package org.gcube.portlets.widgets.ckandatapublisherwidget.client.ui.TwinColumnSelection;

import com.google.gwt.event.dom.client.ScrollEvent;
import com.google.gwt.event.dom.client.ScrollHandler;
import com.google.gwt.user.cellview.client.AbstractPager;
import com.google.gwt.user.client.ui.ScrollPanel;
import com.google.gwt.user.client.ui.Widget;
import com.google.gwt.view.client.HasRows;

/**
 * Basically a scroll panel
 * Partially changed from the code at http://samples.gwtproject.org/samples/Showcase/Showcase.html#!CwCellList
 * @author Costantino Perciante at ISTI-CNR (costantino.perciante@isti.cnr.it)
 */
public class ShowMorePagerPanel extends AbstractPager{

	/**
	 * The default increment size.
	 */
	public static final int DEFAULT_INCREMENT = 10;

	/**
	 * The increment size.
	 */
	private int incrementSize = DEFAULT_INCREMENT;

	/**
	 * The last scroll position.
	 */
	private int lastScrollPos = 0;

	/**
	 * The scrollable panel.
	 */
	private final ScrollPanel scrollable = new ScrollPanel();

	/**
	 * Construct a new {@link ShowMorePagerPanel}.
	 */
	public ShowMorePagerPanel() {
		initWidget(scrollable);

		// Do not let the scrollable take tab focus.
		scrollable.getElement().setTabIndex(-1);

		// Handle scroll events.
		scrollable.addScrollHandler(new ScrollHandler() {
			public void onScroll(ScrollEvent event) {
				// If scrolling up, ignore the event.
				int oldScrollPos = lastScrollPos;
				lastScrollPos = scrollable.getVerticalScrollPosition();
				if (oldScrollPos >= lastScrollPos) {
					return;
				}

				HasRows display = getDisplay();
				if (display == null) {
					return;
				}
				int maxScrollTop = scrollable.getWidget().getOffsetHeight()
						- scrollable.getOffsetHeight();
				if (lastScrollPos >= maxScrollTop) {
					// We are near the end, so increase the page size.
					int newPageSize = Math.min(
							display.getVisibleRange().getLength() + incrementSize,
							display.getRowCount());
					display.setVisibleRange(0, newPageSize);
				}
			}
		});
	}

	/**
	 * Get the number of rows by which the range is increased when the scrollbar
	 * reaches the bottom.
	 * @return the increment size
	 */
	public int getIncrementSize() {
		return incrementSize;
	}

	@Override
	public void setDisplay(HasRows display) {
		assert display instanceof Widget : "display must extend Widget";
	scrollable.setWidget((Widget) display);
	super.setDisplay(display);
	}

	/**
	 * Set the number of rows by which the range is increased when the scrollbar
	 * reaches the bottom.
	 * @param incrementSize the incremental number of rows
	 */
	public void setIncrementSize(int incrementSize) {
		this.incrementSize = incrementSize;
	}

	@Override
	protected void onRangeOrRowCountChanged() {
	}
}