Display toast on load errors

Tusker/Screens/Utilities/DiffableTimelineLikeTableViewController.swift

@@ -59,6 +59,7 @@ class DiffableTimelineLikeTableViewController<Section: Hashable & CaseIterable,
         super.viewDidDisappear(animated)
         
         pruneOffscreenRows()
+        currentToast?.dismissToast(animated: false)
     }
     
     class func refreshCommandTitle() -> String {
@@ -111,13 +112,26 @@ class DiffableTimelineLikeTableViewController<Section: Hashable & CaseIterable,
         state = .loadingInitial
         
         loadInitialItems() { result in
-            guard case let .success(snapshot) = result else {
-                self.state = .unloaded
-                return
-            }
             DispatchQueue.main.async {
+                switch result {
+                case let .success(snapshot):
                     self.dataSource.apply(snapshot, animatingDifferences: false)
                     self.state = .loaded
+                case let .failure(.client(error)):
+                    self.state = .unloaded
+                    var config = ToastConfiguration(title: "Error Loading")
+                    config.subtitle = error.localizedDescription
+                    config.systemImageName = error.systemImageName
+                    config.actionTitle = "Retry"
+                    config.action = { [weak self] (toast) in
+                        toast.dismissToast(animated: true)
+                        self?.loadInitial()
+                    }
+                    self.showToast(configuration: config, animated: true)
+                    
+                default:
+                    self.state = .unloaded
+                }
             }
        }
     }
@@ -133,13 +147,27 @@ class DiffableTimelineLikeTableViewController<Section: Hashable & CaseIterable,
         state = .loadingOlder
         
         loadOlderItems(currentSnapshot: dataSource.snapshot()) { result in
-            guard case let .success(snapshot) = result else {
-                self.state = .loaded
-                return
-            }
             DispatchQueue.main.async {
-                self.dataSource.apply(snapshot, animatingDifferences: false)
                 self.state = .loaded
+                
+                switch result {
+                case let .success(snapshot):
+                    self.dataSource.apply(snapshot, animatingDifferences: false)
+                    
+                case let .failure(.client(error)):
+                    var config = ToastConfiguration(title: "Error Loading Older")
+                    config.subtitle = error.localizedDescription
+                    config.systemImageName = error.systemImageName
+                    config.actionTitle = "Retry"
+                    config.action = { [weak self] (toast) in
+                        toast.dismissToast(animated: true)
+                        self?.loadOlder()
+                    }
+                    self.showToast(configuration: config, animated: true)
+                    
+                default:
+                    break
+                }
             }
         }
     }
@@ -196,24 +224,33 @@ class DiffableTimelineLikeTableViewController<Section: Hashable & CaseIterable,
         }
         
         loadNewerItems(currentSnapshot: snapshot) { result in
-            guard case let .success(snapshot) = result else {
             DispatchQueue.main.async {
                 self.refreshControl?.endRefreshing()
                 self.state = .loaded
-                }
-                return
-            }
                 
-            DispatchQueue.main.async {
+                switch result {
-                self.refreshControl?.endRefreshing()
+                case let .success(snapshot):
                     self.dataSource.apply(snapshot, animatingDifferences: false)
-                self.state = .loaded
-
                     if let item = item,
                        let indexPath = self.dataSource.indexPath(for: item) {
                         // maintain the current position in the list (don't scroll to top)
                         self.tableView.scrollToRow(at: indexPath, at: .top, animated: false)
                     }
+                    
+                case let .failure(.client(error)):
+                    var config = ToastConfiguration(title: "Error Loading Newer")
+                    config.subtitle = error.localizedDescription
+                    config.systemImageName = error.systemImageName
+                    config.actionTitle = "Retry"
+                    config.action = { [weak self] (toast) in
+                        toast.dismissToast(animated: true)
+                        self?.refresh()
+                    }
+                    self.showToast(configuration: config, animated: true)
+                    
+                default:
+                    break
+                }
             }
         }
     }
@@ -267,5 +304,20 @@ extension DiffableTimelineLikeTableViewController {
 extension DiffableTimelineLikeTableViewController: BackgroundableViewController {
     func sceneDidEnterBackground() {
         pruneOffscreenRows()
+        currentToast?.dismissToast(animated: false)
+    }
+}
+
+extension DiffableTimelineLikeTableViewController: ToastableViewController {
+}
+
+fileprivate extension Client.Error {
+    var systemImageName: String {
+        switch self {
+        case .networkError(_):
+            return "wifi.exclamationmark"
+        default:
+            return "exclamationmark.triangle"
+        }
     }
 }