Drop observable-hooks in favor of useBehavior

With this change, views now read every reactive value through `useBehavior`, as
`architecture.md` already prescribes. Where a view reads a plain stream, the view
model now exposes a `Behavior`.

src/state/media/MediaViewModel.test.ts

@@ -25,6 +25,7 @@ import {
   mockRemoteScreenShare,
 } from "../../utils/test";
 import { constant } from "../Behavior";
+import { showConnectionStats } from "../../settings/settings";
 
 global.MediaStreamTrack = class {} as unknown as {
   new (): MediaStreamTrack;
@@ -42,6 +43,12 @@ vi.mock("../../Platform", () => ({
   },
 }));
 
+const observeRtpStreamStatsMock = vi.hoisted(() => vi.fn());
+vi.mock("./observeRtpStreamStats", async (importOriginal) => ({
+  ...(await importOriginal<Record<string, unknown>>()),
+  observeRtpStreamStats$: observeRtpStreamStatsMock,
+}));
+
 const rtcMembership = mockRtcMembership("@alice:example.org", "AAAA");
 
 test("control a participant's volume", () => {
@@ -289,3 +296,37 @@ test("remote media is not in waiting state when user does not intend to publish
   );
   expect(vm.waitingForMedia$.value).toBe(false);
 });
+
+test("user media polls stream stats only while the setting is on", () => {
+  const participant = mockRemoteParticipant({});
+  const vm = mockRemoteMedia(rtcMembership, {}, participant);
+  onTestFinished(() => showConnectionStats.setValue(false));
+  withTestScheduler(({ cold, expectObservable, schedule }) => {
+    const stats = { type: "inbound-rtp" } as RTCInboundRtpStreamStats;
+    observeRtpStreamStatsMock.mockImplementation(() =>
+      cold("-s", { s: stats }),
+    );
+    schedule("-a-b", {
+      a() {
+        showConnectionStats.setValue(true);
+      },
+      b() {
+        showConnectionStats.setValue(false);
+      },
+    });
+    expectObservable(vm.audioStreamStats$).toBe("u-su", {
+      u: undefined,
+      s: stats,
+    });
+  });
+  expect(observeRtpStreamStatsMock).toHaveBeenCalledWith(
+    participant,
+    Track.Source.Microphone,
+    "inbound-rtp",
+  );
+  expect(observeRtpStreamStatsMock).toHaveBeenCalledWith(
+    participant,
+    Track.Source.Camera,
+    "inbound-rtp",
+  );
+});

src/state/media/UserMediaViewModel.ts

@@ -10,7 +10,6 @@ import {
   BehaviorSubject,
   combineLatest,
   map,
-  type Observable,
   of,
   Subject,
   switchMap,
@@ -54,10 +53,10 @@ export interface BaseUserMediaViewModel extends BaseMemberMediaViewModel {
   rtcBackendIdentity: string;
   handRaised$: Behavior<Date | null>;
   reaction$: Behavior<ReactionOption | null>;
-  audioStreamStats$: Observable<
+  audioStreamStats$: Behavior<
     RTCInboundRtpStreamStats | RTCOutboundRtpStreamStats | undefined
   >;
-  videoStreamStats$: Observable<
+  videoStreamStats$: Behavior<
     RTCInboundRtpStreamStats | RTCOutboundRtpStreamStats | undefined
   >;
   /**
@@ -94,6 +93,21 @@ export function createBaseUserMedia(
   );
   const toggleCropVideo$ = new Subject<void>();
   const videoAspectRatio$ = new BehaviorSubject(NaN);
+  const streamStats$ = (
+    scope: ObservableScope,
+    source: Track.Source,
+  ): Behavior<
+    RTCInboundRtpStreamStats | RTCOutboundRtpStreamStats | undefined
+  > =>
+    scope.behavior(
+      combineLatest([participant$, showConnectionStats.value$]).pipe(
+        switchMap(([p, showConnectionStats]) =>
+          !p || !showConnectionStats
+            ? of(undefined)
+            : observeRtpStreamStats$(p, source, statsType),
+        ),
+      ),
+    );
 
   return {
     ...createMemberMedia(scope, {
@@ -130,25 +144,8 @@ export function createBaseUserMedia(
     rtcBackendIdentity,
     handRaised$,
     reaction$,
-    audioStreamStats$: combineLatest([
-      participant$,
-      showConnectionStats.value$,
-    ]).pipe(
-      switchMap(([p, showConnectionStats]) => {
-        //
-        if (!p || !showConnectionStats) return of(undefined);
-        return observeRtpStreamStats$(p, Track.Source.Microphone, statsType);
-      }),
-    ),
-    videoStreamStats$: combineLatest([
-      participant$,
-      showConnectionStats.value$,
-    ]).pipe(
-      switchMap(([p, showConnectionStats]) => {
-        if (!p || !showConnectionStats) return of(undefined);
-        return observeRtpStreamStats$(p, Track.Source.Camera, statsType);
-      }),
-    ),
+    audioStreamStats$: streamStats$(scope, Track.Source.Microphone),
+    videoStreamStats$: streamStats$(scope, Track.Source.Camera),
     setVideoAspectRatio: (ratio) => videoAspectRatio$.next(ratio),
   };
 }