import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.StaggeredGridLayoutManager;

/**
 * Created by jihoon on 2016. 8. 11..
 */

public abstract class OnScrollEndListener extends RecyclerView.OnScrollListener {

    public static int REVERSE = 1;


    private boolean isArray;
    private boolean reverse;
    private StaggeredGridLayoutManager staggeredGridLayoutManager;
    private LinearLayoutManager linearLayoutManager;

    public OnScrollEndListener(RecyclerView.LayoutManager layoutManager) {
        init(layoutManager);
    }

    public OnScrollEndListener(RecyclerView.LayoutManager layoutManager, int direction) {
        this.reverse = direction == REVERSE;
        init(layoutManager);
    }

    private void init(RecyclerView.LayoutManager layoutManager) {
        isArray = layoutManager instanceof StaggeredGridLayoutManager;
        if (isArray)
            staggeredGridLayoutManager = ((StaggeredGridLayoutManager) layoutManager);
        else
            linearLayoutManager = ((LinearLayoutManager) layoutManager);
    }

    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
        super.onScrolled(recyclerView, dx, dy);


        if (isArray) {

            int[] positions =
                    reverse ? staggeredGridLayoutManager.findFirstCompletelyVisibleItemPositions(null)
                            : staggeredGridLayoutManager.findLastCompletelyVisibleItemPositions(null);

            // positions array length equals spancount

            int lastPosition = staggeredGridLayoutManager.getItemCount() - 1;

            for (int position : positions) {
                callbackIfLastPosition(lastPosition, position);
            }

        } else {
            // LinearLayoutManager is super class of GridLayoutManager .
            int position =
                    reverse ? linearLayoutManager.findFirstCompletelyVisibleItemPosition()
                            : linearLayoutManager.findLastCompletelyVisibleItemPosition();

            int lastPosition = linearLayoutManager.getItemCount() - 1;  //    linearLayoutManager.getItemCount() - 1 - preLoadCount

            callbackIfLastPosition(lastPosition, position);
        }
    }

    private void callbackIfLastPosition(int lastPosition, int position) {
        if (position == lastPosition) {
            loadMore(position);
        }
    }

    public abstract void loadMore(int position);


}