/*
 * @(#)ViewportLayout.java	1.28 01/11/29
 *
 * Copyright 2002 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package javax.swing;

import java.awt.LayoutManager;
import java.awt.Component;
import java.awt.Container;
import java.awt.Rectangle;
import java.awt.Point;
import java.awt.Dimension;
import java.awt.Insets;
import java.io.Serializable;

/**
 * The default layout manager for JViewport.  JViewportLayout defines
 * a policy for layout that should be useful for most applications.
 * The viewport makes its view the same size as the viewport,
 * however it will not make the view smaller than its minimum size.
 * As the viewport grows the view is kept bottom justified until
 * the entire view is visible, subsequently the view is kept top
 * justified.
 * <p>
 * <strong>Warning:</strong>
 * Serialized objects of this class will not be compatible with
 * future Swing releases.  The current serialization support is appropriate
 * for short term storage or RMI between applications running the same
 * version of Swing.  A future release of Swing will provide support for
 * long term persistence.
 *
 * @version 1.28 11/29/01
 * @author Hans Muller
 */
public class ViewportLayout implements LayoutManager, Serializable
{
    /**
     * Adds the specified component to the layout. Not used by this class.
     * @param name the name of the component
     * @param comp the the component to be added
     */
    public void addLayoutComponent(String name, Component c) { }

    /**
     * Removes the specified component from the layout. Not used by
     * this class.
     * @param comp the component to remove
     */
    public void removeLayoutComponent(Component c) { }


    /**
     * Returns the preferred dimensions for this layout given the components
     * in the specified target container.
     * @param target the component which needs to be laid out
     * @return a Dimension object containing the preferred dimensions
     * @see #minimumLayoutSize
     */
    public Dimension preferredLayoutSize(Container parent) {
	Component view = ((JViewport)parent).getView();
	if (view == null) {
	    return new Dimension(0, 0);
	}
	else if (view instanceof Scrollable) {
	    return ((Scrollable)view).getPreferredScrollableViewportSize();
	}
	else {
	    return view.getPreferredSize();
	}
    }


    /**
     * Returns the minimum dimensions needed to layout the components
     * contained in the specified target container.
     *
     * @param target the component which needs to be laid out
     * @return a Dimension object containing the minimum dimensions
     * @see #preferredLayoutSize
     */
    public Dimension minimumLayoutSize(Container parent) {
	return new Dimension(4, 4);
    }


    /**
     * Called by the AWT when the specified container needs to be laid out.
     *
     * @param parent  the container to lay out
     *
     * @exception AWTError  if the target isn't the container specified to the
     *                      BoxLayout constructor
     */
    public void layoutContainer(Container parent)
    {
	JViewport vp = (JViewport)parent;
	Component view = vp.getView();
	Scrollable scrollableView = null;

	if (view == null) {
	    return;
	}
	else if (view instanceof Scrollable) {
	    scrollableView = (Scrollable) view;
	}

	/* All of the dimensions below are in view coordinates, except
	 * vpSize which we're converting.
	 */

	Insets insets = vp.getInsets();
	Dimension viewPrefSize = view.getPreferredSize();
	Dimension vpSize = vp.getSize();
	Dimension extentSize = vp.toViewCoordinates(vpSize);
	Dimension viewSize = new Dimension(viewPrefSize);

	if (scrollableView != null) {
	    if (scrollableView.getScrollableTracksViewportWidth()) {
		viewSize.width = vpSize.width;
	    }
	    if (scrollableView.getScrollableTracksViewportHeight()) {
		viewSize.height = vpSize.height;
	    }
	}

	Point viewPosition = vp.getViewPosition();

	/* If the new viewport size would leave empty space to the
	 * right of the view, right justify the view or left justify
	 * the view when the width of the view is smaller than the
	 * container.
	 */
	if ((viewPosition.x + extentSize.width) > viewSize.width) {
	    viewPosition.x = Math.max(0, viewSize.width - extentSize.width);
	}

	/* If the new viewport size would leave empty space below the
	 * view, bottom justify the view or top justify the view when
	 * the height of the view is smaller than the container.
	 */
	if ((viewPosition.y + extentSize.height) > viewSize.height) {
	    viewPosition.y = Math.max(0, viewSize.height - extentSize.height);
	}

	/* If we haven't been advised about how the viewports size 
	 * should change wrt to the viewport, i.e. if the view isn't
	 * an instance of Scrollable, then adjust the views size as follows.
	 * 
	 * If the orgin of the view is showing and the viewport is
	 * bigger than the views preferred size, then make the view
	 * the same size as the viewport.
	 */
	if (scrollableView == null) {
            if ((viewPosition.x == 0) && (vpSize.width > viewPrefSize.width)) {
        	viewSize.width = vpSize.width;
            }
            if ((viewPosition.y == 0) && (vpSize.height > viewPrefSize.height)) {
        	viewSize.height = vpSize.height;
            }
        }
	vp.setViewPosition(viewPosition);
	vp.setViewSize(viewSize);
    }
}