Handle authentication required error for instance timelines

Tusker/Screens/Timeline/InstanceTimelineViewController.swift

@@ -81,7 +81,53 @@ class InstanceTimelineViewController: TimelineViewController {
         super.collectionView(collectionView, didSelectItemAt: indexPath)
     }
     
-    // MARK: - Interaction
+    // MARK: Timeline
+    
+    override func handleLoadAllError(_ error: Swift.Error) async {
+        switch (error as? Client.Error)?.type {
+        case .mastodonError(422, _), .unexpectedStatus(422):
+            collectionView.isHidden = true
+            view.backgroundColor = .systemBackground
+            
+            let image = UIImageView(image: UIImage(systemName: "lock.fill"))
+            image.tintColor = .secondaryLabel
+            image.contentMode = .scaleAspectFit
+            
+            let title = UILabel()
+            title.textColor = .secondaryLabel
+            title.font = .preferredFont(forTextStyle: .title1).withTraits(.traitBold)!
+            title.adjustsFontForContentSizeCategory = true
+            title.numberOfLines = 0
+            title.textAlignment = .center
+            title.text = "This instance requires an account to view."
+            
+            let stack = UIStackView(arrangedSubviews: [
+                image,
+                title,
+            ])
+            stack.axis = .vertical
+            stack.alignment = .center
+            stack.spacing = 8
+            stack.isAccessibilityElement = true
+            stack.accessibilityLabel = title.text!
+            
+            stack.translatesAutoresizingMaskIntoConstraints = false
+            view.addSubview(stack)
+            NSLayoutConstraint.activate([
+                image.widthAnchor.constraint(equalToConstant: 64),
+                image.heightAnchor.constraint(equalToConstant: 64),
+                
+                stack.leadingAnchor.constraint(equalToSystemSpacingAfter: view.safeAreaLayoutGuide.leadingAnchor, multiplier: 1),
+                view.safeAreaLayoutGuide.trailingAnchor.constraint(equalToSystemSpacingAfter: stack.trailingAnchor, multiplier: 1),
+                stack.centerYAnchor.constraint(equalTo: view.safeAreaLayoutGuide.centerYAnchor),
+            ])
+            
+        default:
+            await super.handleLoadAllError(error)
+        }
+    }
+    
+    // MARK: Interaction
     @objc func toggleSaveButtonPressed() {
         let context = parentMastodonController!.persistentContainer.viewContext
         let req = SavedInstance.fetchRequest(url: instanceURL, account: parentMastodonController!.accountInfo!)

Tusker/Screens/Timeline/TimelineViewController.swift

@@ -856,6 +856,17 @@ class TimelineViewController: UIViewController, TimelineLikeCollectionViewContro
             self.dataSource.apply(snapshot, animatingDifferences: true)
         }
     }
+    
+    // this is only implemented here so it's overridable by InstanceTimelineViewController
+    func handleLoadAllError(_ error: Swift.Error) async {
+        let config = ToastConfiguration(from: error, with: "Error Loading", in: self) { [weak self] toast in
+            toast.dismissToast(animated: true)
+            Task {
+                await self?.controller.loadInitial()
+            }
+        }
+        self.showToast(configuration: config, animated: true)
+    }
 }
 
 extension TimelineViewController {