Refactor the dynamic timeline modifiers and make sure they fire in the right order

ElementX/Sources/Screens/HomeScreen/HomeScreenModels.swift

@@ -39,7 +39,7 @@ enum HomeScreenViewAction {
     case userMenu(action: HomeScreenViewUserMenuAction)
     case verifySession
     case skipSessionVerification
-    case updatedVisibleItemRange(Range<Int>)
+    case updateVisibleItemRange(range: Range<Int>, isScrolling: Bool)
 }
 
 enum HomeScreenRoomListMode: CustomStringConvertible {
@@ -91,8 +91,6 @@ struct HomeScreenViewState: BindableState {
 struct HomeScreenViewStateBindings {
     var searchQuery = ""
     
-    var isScrolling = false
-    
     var alertInfo: AlertInfo<UUID>?
 }
 

ElementX/Sources/Screens/HomeScreen/HomeScreenViewModel.swift

@@ -29,7 +29,8 @@ class HomeScreenViewModel: HomeScreenViewModelType, HomeScreenViewModelProtocol
     private let allRoomsSummaryProvider: RoomSummaryProviderProtocol?
     private let attributedStringBuilder: AttributedStringBuilderProtocol
     
-    private let visibleItemRangePublisher = CurrentValueSubject<Range<Int>, Never>(0..<0)
+    private var visibleItemRangeObservationToken: AnyCancellable?
+    private let visibleItemRangePublisher = CurrentValueSubject<(range: Range<Int>, isScrolling: Bool), Never>((0..<0, false))
     
     var callback: ((HomeScreenViewModelAction) -> Void)?
     
@@ -58,24 +59,6 @@ class HomeScreenViewModel: HomeScreenViewModelType, HomeScreenViewModelProtocol
             }
             .store(in: &cancellables)
         
-        visibleItemRangePublisher
-            .debounce(for: 0.1, scheduler: DispatchQueue.main)
-            .removeDuplicates()
-            .sink { [weak self] range in
-                guard let self else { return }
-                
-                guard self.state.bindings.searchQuery.isEmpty else {
-                    return
-                }
-                
-                if self.state.bindings.isScrolling {
-                    self.updateVisibleRange(range, timelineLimit: SlidingSyncConstants.lastMessageTimelineLimit)
-                } else {
-                    self.updateVisibleRange(range, timelineLimit: SlidingSyncConstants.timelinePrecachingTimelineLimit)
-                }
-            }
-            .store(in: &cancellables)
-        
         guard let visibleRoomsSummaryProvider, let allRoomsSummaryProvider else {
             MXLog.error("Room summary provider unavailable")
             return
@@ -136,9 +119,14 @@ class HomeScreenViewModel: HomeScreenViewModelType, HomeScreenViewModelProtocol
             .store(in: &cancellables)
         
         allRoomsSummaryProvider.roomListPublisher
+            .dropFirst(1) // We don't care about its initial value
             .receive(on: DispatchQueue.main)
             .sink { [weak self] _ in
                 self?.updateRooms()
+                
+                // Wait for the all rooms view to receive its first update before installing
+                // dynamic timeline modifiers
+                self?.installDynamicTimelineLimitModifiers()
             }
             .store(in: &cancellables)
         
@@ -166,8 +154,8 @@ class HomeScreenViewModel: HomeScreenViewModelType, HomeScreenViewModelProtocol
             callback?(.presentSessionVerificationScreen)
         case .skipSessionVerification:
             state.showSessionVerificationBanner = false
-        case .updatedVisibleItemRange(let range):
-            visibleItemRangePublisher.send(range)
+        case .updateVisibleItemRange(let range, let isScrolling):
+            visibleItemRangePublisher.send((range, isScrolling))
         }
     }
     
@@ -181,6 +169,29 @@ class HomeScreenViewModel: HomeScreenViewModelType, HomeScreenViewModelProtocol
     }
     
