/* 
 * Copyright (c) 2006 Stiftung Deutsches Elektronen-Synchroton, 
 * Member of the Helmholtz Association, (DESY), HAMBURG, GERMANY.
 *
 * THIS SOFTWARE IS PROVIDED UNDER THIS LICENSE ON AN "../AS IS" BASIS. 
 * WITHOUT WARRANTY OF ANY KIND, EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED 
 * TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR PARTICULAR PURPOSE AND 
 * NON-INFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE 
 * FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, 
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR 
 * THE USE OR OTHER DEALINGS IN THE SOFTWARE. SHOULD THE SOFTWARE PROVE DEFECTIVE 
 * IN ANY RESPECT, THE USER ASSUMES THE COST OF ANY NECESSARY SERVICING, REPAIR OR 
 * CORRECTION. THIS DISCLAIMER OF WARRANTY CONSTITUTES AN ESSENTIAL PART OF THIS LICENSE. 
 * NO USE OF ANY SOFTWARE IS AUTHORIZED HEREUNDER EXCEPT UNDER THIS DISCLAIMER.
 * DESY HAS NO OBLIGATION TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, 
 * OR MODIFICATIONS.
 * THE FULL LICENSE SPECIFYING FOR THE SOFTWARE THE REDISTRIBUTION, MODIFICATION, 
 * USAGE AND OTHER RIGHTS AND OBLIGATIONS IS INCLUDED WITH THE DISTRIBUTION OF THIS 
 * PROJECT IN THE FILE LICENSE.HTML. IF THE LICENSE IS NOT INCLUDED YOU MAY FIND A COPY 
 * AT HTTP://WWW.DESY.DE/LEGAL/LICENSE.HTM
 */
package org.csstudio.sds.internal.persistence;

import java.util.HashMap;

import org.csstudio.sds.SdsPlugin;
import org.csstudio.sds.model.PropertyTypesEnum;
import org.eclipse.core.runtime.IConfigurationElement;
import org.eclipse.core.runtime.IExtensionRegistry;
import org.eclipse.core.runtime.Platform;

/**
 * Central registry for extensions of the
 * <code>propertyPersistenceHandlers</code> extension point.
 * 
 * @author Alexander Will
 * @version $Revision: 1.1 $
 * 
 */
public final class PropertyPersistenceHandlerRegistry {
	/**
	 * The singleton instance.
	 */
	private static PropertyPersistenceHandlerRegistry _instance;

	/**
	 * Contains the persistence handler descriptors.
	 */
	private HashMap<PropertyTypesEnum, PropertyPersistenceHandlerDescriptor> _persistenceHandlers;

	/**
	 * Private constructor.
	 */
	private PropertyPersistenceHandlerRegistry() {
		lookup();
	}

	/**
	 * @return The singleton instance.
	 */
	public static PropertyPersistenceHandlerRegistry getInstance() {
		if (_instance == null) {
			_instance = new PropertyPersistenceHandlerRegistry();
		}

		return _instance;
	}

	/**
	 * Internal lookup of the Eclipse extension registry.
	 */
	private void lookup() {
		_persistenceHandlers = new HashMap<PropertyTypesEnum, PropertyPersistenceHandlerDescriptor>();

		IExtensionRegistry extReg = Platform.getExtensionRegistry();
		String id = SdsPlugin.EXTPOINT_PROPERTY_PERSISTENCE_HANDLERS;
		IConfigurationElement[] confElements = extReg
				.getConfigurationElementsFor(id);

		for (IConfigurationElement element : confElements) {
			String typeString= element.getAttribute("typeId"); //$NON-NLS-1$

			
			PropertyTypesEnum typeId;
			try {
				typeId = PropertyTypesEnum.createFromPortable(typeString);
			} catch (Exception e) {
				// apply String as default
				typeId = PropertyTypesEnum.STRING;
			}
			
			if (_persistenceHandlers.containsKey(typeId)) {
				throw new IllegalArgumentException(
						"Only one item factory for the type >>" + typeId //$NON-NLS-1$
								+ "<< should be registered."); //$NON-NLS-1$
			}
			_persistenceHandlers.put(typeId,
					new PropertyPersistenceHandlerDescriptor(element));
		}
	}

	/**
	 * Instantiate and return the persistence handler for the given property
	 * type.
	 * 
	 * @param typeId
	 *            The property type Id.
	 * @return The persistence handler for the given property type.
	 */
	public AbstractPropertyPersistenceHandler getPersistenceHandler(
			final PropertyTypesEnum typeId) {
		AbstractPropertyPersistenceHandler result = null;

		PropertyPersistenceHandlerDescriptor descriptor = _persistenceHandlers
				.get(typeId);

		if (descriptor != null) {
			result = descriptor.getPersistenceHandler();
			assert result != null : "type id was valid, but no persistence handler was instantiated"; //$NON-NLS-1$
		}

		return result;
	}
}