ios: optimize marking messages read (#4530)

* ios: optimize marking messages read

* remove view ifs

apps/ios/Shared/Views/Chat/ChatView.swift

@@ -646,23 +646,38 @@ struct ChatView: View {
                 }
             }
             .onAppear {
-                markRead(
-                    chatItems: range.flatMap { m.reversedChatItems[$0] }
-                    ?? [chatItem]
-                )
-            }
-        }
-
-        private func markRead(chatItems: Array<ChatItem>.SubSequence) {
-            let unreadItems = chatItems.filter { $0.isRcvNew }
-            if unreadItems.isEmpty { return }
-            DispatchQueue.main.asyncAfter(deadline: .now() + 0.6) {
-                if m.chatId == chat.chatInfo.id {
-                    Task {
-                        for unreadItem in unreadItems {
-                            await apiMarkChatItemRead(chat.chatInfo, unreadItem)
+                if let range {
+                    if let items = unreadItems(range) {
+                        waitToMarkRead {
+                            for ci in items {
+                                await apiMarkChatItemRead(chat.chatInfo, ci)
+                            }
                         }
                     }
+                } else if chatItem.isRcvNew  {
+                    waitToMarkRead {
+                        await apiMarkChatItemRead(chat.chatInfo, chatItem)
+                    }
+                }
+            }
+        }
+        
+        private func unreadItems(_ range: ClosedRange<Int>) -> [ChatItem]? {
+            let items = range.compactMap { i in
+                if i >= 0 && i < m.reversedChatItems.count {
+                    let ci = m.reversedChatItems[i]
+                    return if ci.isRcvNew { ci } else { nil }
+                } else {
+                    return nil
+                }
+            }
+            return if items.isEmpty { nil } else { items }
+        }
+        
+        private func waitToMarkRead(_ op: @Sendable @escaping () async -> Void) {
+            DispatchQueue.main.asyncAfter(deadline: .now() + 0.6) {
+                if m.chatId == chat.chatInfo.id {
+                    Task(operation: op)
                 }
             }
         }