Fix crash when conversation loading fails

Tusker/Screens/Conversation/ConversationTableViewController.swift

@@ -36,6 +36,8 @@ class ConversationTableViewController: EnhancedTableViewController {
     var showStatusesAutomatically = false
     var visibilityBarButtonItem: UIBarButtonItem!
     
+    private var loadingState = LoadingState.unloaded
+    
     init(for mainStatusID: String, state: StatusState = .unknown, mastodonController: MastodonController) {
         self.mainStatusID = mainStatusID
         self.mainStatusState = state
@@ -136,9 +138,12 @@ class ConversationTableViewController: EnhancedTableViewController {
     }
     
     private func loadMainStatus() {
+        guard loadingState == .unloaded else { return }
+        
         if let mainStatus = mastodonController.persistentContainer.status(for: mainStatusID) {
             self.mainStatusLoaded(mainStatus)
         } else {
+            loadingState = .loadingMain
             let request = Client.getStatus(id: mainStatusID)
             mastodonController.run(request) { (response) in
                 switch response {
@@ -148,14 +153,24 @@ class ConversationTableViewController: EnhancedTableViewController {
                         self.mainStatusLoaded(statusMO)
                     }
                     
-                case .failure(_):
+                case let .failure(error):
-                    fatalError()
+                    DispatchQueue.main.async {
+                        self.loadingState = .unloaded
+                        
+                        let config = ToastConfiguration(from: error, with: "Error Loading Status") { [weak self] (toast) in
+                            toast.dismissToast(animated: true)
+                            self?.loadMainStatus()
+                        }
+                        self.showToast(configuration: config, animated: true)
+                    }
                 }
             }
         }
     }
     
     private func mainStatusLoaded(_ mainStatus: StatusMO) {
+        mainStatus.incrementReferenceCount()
+        
         let mainStatusItem = Item.status(id: mainStatusID, state: mainStatusState)
         
         var snapshot = NSDiffableDataSourceSnapshot<Section, Item>()
@@ -163,48 +178,78 @@ class ConversationTableViewController: EnhancedTableViewController {
         snapshot.appendItems([mainStatusItem], toSection: .statuses)
         dataSource.apply(snapshot, animatingDifferences: false)
 
+        loadingState = .loadedMain
+
+        loadContext(for: mainStatus)
+    }
+    
+    private func loadContext(for mainStatus: StatusMO) {
+        guard loadingState == .loadedMain else { return }
+        
+        loadingState = .loadingContext
+        
+        // save the id here because we can't access the MO from the whatever thread the network callback happens on
         let mainStatusInReplyToID = mainStatus.inReplyToID
-        mainStatus.incrementReferenceCount()
         
         // todo: it would be nice to cache these contexts
         let request = Status.getContext(mainStatusID)
         mastodonController.run(request) { response in
-            guard case let .success(context, _) = response else { fatalError() }
+            switch response {
+            case let .success(context, _):
+                let parentIDs = self.getDirectParents(inReplyTo: mainStatusInReplyToID, from: context.ancestors)
+                let parentStatuses = context.ancestors.filter { parentIDs.contains($0.id) }
                 
-            let parents = self.getDirectParents(inReplyTo: mainStatusInReplyToID, from: context.ancestors)
+                // todo: should this really be blindly adding all the descendants?
-            let parentStatuses = context.ancestors.filter { parents.contains($0.id) }
+                self.mastodonController.persistentContainer.addAll(statuses: parentStatuses + context.descendants) {
+                    DispatchQueue.main.async {
+                        self.contextLoaded(mainStatus: mainStatus, context: context, parentIDs: parentIDs)
+                    }
+                }
                 
-            // todo: should this really be blindly adding all the descendants?
+            case let .failure(error):
-            self.mastodonController.persistentContainer.addAll(statuses: parentStatuses + context.descendants) {
                 DispatchQueue.main.async {
-                    var snapshot = self.dataSource.snapshot()
+                    self.loadingState = .loadedMain
-                    snapshot.insertItems(parents.map { .status(id: $0, state: .unknown) }, beforeItem: mainStatusItem)
                     
-                    // fetch all descendant status managed objects
+                    let config = ToastConfiguration(from: error, with: "Error Loading Content") { [weak self] (toast) in
-                    let descendantIDs = context.descendants.map(\.id)
+                        toast.dismissToast(animated: true)
-                    let request: NSFetchRequest<StatusMO> = StatusMO.fetchRequest()
+                        self?.loadContext(for: mainStatus)
-                    request.predicate = NSPredicate(format: "id in %@", descendantIDs)
-                    
-                    if let descendants = try? self.mastodonController.persistentContainer.viewContext.fetch(request) {
-                        // convert array of descendant statuses into tree of sub-threads
-                        let childThreads = self.getDescendantThreads(mainStatus: mainStatus, descendants: descendants)
-                        
-                        // convert sub-threads into items for section and add to snapshot
-                        self.addFlattenedChildThreadsToSnapshot(childThreads, mainStatus: mainStatus, snapshot: &snapshot)
-                    }
-                    
-                    self.dataSource.apply(snapshot, animatingDifferences: false) {
-                        // ensure that the main status is on-screen after newly loaded statuses are added
-                        // todo: should this not happen if the user has already started scrolling (e.g. because the main status is very long)?
-                        if let indexPath = self.dataSource.indexPath(for: mainStatusItem) {
-                            self.tableView.scrollToRow(at: indexPath, at: .middle, animated: false)
-                        }
                     }
+                    self.showToast(configuration: config, animated: true)
                 }
             }
         }
     }
     
