Detect if user is online or offline in Firebase Swift

Question

Please I'm trying to detect if the user is online or offline and I wrote the code below.

    Database.database().isPersistenceEnabled = true
        let presenceRef = Database.database().reference(withPath: "disconnectmessage");
        // Write a string when this client loses connection
        presenceRef.onDisconnectSetValue("I disconnected!")
        
        presenceRef.onDisconnectRemoveValue { error, reference in
          if let error = error {
            print("Could not establish onDisconnect event: \(error)")
          }
        }
        
        let connectedRef = Database.database().reference(withPath: ".info/connected")
        connectedRef.observe(.value, with: { snapshot in
          if snapshot.value as? Bool ?? false {
              
            print("Connected")
              if Auth.auth().currentUser != nil {
                  OnlineOfflineService.online(for: (Auth.auth().currentUser?.uid)!, status: true)
              }
              
          } else {
            print("Not connected")
              if Auth.auth().currentUser != nil {
                  OnlineOfflineService.online(for: (Auth.auth().currentUser?.uid)!, status: false)
              }
          }
        })

and I tried to open the permission.

rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {
    match /{document=**} {
      allow read, write: if true;
    }
  }
}

I tried also to use.

func applicationWillTerminate(_ application: UIApplication) {
        if Auth.auth().currentUser != nil {
            OnlineOfflineService.online(for: (Auth.auth().currentUser?.uid)!, status: false)
        }
 }

The question is, how can I detect if the user is online or offline? Any suggestions, please??