Voice Broadcast playback UI (#9362)

* Implement Voice Broadcast UI

* Update src/voice-broadcast/models/VoiceBroadcastPlayback.ts

Co-authored-by: Travis Ralston <travisr@matrix.org>

Co-authored-by: Travis Ralston <travisr@matrix.org>

src/voice-broadcast/models/VoiceBroadcastPlayback.ts

@@ -0,0 +1,76 @@
+/*
+Copyright 2022 The Matrix.org Foundation C.I.C.
+
+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 { MatrixEvent } from "matrix-js-sdk/src/matrix";
+import { TypedEventEmitter } from "matrix-js-sdk/src/models/typed-event-emitter";
+
+import { IDestroyable } from "../../utils/IDestroyable";
+
+export enum VoiceBroadcastPlaybackState {
+    Paused,
+    Playing,
+    Stopped,
+}
+
+export enum VoiceBroadcastPlaybackEvent {
+    StateChanged = "state_changed",
+}
+
+interface EventMap {
+    [VoiceBroadcastPlaybackEvent.StateChanged]: (state: VoiceBroadcastPlaybackState) => void;
+}
+
+export class VoiceBroadcastPlayback
+    extends TypedEventEmitter<VoiceBroadcastPlaybackEvent, EventMap>
+    implements IDestroyable {
+    private state = VoiceBroadcastPlaybackState.Stopped;
+
+    public constructor(
+        public readonly infoEvent: MatrixEvent,
+    ) {
+        super();
+    }
+
+    public start() {
+        this.setState(VoiceBroadcastPlaybackState.Playing);
+    }
+
+    public stop() {
+        this.setState(VoiceBroadcastPlaybackState.Stopped);
+    }
+
+    public toggle() {
+        if (this.state === VoiceBroadcastPlaybackState.Stopped) {
+            this.setState(VoiceBroadcastPlaybackState.Playing);
+            return;
+        }
+
+        this.setState(VoiceBroadcastPlaybackState.Stopped);
+    }
+
+    public getState(): VoiceBroadcastPlaybackState {
+        return this.state;
+    }
+
+    private setState(state: VoiceBroadcastPlaybackState): void {
+        this.state = state;
+        this.emit(VoiceBroadcastPlaybackEvent.StateChanged, state);
+    }
+
+    public destroy(): void {
+        this.removeAllListeners();
+    }
+}