Initial support for notification settings

Signed-off-by: Travis Ralston <travpc@gmail.com>

src/settings/handlers/LocalEchoWrapper.js

@@ -0,0 +1,67 @@
+/*
+Copyright 2017 Travis Ralston
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import SettingsHandler from "./SettingsHandler";
+
+/**
+ * A wrapper for a SettingsHandler that performs local echo on
+ * changes to settings. This wrapper will use the underlying
+ * handler as much as possible to ensure values are not stale.
+ */
+export default class LocalEchoWrapper extends SettingsHandler {
+    /**
+     * Creates a new local echo wrapper
+     * @param {SettingsHandler} handler The handler to wrap
+     */
+    constructor(handler) {
+        super();
+        this._handler = handler;
+        this._cache = {
+            // settingName: { roomId: value }
+        };
+    }
+
+    getValue(settingName, roomId) {
+        const cacheRoomId = roomId ? roomId : "UNDEFINED"; // avoid weird keys
+        const bySetting = this._cache[settingName];
+        if (bySetting && bySetting.hasOwnProperty(cacheRoomId)) {
+            return bySetting[roomId];
+        }
+
+        return this._handler.getValue(settingName, roomId);
+    }
+
+    setValue(settingName, roomId, newValue) {
+        if (!this._cache[settingName]) this._cache[settingName] = {};
+        const bySetting = this._cache[settingName];
+
+        const cacheRoomId = roomId ? roomId : "UNDEFINED"; // avoid weird keys
+        bySetting[cacheRoomId] = newValue;
+
+        return this._handler.setValue(settingName, roomId, newValue).finally(() => {
+            delete bySetting[cacheRoomId];
+        });
+    }
+
+
+    canSetValue(settingName, roomId) {
+        return this._handler.canSetValue(settingName, roomId);
+    }
+
+    isSupported() {
+        return this._handler.isSupported();
+    }
+}