[trello.com/c/esjdkfhK] Bug/UI: Extra scroll on many new messages

Author: vovameister

Adamant/Modules/Chat/View/ChatViewController.swift

@@ -741,14 +741,11 @@ private extension ChatViewController {
 
 private extension ChatViewController {
     func updateIsScrollPositionNearlyTheBottom() {
-        let oldValue = isScrollPositionNearlyTheBottom
         isScrollPositionNearlyTheBottom = chatMessagesCollectionView.bottomOffset < 150
-        
-        guard oldValue != isScrollPositionNearlyTheBottom else { return }
     }
 
     func updateMessages() {
-        chatMessagesCollectionView.reloadData(newIds: viewModel.messages.map { $0.id })
+        chatMessagesCollectionView.reloadData(newIds: viewModel.messages.map { $0.id }, isOnBottom: isScrollPositionNearlyTheBottom)
         scrollDownOnNewMessageIfNeeded(previousBottomMessageId: bottomMessageId)
         bottomMessageId = viewModel.messages.last?.messageId
     }

Adamant/Modules/Chat/View/Subviews/ChatMessagesCollection.swift

@@ -43,14 +43,20 @@ final class ChatMessagesCollectionView: MessagesCollectionView {
         }
     }
 
-    func reloadData(newIds: [String]) {
-        guard newIds.last == currentIds.last || newIds.first != currentIds.first else {
+    func reloadData(newIds: [String], isOnBottom: Bool) {
+        let hasNewMessagesAtTop = newIds.first != currentIds.first
+        let hasNewMessagesAtBottom = newIds.last != currentIds.last
+
+        guard hasNewMessagesAtTop || hasNewMessagesAtBottom else {
             return applyNewIds(newIds)
         }
-        
+
         let bottomOffset = self.bottomOffset
         applyNewIds(newIds)
-        setBottomOffset(bottomOffset, safely: !isDragging && !isDecelerating)
+
+        if hasNewMessagesAtTop || (hasNewMessagesAtBottom && isOnBottom) {
+            setBottomOffset(bottomOffset, safely: !isDragging && !isDecelerating)
+        }
     }
 
     func setFullBottomInset(_ inset: CGFloat) {