How to get a "Sequence" or counters like structure in firebase realtime database

I am moving from sql to nosql database,as a part of it I am working on a flutter project where I am implementing a sequence like structure as below.

  static Future<int> get nextId async {
    return database.get().then((snapshot) {
      return snapshot.value;
    }).then((value) {
      database.set(value + 1);
      return value + 1;
    });
  }

It works, each time i am using nextID it increments in the database. My question is that is it possible when two different users happens to get the same value on invoking nextId.

If you want to prevent multiple users from modifying the same value in conflicting ways, you'll want to use a transaction.

In this case, since you seem to be simply incrementing a value, you may also be helped by using the atomic increment operation which is significantly faster as I showed in: How quickly can you atomically increment a value on the Firebase Realtime Database?