Add loading indicator to conversation screen

Tusker/Screens/Conversation/ConversationCollectionViewController.swift

@@ -94,6 +94,9 @@ class ConversationCollectionViewController: UIViewController, CollectionViewCont
         let expandThreadCell = UICollectionView.CellRegistration<ExpandThreadCollectionViewCell, ([ConversationNode], Bool)> { cell, indexPath, item in
             cell.updateUI(childThreads: item.0, inline: item.1)
         }
+        let loadingCell = UICollectionView.CellRegistration<LoadingCollectionViewCell, Void> { cell, indexPath, itemIdentifier in
+            cell.indicator.startAnimating()
+        }
         return UICollectionViewDiffableDataSource(collectionView: collectionView) { [unowned self] collectionView, indexPath, itemIdentifier in
             switch itemIdentifier {
             case let .status(id: id, state: state, prevLink: prevLink, nextLink: nextLink):
@@ -104,17 +107,31 @@ class ConversationCollectionViewController: UIViewController, CollectionViewCont
                 }
             case .expandThread(childThreads: let childThreads, inline: let inline):
                 return collectionView.dequeueConfiguredReusableCell(using: expandThreadCell, for: indexPath, item: (childThreads, inline))
+            case .loadingIndicator:
+                return collectionView.dequeueConfiguredReusableCell(using: loadingCell, for: indexPath, item: ())
             }
         }
     }
     
+    override func viewWillAppear(_ animated: Bool) {
+        super.viewWillAppear(animated)
+        
+        clearSelectionOnAppear(animated: animated)
+    }
+    
     func addMainStatus(_ status: StatusMO) {
         loadViewIfNeeded()
         
         var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
         snapshot.appendSections([.statuses])
+        
+        if status.inReplyToID != nil {
+            snapshot.appendItems([.loadingIndicator], toSection: .statuses)
+        }
+        
         let mainStatusItem = Item.status(id: mainStatusID, state: mainStatusState, prevLink: status.inReplyToID != nil, nextLink: false)
         snapshot.appendItems([mainStatusItem], toSection: .statuses)
+        
         dataSource.apply(snapshot, animatingDifferences: false)
     }
     
@@ -125,6 +142,7 @@ class ConversationCollectionViewController: UIViewController, CollectionViewCont
         await mastodonController.persistentContainer.addAll(statuses: parentStatuses + context.descendants)
         
         var snapshot = dataSource.snapshot()
+        snapshot.deleteItems([.loadingIndicator])
         let mainStatusItem = Item.status(id: mainStatusID, state: mainStatusState, prevLink: mainStatus.inReplyToID != nil, nextLink: false)
         let parentItems = parentIDs.enumerated().map { index, id in
             Item.status(id: id, state: .unknown, prevLink: index > 0, nextLink: true)
@@ -299,6 +317,7 @@ extension ConversationCollectionViewController {
     enum Item: Hashable {
         case status(id: String, state: CollapseState, prevLink: Bool, nextLink: Bool)
         case expandThread(childThreads: [ConversationNode], inline: Bool)
+        case loadingIndicator
         
         static func ==(lhs: Item, rhs: Item) -> Bool {
             switch (lhs, rhs) {
@@ -306,6 +325,8 @@ extension ConversationCollectionViewController {
                 return a == b && aPrev == bPrev && aNext == bNext
             case let (.expandThread(childThreads: a, inline: aInline), .expandThread(childThreads: b, inline: bInline)):
                 return a.count == b.count && zip(a, b).allSatisfy { $0.status.id == $1.status.id } && aInline == bInline
+            case (.loadingIndicator, .loadingIndicator):
+                return true
             default:
                 return false
             }
@@ -324,6 +345,8 @@ extension ConversationCollectionViewController {
                     hasher.combine(thread.status.id)
                 }
                 hasher.combine(inline)
+            case .loadingIndicator:
+                hasher.combine(2)
             }
         }
     }
@@ -331,11 +354,13 @@ extension ConversationCollectionViewController {
 
 extension ConversationCollectionViewController: UICollectionViewDelegate {
     func collectionView(_ collectionView: UICollectionView, shouldSelectItemAt indexPath: IndexPath) -> Bool {
-        if case .status(id: let id, _, _, _) = dataSource.itemIdentifier(for: indexPath),
-           id == mainStatusID {
-            return false
-        } else {
+        switch dataSource.itemIdentifier(for: indexPath) {
+        case .status(id: let id, state: _, prevLink: _, nextLink: _):
+            return id != mainStatusID
+        case .expandThread(childThreads: _, inline: _):
             return true
+        default:
+            return false
         }
     }
     
@@ -343,6 +368,8 @@ extension ConversationCollectionViewController: UICollectionViewDelegate {
         switch dataSource.itemIdentifier(for: indexPath) {
         case nil:
             break
+        case .loadingIndicator:
+            break
         case .status(id: let id, state: let state, _, _):
             selected(status: id, state: state.copy())
         case .expandThread(childThreads: let childThreads, inline: _):