Extract the spotlight and PiP choice into a pure function

src/state/layoutMedia.test.ts

@@ -7,15 +7,22 @@ Please see LICENSE in the repository root for full details.
 
 import { describe, expect, it } from "vitest";
 
-import { chooseSpotlightSpeaker } from "./layoutMedia";
+import { chooseSpotlightSpeaker, computeSpotlight } from "./layoutMedia";
 import { type LocalUserMediaViewModel } from "./media/LocalUserMediaViewModel";
 import { type RemoteUserMediaViewModel } from "./media/RemoteUserMediaViewModel";
+import { type RingingMediaViewModel } from "./media/RingingMediaViewModel";
+import { type ScreenShareViewModel } from "./media/ScreenShareViewModel";
 
 // The layout functions only look at `type` and `local`, so stubs suffice
 const local = { type: "user", local: true } as LocalUserMediaViewModel;
 const alice = { type: "user", local: false } as RemoteUserMediaViewModel;
 const bob = { type: "user", local: false } as RemoteUserMediaViewModel;
 const carol = { type: "user", local: false } as RemoteUserMediaViewModel;
+const screenShare = {
+  type: "screen share",
+  local: false,
+} as ScreenShareViewModel;
+const ringing = { type: "ringing" } as RingingMediaViewModel;
 
 describe("chooseSpotlightSpeaker", () => {
   const items = (
@@ -60,3 +67,46 @@ describe("chooseSpotlightSpeaker", () => {
     expect(chooseSpotlightSpeaker(local, items())).toBe(alice);
   });
 });
+
+describe("computeSpotlight", () => {
+  it("spotlights ringing media with the local user in the PiP", () => {
+    expect(
+      computeSpotlight({
+        ringing,
+        screenShares: [screenShare],
+        speaker: alice,
+        localPip: local,
+      }),
+    ).toEqual({ spotlight: [ringing], pip: local });
+  });
+
+  it("spotlights screen shares with the speaker in the PiP", () => {
+    expect(
+      computeSpotlight({
+        ringing: null,
+        screenShares: [screenShare],
+        speaker: alice,
+        localPip: local,
+      }),
+    ).toEqual({ spotlight: [screenShare], pip: alice });
+  });
+
+  it("otherwise spotlights the speaker and hides a redundant PiP", () => {
+    expect(
+      computeSpotlight({
+        ringing: null,
+        screenShares: [],
+        speaker: alice,
+        localPip: local,
+      }),
+    ).toEqual({ spotlight: [alice], pip: local });
+    expect(
+      computeSpotlight({
+        ringing: null,
+        screenShares: [],
+        speaker: local,
+        localPip: local,
+      }),
+    ).toEqual({ spotlight: [local], pip: undefined });
+  });
+});