/* 
 * Copyright (c) 2008 Stiftung Deutsches Elektronen-Synchrotron, 
 * Member of the Helmholtz Association, (DESY), HAMBURG, GERMANY.
 *
 * THIS SOFTWARE IS PROVIDED UNDER THIS LICENSE ON AN "../AS IS" BASIS. 
 * WITHOUT WARRANTY OF ANY KIND, EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED 
 * TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR PARTICULAR PURPOSE AND 
 * NON-INFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE 
 * FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, 
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR 
 * THE USE OR OTHER DEALINGS IN THE SOFTWARE. SHOULD THE SOFTWARE PROVE DEFECTIVE 
 * IN ANY RESPECT, THE USER ASSUMES THE COST OF ANY NECESSARY SERVICING, REPAIR OR 
 * CORRECTION. THIS DISCLAIMER OF WARRANTY CONSTITUTES AN ESSENTIAL PART OF THIS LICENSE. 
 * NO USE OF ANY SOFTWARE IS AUTHORIZED HEREUNDER EXCEPT UNDER THIS DISCLAIMER.
 * DESY HAS NO OBLIGATION TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, 
 * OR MODIFICATIONS.
 * THE FULL LICENSE SPECIFYING FOR THE SOFTWARE THE REDISTRIBUTION, MODIFICATION, 
 * USAGE AND OTHER RIGHTS AND OBLIGATIONS IS INCLUDED WITH THE DISTRIBUTION OF THIS 
 * PROJECT IN THE FILE LICENSE.HTML. IF THE LICENSE IS NOT INCLUDED YOU MAY FIND A COPY 
 * AT HTTP://WWW.DESY.DE/LEGAL/LICENSE.HTM
 */
 package org.csstudio.sds.ui.internal.preferences;

import org.eclipse.swt.SWT;
import org.eclipse.swt.events.SelectionAdapter;
import org.eclipse.swt.events.SelectionEvent;
import org.eclipse.swt.widgets.TreeItem;

/**
 * tree.addSelectionListener(new TreeCheckSelectionListener());.
 * @author Toasta
 */
public class TreeCheckSelectionListener extends SelectionAdapter {

	/* (non-Javadoc)
	 * @see org.eclipse.swt.events.SelectionAdapter#widgetSelected(org.eclipse.swt.events.SelectionEvent)
	 */
	@Override
	public void widgetSelected(SelectionEvent event) {
		if (event.detail == SWT.CHECK) {
			this.handleCheckedItem((TreeItem) event.item);
		}
	}
	
	/**
	 * Updates the check-status of every affected <code>TreeItem</code> if the given item has been checked or unchecked. 
	 * @param item the <code>TreeItem</code>
	 */
	private void handleCheckedItem(TreeItem item) {
		//somebody selected the item, so it can't be grayed
		item.setGrayed(false);
		//check all children of the selected item
		this.checkAllChildren(item);
		//check all parents of the selected item
		this.checkAllParents(item);
	}
	
	/**
	 * Checks all children of the given <code>TreeItem</code> like that item (checked or unchecked).
	 * <code>Grayed</code> is set to <code>false</code> at all children in any case, because every child
	 * just can be checked or unchecked.
	 * @param parent the <code>TreeItem</code>
	 */
	private void checkAllChildren(TreeItem parent) {
		for (TreeItem child : parent.getItems()) {
			child.setChecked(parent.getChecked());
			child.setGrayed(false);
			this.checkAllChildren(child);
		}
	}
	
	/**
	 * Checks all parents of the given <code>TreeItem</code> depend on the check-status of their cildren.
	 * @param item the <code>TreeItem</code>
	 */
	private void checkAllParents(TreeItem item) {
		TreeItem parent = item.getParentItem();
		if (parent!=null) {
			if (allDirectChildrenChecked(parent)) {
				parent.setGrayed(false);
				parent.setChecked(true);
			} else {
				if (allDirectChildrenUnchecked(parent)) {
					parent.setGrayed(false);
					parent.setChecked(false);
				} else {
					parent.setGrayed(true);
					parent.setChecked(true);
				}
			}
			this.checkAllParents(parent);
		}
	}
	
	/**
	 * Returns whether all direct children of the given parent are really checked or not.
	 * Really checked means, that all children are checked without being grayed.
	 * @param parent the <code>TreeItem</code>
	 * @return <code>true</code>, if all direct children of the given parent are really checked, <code>false</code> otherwise
	 */
	private boolean allDirectChildrenChecked(TreeItem parent) {
		TreeItem[] children = parent.getItems();
		for (TreeItem child : children) {
			if (!child.getChecked() || (child.getChecked() && child.getGrayed())) {
				return false;
			}
		}
		return true;
	}
	
	/**
	 * Returns whether all direct children of the given parent are really unchecked or not.
	 * Really unchecked means, that all children are unchecked never mind being grayed or not.
	 * @param parent the <code>TreeItem</code>
	 * @return <code>true</code>, if all direct children of the given parent are unchecked, <code>false</code> otherwise
	 */
	private boolean allDirectChildrenUnchecked(TreeItem parent) {
		TreeItem[] children = parent.getItems();
		for (TreeItem child : children) {
			if (child.getChecked()) {
				return false;
			}
		}
		return true;
	}

}