ios: scroll chat list to bottom, when items are added (#4651)

* scroll chat list to bottom

* simpler

* is really near bottom

* reduce thresholds

* comment

* itemAdded

---------

Co-authored-by: Evgeny Poberezkin <evgeny@poberezkin.com>

apps/ios/Shared/Model/ChatModel.swift

@@ -50,6 +50,10 @@ class ItemsModel: ObservableObject {
     var reversedChatItems: [ChatItem] = [] {
         willSet { publisher.send() }
     }
+    var itemAdded = false {
+        willSet { publisher.send() }
+    }
+    
     init() {
         publisher
             .throttle(for: 0.25, scheduler: DispatchQueue.main, latest: true)
@@ -389,6 +393,7 @@ final class ChatModel: ObservableObject {
                     ci.meta.itemStatus = status
                 }
                 im.reversedChatItems.insert(ci, at: hasLiveDummy ? 1 : 0)
+                im.itemAdded = true
             }
             return true
         }
@@ -483,6 +488,7 @@ final class ChatModel: ObservableObject {
         let cItem = ChatItem.liveDummy(chatInfo.chatType)
         withAnimation {
             im.reversedChatItems.insert(cItem, at: 0)
+            im.itemAdded = true
         }
         return cItem
     }
@@ -842,7 +848,13 @@ final class ChatModel: ObservableObject {
             }
             i += 1
         }
-        return UnreadChatItemCounts(isNearBottom: totalBelow < 16, unreadBelow: unreadBelow)
+        return UnreadChatItemCounts(
+            // TODO these thresholds account for the fact that items are still "visible" while
+            // covered by compose area, they should be replaced with the actual height in pixels below the screen.
+            isNearBottom: totalBelow < 15,
+            isReallyNearBottom: totalBelow < 2,
+            unreadBelow: unreadBelow
+        )
     }
 
     func topItemInView(itemsInView: Set<String>) -> ChatItem? {
@@ -881,6 +893,7 @@ struct NTFContactRequest {
 
 struct UnreadChatItemCounts: Equatable {
     var isNearBottom: Bool
+    var isReallyNearBottom: Bool
     var unreadBelow: Int
 }
 

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

@@ -413,11 +413,20 @@ struct ChatView: View {
                     chat.copyFrom(c)
                     showChatInfoSheet = false
                     loadChat(chat: c)
+                    scrollModel.scrollToBottom()
                 }
             }
             .onChange(of: im.reversedChatItems) { _ in
                 floatingButtonModel.chatItemsChanged()
             }
+            .onChange(of: im.itemAdded) { added in
+                if added {
+                    im.itemAdded = false
+                    if floatingButtonModel.unreadChatItemCounts.isReallyNearBottom {
+                        scrollModel.scrollToBottom()
+                    }
+                }
+            }
         }
     }
 
@@ -450,19 +459,19 @@ struct ChatView: View {
         init() {
             unreadChatItemCounts = UnreadChatItemCounts(
                 isNearBottom: true,
+                isReallyNearBottom: true,
                 unreadBelow: 0
             )
             events
                 .receive(on: DispatchQueue.global(qos: .background))
                 .scan(Set<String>()) { itemsInView, event in
-                    return switch event {
-                    case let .appeared(viewId):
-                        itemsInView.union([viewId])
-                    case let .disappeared(viewId):
-                        itemsInView.subtracting([viewId])
-                    case .chatItemsChanged:
-                        itemsInView
+                    var updated = itemsInView
+                    switch event {
+                    case let .appeared(viewId): updated.insert(viewId)
+                    case let .disappeared(viewId): updated.remove(viewId)
+                    case .chatItemsChanged: ()
                     }
+                    return updated
                 }
                 .map { ChatModel.shared.unreadChatItemCounts(itemsInView: $0) }
                 .removeDuplicates()