Attachment reordering

Packages/ComposeUI/Sources/ComposeUI/Views/AttachmentsListView.swift

@@ -62,6 +62,11 @@ private struct Callbacks {
         draft.attachments = NSMutableOrderedSet(array: array)
     }
     
+    func reorderAttachments(with difference: CollectionDifference<DraftAttachment>) {
+        let array = draft.draftAttachments.applying(difference)!
+        draft.attachments = NSMutableOrderedSet(array: array)
+    }
+    
     func addPhoto() {
         presentAssetPicker?() {
             insertAttachments(at: draft.attachments.count, itemProviders: $0.map(\.itemProvider))
@@ -100,6 +105,31 @@ private struct WrappedCollectionView: UIViewRepresentable {
         context.coordinator.dataSource = dataSource
         view.delegate = context.coordinator
         view.isScrollEnabled = false
+        
+        dataSource.reorderingHandlers.canReorderItem = {
+            if case .attachment(_) = $0 {
+                true
+            } else {
+                false
+            }
+        }
+        dataSource.reorderingHandlers.didReorder = { transaction in
+            let attachmentsChanges = transaction.difference.map {
+                switch $0 {
+                case .insert(let offset, let element, let associatedWith):
+                    guard case .attachment(let attachment) = element else { fatalError() }
+                    return CollectionDifference<DraftAttachment>.Change.insert(offset: offset, element: attachment, associatedWith: associatedWith)
+                case .remove(let offset, let element, let associatedWith):
+                    guard case .attachment(let attachment) = element else { fatalError() }
+                    return CollectionDifference<DraftAttachment>.Change.remove(offset: offset, element: attachment, associatedWith: associatedWith)
+                }
+            }
+            let attachmentsDiff = CollectionDifference(attachmentsChanges)!
+            callbacks.reorderAttachments(with: attachmentsDiff)
+        }
+        let longPressRecognizer = UILongPressGestureRecognizer(target: context.coordinator, action: #selector(WrappedCollectionViewCoordinator.reorderingLongPressRecognized))
+        longPressRecognizer.delegate = context.coordinator
+        view.addGestureRecognizer(longPressRecognizer)
         return view
     }
     
@@ -188,7 +218,7 @@ private final class IntrinsicContentSizeCollectionView: UICollectionView {
 }
 
 @available(iOS 16.0, *)
-private final class WrappedCollectionViewCoordinator: NSObject, UICollectionViewDelegate {
+private final class WrappedCollectionViewCoordinator: NSObject, UICollectionViewDelegate, UIGestureRecognizerDelegate {
     var callbacks: Callbacks
     var setHeightOfCellBeingDeleted: ((CGFloat) -> Void)?
     
@@ -277,6 +307,41 @@ private final class WrappedCollectionViewCoordinator: NSObject, UICollectionView
             callbacks.togglePoll()
         }
     }
+    
+    func collectionView(_ collectionView: UICollectionView, targetIndexPathForMoveOfItemFromOriginalIndexPath originalIndexPath: IndexPath, atCurrentIndexPath currentIndexPath: IndexPath, toProposedIndexPath proposedIndexPath: IndexPath) -> IndexPath {
+        let snapshot = dataSource.snapshot()
+        let attachmentsSection = snapshot.indexOfSection(.attachments)!
+        if proposedIndexPath.section != attachmentsSection {
+            return IndexPath(item: snapshot.itemIdentifiers(inSection: .attachments).count - 1, section: attachmentsSection)
+        } else {
+            return proposedIndexPath
+        }
+    }
+    
+    func gestureRecognizerShouldBegin(_ gestureRecognizer: UIGestureRecognizer) -> Bool {
+        let collectionView = gestureRecognizer.view as! UICollectionView
+        let location = gestureRecognizer.location(in: collectionView)
+        guard let indexPath = collectionView.indexPathForItem(at: location) else {
+            return false
+        }
+        return collectionView.beginInteractiveMovementForItem(at: indexPath)
+    }
+    
+    @objc func reorderingLongPressRecognized(_ recognizer: UILongPressGestureRecognizer) {
+        let collectionView = recognizer.view as! UICollectionView
+        switch recognizer.state {
+        case .began:
+            break
+        case .changed:
+            collectionView.updateInteractiveMovementTargetPosition(recognizer.location(in: collectionView))
+        case .ended:
+            collectionView.endInteractiveMovement()
+        case .cancelled:
+            collectionView.cancelInteractiveMovement()
+        default:
+            break
+        }
+    }
 }