UserBoundaryCallback.kt

class UserBoundaryCallback constructor(val userDao: UserDao?) :
    PagedList.BoundaryCallback<User?>() {
    private val compositeDisposable: CompositeDisposable = CompositeDisposable()

    override fun onZeroItemsLoaded() {
        fetchUsers()
    }

    override fun onItemAtFrontLoaded(itemAtFront: User) {
        fetchUsers()
    }

    override fun onItemAtEndLoaded(itemAtEnd: User) {
        fetchUsers()
    }

    /**
     * Fetches contributions using the MediaWiki API
     */
    fun fetchUsers() {
        compositeDisposable.add(
            mockGetUsers()
                .subscribeOn(Schedulers.io())
                .subscribe(
                    ::saveUsersToDb
                ) { error: Throwable ->
                    // do nothing
                }
        )
    }

    fun mockGetUsers(): Observable<MutableList<User>> {
        val users = mutableListOf<User>()
        for (i in 0..9) {
            users.add(i, getUser())
        }
        return Observable.just(users)
    }

    fun getUser(): User {
        return User(0, getRandomString(5), getRandomString(8))
    }

    fun getRandomString(length: Int): String {
        val allowedChars = ('A'..'Z') + ('a'..'z')
        return (1..length)
            .map { allowedChars.random() }
            .joinToString("")
    }

    private fun saveUsersToDb(contributions: List<User>) {
        compositeDisposable.add(
            userDao!!.save(contributions)
                .subscribeOn(Schedulers.io())
                .subscribe { longs: List<Long?>? ->
                    //do nothing
                }
        )
    }
}