Update UI in responds to remote changes of saved hashtags/instances

Tusker/CoreData/MastodonCachePersistentStore.swift

@@ -39,6 +39,9 @@ class MastodonCachePersistentStore: NSPersistentCloudKitContainer {
         return context
     }()
     
+    private var remoteChangeHandlerQueue = DispatchQueue(label: "PersistentStore remote changes")
+    private var lastRemoteChangeToken: NSPersistentHistoryToken?
+    
     // TODO: consider sending managed objects through this to avoid re-fetching things unnecessarily
     // would need to audit existing uses to make sure everything happens on the main thread
     // and when updating things on the background context would need to switch to main, refetch, and then publish
@@ -63,6 +66,8 @@ class MastodonCachePersistentStore: NSPersistentCloudKitContainer {
             localStoreLocation.appendPathComponent("\(accountInfo!.persistenceKey)_cache.sqlite", isDirectory: false)
             let localStoreDescription = NSPersistentStoreDescription(url: localStoreLocation)
             localStoreDescription.configuration = "Local"
+            localStoreDescription.setOption(true as NSNumber, forKey: NSPersistentHistoryTrackingKey)
+            localStoreDescription.setOption(true as NSNumber, forKey: NSPersistentStoreRemoteChangeNotificationPostOptionKey)
             
             var cloudStoreLocation = FileManager.default.urls(for: .applicationSupportDirectory, in: .userDomainMask).first!
             cloudStoreLocation.appendPathComponent("cloud.sqlite", isDirectory: false)
@@ -71,6 +76,8 @@ class MastodonCachePersistentStore: NSPersistentCloudKitContainer {
             let options = NSPersistentCloudKitContainerOptions(containerIdentifier: "iCloud.space.vaccor.Tusker")
             options.databaseScope = .private
             cloudStoreDescription.cloudKitContainerOptions = options
+            cloudStoreDescription.setOption(true as NSNumber, forKey: NSPersistentHistoryTrackingKey)
+            cloudStoreDescription.setOption(true as NSNumber, forKey: NSPersistentStoreRemoteChangeNotificationPostOptionKey)
             
             persistentStoreDescriptions = [
                 cloudStoreDescription,
@@ -167,6 +174,7 @@ class MastodonCachePersistentStore: NSPersistentCloudKitContainer {
         viewContext.mergePolicy = NSMergePolicy.mergeByPropertyObjectTrump
         
         NotificationCenter.default.addObserver(self, selector: #selector(managedObjectsDidChange), name: .NSManagedObjectContextObjectsDidChange, object: viewContext)
+        NotificationCenter.default.addObserver(self, selector: #selector(remoteChanges), name: .NSPersistentStoreRemoteChange, object: persistentStoreCoordinator)
     }
     
     func save(context: NSManagedObjectContext) {
@@ -475,4 +483,45 @@ class MastodonCachePersistentStore: NSPersistentCloudKitContainer {
         return changes
     }
     
+    // the remote change notifications only handle deletes, inserts get handled by the regular managed object did change notifications
+    @objc private func remoteChanges(_ notification: Foundation.Notification) {
+        guard let token = notification.userInfo?[NSPersistentHistoryTokenKey] as? NSPersistentHistoryToken else {
+            return
+        }
+        remoteChangeHandlerQueue.async {
+            defer {
+                self.lastRemoteChangeToken = token
+            }
+            let req = NSPersistentHistoryChangeRequest.fetchHistory(after: self.lastRemoteChangeToken)
+            self.backgroundContext.performAndWait {
+                if let result = try? self.backgroundContext.execute(req) as? NSPersistentHistoryResult,
+                   let transactions = result.result as? [NSPersistentHistoryTransaction] {
+                    var changes: (hashtags: Bool, instances: Bool) = (false, false)
+                    outer: for transaction in transactions {
+                        for change in transaction.changes ?? [] {
+                            if change.changedObjectID.entity.name == "SavedHashtag" {
+                                changes.hashtags = true
+                            } else if change.changedObjectID.entity.name == "SavedInstance" {
+                                changes.instances = true
+                            }
+                            if changes.hashtags && changes.instances {
+                                break outer
+                            }
+                        }
+                    }
+                    if changes.hashtags {
+                        DispatchQueue.main.async {
+                            NotificationCenter.default.post(name: .savedHashtagsChanged, object: nil)
+                        }
+                    }
+                    if changes.instances {
+                        DispatchQueue.main.async {
+                            NotificationCenter.default.post(name: .savedInstancesChanged, object: nil)
+                        }
+                    }
+                }
+            }
+        }
+    }
+    
 }