/* 
 * Copyright 2008-2013, ETH Zürich, Samuel Welten, Michael Kuhn, Tobias Langner,
 * Sandro Affentranger, Lukas Bossard, Michael Grob, Rahul Jain, 
 * Dominic Langenegger, Sonia Mayor Alonso, Roger Odermatt, Tobias Schlueter,
 * Yannick Stucki, Sebastian Wendland, Samuel Zehnder, Samuel Zihlmann,       
 * Samuel Zweifel
 *
 * This file is part of Jukefox.
 *
 * Jukefox is free software: you can redistribute it and/or modify it under the
 * terms of the GNU General Public License as published by the Free Software 
 * Foundation, either version 3 of the License, or any later version. Jukefox is
 * distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; 
 * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A 
 * PARTICULAR PURPOSE. See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along with
 * Jukefox. If not, see <http://www.gnu.org/licenses/>.
 */
/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * 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 ch.ethz.dcg.pancho3.tablet.widget;

import android.content.Context;
import android.util.AttributeSet;
import android.widget.ListView;

/**
 * A ListView that can be asked to scroll (smoothly or otherwise) to a specific
 * position. This class takes advantage of similar functionality that exists in
 * {@link ListView} and enhances it.
 */
public class AutoScrollListView extends ListView {

	/**
	 * Position the element at about 1/3 of the list height
	 */
	private static final float PREFERRED_SELECTION_OFFSET_FROM_TOP = 0.33f;

	private int mRequestedScrollPosition = -1;
	private boolean mSmoothScrollRequested;

	public AutoScrollListView(Context context) {
		super(context);
	}

	public AutoScrollListView(Context context, AttributeSet attrs) {
		super(context, attrs);
	}

	public AutoScrollListView(Context context, AttributeSet attrs, int defStyle) {
		super(context, attrs, defStyle);
	}

	/**
	 * Brings the specified position to view by optionally performing a
	 * jump-scroll maneuver: first it jumps to some position near the one
	 * requested and then does a smooth scroll to the requested position. This
	 * creates an impression of full smooth scrolling without actually
	 * traversing the entire list. If smooth scrolling is not requested,
	 * instantly positions the requested item at a preferred offset.
	 */
	public void requestPositionToScreen(int position, boolean smoothScroll) {
		mRequestedScrollPosition = position;
		mSmoothScrollRequested = smoothScroll;
		requestLayout();
	}

	@Override
	protected void layoutChildren() {
		super.layoutChildren();
		if (mRequestedScrollPosition == -1) {
			return;
		}

		final int position = mRequestedScrollPosition;
		mRequestedScrollPosition = -1;

		int firstPosition = getFirstVisiblePosition() + 1;
		int lastPosition = getLastVisiblePosition();
		if (position >= firstPosition && position <= lastPosition) {
			return; // Already on screen
		}

		final int offset = (int) (getHeight() * PREFERRED_SELECTION_OFFSET_FROM_TOP);
		if (!mSmoothScrollRequested) {
			setSelectionFromTop(position, offset);

			// Since we have changed the scrolling position, we need to redo child layout
			// Calling "requestLayout" in the middle of a layout pass has no effect,
			// so we call layoutChildren explicitly
			super.layoutChildren();

		} else {
			// We will first position the list a couple of screens before or after
			// the new selection and then scroll smoothly to it.
			int twoScreens = (lastPosition - firstPosition) * 2;
			int preliminaryPosition;
			if (position < firstPosition) {
				preliminaryPosition = position + twoScreens;
				if (preliminaryPosition >= getCount()) {
					preliminaryPosition = getCount() - 1;
				}
				if (preliminaryPosition < firstPosition) {
					setSelection(preliminaryPosition);
					super.layoutChildren();
				}
			} else {
				preliminaryPosition = position - twoScreens;
				if (preliminaryPosition < 0) {
					preliminaryPosition = 0;
				}
				if (preliminaryPosition > lastPosition) {
					setSelection(preliminaryPosition);
					super.layoutChildren();
				}
			}

			smoothScrollToPositionFromTop(position, offset);
		}
	}
}