/*******************************************************************************
 * 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.gef.editparts;

import org.eclipse.draw2d.IFigure;

import org.eclipse.gef.EditPart;

/**
 * Responsible for locating <i>layers</i> in a <code>GraphicalViewer</code>.
 * Layers are just transparent {@link org.eclipse.draw2d.Figure figures}.
 * <P>
 * Typically, the <code>RootEditPart</code> will register() itself as the
 * LayerManager for the GraphicalViewer. All other EditParts/EditPolicies
 * looking for a layer use the Viewer's
 * {@link org.eclipse.gef.EditPartViewer#getEditPartRegistry() editPartRegsitry}
 * to find the <code>LayerManager</code>.
 * 
 * @author hudsonr
 * @since 2.0
 */
public interface LayerManager {

	/**
	 * This key used to register the LayerManager in the Viewer's
	 * EditPartRegistry.
	 */
	Object ID = new Object();

	/**
	 * Returns a specified layer.
	 * 
	 * @param key
	 *            a key identifying the layer
	 * @return the specified layer
	 */
	IFigure getLayer(Object key);

	/**
	 * A static helper
	 * 
	 * @since 2.0
	 */
	class Helper {
		/**
		 * Finds the LayerManager given any EditPart in the Viewer.
		 * 
		 * @param part
		 *            any EditPart in a GraphicalViewer
		 * @return the <code>LayerManager</code>
		 */
		public static LayerManager find(EditPart part) {
			return (LayerManager) part.getViewer().getEditPartRegistry()
					.get(ID);
		}
	}

}