/*
 * Copyright (C) 2016 Piotr Wittchen
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.mian.gitnex.helpers;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

/**
 * InfiniteScrollListener, which can be added to RecyclerView with addOnScrollListener
 * to detect moment when RecyclerView was scrolled to the end.
 */
public abstract class InfiniteScrollListener extends RecyclerView.OnScrollListener {
	private final int maxItemsPerRequest;
	private final LinearLayoutManager layoutManager;

	/**
	 * Initializes InfiniteScrollListener, which can be added
	 * to RecyclerView with addOnScrollListener method
	 *
	 * @param maxItemsPerRequest Max items to be loaded in a single request.
	 * @param layoutManager LinearLayoutManager created in the Activity.
	 */
	public InfiniteScrollListener(int maxItemsPerRequest, LinearLayoutManager layoutManager) {
		assert maxItemsPerRequest > 0;
		assert layoutManager != null;

		this.maxItemsPerRequest = maxItemsPerRequest;
		this.layoutManager = layoutManager;
	}

	/**
	 * Callback method to be invoked when the RecyclerView has been scrolled
	 *
	 * @param recyclerView The RecyclerView which scrolled.
	 * @param dx The amount of horizontal scroll.
	 * @param dy The amount of vertical scroll.
	 */
	@Override public void onScrolled(@NonNull RecyclerView recyclerView, int dx, int dy) {
		super.onScrolled(recyclerView, dx, dy);
		if (canLoadMoreItems()) {
			onScrolledToEnd(layoutManager.findFirstVisibleItemPosition());
		}
	}

	/**
	 * Refreshes RecyclerView by setting new adapter,
	 * calling invalidate method and scrolling to given position
	 *
	 * @param view RecyclerView to be refreshed
	 * @param adapter adapter with new list of items to be loaded
	 * @param position position to which RecyclerView will be scrolled
	 */
	protected void refreshView(RecyclerView view, RecyclerView.Adapter adapter, int position) {
		view.setAdapter(adapter);
		view.invalidate();
		view.scrollToPosition(position);
	}

	/**
	 * Checks if more items can be loaded to the RecyclerView
	 *
	 * @return boolean Returns true if can load more items or false if not.
	 */
	protected boolean canLoadMoreItems() {
		final int visibleItemsCount = layoutManager.getChildCount();
		final int totalItemsCount = layoutManager.getItemCount();
		final int pastVisibleItemsCount = layoutManager.findFirstVisibleItemPosition();
		final boolean lastItemShown = visibleItemsCount + pastVisibleItemsCount >= totalItemsCount;
		return lastItemShown && totalItemsCount >= maxItemsPerRequest;
	}

	/**
	 * Callback method to be invoked when the RecyclerView has been scrolled to the end
	 *
	 * @param firstVisibleItemPosition Id of the first visible item on the list.
	 */
	public abstract void onScrolledToEnd(final int firstVisibleItemPosition);
}