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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 Services = require("Services");
const EventEmitter = require("devtools/shared/event-emitter");
/**
* Shortcuts for lazily accessing and setting various preferences.
* Usage:
* let prefs = new Prefs("root.path.to.branch", {
* myIntPref: ["Int", "leaf.path.to.my-int-pref"],
* myCharPref: ["Char", "leaf.path.to.my-char-pref"],
* myJsonPref: ["Json", "leaf.path.to.my-json-pref"],
* myFloatPref: ["Float", "leaf.path.to.my-float-pref"]
* ...
* });
*
* Get/set:
* prefs.myCharPref = "foo";
* let aux = prefs.myCharPref;
*
* Observe:
* prefs.registerObserver();
* prefs.on("pref-changed", (prefName, prefValue) => {
* ...
* });
*
* @param string prefsRoot
* The root path to the required preferences branch.
* @param object prefsBlueprint
* An object containing { accessorName: [prefType, prefName] } keys.
*/
function PrefsHelper(prefsRoot = "", prefsBlueprint = {}) {
EventEmitter.decorate(this);
let cache = new Map();
for (let accessorName in prefsBlueprint) {
let [prefType, prefName] = prefsBlueprint[accessorName];
map(this, cache, accessorName, prefType, prefsRoot, prefName);
}
let observer = makeObserver(this, cache, prefsRoot, prefsBlueprint);
this.registerObserver = () => observer.register();
this.unregisterObserver = () => observer.unregister();
}
/**
* Helper method for getting a pref value.
*
* @param Map cache
* @param string prefType
* @param string prefsRoot
* @param string prefName
* @return any
*/
function get(cache, prefType, prefsRoot, prefName) {
let cachedPref = cache.get(prefName);
if (cachedPref !== undefined) {
return cachedPref;
}
let value = Services.prefs["get" + prefType + "Pref"](
[prefsRoot, prefName].join(".")
);
cache.set(prefName, value);
return value;
}
/**
* Helper method for setting a pref value.
*
* @param Map cache
* @param string prefType
* @param string prefsRoot
* @param string prefName
* @param any value
*/
function set(cache, prefType, prefsRoot, prefName, value) {
Services.prefs["set" + prefType + "Pref"](
[prefsRoot, prefName].join("."),
value
);
cache.set(prefName, value);
}
/**
* Maps a property name to a pref, defining lazy getters and setters.
* Supported types are "Bool", "Char", "Int", "Float" (sugar around "Char"
* type and casting), and "Json" (which is basically just sugar for "Char"
* using the standard JSON serializer).
*
* @param PrefsHelper self
* @param Map cache
* @param string accessorName
* @param string prefType
* @param string prefsRoot
* @param string prefName
* @param array serializer [optional]
*/
function map(self, cache, accessorName, prefType, prefsRoot, prefName,
serializer = { in: e => e, out: e => e }) {
if (prefName in self) {
throw new Error(`Can't use ${prefName} because it overrides a property` +
"on the instance.");
}
if (prefType == "Json") {
map(self, cache, accessorName, "Char", prefsRoot, prefName, {
in: JSON.parse,
out: JSON.stringify
});
return;
}
if (prefType == "Float") {
map(self, cache, accessorName, "Char", prefsRoot, prefName, {
in: Number.parseFloat,
out: (n) => n + ""
});
return;
}
Object.defineProperty(self, accessorName, {
get: () => serializer.in(get(cache, prefType, prefsRoot, prefName)),
set: (e) => set(cache, prefType, prefsRoot, prefName, serializer.out(e))
});
}
/**
* Finds the accessor for the provided pref, based on the blueprint object
* used in the constructor.
*
* @param PrefsHelper self
* @param object prefsBlueprint
* @return string
*/
function accessorNameForPref(somePrefName, prefsBlueprint) {
for (let accessorName in prefsBlueprint) {
let [, prefName] = prefsBlueprint[accessorName];
if (somePrefName == prefName) {
return accessorName;
}
}
return "";
}
/**
* Creates a pref observer for `self`.
*
* @param PrefsHelper self
* @param Map cache
* @param string prefsRoot
* @param object prefsBlueprint
* @return object
*/
function makeObserver(self, cache, prefsRoot, prefsBlueprint) {
return {
register: function () {
this._branch = Services.prefs.getBranch(prefsRoot + ".");
this._branch.addObserver("", this, false);
},
unregister: function () {
this._branch.removeObserver("", this);
},
observe: function (subject, topic, prefName) {
// If this particular pref isn't handled by the blueprint object,
// even though it's in the specified branch, ignore it.
let accessorName = accessorNameForPref(prefName, prefsBlueprint);
if (!(accessorName in self)) {
return;
}
cache.delete(prefName);
self.emit("pref-changed", accessorName, self[accessorName]);
}
};
}
exports.PrefsHelper = PrefsHelper;
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