |this| when calling a Function callback
*
* @returns the observer
*/
var add = exports.add = function add(topic, callback, target) {
var observer = Observer.new(topic, callback, target);
service.addObserver(observer, topic, true);
cache.push(observer);
return observer;
};
/**
* Unregister the given callback as an observer of the given topic.
*
* @param topic {String}
* the topic being observed
*
* @param callback {Object}
* the callback doing the observing
*
* @param target {Object} [optional]
* the object being used as |this| when calling a Function callback
*/
var remove = exports.remove = function remove(topic, callback, target) {
// This seems fairly inefficient, but I'm not sure how much better
// we can make it. We could index by topic, but we can't index by callback
// or target, as far as I know, since the keys to JavaScript hashes
// (a.k.a. objects) can apparently only be primitive values.
let observers = cache.filter(function(v) {
return (v.topic == topic &&
v.callback == callback &&
v.target == target);
});
if (observers.length) {
service.removeObserver(observers[0], topic);
cache.splice(cache.indexOf(observers[0]), 1);
}
};
/**
* Notify observers about something.
*
* @param topic {String}
* the topic to notify observers about
*
* @param subject {Object} [optional]
* some information about the topic; can be any JS object or primitive
*
* @param data {String} [optional] [deprecated]
* some more information about the topic; deprecated as the subject
* is sufficient to pass all needed information to the JS observers
* that this module targets; if you have multiple values to pass to
* the observer, wrap them in an object and pass them via the subject
* parameter (i.e.: { foo: 1, bar: "some string", baz: myObject })
*/
var notify = exports.notify = function notify(topic, subject, data) {
subject = (typeof subject == "undefined") ? null : Subject.new(subject);
data = (typeof data == "undefined") ? null : data;
service.notifyObservers(subject, topic, data);
};
const Observer = Unknown.extend({
initialize: function initialize(topic, callback, target) {
memory.track(this);
this.topic = topic;
this.callback = callback;
this.target = target;
},
interfaces: [ 'nsIObserver', 'nsISupportsWeakReference' ],
observe: function(subject, topic, data) {
// Extract the wrapped object for subjects that are one of our
// wrappers around a JS object. This way we support both wrapped
// subjects created using this module and those that are real
// XPCOM components.
if (subject && typeof subject == "object" &&
("wrappedJSObject" in subject) &&
("observersModuleSubjectWrapper" in subject.wrappedJSObject))
subject = subject.wrappedJSObject.object;
try {
if (typeof this.callback == "function") {
if (this.target)
this.callback.call(this.target, subject, data);
else
this.callback(subject, data);
} else // typeof this.callback == "object" (nsIObserver)
this.callback.observe(subject, topic, data);
} catch (e) {
console.exception(e);
}
}
});
const Subject = Unknown.extend({
initialize: function initialize(object) {
// Double-wrap the object and set a property identifying the
// wrappedJSObject as one of our wrappers to distinguish between
// subjects that are one of our wrappers (which we should unwrap
// when notifying our observers) and those that are real JS XPCOM
// components (which we should pass through unaltered).
this.wrappedJSObject = {
observersModuleSubjectWrapper: true,
object: object
};
},
getHelperForLanguage: function() {},
getInterfaces: function() {}
});
unload(function() {
// Make a copy of cache first, since cache will be changing as we
// iterate through it.
cache.slice().forEach(function({ topic, callback, target }) {
remove(topic, callback, target);
});
})
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