Add throttling to mark as read

Author: martinmitrevski

CHANGELOG.md

@@ -6,6 +6,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ### 🐞 Fixed
 - Fixed visibility for deleted messages indicator for current user
 
+### ✅ Added
+- Add throttling to mark as read
+
 # [4.38.0](https://github.com/GetStream/stream-chat-swiftui/releases/tag/4.38.0)
 _September 29, 2023_
 

Sources/StreamChatSwiftUI/ChatChannel/ChatChannelViewModel.swift

@@ -38,6 +38,7 @@ open class ChatChannelViewModel: ObservableObject, MessagesDataSource {
     private var disableDateIndicator = false
     private var channelName = ""
     private var onlineIndicatorShown = false
+    private let throttler = Throttler(interval: 3, broadcastLatestEvent: true)
 
     public var channelController: ChatChannelController
     public var messageController: ChatMessageController?
@@ -343,7 +344,9 @@ open class ChatChannelViewModel: ObservableObject, MessagesDataSource {
     private func maybeSendReadEvent(for message: ChatMessage) {
         if message.id != lastMessageRead {
             lastMessageRead = message.id
-            channelController.markRead()
+            throttler.throttle { [weak self] in
+                self?.channelController.markRead()
+            }
         }
     }
 

Sources/StreamChatSwiftUI/ChatChannel/Utils/Throttler.swift

@@ -0,0 +1,54 @@
+//
+// Copyright © 2023 Stream.io Inc. All rights reserved.
+//
+
+import Foundation
+
+/// A throttler implementation. The action provided will only be executed if the last action executed has passed an amount of time.
+/// Based on the implementation from Apple: https://developer.apple.com/documentation/combine/anypublisher/throttle(for:scheduler:latest:)
+class Throttler {
+    private var workItem: DispatchWorkItem?
+    private let queue = DispatchQueue(label: "com.stream.throttler", qos: .background)
+    private var previousRun: Date = Date.distantPast
+    let interval: TimeInterval
+    let broadcastLatestEvent: Bool
+
+    /// - Parameters:
+    ///   - interval: The interval that an action can be executed.
+    ///   - broadcastLatestEvent: A Boolean value that indicates whether we should be using the first or last event of the ones that are being throttled.
+    ///   This last action will have a delay of the provided interval until it is executed.
+    init(interval: TimeInterval, broadcastLatestEvent: Bool = true) {
+        self.interval = interval
+        self.broadcastLatestEvent = broadcastLatestEvent
+    }
+
+    /// Throttle an action. It will cancel the previous action if exists, and it will execute the action immediately
+    /// if the last action executed was past the interval provided. If not, it will only be executed after a delay.
+    /// - Parameter action: The closure to be performed.
+    func throttle(_ action: @escaping () -> Void) {
+        workItem?.cancel()
+
+        let workItem = DispatchWorkItem { [weak self] in
+            guard let workItem = self?.workItem, !workItem.isCancelled else { return }
+            action()
+            self?.previousRun = Date()
+            self?.workItem = nil
+        }
+
+        self.workItem = workItem
+
+        let timeSinceLastRun = Date().timeIntervalSince(previousRun)
+        let delay = timeSinceLastRun > interval ? 0 : interval
+        // If the delay is 0, we always execute the action immediately.
+        // If the delay is bigger than 0, we only execute it if `latest` was enabled.
+        if delay == 0 || delay > 0 && broadcastLatestEvent {
+            queue.asyncAfter(deadline: .now() + delay, execute: workItem)
+        }
+    }
+
+    /// Cancel any active action.
+    func cancel() {
+        workItem?.cancel()
+        workItem = nil
+    }
+}

StreamChatSwiftUI.xcodeproj/project.pbxproj

@@ -215,6 +215,7 @@
 		84782785284A4DB500D2EE11 /* ChatClient_Mock.swift in Sources */ = {isa = PBXBuildFile; fileRef = 84C94CCB27578B92007FE2B9 /* ChatClient_Mock.swift */; };
 		847CEFEE27C38ABE00606257 /* MessageCachingUtils.swift in Sources */ = {isa = PBXBuildFile; fileRef = 847CEFED27C38ABE00606257 /* MessageCachingUtils.swift */; };
 		847F7949282A91AD0009F74C /* ChatChannelView_Tests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 847F7948282A91AD0009F74C /* ChatChannelView_Tests.swift */; };
+		8482094E2ACFFCD900EF3261 /* Throttler.swift in Sources */ = {isa = PBXBuildFile; fileRef = 8482094D2ACFFCD900EF3261 /* Throttler.swift */; };
 		848399EA275FB3E9003075E4 /* SnapshotTesting in Frameworks */ = {isa = PBXBuildFile; productRef = 848399E9275FB3E9003075E4 /* SnapshotTesting */; };
 		848399EC275FB41B003075E4 /* ChatChannelListView_Tests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 848399EB275FB41B003075E4 /* ChatChannelListView_Tests.swift */; };
 		848399F227601231003075E4 /* ReactionsOverlayView_Tests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 848399F127601231003075E4 /* ReactionsOverlayView_Tests.swift */; };
@@ -628,6 +629,7 @@
 		847BA08827E0BAEE00ED20C7 /* WebSocketEngineMock.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = WebSocketEngineMock.swift; sourceTree = "<group>"; };
 		847CEFED27C38ABE00606257 /* MessageCachingUtils.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = MessageCachingUtils.swift; sourceTree = "<group>"; };
 		847F7948282A91AD0009F74C /* ChatChannelView_Tests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ChatChannelView_Tests.swift; sourceTree = "<group>"; };
+		8482094D2ACFFCD900EF3261 /* Throttler.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = Throttler.swift; sourceTree = "<group>"; };
 		848399EB275FB41B003075E4 /* ChatChannelListView_Tests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ChatChannelListView_Tests.swift; sourceTree = "<group>"; };
 		848399F127601231003075E4 /* ReactionsOverlayView_Tests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ReactionsOverlayView_Tests.swift; sourceTree = "<group>"; };
 		8492974727ABD97F00A8EEB0 /* DemoAppSwiftUI.entitlements */ = {isa = PBXFileReference; lastKnownFileType = text.plist.entitlements; path = DemoAppSwiftUI.entitlements; sourceTree = "<group>"; };
@@ -1201,6 +1203,7 @@
 				8465FD2B2746A95600AF091E /* ChatChannelHelpers.swift */,
 				8465FD2C2746A95600AF091E /* ChatChannelExtensions.swift */,
 				91CC2039283C3E7F0049A146 /* URLExtensions.swift */,
+				8482094D2ACFFCD900EF3261 /* Throttler.swift */,
 			);
 			path = Utils;
 			sourceTree = "<group>";
@@ -1984,6 +1987,7 @@
 				8465FDA72746A95700AF091E /* KeyboardHandling.swift in Sources */,
 				8465FDD72746A95800AF091E /* Appearance.swift in Sources */,
 				8465FD8A2746A95700AF091E /* DiscardAttachmentButton.swift in Sources */,
+				8482094E2ACFFCD900EF3261 /* Throttler.swift in Sources */,
 				8465FDCB2746A95700AF091E /* ChatChannelListView.swift in Sources */,
 				841B2EF4278DB9E500ED619E /* MessageListHelperViews.swift in Sources */,
 				84C0C9A328CF18F700CD0136 /* SnapshotCreator.swift in Sources */,