Allow screen share takeover

kkkmeet-server.el

@@ -500,7 +500,21 @@ When KEEP-OPEN is nil, close PROCESS after writing."
                          (sharing . ,(if (alist-get 'sharing payload) t :false))
                          (updatedAt . ,(floor (* 1000 (float-time)))))))
             (if (alist-get 'sharing payload)
-                (puthash safe-room-id event kkkmeet-server--presentation-states)
+                (let ((previous (gethash safe-room-id kkkmeet-server--presentation-states)))
+                  (when (and previous
+                             (alist-get 'peerId previous)
+                             (not (equal (alist-get 'peerId previous) from)))
+                    (kkkmeet-server--broadcast
+                     safe-room-id from `((type . "presentation-state")
+                                         (from . ,(alist-get 'peerId previous))
+                                         (peerId . ,(alist-get 'peerId previous))
+                                         (name . ,(alist-get 'name previous))
+                                         (sharing . :false)
+                                         (reason . "takeover")
+                                         (replacedBy . ,from)
+                                         (replacedByName . ,(alist-get 'name event))
+                                         (updatedAt . ,(floor (* 1000 (float-time)))))))
+                  (puthash safe-room-id event kkkmeet-server--presentation-states))
               (when (equal (alist-get 'peerId (gethash safe-room-id kkkmeet-server--presentation-states))
                            from)
                 (remhash safe-room-id kkkmeet-server--presentation-states)))

public/app.js

@@ -1337,10 +1337,20 @@ async function handleSignal(message) {
   }
 
   if (message.type === "presentation-state") {
+    if (
+      message.reason === "takeover" &&
+      message.from === peerId &&
+      !message.sharing &&
+      screenStream
+    ) {
+      await stopScreenShare({ announce: false });
+    }
     setRemotePresentation(message.from, message.sharing, message.name);
     setActivity(
       message.name,
-      message.sharing ? "started sharing their screen." : "stopped sharing their screen."
+      message.reason === "takeover"
+        ? `was replaced by ${participantDisplayName(message.replacedByName)} as presenter.`
+        : message.sharing ? "started sharing their screen." : "stopped sharing their screen."
     );
     return;
   }
@@ -1576,7 +1586,7 @@ async function startScreenShare() {
   }
 }
 
-async function stopScreenShare() {
+async function stopScreenShare({ announce = true } = {}) {
   if (!screenStream || stoppingScreenShare) return;
 
   stoppingScreenShare = true;
@@ -1590,8 +1600,10 @@ async function stopScreenShare() {
       await replaceOutboundVideoTrack(cameraTrack);
     }
     shareButton.textContent = "Share Screen";
-    await sendRoomEvent({ type: "presentation-state", sharing: false });
-    setActivity(displayName, "stopped sharing their screen.");
+    if (announce) {
+      await sendRoomEvent({ type: "presentation-state", sharing: false });
+      setActivity(displayName, "stopped sharing their screen.");
+    }
   } finally {
     streamToStop.getTracks().forEach((track) => {
       track.onended = null;

server.js

@@ -327,6 +327,20 @@ const server = http.createServer(async (req, res) => {
       };
 
       if (event.sharing) {
+        const previous = presentationStates.get(roomId);
+        if (previous?.peerId && previous.peerId !== payload.from) {
+          broadcast(roomId, payload.from, {
+            type: "presentation-state",
+            from: previous.peerId,
+            peerId: previous.peerId,
+            name: previous.name,
+            sharing: false,
+            reason: "takeover",
+            replacedBy: payload.from,
+            replacedByName: event.name,
+            updatedAt: Date.now()
+          });
+        }
         presentationStates.set(roomId, { ...event, peerId: payload.from });
       } else if (presentationStates.get(roomId)?.peerId === payload.from) {
         presentationStates.delete(roomId);