feat: add notification gap fetcher

Mastodon/Diffiable/Notification/NotificationSection.swift

@@ -49,8 +49,10 @@ extension NotificationSection {
                     )
                 }
                 return cell
-            case .feedLoader(let record):
-                return UITableViewCell()
+            case .feedLoader:
+                let cell = tableView.dequeueReusableCell(withIdentifier: String(describing: TimelineBottomLoaderTableViewCell.self), for: indexPath) as! TimelineBottomLoaderTableViewCell
+                cell.activityIndicatorView.startAnimating()
+                return cell
             case .bottomLoader:
                 let cell = tableView.dequeueReusableCell(withIdentifier: String(describing: TimelineBottomLoaderTableViewCell.self), for: indexPath) as! TimelineBottomLoaderTableViewCell
                 cell.activityIndicatorView.startAnimating()

Mastodon/Scene/Notification/NotificationTimeline/NotificationTimelineViewController.swift

@@ -135,6 +135,18 @@ extension NotificationTimelineViewController: UITableViewDelegate, AutoGenerateT
     }
 
     // sourcery:end
+    
+    func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
+        guard let item = viewModel.diffableDataSource?.itemIdentifier(for: indexPath) else {
+            return
+        }
+        
+        // check item type inside `loadMore`
+        Task {
+            await viewModel.loadMore(item: item)
+        }
+    }
+    
 }
 
 // MARK: - NotificationTableViewCellDelegate

Mastodon/Scene/Notification/NotificationTimeline/NotificationTimelineViewModel.swift

@@ -156,4 +156,35 @@ extension NotificationTimelineViewModel {
         }
     }
     
+    // load timeline gap
+    func loadMore(item: NotificationItem) async {
+        guard case let .feedLoader(record) = item else { return }
+        guard let authenticationBox = context.authenticationService.activeMastodonAuthenticationBox.value else { return }
+        
+        let managedObjectContext = context.managedObjectContext
+        let key = "LoadMore@\(record.objectID)"
+        
+        // return when already loading state
+        guard managedObjectContext.cache(froKey: key) == nil else { return }
+
+        guard let feed = record.object(in: managedObjectContext) else { return }
+        guard let maxID = feed.notification?.id else { return }
+        // keep transient property live
+        managedObjectContext.cache(feed, key: key)
+        defer {
+            managedObjectContext.cache(nil, key: key)
+        }
+        
+        // fetch data
+        do {
+            _ = try await context.apiService.notifications(
+                maxID: maxID,
+                scope: scope,
+                authenticationBox: authenticationBox
+            )
+        } catch {
+            logger.log(level: .debug, "\((#file as NSString).lastPathComponent, privacy: .public)[\(#line, privacy: .public)], \(#function, privacy: .public): fetch more failure: \(error.localizedDescription)")
+        }
+    }
+    
 }