Improved read indicator updates

Author: martinmitrevski

Sources/StreamChatSwiftUI/ChatChannel/ChatChannelViewModel.swift

@@ -26,6 +26,7 @@ open class ChatChannelViewModel: ObservableObject, MessagesDataSource {
     }
 
     private var isActive = true
+    private var readsString = ""
 
     private let messageListDateOverlay: DateFormatter = {
         let df = DateFormatter()
@@ -195,6 +196,7 @@ open class ChatChannelViewModel: ObservableObject, MessagesDataSource {
         didUpdateChannel channel: EntityChange<ChatChannel>,
         channelController: ChatChannelController
     ) {
+        checkReadIndicators(for: channel)
         checkHeaderType()
     }
 
@@ -278,6 +280,23 @@ open class ChatChannelViewModel: ObservableObject, MessagesDataSource {
         }
     }
 
+    private func checkReadIndicators(for channel: EntityChange<ChatChannel>) {
+        switch channel {
+        case let .update(chatChannel):
+            let newReadsString = chatChannel.readsString
+            if readsString == "" {
+                readsString = newReadsString
+                return
+            }
+            if readsString != newReadsString && isActive {
+                messages = channelDataSource.messages
+                readsString = newReadsString
+            }
+        default:
+            log.debug("skip updating of messages in channel update")
+        }
+    }
+    
     private func checkNameChange() {
         let currentChannelName = channel?.name ?? ""
         var nameChanged = false
@@ -470,6 +489,17 @@ extension ChatMessage: Identifiable {
     }
 }
 
+extension ChatChannel {
+    
+    var readsString: String {
+        reads.map { read in
+            "\(read.user.id)-\(read.lastReadAt)"
+        }
+        .sorted()
+        .joined(separator: "-")
+    }
+}
+
 /// The type of header shown in the chat channel screen.
 public enum ChannelHeaderType {
     /// The regular header showing the channel name and members.

StreamChatSwiftUITests/Tests/ChatChannel/ChatChannelViewModel_Tests.swift

@@ -294,6 +294,33 @@ class ChatChannelViewModel_Tests: StreamChatTestCase {
         XCTAssert(initial.count < after.count)
     }
 
+    func test_chatChannelVM_updateReadIndicators() {
+        // Given
+        let channelController = makeChannelController()
+        let viewModel = ChatChannelViewModel(channelController: channelController)
+        let channel = ChatChannel.mockDMChannel()
+        let read = ChatChannelRead.mock(lastReadAt: Date(), unreadMessagesCount: 1, user: .mock(id: .unique))
+        let newChannel = ChatChannel.mockDMChannel(reads: [read])
+        
+        // When
+        channelController.simulate(
+            channel: channel,
+            change: .update(channel),
+            typingUsers: nil
+        )
+        let readsString = channel.readsString
+        channelController.simulate(
+            channel: newChannel,
+            change: .update(newChannel),
+            typingUsers: nil
+        )
+        let newChannelReadsString = newChannel.readsString
+        
+        // Then
+        XCTAssert(viewModel.channel! == newChannel)
+        XCTAssert(readsString != newChannelReadsString)
+    }
+    
     // MARK: - private
 
     private func makeChannelController(