MovieHunt blog part3. list data source

MovieListDataSource.kt

class MovieListDataSource(
    private val category: MovieCategory,
    private val initLoadState: BehaviorSubject<NetworkState>,
    private val loadMoreState: BehaviorSubject<NetworkState>
) : PageKeyedDataSource<Int, MovieModel>(), KoinComponent {

    private val api: MovieApiService by inject()
    private var currentPage: Int = -1

    override fun loadInitial(
        params: LoadInitialParams<Int>,
        callback: LoadInitialCallback<Int, MovieModel>
    ) {
        currentPage = 1
        api.fetchMovieList(category.key, currentPage)
            .doOnSubscribe { initLoadState.onNext(NetworkState.LOADING) }
            .doOnSuccess {
                it.results?.run {
                    callback.onResult(
                        this.mapToMovieModels(),
                        null,
                        calculateNextPage(it.totalPages)
                    )
                }
                initLoadState.onNext(NetworkState.IDLE)
            }
            .doOnError { initLoadState.onNext(NetworkState.ERROR) }
            .subscribe()
    }

    override fun loadAfter(params: LoadParams<Int>, callback: LoadCallback<Int, MovieModel>) {
        if (-1 == params.key || NetworkState.LOADING == loadMoreState.value) return
        api.fetchMovieList(category.key, params.key)
            .doOnSubscribe { loadMoreState.onNext(NetworkState.LOADING) }
            .doOnSuccess {
                it.results?.run {
                    callback.onResult(this.mapToMovieModels(), calculateNextPage(it.totalPages))
                }
                loadMoreState.onNext(NetworkState.IDLE)
            }
            .doOnError { loadMoreState.onNext(NetworkState.ERROR) }
            .subscribe()
    }

    override fun loadBefore(params: LoadParams<Int>, callback: LoadCallback<Int, MovieModel>) {
        // we don't need this
    }

    private fun calculateNextPage(totalPage: Int?): Int {
        totalPage?.run {
            currentPage = if (currentPage in 1 until totalPage) {
                currentPage.plus(1)
            } else {
                -1
            }
        }
        return currentPage
    }
}