Get firebase paginated list

FirebaseGetListExtension.kt

inline fun <reified FirebaseObject : FirebaseIdentifiableModel> FirebaseFirestore.getPaginatedFirebaseList(
    path: String,
    page: FirebasePage
): Single<List<FirebaseObject>> {
    val firstDocumentMaybe = getFirstDocument(path, page)

    return firstDocumentMaybe.isEmpty.flatMap {
        return@flatMap if (it) {
            Single.just(emptyList())
        } else {
            firstDocumentMaybe.flatMapSingle { firstDocument ->
                return@flatMapSingle Single.create<List<FirebaseObject>> { emitter ->
                    val collectionReference = collection(path).orderBy(page.orderBy, page.direction)
                        .startAt(firstDocument)
                        .limit(page.size)

                    val listenerRegistration: ListenerRegistration = collectionReference.addSnapshotListener { querySnapshot, exception ->
                        querySnapshot?.run {
                            emitter.onSuccess(toFirebaseObjectList())
                        } ?: exception?.run {
                            emitter.onError(this)
                        } ?: kotlin.run { emitter.onError(FirebaseUnexpectedException()) }
                    }

                    emitter.setCancellable { listenerRegistration.remove() }
                }
            }
        }
    }
}