/*******************************************************************************
 * Copyright (c) 2000, 2005 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
 * Port to the D programming language:
 *     Frank Benoit <benoit@tionex.de>
 *******************************************************************************/
module dwtx.draw2d.FocusTraverseManager;

import dwt.dwthelper.utils;
import dwtx.dwtxhelper.Collection;
import dwtx.draw2d.IFigure;

/**
 * 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 this() { }

private IFigure findDeepestRightmostChildOf(IFigure fig) {
    while (fig.getChildren().size() !is 0) {
        fig = cast(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) {
    bool found = false;
    IFigure nextFocus = prevFocus;

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

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

                if (gp !is null) {
                    int parentSiblingCount = gp.getChildren().size();
                    int parentIndex = gp.getChildren().indexOf(cast(Object)p);
                    if (parentIndex < parentSiblingCount - 1) {
                        nextFocus = (cast(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 is null)
        return null;

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

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

        List siblings = parent.getChildren();
        int siblingPos = siblings.indexOf(cast(Object)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 !is 0) {
            IFigure child =
                    findDeepestRightmostChildOf(cast(IFigure)siblings.get(siblingPos - 1));
            if (isFocusEligible(child)) {
                found = true;
                nextFocus = child;
            } else if ((cast(Object)child).opEquals(cast(Object)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 bool isFocusEligible(IFigure fig) {
    return (fig !is null && fig.isFocusTraversable() && fig.isShowing());
}

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

}