RecyclerPaginationListener

class RecyclerPaginationListener(
    private val feedViewModel: FeedViewModel
) : RecyclerView.OnScrollListener() {

    private var scrollState = -1

    private val ITEMS_LEFT_IN_BOTTOM = 2

    override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
        super.onScrollStateChanged(recyclerView, newState)
        scrollState = newState
        if (!feedViewModel.isLoading && scrollState == RecyclerView.SCROLL_STATE_IDLE) {
            recyclerView.layoutManager?.let {
                val visibleItemCount = it.childCount
                val totalItemCount = it.itemCount
                val firstVisibleItemPosition = (it as LinearLayoutManager).findFirstVisibleItemPosition()
                if ((visibleItemCount + firstVisibleItemPosition) >= (totalItemCount - ITEMS_LEFT_IN_BOTTOM)
                    && firstVisibleItemPosition >= 0
                    && totalItemCount >= feedViewModel.feedSize
                ) {
                    feedViewModel.loadMoreItems()
                }
            }
        }
    }
}