Fixes #2840 - Use both the room list room and the room preview details to populate the join room screen

- the room summary API is indeed enabled on matrix.org and working fine for most rooms
- it is not however capable of giving us data about non-joined + private rooms
- the SDK addresses that by first trying to use known rooms before resorting to the preview endpoint
- that fails if it's a brand new room that the client doesn't know about yet i.e. a sync hasn't ran, which is exactly what's happening here
- the ClientProxy instead does wait for the room list to go into the first loaded before returning the room

ElementX/Sources/Screens/JoinRoomScreen/JoinRoomScreenModels.swift

@@ -29,11 +29,19 @@ enum JoinRoomScreenInteractionMode {
     case knock
 }
 
+struct JoinRoomScreenRoomDetails {
+    let name: String?
+    let topic: String?
+    let canonicalAlias: String?
+    let avatar: RoomAvatar
+    let memberCount: UInt
+}
+
 struct JoinRoomScreenViewState: BindableState {
     // Maybe use room summary details or similar here??
     let roomID: String
     
-    var roomDetails: RoomPreviewDetails?
+    var roomDetails: JoinRoomScreenRoomDetails?
     
     var mode: JoinRoomScreenInteractionMode = .loading
     
@@ -52,7 +60,7 @@ struct JoinRoomScreenViewState: BindableState {
     }
     
     var avatar: RoomAvatar {
-        .room(id: roomID, name: title, avatarURL: roomDetails?.avatarURL)
+        roomDetails?.avatar ?? .room(id: roomID, name: title, avatarURL: nil)
     }
 }
 

ElementX/Sources/Screens/JoinRoomScreen/JoinRoomScreenViewModel.swift

@@ -26,6 +26,9 @@ class JoinRoomScreenViewModel: JoinRoomScreenViewModelType, JoinRoomScreenViewMo
     private let clientProxy: ClientProxyProtocol
     private let userIndicatorController: UserIndicatorControllerProtocol
     
+    private var roomPreviewDetails: RoomPreviewDetails?
+    private var roomProxy: RoomProxyProtocol?
+    
     private let actionsSubject: PassthroughSubject<JoinRoomScreenViewModelAction, Never> = .init()
     var actionsPublisher: AnyPublisher<JoinRoomScreenViewModelAction, Never> {
         actionsSubject.eraseToAnyPublisher()
@@ -77,13 +80,23 @@ class JoinRoomScreenViewModel: JoinRoomScreenViewModelType, JoinRoomScreenViewMo
         showLoadingIndicator()
         
         defer {
-            updateMode()
             hideLoadingIndicator()
         }
         
+        // Using only the preview API isn't enough as it's not capable
+        // of giving us information for non-joined rooms (at least not on synapse)
+        // See if we known about the room locally and, if so, have that
+        // take priority over the preview one.
+        
+        if let roomProxy = await clientProxy.roomForIdentifier(roomID) {
+            self.roomProxy = roomProxy
+            updateRoomDetails()
+        }
+        
         switch await clientProxy.roomPreviewForIdentifier(roomID, via: via) {
-        case .success(let roomDetails):
+        case .success(let roomPreviewDetails):
-            state.roomDetails = roomDetails
+            self.roomPreviewDetails = roomPreviewDetails
+            updateRoomDetails()
         case .failure(.roomPreviewIsPrivate):
             break // Handled by the mode, we don't need an error indicator.
         case .failure:
@@ -91,17 +104,32 @@ class JoinRoomScreenViewModel: JoinRoomScreenViewModelType, JoinRoomScreenViewMo
         }
     }
     
+    private func updateRoomDetails() {
+        if roomProxy == nil, roomPreviewDetails == nil {
+            return
+        }
+        
+        let name = roomProxy?.name ?? roomPreviewDetails?.name
+        state.roomDetails = JoinRoomScreenRoomDetails(name: name,
+                                                      topic: roomProxy?.topic ?? roomPreviewDetails?.topic,
+                                                      canonicalAlias: roomProxy?.canonicalAlias ?? roomPreviewDetails?.canonicalAlias,
+                                                      avatar: roomProxy?.avatar ?? .room(id: roomID, name: name ?? "", avatarURL: roomPreviewDetails?.avatarURL),
+                                                      memberCount: UInt(roomProxy?.activeMembersCount ?? Int(roomPreviewDetails?.memberCount ?? 0)))
+        
+        updateMode()
+    }
+    
     private func updateMode() {
-        guard let roomDetails = state.roomDetails else {
+        if roomProxy == nil, roomPreviewDetails == nil {
             state.mode = .unknown
             return
         }
         
-        if roomDetails.isPublic {
+        if roomProxy?.isPublic ?? false || roomPreviewDetails?.isPublic ?? false {
             state.mode = .join
-        } else if roomDetails.isInvited {
+        } else if roomProxy?.membership == .invited || roomPreviewDetails?.isInvited ?? false {
             state.mode = .invited
-        } else if roomDetails.canKnock, allowKnocking { // Knocking is not supported yet, the flag is purely for preview tests.
+        } else if roomPreviewDetails?.canKnock ?? false, allowKnocking { // Knocking is not supported yet, the flag is purely for preview tests.
             state.mode = .knock
         } else {
             state.mode = .unknown