/*******************************************************************************
 * Copyright (c) 2000, 2010 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.draw2d;

import java.util.List;

/**
 * This class is a helper to the {@link SWTEventDispatcher}. It handles the task
 * of determining which Figure will gain focus upon a tab/shift-tab. It also
 * keeps track of the Figure with current focus.
 * <p>
 * Note: When a Canvas with a {@link LightweightSystem} gains focus, it gives
 * focus to the child Figure who had focus when this Canvas lost focus. If the
 * canvas is gaining focus for the first time, focus is given to its first child
 * Figure.
 */
public class FocusTraverseManager {

	IFigure currentFocusOwner;

	/**
	 * Default constructor.
	 */
	public FocusTraverseManager() {
	}

	private IFigure findDeepestRightmostChildOf(IFigure fig) {
		while (fig.getChildren().size() != 0) {
			fig = (IFigure) fig.getChildren().get(fig.getChildren().size() - 1);
		}
		return fig;
	}

	/**
	 * Returns the IFigure that will receive focus upon a 'tab' traverse event.
	 * 
	 * @param root
	 *            the {@link LightweightSystem LightweightSystem's} root figure
	 * @param prevFocus
	 *            the IFigure who currently owns focus
	 * @return the next focusable figure
	 */
	public IFigure getNextFocusableFigure(IFigure root, IFigure prevFocus) {
		boolean found = false;
		IFigure nextFocus = prevFocus;

		/*
		 * If no Figure currently has focus, apply focus to root's first
		 * focusable child.
		 */
		if (prevFocus == null) {
			if (root.getChildren().size() != 0) {
				nextFocus = ((IFigure) root.getChildren().get(0));
				if (isFocusEligible(nextFocus))
					return nextFocus;
			} else
				return null;
		}

		int siblingPos = nextFocus.getParent().getChildren().indexOf(nextFocus);
		while (!found) {
			IFigure parent = nextFocus.getParent();

			/*
			 * Figure traversal is implemented using the pre-order left to right
			 * tree traversal algorithm.
			 * 
			 * If the focused sibling has children, traverse to its leftmost
			 * child. If the focused sibling has no children, traverse to the
			 * sibling to its right. If there is no sibling to the right, go up
			 * the tree until a node with un-traversed siblings is found.
			 */
			List siblings = parent.getChildren();

			if (nextFocus.getChildren().size() != 0) {
				nextFocus = (IFigure) nextFocus.getChildren().get(0);
				siblingPos = 0;
				if (isFocusEligible(nextFocus))
					found = true;
			} else if (siblingPos < siblings.size() - 1) {
				nextFocus = ((IFigure) (siblings.get(++siblingPos)));
				if (isFocusEligible(nextFocus))
					found = true;
			} else {
				boolean untraversedSiblingFound = false;
				while (!untraversedSiblingFound) {
					IFigure p = nextFocus.getParent();
					IFigure gp = p.getParent();

					if (gp != null) {
						int parentSiblingCount = gp.getChildren().size();
						int parentIndex = gp.getChildren().indexOf(p);
						if (parentIndex < parentSiblingCount - 1) {
							nextFocus = ((IFigure) p.getParent().getChildren()
									.get(parentIndex + 1));
							siblingPos = parentIndex + 1;
							untraversedSiblingFound = true;
							if (isFocusEligible(nextFocus))
								found = true;
						} else
							nextFocus = p;
					} else {
						nextFocus = null;
						untraversedSiblingFound = true;
						found = true;
					}
				}
			}
		}
		return nextFocus;
	}

	/**
	 * Returns the IFigure that will receive focus upon a 'shift-tab' traverse
	 * event.
	 * 
	 * @param root
	 *            The {@link LightweightSystem LightweightSystem's} root figure
	 * @param prevFocus
	 *            The IFigure who currently owns focus
	 * @return the previous focusable figure
	 */
	public IFigure getPreviousFocusableFigure(IFigure root, IFigure prevFocus) {
		if (prevFocus == null)
			return null;

		boolean found = false;
		IFigure nextFocus = prevFocus;
		while (!found) {
			IFigure parent = nextFocus.getParent();

			/*
			 * At root, return null to indicate traversal is complete.
			 */
			if (parent == null)
				return null;

			List siblings = parent.getChildren();
			int siblingPos = siblings.indexOf(nextFocus);

			/*
			 * Figure traversal is implemented using the post-order right to
			 * left tree traversal algorithm.
			 * 
			 * Find the rightmost child. If this child is focusable, return it
			 * If not focusable, traverse to its sibling and repeat. If there is
			 * no sibling, traverse its parent.
			 */
			if (siblingPos != 0) {
				IFigure child = findDeepestRightmostChildOf((IFigure) siblings
						.get(siblingPos - 1));
				if (isFocusEligible(child)) {
					found = true;
					nextFocus = child;
				} else if (child.equals(nextFocus)) {
					if (isFocusEligible(nextFocus))
						found = true;
				} else
					nextFocus = child;
			} else {
				nextFocus = parent;
				if (isFocusEligible(nextFocus))
					found = true;
			}
		}
		return nextFocus;
	}

	/**
	 * @return the figure that currently has focus
	 */
	public IFigure getCurrentFocusOwner() {
		return currentFocusOwner;
	}

	private boolean isFocusEligible(IFigure fig) {
		return (fig != null && fig.isFocusTraversable() && fig.isShowing());
	}

	/**
	 * Sets the currently focused figure.
	 * 
	 * @param fig
	 *            the figure to get focus
	 */
	public void setCurrentFocusOwner(IFigure fig) {
		currentFocusOwner = fig;
	}

}