PaginatedFlow.kt

override fun getLeaders(lastVisibleItem: Flow<Int>): Flow<List<User>> =
    flow {
        val users = mutableListOf<DocumentSnapshot>()
        users.addAll(
            suspendCoroutine<List<DocumentSnapshot>> { c ->
                collection("users")
                    .whereGreaterThan("points", 0)
                    .orderBy("points", Query.Direction.DESCENDING)
                    .limit(25)
                    .get().addOnSuccessListener {
                        c.resume(it.documents)
                    }
            }
        )

        emit(users.map { it.toUserDto().toUser() })

        lastVisibleItem.transform { lastVisibleItem ->
            if (lastVisibleItem == users.size) {
                users.addAll(
                    suspendCoroutine<List<DocumentSnapshot>> { c ->
                        collection("users")
                            .whereGreaterThan("points", 0)
                            .orderBy("points", Query.Direction.DESCENDING)
                            .startAfter(users.last())
                            .limit(25)
                            .get().addOnSuccessListener {
                                c.resume(it.documents)
                            }
                    }
                )
                emit(users.map { it.toUserDto().toUser() })
            }
        }.collect { newUsers: List<User> ->
            emit(newUsers)
        }
    }