     // MARK: - Private
+    
+    /// We want the timeline limit to be set to 1 while scrolling the list so that last messages load up fast. We also want to set that back to 20 when the scrolling
+    /// stops to load room history. Also we don't want this to be setup before the initial sync is over so we only call it when the allRoomsSummaryProvider
+    /// first receives some changes
+    private func installDynamicTimelineLimitModifiers() {
+        guard visibleItemRangeObservationToken == nil else {
+            return
+        }
+        
+        visibleItemRangeObservationToken = visibleItemRangePublisher
+            .removeDuplicates(by: { $0.isScrolling == $1.isScrolling && $0.range == $1.range })
+            .throttle(for: 0.5, scheduler: DispatchQueue.main, latest: true)
+            .sink { [weak self] value in
+                guard let self else { return }
+                
+                // Ignore scrolling while filtering rooms
+                guard self.state.bindings.searchQuery.isEmpty else {
+                    return
+                }
+                
+                self.updateVisibleRange(value.range, timelineLimit: value.isScrolling ? SlidingSyncConstants.lastMessageTimelineLimit : SlidingSyncConstants.timelinePrecachingTimelineLimit)
+            }
+    }
         
     /// This method will update all view state rooms by merging the data from both summary providers
     /// If a room is empty in the visible room summary provider it will try to get it from the allRooms one

ElementX/Sources/Screens/HomeScreen/View/HomeScreen.swift

@@ -21,8 +21,11 @@ struct HomeScreen: View {
     
     @State private var scrollViewAdapter = ScrollViewAdapter()
     @State private var showingLogoutConfirmation = false
-    @State private var visibleItemIdentifiers = Set<String>()
-    @State private var hasTriggeredInitialVisibleItemUpdate = false
+    @State private var visibleItemIdentifiers = Set<String>() {
+        didSet {
+            updateVisibleRange()
+        }
+    }
     
     var body: some View {
         ScrollView {
@@ -65,6 +68,11 @@ struct HomeScreen: View {
             guard scrollView != scrollViewAdapter.scrollView else { return }
             scrollViewAdapter.scrollView = scrollView
         }
+        .onReceive(scrollViewAdapter.isScrolling) { isScrolling in
+            if !isScrolling {
+                updateVisibleRange()
+            }
+        }
         .scrollDismissesKeyboard(.immediately)
         .disabled(context.viewState.roomListMode == .skeletons)
         .animation(.elementDefault, value: context.viewState.showSessionVerificationBanner)
@@ -76,17 +84,6 @@ struct HomeScreen: View {
                 userMenuButton
             }
         }
-        .onChange(of: visibleItemIdentifiers) { _ in
-            if !hasTriggeredInitialVisibleItemUpdate {
-                updateVisibleRange()
-                hasTriggeredInitialVisibleItemUpdate = true
-            }
-        }
-        .onReceive(scrollViewAdapter.isScrolling) { isScrolling in
-            context.isScrolling = isScrolling
-
-            updateVisibleRange()
-        }
         .background(Color.element.background)
     }
 
@@ -196,7 +193,7 @@ struct HomeScreen: View {
             return
         }
         
-        context.send(viewAction: .updatedVisibleItemRange(firstIndex..<lastIndex))
+        context.send(viewAction: .updateVisibleItemRange(range: firstIndex..<lastIndex, isScrolling: scrollViewAdapter.isScrolling.value))
     }
 }
 

ElementX/Sources/Services/Client/SlidingSyncViewProxy.swift

@@ -103,7 +103,7 @@ class SlidingSyncViewProxy {
     }
     
     func updateVisibleRange(_ range: Range<Int>, timelineLimit: UInt) {
-        MXLog.info("Setting sliding sync view range to \(range), timelineLimit: \(timelineLimit)")
+        MXLog.info("Setting sliding sync view range to \(range), timeline limit: \(timelineLimit)")
         
         slidingSyncView.setRange(start: UInt32(range.lowerBound), end: UInt32(range.upperBound))
         slidingSyncView.setTimelineLimit(value: UInt32(timelineLimit))