Replace generateKeyed$ with a redesigned generateItems operator

And use it to clean up a number of code smells, fix some reactivity bugs, and avoid some resource leaks.

src/state/UserMedia.ts

@@ -5,17 +5,9 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import {
-  BehaviorSubject,
-  combineLatest,
-  map,
-  type Observable,
-  of,
-  switchMap,
-} from "rxjs";
+import { combineLatest, map, type Observable, of, switchMap } from "rxjs";
 import {
   type LocalParticipant,
-  type Participant,
   ParticipantEvent,
   type RemoteParticipant,
   type Room as LivekitRoom,
@@ -29,11 +21,12 @@ import {
   type UserMediaViewModel,
 } from "./MediaViewModel.ts";
 import type { Behavior } from "./Behavior.ts";
-import type { RoomMember } from "matrix-js-sdk";
 import type { EncryptionSystem } from "../e2ee/sharedKeyManagement.ts";
 import type { MediaDevices } from "./MediaDevices.ts";
 import type { ReactionOption } from "../reactions";
 import { observeSpeaker$ } from "./observeSpeaker.ts";
+import { generateItems } from "../utils/observable.ts";
+import { ScreenShare } from "./ScreenShare.ts";
 
 /**
  * Sorting bins defining the order in which media tiles appear in the layout.
@@ -72,35 +65,35 @@ enum SortingBin {
 /**
  * A user media item to be presented in a tile. This is a thin wrapper around
  * UserMediaViewModel which additionally determines the media item's sorting bin
- * for inclusion in the call layout.
+ * for inclusion in the call layout and tracks associated screen shares.
  */
 export class UserMedia {
-  private readonly participant$ = new BehaviorSubject(this.initialParticipant);
-
   public readonly vm: UserMediaViewModel = this.participant$.value?.isLocal
     ? new LocalUserMediaViewModel(
         this.scope,
         this.id,
-        this.member,
+        this.userId,
         this.participant$ as Behavior<LocalParticipant | null>,
         this.encryptionSystem,
-        this.livekitRoom,
-        this.focusURL,
+        this.livekitRoom$,
+        this.focusUrl$,
         this.mediaDevices,
-        this.scope.behavior(this.displayname$),
+        this.displayName$,
+        this.mxcAvatarUrl$,
         this.scope.behavior(this.handRaised$),
         this.scope.behavior(this.reaction$),
       )
     : new RemoteUserMediaViewModel(
         this.scope,
         this.id,
-        this.member,
+        this.userId,
         this.participant$ as Behavior<RemoteParticipant | null>,
         this.encryptionSystem,
-        this.livekitRoom,
-        this.focusURL,
+        this.livekitRoom$,
+        this.focusUrl$,
         this.pretendToBeDisconnected$,
-        this.scope.behavior(this.displayname$),
+        this.displayName$,
+        this.mxcAvatarUrl$,
         this.scope.behavior(this.handRaised$),
         this.scope.behavior(this.reaction$),
       );
@@ -109,12 +102,55 @@ export class UserMedia {
     observeSpeaker$(this.vm.speaking$),
   );
 
-  private readonly presenter$ = this.scope.behavior(
+  /**
+   * All screen share media associated with this user media.
+   */
+  public readonly screenShares$ = this.scope.behavior(
     this.participant$.pipe(
-      switchMap((p) => (p === null ? of(false) : sharingScreen$(p))),
+      switchMap((p) =>
+        p === null
+          ? of([])
+          : observeParticipantEvents(
+              p,
+              ParticipantEvent.TrackPublished,
+              ParticipantEvent.TrackUnpublished,
+              ParticipantEvent.LocalTrackPublished,
+              ParticipantEvent.LocalTrackUnpublished,
+            ).pipe(
+              // Technically more than one screen share might be possible... our
+              // MediaViewModels don't support it though since they look for a unique
+              // track for the given source. So generateItems here is a bit overkill.
+              generateItems(
+                function* (p) {
+                  if (p.isScreenShareEnabled)
+                    yield {
+                      keys: ["screen-share"],
+                      data: undefined,
+                    };
+                },
+                (scope, _data$, key) =>
+                  new ScreenShare(
+                    scope,
+                    `${this.id}:${key}`,
+                    this.userId,
+                    p,
+                    this.encryptionSystem,
+                    this.livekitRoom$,
+                    this.focusUrl$,
+                    this.pretendToBeDisconnected$,
+                    this.displayName$,
+                    this.mxcAvatarUrl$,
+                  ),
+              ),
+            ),
+      ),
     ),
   );
 
+  private readonly presenter$ = this.scope.behavior(
+    this.screenShares$.pipe(map((screenShares) => screenShares.length > 0)),
+  );
+
   /**
    * Which sorting bin the media item should be placed in.
    */
@@ -147,37 +183,18 @@ export class UserMedia {
   public constructor(
     private readonly scope: ObservableScope,
     public readonly id: string,
-    private readonly member: RoomMember,
-    private readonly initialParticipant:
-      | LocalParticipant
-      | RemoteParticipant
-      | null = null,
+    private readonly userId: string,
+    private readonly participant$: Behavior<
+      LocalParticipant | RemoteParticipant | null
+    >,
     private readonly encryptionSystem: EncryptionSystem,
-    private readonly livekitRoom: LivekitRoom,
-    private readonly focusURL: string,
+    private readonly livekitRoom$: Behavior<LivekitRoom | undefined>,
+    private readonly focusUrl$: Behavior<string | undefined>,
     private readonly mediaDevices: MediaDevices,
     private readonly pretendToBeDisconnected$: Behavior<boolean>,
-    private readonly displayname$: Observable<string>,
+    private readonly displayName$: Behavior<string>,
+    private readonly mxcAvatarUrl$: Behavior<string | undefined>,
     private readonly handRaised$: Observable<Date | null>,
     private readonly reaction$: Observable<ReactionOption | null>,
   ) {}
-
-  public updateParticipant(
-    newParticipant: LocalParticipant | RemoteParticipant | null = null,
-  ): void {
-    if (this.participant$.value !== newParticipant) {
-      // Update the BehaviourSubject in the UserMedia.
-      this.participant$.next(newParticipant);
-    }
-  }
-}
-
-export function sharingScreen$(p: Participant): Observable<boolean> {
-  return observeParticipantEvents(
-    p,
-    ParticipantEvent.TrackPublished,
-    ParticipantEvent.TrackUnpublished,
-    ParticipantEvent.LocalTrackPublished,
-    ParticipantEvent.LocalTrackUnpublished,
-  ).pipe(map((p) => p.isScreenShareEnabled));
 }