pull out all screen share related logic.

src/state/CallViewModel/remoteMembers/displayname.ts

@@ -0,0 +1,87 @@
+/*
+Copyright 2025 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { type RoomMember, RoomStateEvent } from "matrix-js-sdk";
+import {
+  combineLatest,
+  fromEvent,
+  map,
+  type Observable,
+  startWith,
+} from "rxjs";
+import { type CallMembership } from "matrix-js-sdk/lib/matrixrtc";
+import { logger } from "matrix-js-sdk/lib/logger";
+import { type Room as MatrixRoom } from "matrix-js-sdk/lib/matrix";
+// eslint-disable-next-line rxjs/no-internal
+import { type NodeStyleEventEmitter } from "rxjs/internal/observable/fromEvent";
+
+import { Epoch, type ObservableScope } from "../../ObservableScope";
+import {
+  calculateDisplayName,
+  shouldDisambiguate,
+} from "../../../utils/displayname";
+import { type Behavior } from "../../Behavior";
+
+/**
+ * Displayname for each member of the call. This will disambiguate
+ * any displayname that clashes with another member. Only members
+ * joined to the call are considered here.
+ *
+ * @returns Map<member.id, displayname> uses the rtc member idenitfier as the key.
+ */
+// don't do this work more times than we need to. This is achieved by converting to a behavior:
+export const memberDisplaynames$ = (
+  scope: ObservableScope,
+  matrixRoom: Pick<MatrixRoom, "getMember"> & NodeStyleEventEmitter,
+  memberships$: Observable<Epoch<CallMembership[]>>,
+): Behavior<Epoch<Map<string, string>>> =>
+  scope.behavior(
+    combineLatest([
+      // Handle call membership changes
+      memberships$,
+      // Additionally handle display name changes (implicitly reacting to them)
+      fromEvent(matrixRoom, RoomStateEvent.Members).pipe(startWith(null)),
+      // TODO: do we need: pauseWhen(this.pretendToBeDisconnected$),
+    ]).pipe(
+      map(([epochMemberships, _displayNames]) => {
+        const { epoch, value: memberships } = epochMemberships;
+        const displaynameMap = new Map<string, string>();
+        const room = matrixRoom;
+
+        // We only consider RTC members for disambiguation as they are the only visible members.
+        for (const rtcMember of memberships) {
+          // TODO a hard-coded participant ID ? should use rtcMember.membershipID instead?
+          const matrixIdentifier = `${rtcMember.userId}:${rtcMember.deviceId}`;
+          const { member } = getRoomMemberFromRtcMember(rtcMember, room);
+          if (!member) {
+            logger.error(
+              "Could not find member for participant id:",
+              matrixIdentifier,
+            );
+            continue;
+          }
+          const disambiguate = shouldDisambiguate(member, memberships, room);
+          displaynameMap.set(
+            matrixIdentifier,
+            calculateDisplayName(member, disambiguate),
+          );
+        }
+        return new Epoch(displaynameMap, epoch);
+      }),
+    ),
+    new Epoch(new Map<string, string>()),
+  );
+
+export function getRoomMemberFromRtcMember(
+  rtcMember: CallMembership,
+  room: Pick<MatrixRoom, "getMember">,
+): { id: string; member: RoomMember | undefined } {
+  return {
+    id: rtcMember.userId + ":" + rtcMember.deviceId,
+    member: room.getMember(rtcMember.userId) ?? undefined,
+  };
+}