Fixed restoring position at the top for the last message in the conversation

Author: ekazaev

ChatLayout/Classes/Core/CollectionViewChatLayout.swift

@@ -620,12 +620,12 @@ public final class CollectionViewChatLayout: UICollectionViewLayout {
             if let frame = controller.itemFrame(for: currentPositionSnapshot.indexPath.itemPath, kind: currentPositionSnapshot.kind, at: state, isFinal: true),
                contentHeight != 0,
                contentHeight > visibleBounds.size.height {
+                let maxAllowed = max(-collectionView.adjustedContentInset.top, contentHeight - collectionView.frame.height + collectionView.adjustedContentInset.bottom)
                 switch currentPositionSnapshot.edge {
                 case .top:
-                    let desiredOffset = frame.minY - currentPositionSnapshot.offset - collectionView.adjustedContentInset.top - settings.additionalInsets.top
+                    let desiredOffset = max(min(maxAllowed, frame.minY - currentPositionSnapshot.offset - collectionView.adjustedContentInset.top - settings.additionalInsets.top), -collectionView.adjustedContentInset.top)
                     context.contentOffsetAdjustment.y = desiredOffset - collectionView.contentOffset.y
                 case .bottom:
-                    let maxAllowed = max(-collectionView.adjustedContentInset.top, contentHeight - collectionView.frame.height + collectionView.adjustedContentInset.bottom)
                     let desiredOffset = max(min(maxAllowed, frame.maxY + currentPositionSnapshot.offset - collectionView.bounds.height + collectionView.adjustedContentInset.bottom + settings.additionalInsets.bottom), -collectionView.adjustedContentInset.top)
                     context.contentOffsetAdjustment.y = desiredOffset - collectionView.contentOffset.y
                 }

ChatLayout/Classes/Core/Extensions/CGRect+Extension.swift

@@ -23,6 +23,10 @@ extension CGRect {
         CGPoint(x: origin.x + size.width, y: origin.y + size.height)
     }
 
+    var centerPoint: CGPoint {
+        CGPoint(x: origin.x + size.width / 2, y: origin.y + size.height / 2)
+    }
+
     @inline(__always) mutating func offsettingBy(dx: CGFloat, dy: CGFloat) {
         origin.x += dx
         origin.y += dy