Add a RoomScreenHook.

ElementX/Sources/Screens/RoomScreen/RoomScreenModels.swift

@@ -43,9 +43,18 @@ struct RoomScreenViewState: BindableState {
     }
     
     var canSendMessage = true
+    
+    /// Whether or not starting a call is supported.
+    var isCallingEnabled = true
+    /// Whether or not the user is allowed to join calls in this room.
     var canJoinCall = false
+    /// Whether or not this room currently has a call in progress.
     var hasOngoingCall: Bool
-    var shouldShowCallButton = true
+    /// Whether or not the user is already part of a call in another room.
+    var isParticipatingInOngoingCall = false
+    var shouldShowCallButton: Bool {
+        isCallingEnabled && !isParticipatingInOngoingCall // Hide the join call button when already in the call
+    }
     
     var isKnockingEnabled = false
     var isKnockableRoom = false
@@ -70,7 +79,7 @@ struct RoomScreenViewState: BindableState {
     
     var footerDetails: RoomScreenFooterViewDetails?
     
-    var bindings: RoomScreenViewStateBindings
+    var bindings = RoomScreenViewStateBindings()
 }
 
 struct RoomScreenViewStateBindings {