Moving a Core Data store without disrupting CloudKit integration

fileprivate func migrateCoreDataStoreToAppGroup() {
      DBLog.info("🧮 Check if need to migrate sqlite file")

      let container = NSPersistentCloudKitContainer(name: "Model")
      guard let storeDescription = container.persistentStoreDescriptions.first else {
          // do something nice instead of this
          fatalError("###\(#function): Failed to retrieve a persistent store description.")
      }

      guard let modelURL = Bundle.main.url(forResource: "Model", withExtension: "momd"), let mom = NSManagedObjectModel(contentsOf: modelURL) else {
          /// do something nice instead of this
          fatalError("###\(#function): Failed to retrieve the managed object model file.")
      }

      // Verify if old file il there
      //
      guard let fromStoreURL = storeDescription.url, FileManager.default.fileExists(atPath: fromStoreURL.path) else {
          DBLog.info("🧮 No need to migrate sqlite")
          return
      }

      DBLog.info("🧮 Need to migrate sqlite file to App Group")

      let toStoreURL = StoreManager.sqliteStoreURL
      let psc = NSPersistentStoreCoordinator(managedObjectModel: mom)
      do {
          try psc.replacePersistentStore(at: toStoreURL, destinationOptions: nil,
                                 withPersistentStoreFrom: fromStoreURL, sourceOptions: nil,
                                 ofType: NSSQLiteStoreType)
          DBLog.info("🧮 Successfully migrate sqlite to app group")

          // Delete old store
          //
          let fileCoordinator = NSFileCoordinator(filePresenter: nil)
          fileCoordinator.coordinate(writingItemAt: fromStoreURL, options: .forDeleting, error: nil, byAccessor: { _ in
              do {
                  try FileManager.default.removeItem(at: fromStoreURL)
                  DBLog.info("🧮 Successfully removed sqlite (non-app-group)")
              } catch {
                  DBLog.error(error.localizedDescription)
              }
          })

      } catch {
          DBLog.error("Cannot replace persistent store \(error)") // Error handling.
      }
  }

static var appGroupPath: URL {
    FileManager.default.containerURL(forSecurityApplicationGroupIdentifier: StoreManager.appGroupIdentifier)!
}


lazy var persistentContainer: NSPersistentContainer = {

    // 1) create store, use app store group url
    let container = NSPersistentCloudKitContainer(name: "Model")

    // Early if no description is present
    //
    guard let defaultStoreDescription = container.persistentStoreDescriptions.first else {
        // do something nice instead of this
        fatalError("###\(#function): Failed to retrieve a persistent store description.")
    }

    // 2) Set app group store url and make sure to retain all default options
    //
    let appGroupStoreURL = StoreManager.appGroupPath.appendingPathComponent("Model.sqlite")
    DBLog.info("🗄 SQlite url: \(appGroupStoreURL.path)")
    let appGroupStoreDescription = NSPersistentStoreDescription(url: appGroupStoreURL)
		
    // 3) apply options
    //
    for option in defaultStoreDescription.options {
        appGroupStoreDescription.setOption(option.value, forKey: option.key)
    }
		
    // 4) Enable history tracking and remote notifications
    // 

    appGroupStoreDescription.setOption(true as NSNumber, forKey: NSPersistentHistoryTrackingKey)
    appGroupStoreDescription.setOption(true as NSNumber, forKey: NSPersistentStoreRemoteChangeNotificationPostOptionKey)

    appGroupStoreDescription.cloudKitContainerOptions = defaultStoreDescription.cloudKitContainerOptions
    container.persistentStoreDescriptions = [appGroupStoreDescription]

    // 5) Load the container store
    container.loadPersistentStores(completionHandler: { _, error in
        if let error = error as NSError? {
            // Replace this implementation with code to handle the error appropriately.
            fatalError("Unresolved error \(error), \(error.userInfo)")
        }

    })
    // 6) Set merge policies
    container.viewContext.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy
    container.viewContext.transactionAuthor = appTransactionAuthorName

    // Pin the viewContext to the current generation token and set it to keep itself up to date with local changes.
    container.viewContext.automaticallyMergesChangesFromParent = true
    do {
        try container.viewContext.setQueryGenerationFrom(.current)
    } catch {
        fatalError("###\(#function): Failed to pin viewContext to the current generation:\(error)")
    }
		
    // 7) Observe Core Data remote change notifications.
    //
    NotificationCenter.default.addObserver(
        self, selector: #selector(StoreManager.storeRemoteChange(_:)),
        name: .NSPersistentStoreRemoteChange, object: container.persistentStoreCoordinator)

    return container

}()