org.eclipse.gmf.runtime.diagram.ui/src/org/eclipse/gmf/runtime/diagram/ui/internal/services/decorator/DecoratorService.java

/******************************************************************************
 * Copyright (c) 2002, 2009 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.gmf.runtime.diagram.ui.internal.services.decorator;

import org.eclipse.core.runtime.Assert;
import org.eclipse.core.runtime.IConfigurationElement;
import org.eclipse.gmf.runtime.common.core.service.ExecutionStrategy;
import org.eclipse.gmf.runtime.common.core.service.IOperation;
import org.eclipse.gmf.runtime.common.core.service.Service;
import org.eclipse.gmf.runtime.diagram.ui.internal.DiagramUIPlugin;
import org.eclipse.gmf.runtime.diagram.ui.services.decorator.CreateDecoratorsOperation;
import org.eclipse.gmf.runtime.diagram.ui.services.decorator.IDecoratorProvider;
import org.eclipse.gmf.runtime.diagram.ui.services.decorator.IDecoratorTarget;

/**
 * This service is used to add decorators so that shapes and connections on a
 * diagram can be decorated with adornments.
 * 
 * @author cmahoney
 */
public class DecoratorService
	extends Service
	implements IDecoratorProvider {

	/**
	 * A descriptor for <code>IDecoratorProvider</code> defined by a
	 * configuration element.
	 */
	protected static class ProviderDescriptor
		extends Service.ProviderDescriptor {

		/** the provider configuration parsed from XML */
		private DecoratorProviderConfiguration providerConfiguration;

		/**
		 * Constructs an <code>IDecoratorProvider</code> descriptor for the
		 * specified configuration element.
		 * 
		 * @param element
		 *            The configuration element describing the provider.
		 */
		public ProviderDescriptor(IConfigurationElement element) {
			super(element);

			this.providerConfiguration = DecoratorProviderConfiguration
				.parse(element);
			Assert.isNotNull(providerConfiguration);
		}

		/**
		 * @see org.eclipse.gmf.runtime.common.core.service.IProvider#provides(org.eclipse.gmf.runtime.common.core.service.IOperation)
		 */
		public boolean provides(IOperation operation) {
			if (!policyInitialized){
				policy = getPolicy();
				policyInitialized = true;
			}
			if (policy != null)
				return policy.provides(operation);
			if (provider == null) {
				if (isSupportedInExtention(operation)) {
					providerConfiguration = null;
					return getProvider().provides(operation);
				}
				return false;
			}
			return getProvider().provides(operation);
		}

		/**
		 * Checks if the operation is supported by the XML extension
		 * 
		 * @param operation
		 * @return true if the operation is supported by the XML extension,
		 *         false otherwise
		 */
		private boolean isSupportedInExtention(IOperation operation) {
			if (operation instanceof CreateDecoratorsOperation) {
				CreateDecoratorsOperation o = (CreateDecoratorsOperation) operation;

				return providerConfiguration.supports(o.getDecoratorTarget());
			}
			return false;
		}
	}

	/** The singleton instance of the decorator service. */
	private final static DecoratorService service = new DecoratorService();

	static {
		service.configureProviders(DiagramUIPlugin.getPluginId(), "decoratorProviders"); //$NON-NLS-1$
	}

	/**
	 * Retrieves the singleton instance of the decorator service.
	 * 
	 * @return The decorator service singleton.
	 */
	public static DecoratorService getInstance() {
		return service;
	}

	/**
	 * Executes a <code>CreateDecoratorsOperation</code> with a
	 * <code>REVERSE</code> execution strategy. This allows higher priority
	 * providers to install their decorators after lower priority providers so
	 * that their decorations will appear on top.
	 * 
	 * @see org.eclipse.gmf.runtime.diagram.ui.services.decorator.IDecoratorProvider#createDecorators(org.eclipse.gmf.runtime.diagram.ui.services.decorator.IDecoratorTarget)
	 */
	public void createDecorators(IDecoratorTarget decoratorTarget) {
		execute(ExecutionStrategy.REVERSE, new CreateDecoratorsOperation(
			decoratorTarget));
	}

	/**
	 * @see org.eclipse.gmf.runtime.common.core.service.Service#newProviderDescriptor(org.eclipse.core.runtime.IConfigurationElement)
	 */
	protected Service.ProviderDescriptor newProviderDescriptor(
		IConfigurationElement element) {
		return new ProviderDescriptor(element);
	}
}