+    private func contextLoaded(mainStatus: StatusMO, context: ConversationContext, parentIDs: [String]) {
+        let mainStatusItem = Item.status(id: mainStatusID, state: mainStatusState)
+        
+        var snapshot = self.dataSource.snapshot()
+        snapshot.insertItems(parentIDs.map { .status(id: $0, state: .unknown) }, beforeItem: mainStatusItem)
+        
+        // fetch all descendant status managed objects
+        let descendantIDs = context.descendants.map(\.id)
+        let request: NSFetchRequest<StatusMO> = StatusMO.fetchRequest()
+        request.predicate = NSPredicate(format: "id in %@", descendantIDs)
+        
+        if let descendants = try? self.mastodonController.persistentContainer.viewContext.fetch(request) {
+            // convert array of descendant statuses into tree of sub-threads
+            let childThreads = self.getDescendantThreads(mainStatus: mainStatus, descendants: descendants)
+            
+            // convert sub-threads into items for section and add to snapshot
+            self.addFlattenedChildThreadsToSnapshot(childThreads, mainStatus: mainStatus, snapshot: &snapshot)
+        }
+        
+        self.dataSource.apply(snapshot, animatingDifferences: false) {
+            // ensure that the main status is on-screen after newly loaded statuses are added
+            // todo: should this not happen if the user has already started scrolling (e.g. because the main status is very long)?
+            if let indexPath = self.dataSource.indexPath(for: mainStatusItem) {
+                self.tableView.scrollToRow(at: indexPath, at: .middle, animated: false)
+            }
+        }
+        
+        self.loadingState = .loadedAll
+    }
+
     private func getDirectParents(inReplyTo inReplyToID: String?, from statuses: [Status]) -> [String] {
         var statuses = statuses
         var parents = [String]()
@@ -390,6 +435,16 @@ extension ConversationTableViewController {
     }
 }
 
+extension ConversationTableViewController {
+    private enum LoadingState: Equatable {
+        case unloaded
+        case loadingMain
+        case loadedMain
+        case loadingContext
+        case loadedAll
+    }
+}
+
 extension ConversationTableViewController: TuskerNavigationDelegate {
     func conversation(mainStatusID: String, state: StatusState) -> ConversationTableViewController {
         let vc = ConversationTableViewController(for: mainStatusID, state: state, mastodonController: mastodonController)
@@ -419,3 +474,6 @@ extension ConversationTableViewController: UITableViewDataSourcePrefetching, Sta
         cancelPrefetchingStatuses(with: ids)
     }
 }
+
+extension ConversationTableViewController: ToastableViewController {
+}

Tusker/Screens/Utilities/DiffableTimelineLikeTableViewController.swift

@@ -121,11 +121,7 @@ class DiffableTimelineLikeTableViewController<Section: Hashable & CaseIterable,
                     
                 case let .failure(.client(error)):
                     self.state = .unloaded
-                    var config = ToastConfiguration(title: "Error Loading")
+                    let config = ToastConfiguration(from: error, with: "Error Loading") { [weak self] (toast) in
-                    config.subtitle = error.localizedDescription
-                    config.systemImageName = error.systemImageName
-                    config.actionTitle = "Retry"
-                    config.action = { [weak self] (toast) in
                         toast.dismissToast(animated: true)
                         self?.loadInitial()
                     }
@@ -157,11 +153,7 @@ class DiffableTimelineLikeTableViewController<Section: Hashable & CaseIterable,
                     self.dataSource.apply(snapshot, animatingDifferences: false)
                     
                 case let .failure(.client(error)):
-                    var config = ToastConfiguration(title: "Error Loading Older")
+                    let config = ToastConfiguration(from: error, with: "Error Loading Older") { [weak self] (toast) in
-                    config.subtitle = error.localizedDescription
-                    config.systemImageName = error.systemImageName
-                    config.actionTitle = "Retry"
-                    config.action = { [weak self] (toast) in
                         toast.dismissToast(animated: true)
                         self?.loadOlder()
                     }
@@ -244,11 +236,7 @@ class DiffableTimelineLikeTableViewController<Section: Hashable & CaseIterable,
                     }
                     
                 case let .failure(.client(error)):
-                    var config = ToastConfiguration(title: "Error Loading Newer")
+                    let config = ToastConfiguration(from: error, with: "Error Loading Newer") { [weak self] (toast) in
-                    config.subtitle = error.localizedDescription
-                    config.systemImageName = error.systemImageName
-                    config.actionTitle = "Retry"
-                    config.action = { [weak self] (toast) in
                         toast.dismissToast(animated: true)
                         self?.refresh()
                     }
@@ -326,14 +314,3 @@ extension DiffableTimelineLikeTableViewController: BackgroundableViewController
 
 extension DiffableTimelineLikeTableViewController: ToastableViewController {
 }
-
-fileprivate extension Client.Error {
-    var systemImageName: String {
-        switch self {
-        case .networkError(_):
-            return "wifi.exclamationmark"
-        default:
-            return "exclamationmark.triangle"
-        }
-    }
-}

Tusker/Views/Toast/ToastConfiguration.swift

@@ -7,6 +7,7 @@
 //
 
 import UIKit
+import Pachyderm
 
 struct ToastConfiguration {
     var systemImageName: String?
@@ -31,3 +32,24 @@ struct ToastConfiguration {
         case automatic
     }
 }
+
+extension ToastConfiguration {
+    init(from error: Client.Error, with title: String, retryAction: @escaping (ToastView) -> Void) {
+        self.init(title: title)
+        self.subtitle = error.localizedDescription
+        self.systemImageName = error.systemImageName
+        self.actionTitle = "Retry"
+        self.action = retryAction
+    }
+}
+
+fileprivate extension Client.Error {
+    var systemImageName: String {
+        switch self {
+        case .networkError(_):
+            return "wifi.exclamationmark"
+        default:
+            return "exclamationmark.triangle"
+        }
+    }
+}