/**
 * 
 */
package org.csstudio.sds.ui.internal.viewer;

import org.eclipse.gef.ui.parts.GraphicalViewerImpl;
import org.eclipse.gef.ui.parts.ScrollingGraphicalViewer;
import org.eclipse.jface.action.IMenuListener;
import org.eclipse.jface.action.IMenuManager;
import org.eclipse.jface.action.MenuManager;
import org.eclipse.jface.viewers.ISelection;
import org.eclipse.jface.viewers.IStructuredSelection;
import org.eclipse.swt.events.DisposeEvent;
import org.eclipse.swt.events.DisposeListener;
import org.eclipse.swt.widgets.Control;
import org.eclipse.ui.internal.ObjectPluginAction;

/**
 * Patched graphical viewer implementation.
 * 
 * @author swende
 * 
 */
public class PatchedGraphicalViewer extends ScrollingGraphicalViewer {
	private MenuManager contextMenu;

	/**
	 * The original implementation in
	 * {@link GraphicalViewerImpl#setContextMenu(MenuManager)} registers a menu
	 * listener on the context menu. This causes a memory leak, because that
	 * listener is never removed.
	 */
	@Override
	public void setContextMenu(MenuManager manager) {
		// code from AbstractEditPartViewer base class (=super.super)
		if (contextMenu != null) {
			contextMenu.dispose();
		}

		contextMenu = manager;

		if (getControl() != null && !getControl().isDisposed()) {
			getControl().setMenu(contextMenu.createContextMenu(getControl()));
		}

		// code from GraphicalViewerImpl (=super)

		// ... is left out

		// ... and rewritten here
		if (contextMenu != null) {
			final IMenuListener menuListener = new IMenuListener() {
				@Override
				public void menuAboutToShow(IMenuManager manager) {
					flush();
				}
			};

			contextMenu.addMenuListener(menuListener);

			final Control control = getControl();

			if (control != null) {
				control.addDisposeListener(new DisposeListener() {
					@Override
					public void widgetDisposed(DisposeEvent e) {
						contextMenu.removeMenuListener(menuListener);
						control.removeDisposeListener(this);
					}
				});
			}
		}
	}

	/**
	 * Patch selections. Return amended selections that keep only weak
	 * references to their underlying objects. This is part of a workaround for
	 * a memory leak which is caused by popup menu actions that are contributed
	 * via extension point 'org.eclipse.ui.popupMenus' and as
	 * 'objectContribution'. Those actions will references the latest workbench
	 * selection for as long as a new selection occurs (see
	 * {@link ObjectPluginAction#selectionChanged(ISelection)}. In certain
	 * situations this behaviour prevents garbage collection of SDS displays.
	 */
	@Override
	public ISelection getSelection() {
		IStructuredSelection selection = (IStructuredSelection) super
				.getSelection();

		if (selection != null) {
			return new WeakStructuredSelection(selection);
		} else {
			return null;
		}
	}

}