☁️ Cirrus

// AppDelegate.swift
func application(
  _ application: UIApplication,
  didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
) -> Bool {
  ...
  application.registerForRemoteNotifications()
  ...
}

import CloudKitCodable

struct Landmark: CloudKitCodable {
  struct Coordinate: Codable {
    let latitude: Double
    let longitude: Double
  }

  let identifier: UUID
  let name: String
  let coordinate: Coordinate

  // MARK: - CloudKitCodable

  /// A key that uniquely identifies the model. Use this identifier to update your 
  /// associated local models when the sync engine emits changes.
  var cloudKitIdentifier: CloudKitIdentifier {
    return identifier.uuidString
  }

  /// Managed by the sync engine, this should be set to nil when creating a new model.
  /// Be sure to save this when persisting models locally.
  var cloudKitSystemFields: Data? = nil

  /// Describes how to handle conflicts between client and server models.
  public static func resolveConflict(clientModel: Self, serverModel: Self) -> Self? {

    // Use `cloudKitLastModifiedDate` to check when models were last saved to the server
    guard let clientDate = clientModel.cloudKitLastModifiedDate,
      let serverDate = serverModel.cloudKitLastModifiedDate else {
      return clientModel
    }
    return clientDate > serverDate ? clientModel : serverModel
  }
}

import Cirrus

let syncEngine = SyncEngine<Landmark>()

// AppDelegate.swift
func application(
  _ application: UIApplication, didReceiveRemoteNotification userInfo: [AnyHashable: Any]
) {
  syncEngine.processRemoteChangeNotification(with: userInfo)
  ...
}

// Upload new or updated models
syncEngine.upload(newLandmarks)

// Delete models
syncEngine.delete(oldLandmark)

// Observe remote model changes
syncEngine.modelsChanged
  .sink { change in
    // Update local models
    switch change {
    case let .updated(models):
      ...
    case let .deleted(modelIDs):
      ...
    }
  }

// Observe iCloud account status changes
syncEngine.$accountStatus
  .sink { accountStatus in
    switch accountStatus {
      case .available:
        ...
      case .noAccount:
        ...
      ...
    }
  }