Fix infinite loop when pinning/unpinning persistent widgets (#8396)

Pinning or unpinning a persistent widget, such as Jitsi, could cause the
PiP view and the app drawer to fight for control over the widget, since
the PiP view never realized that it was supposed to relinquish control.
This was due to a race between the WidgetLayoutStore update and the
AppTile lifecycle tracking update.

src/stores/ActiveWidgetStore.ts

@@ -23,19 +23,25 @@ import WidgetUtils from "../utils/WidgetUtils";
 import { WidgetMessagingStore } from "./widgets/WidgetMessagingStore";
 
 export enum ActiveWidgetStoreEvent {
-    Update = "update",
+    // Indicates a change in the currently persistent widget
+    Persistence = "persistence",
+    // Indicate changes in the currently docked widgets
+    Dock = "dock",
+    Undock = "undock",
 }
 
 /**
  * Stores information about the widgets active in the app right now:
  *  * What widget is set to remain always-on-screen, if any
  *    Only one widget may be 'always on screen' at any one time.
- *  * Negotiated capabilities for active apps
+ *  * Reference counts to keep track of whether a widget is kept docked or alive
+ *    by any components
  */
 export default class ActiveWidgetStore extends EventEmitter {
     private static internalInstance: ActiveWidgetStore;
     private persistentWidgetId: string;
     private persistentRoomId: string;
+    private dockedWidgetsByUid = new Map<string, number>();
 
     public static get instance(): ActiveWidgetStore {
         if (!ActiveWidgetStore.internalInstance) {
@@ -79,7 +85,7 @@ export default class ActiveWidgetStore extends EventEmitter {
             this.persistentWidgetId = widgetId;
             this.persistentRoomId = roomId;
         }
-        this.emit(ActiveWidgetStoreEvent.Update);
+        this.emit(ActiveWidgetStoreEvent.Persistence);
     }
 
     public getWidgetPersistence(widgetId: string, roomId: string): boolean {
@@ -93,6 +99,34 @@ export default class ActiveWidgetStore extends EventEmitter {
     public getPersistentRoomId(): string {
         return this.persistentRoomId;
     }
+
+    // Registers the given widget as being docked somewhere in the UI (not a PiP),
+    // to allow its lifecycle to be tracked.
+    public dockWidget(widgetId: string, roomId: string): void {
+        const uid = WidgetUtils.calcWidgetUid(widgetId, roomId);
+        const refs = this.dockedWidgetsByUid.get(uid) ?? 0;
+        this.dockedWidgetsByUid.set(uid, refs + 1);
+        if (refs === 0) this.emit(ActiveWidgetStoreEvent.Dock);
+    }
+
+    public undockWidget(widgetId: string, roomId: string): void {
+        const uid = WidgetUtils.calcWidgetUid(widgetId, roomId);
+        const refs = this.dockedWidgetsByUid.get(uid);
+        if (refs) this.dockedWidgetsByUid.set(uid, refs - 1);
+        if (refs === 1) this.emit(ActiveWidgetStoreEvent.Undock);
+    }
+
+    // Determines whether the given widget is docked anywhere in the UI (not a PiP)
+    public isDocked(widgetId: string, roomId: string): boolean {
+        const uid = WidgetUtils.calcWidgetUid(widgetId, roomId);
+        const refs = this.dockedWidgetsByUid.get(uid) ?? 0;
+        return refs > 0;
+    }
+
+    // Determines whether the given widget is being kept alive in the UI, including PiPs
+    public isLive(widgetId: string, roomId: string): boolean {
+        return this.isDocked(widgetId, roomId) || this.getWidgetPersistence(widgetId, roomId);
+    }
 }
 
 window.mxActiveWidgetStore = ActiveWidgetStore.instance;