Dynamically adjusting the visibleRoomsView's timeline limit based on the app state

ElementX/Sources/Screens/HomeScreen/HomeScreenModels.swift

@@ -14,6 +14,7 @@
 // limitations under the License.
 //
 
+import Combine
 import Foundation
 import UIKit
 
@@ -90,6 +91,8 @@ struct HomeScreenViewState: BindableState {
 struct HomeScreenViewStateBindings {
     var searchQuery = ""
     
+    var isScrolling = false
+    
     var alertInfo: AlertInfo<UUID>?
 }
 

ElementX/Sources/Screens/HomeScreen/HomeScreenViewModel.swift

@@ -35,7 +35,7 @@ class HomeScreenViewModel: HomeScreenViewModelType, HomeScreenViewModelProtocol
     
     var callback: ((HomeScreenViewModelAction) -> Void)?
     
-    // swiftlint:disable:next function_body_length
+    // swiftlint:disable:next function_body_length cyclomatic_complexity
     init(userSession: UserSessionProtocol, attributedStringBuilder: AttributedStringBuilderProtocol) {
         self.userSession = userSession
         self.attributedStringBuilder = attributedStringBuilder
@@ -64,7 +64,17 @@ class HomeScreenViewModel: HomeScreenViewModelType, HomeScreenViewModelProtocol
             .debounce(for: 0.1, scheduler: DispatchQueue.main)
             .removeDuplicates()
             .sink { [weak self] range in
-                self?.updateVisibleRange(range)
+                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)
         
@@ -234,7 +244,7 @@ class HomeScreenViewModel: HomeScreenViewModelType, HomeScreenViewModelProtocol
         return room
     }
     
-    private func updateVisibleRange(_ range: Range<Int>) {
+    private func updateVisibleRange(_ range: Range<Int>, timelineLimit: UInt) {
         guard visibleRoomsSummaryProvider?.statePublisher.value == .live,
               !range.isEmpty else { return }
         
@@ -246,6 +256,6 @@ class HomeScreenViewModel: HomeScreenViewModelType, HomeScreenViewModelProtocol
         let lowerBound = max(0, range.lowerBound - Constants.slidingWindowBoundsPadding)
         let upperBound = min(Int(visibleRoomsSummaryProvider.countPublisher.value), range.upperBound + Constants.slidingWindowBoundsPadding)
         
-        visibleRoomsSummaryProvider.updateVisibleRange(lowerBound..<upperBound)
+        visibleRoomsSummaryProvider.updateVisibleRange(lowerBound..<upperBound, timelineLimit: timelineLimit)
     }
 }

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

@@ -19,14 +19,10 @@ import SwiftUI
 struct HomeScreen: View {
     @ObservedObject var context: HomeScreenViewModel.Context
     
+    @State private var scrollViewAdapter = ScrollViewAdapter()
     @State private var showingLogoutConfirmation = false
-    @State private var visibleItemIdentifiers = Set<String>() {
-        didSet {
-            if visibleItemIdentifiers != oldValue {
-                updateVisibleRange()
-            }
-        }
-    }
+    @State private var visibleItemIdentifiers = Set<String>()
+    @State private var hasTriggeredInitialVisibleItemUpdate = false
     
     var body: some View {
         ScrollView {
@@ -65,6 +61,10 @@ struct HomeScreen: View {
                 .disableAutocorrection(true)
             }
         }
+        .introspectScrollView { scrollView in
+            guard scrollView != scrollViewAdapter.scrollView else { return }
+            scrollViewAdapter.scrollView = scrollView
+        }
         .scrollDismissesKeyboard(.immediately)
         .disabled(context.viewState.roomListMode == .skeletons)
         .animation(.elementDefault, value: context.viewState.showSessionVerificationBanner)
@@ -76,6 +76,17 @@ 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)
     }