BookingHistoryBoundaryCallback.kt

package com.dryva.data.boilerplate.source.trip

import android.arch.paging.PagedList
import com.dryva.data.boilerplate.repository.driver.DryvaCache
import com.dryva.data.boilerplate.repository.trip.TripCache
import com.dryva.data.boilerplate.repository.trip.TripRemote
import com.dryva.domain.model.BookingData
import io.reactivex.disposables.CompositeDisposable
import io.reactivex.schedulers.Schedulers
import io.reactivex.subjects.PublishSubject
import javax.inject.Inject

/**
 * This boundary callback gets notified when user reaches to the edges of the list
 * for example when the database cannot provide any more data or is empty.
 * It then fetching data from the server and stores in the database
 **/
class BookingHistoryBoundaryCallback @Inject constructor(
    private val remote: TripRemote,
    private val cache: TripCache,
    private val driverCache: DryvaCache
) : PagedList.BoundaryCallback<BookingData>() {

    var compositeDisposable = CompositeDisposable()
    var networkErrors = PublishSubject.create<String>()
    // holds the last requested offset. When the request is successful, increment the offset number.
    private var lastRequestedPage = 0

    // avoid triggering multiple requests in the same time
    private var isRequestInProgress = false

    /**
     * Database returned 0 items. We should query the backend for more items.
     */
    override fun onZeroItemsLoaded() {
        fetchTripHistoryAndSaveInDb()
    }

    /**
     * When all items in the database were loaded, we need to query the backend for more items.
     */
    override fun onItemAtEndLoaded(itemAtEnd: BookingData) {
        fetchTripHistoryAndSaveInDb()
    }

    /**
     * fetches booking data from server and save in db
     */
    private fun fetchTripHistoryAndSaveInDb() {
        if (isRequestInProgress) return

        isRequestInProgress = true
        val disposable = driverCache.getDriverInfo()
            .flatMap { driver ->
                remote.getBookings("Bearer ${driver.token}", driver.id, lastRequestedPage).doOnSuccess {
                    if(lastRequestedPage == 0) {
                        //clear the db of old booking data and start saving fresh booking data
                        cache.clearBookings().subscribe()
                    }
                    lastRequestedPage++
                    isRequestInProgress = false
                    cache.saveBookings(it).subscribe()
                    cache.setIsBookingCached(true)
                }.doOnError { throwable ->
                    //check if booking data is from server is empty and clear bookings in the db
                    if (throwable.message.equals("No active booking")) cache.clearBookings().subscribe()
                    networkErrors.onNext(throwable.localizedMessage)
                }
            }.subscribeOn(Schedulers.computation())
            .subscribe({

            }, { throwable ->
                networkErrors.onNext(throwable.localizedMessage)
            })
        compositeDisposable.add(disposable)
    }
}