/**
 * Data class that is necessary for a UI to show a listing and interact w/ the rest of the system
 */
data class Listing<T>(
        // the LiveData of paged lists for the UI to observe
        val pagedList: LiveData<PagedList<T>>,
        // represents the network request status to show to the user
        val networkState: LiveData<NetworkState>,
        // represents the refresh status to show to the user. Separate from networkState, this
        // value is importantly only when refresh is requested.
        val refreshState: LiveData<NetworkState>,
        // refreshes the whole data and fetches it from scratch.
        val refresh: () -> Unit,
        // retries any failed requests.
        val retry: () -> Unit)


class DataSource(
        private val apiService: ApiService,
        private val retryExecutor: Executor,
        //You can pass all other extra params that you need here.
) : PageKeyedDataSource<Int, Deliverable>() {
    // keep a function reference for the retry event
    private var retry: (() -> Any)? = null

    /**
     * There is no sync on the state because paging will always call loadInitial first then wait
     * for it to return some success value before calling loadAfter.
     */
    val networkState = MutableLiveData<NetworkState>()

    val initialLoad = SingleLiveEvent<NetworkState>()

    fun retryAllFailed() {
        val prevRetry = retry
        retry = null
        prevRetry?.let {
            retryExecutor.execute {
                it.invoke()
            }
        }
    }


    override fun loadInitial(params: LoadInitialParams<Int>, callback: LoadInitialCallback<Int, Deliverable>) {
        Timber.d("Loading initial value")

    }

    override fun loadAfter(params: LoadParams<Int>, callback: LoadCallback<Int, Deliverable>) {
        Timber.d("Load after called. Offset: ${params.key}, Page size: ${params.requestedLoadSize}")

    }

    override fun loadBefore(params: LoadParams<Int>, callback: LoadCallback<Int, Deliverable>) {
        Timber.d("Load before called")
        //This is never used
    }

}

class DataSourceFactory(
        private val apiservice: ApiService,
        private val retryExecutor: Executor,
//You can pass all other extra params that you need here.
) : DataSource.Factory<Int, Deliverable>() {
    val sourceLiveData = MutableLiveData<DataSource>()
    override fun create(): DataSource<Int, Deliverable> {
        val source = DataSource(//Pass all required params here.)
        sourceLiveData.postValue(source)
        return source
    }

}


//Then on the repository or any other place you are creating your data source

  fun history(//Pass params here): Listing<Deliverable> {
        val sourceFactory = DataSourceFactory(//Pass params)

        val config = PagedList.Config.Builder()
                .setPageSize(10)
                .build()
        val livePageList = LivePagedListBuilder(sourceFactory, config)
                .build()

        val refreshState = Transformations.switchMap(sourceFactory.sourceLiveData) {
            it.initialLoad
        }

        return Listing(
                pagedList = livePageList,
                networkState = Transformations.switchMap(sourceFactory.sourceLiveData) {
                    it.networkState
                },
                retry = { sourceFactory.sourceLiveData.value?.retryAllFailed() },
                refresh = { sourceFactory.sourceLiveData.value?.invalidate() },
                refreshState = refreshState
        )
    }

  //The in viewModel, observe network state and trigger retries as follows
     private val repoResult = //create repo list from rrepository

    private val transports = Transformations.switchMap(repoResult) { it.pagedList }!!
    private val networkState = Transformations.switchMap(repoResult) { it.networkState }!!
    private val refreshState = Transformations.switchMap(repoResult) { it.refreshState }!!


    //call refresh and retry as follows
    fun refresh() {
        repoResult.value?.refresh?.invoke()
    }


    fun retry() {
        val listing = repoResult?.value
        listing?.retry?.invoke()
    }