Convert RoomViewStore and ActiveRoomObserver to typescript

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

src/ActiveRoomObserver.ts

@@ -0,0 +1,83 @@
+/*
+Copyright 2017 New Vector Ltd
+
+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 RoomViewStore from './stores/RoomViewStore';
+
+type Listener = (isActive: boolean) => void;
+
+/**
+ * Consumes changes from the RoomViewStore and notifies specific things
+ * about when the active room changes. Unlike listening for RoomViewStore
+ * changes, you can subscribe to only changes relevant to a particular
+ * room.
+ *
+ * TODO: If we introduce an observer for something else, factor out
+ * the adding / removing of listeners & emitting into a common class.
+ */
+export class ActiveRoomObserver {
+    private listeners: {[key: string]: Listener[]} = {};
+    private _activeRoomId = RoomViewStore.getRoomId(); // TODO
+    private readonly roomStoreToken: string;
+
+    constructor() {
+        // TODO: We could self-destruct when the last listener goes away, or at least stop listening.
+        this.roomStoreToken = RoomViewStore.addListener(this.onRoomViewStoreUpdate);
+    }
+
+    public get activeRoomId(): string {
+        return this._activeRoomId;
+    }
+
+    public addListener(roomId, listener) {
+        if (!this.listeners[roomId]) this.listeners[roomId] = [];
+        this.listeners[roomId].push(listener);
+    }
+
+    public removeListener(roomId, listener) {
+        if (this.listeners[roomId]) {
+            const i = this.listeners[roomId].indexOf(listener);
+            if (i > -1) {
+                this.listeners[roomId].splice(i, 1);
+            }
+        } else {
+            console.warn("Unregistering unrecognised listener (roomId=" + roomId + ")");
+        }
+    }
+
+    private emit(roomId, isActive: boolean) {
+        if (!this.listeners[roomId]) return;
+
+        for (const l of this.listeners[roomId]) {
+            l.call(null, isActive);
+        }
+    }
+
+    private onRoomViewStoreUpdate = () => {
+        // emit for the old room ID
+        if (this._activeRoomId) this.emit(this._activeRoomId, false);
+
+        // update our cache
+        this._activeRoomId = RoomViewStore.getRoomId();
+
+        // and emit for the new one
+        if (this._activeRoomId) this.emit(this._activeRoomId, true);
+    };
+}
+
+if (window.mx_ActiveRoomObserver === undefined) {
+    window.mx_ActiveRoomObserver = new ActiveRoomObserver();
+}
+export default window.mx_ActiveRoomObserver;