Add settingObserver module

Auditors: @bsclifton

Fix #4452

Test Plan: None, it'll be tested implicitly when testing regional adblock settings.  Covered by automated.

app/browser/settingObserver.js

@@ -0,0 +1,45 @@
+/* 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/. */
+
+const appStore = require('../../js/stores/appStore')
+const Immutable = require('Immutable')
+const getSetting = require('../../js/settings').getSetting
+let lastSettings = Immutable.Map()
+let watchedPrefs = []
+
+/**
+ * Registers to get notifications when a preference changes.
+ * @param prefKey - The preference key to watch
+ * @param cb - The callback to call when changes occur
+ * @return a function which can be called by the caller to unregister itself
+ */
+const registerForPref = (prefKey, cb) => {
+  watchedPrefs.push({ prefKey, cb })
+  // Return a function which removes itself when called
+  return () => {
+    watchedPrefs = watchedPrefs.filter((pref) => prefKey !== pref.prefKey || cb !== pref.cb)
+  }
+}
+
+const init = () =>
+  appStore.addChangeListener(() => {
+    // Determine if we should check for changes
+    if (lastSettings !== appStore.getState().get('settings')) {
+      watchedPrefs.forEach((pref) => {
+        const prefValue = getSetting(pref.prefKey)
+        if (prefValue !== getSetting(pref.prefKey, lastSettings)) {
+          pref.cb(pref.prefKey, prefValue)
+        }
+      })
+      lastSettings = appStore.getState().get('settings')
+    }
+  })
+
+const getWatchedPrefCount = () => watchedPrefs.length
+
+module.exports = {
+  init,
+  registerForPref,
+  getWatchedPrefCount
+}

test/unit/app/browser/settingObserverTest.js

@@ -0,0 +1,46 @@
+/* global describe, it, before, after, beforeEach */
+const mockery = require('mockery')
+const Immutable = require('immutable')
+const assert = require('assert')
+
+require('../../braveUnit')
+
+describe('setting observer unit test', function () {
+  let appActions
+  let settingObserver
+  before(function () {
+    mockery.enable({
+      warnOnReplace: false,
+      warnOnUnregistered: false,
+      useCleanCache: true
+    })
+    mockery.registerMock('electron', require('../../lib/fakeElectron'))
+    process.type = 'browser'
+    appActions = require('../../../../js/actions/appActions')
+    settingObserver = require('../../../../app/browser/settingObserver')
+    settingObserver.init()
+  })
+
+  beforeEach(function () {
+    appActions.setState(Immutable.fromJS({}))
+  })
+
+  after(function () {
+    mockery.disable()
+  })
+
+  it('observes setting changes and unregisters', function (cb) {
+    const prefKey = 'test.pref'
+    const prefValue = 'value1'
+    assert.equal(settingObserver.getWatchedPrefCount(), 0)
+    const unregister = settingObserver.registerForPref(prefKey, (pref, val) => {
+      assert.equal(prefKey, pref)
+      assert.equal(prefValue, val)
+      unregister()
+      assert.equal(settingObserver.getWatchedPrefCount(), 0)
+      cb()
+    })
+    assert.equal(settingObserver.getWatchedPrefCount(), 1)
+    appActions.changeSetting(prefKey, 'value1')
+  })
+})

test/unit/lib/fakeElectron.js

@@ -0,0 +1,16 @@
+const fakeElectron = {
+  ipcMain: {
+    on: function () { }
+  },
+  remote: {
+    app: {
+      on: function () {
+      }
+    }
+  },
+  app: {
+    on: function () {
+    }
+  }
+}
+module.exports = fakeElectron

test/unit/lib/menuUtilTest.js

@@ -55,17 +55,7 @@ describe('menuUtil', function () {
       useCleanCache: true
     })
 
-    const fakeElectron = {
-      ipcMain: {
-        on: function () { }
-      },
-      remote: {
-        app: { }
-      },
-      app: { }
-    }
-
-    mockery.registerMock('electron', fakeElectron)
+    mockery.registerMock('electron', require('./fakeElectron'))
     menuUtil = require('../../../app/browser/lib/menuUtil')
   })