/* 
 * Copyright (c) 2008 Stiftung Deutsches Elektronen-Synchrotron, 
 * 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.ui.internal.properties;

import java.util.HashMap;
import java.util.Map;

import org.csstudio.sds.model.PropertyTypesEnum;
import org.csstudio.sds.ui.SdsUiPlugin;
import org.csstudio.sds.ui.properties.IPropertyDescriptorFactory;
import org.eclipse.core.runtime.CoreException;
import org.eclipse.core.runtime.IConfigurationElement;
import org.eclipse.core.runtime.IExtensionRegistry;
import org.eclipse.core.runtime.Platform;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * 
 * @author Stefan Hofer
 *
 */
public final class PropertyDescriptorFactoryService {
    private static final Logger LOG = LoggerFactory.getLogger(PropertyDescriptorFactoryService.class);

	/**
	 * Instances of this class serve as delegates to
	 * enable lazy loading of extension point contributions.
	 * 
	 * @author Stefan Hofer
	 */
	class PropertyDescriptorFactoryContribution {
		/**
		 * The configuration element.
		 */
		private final IConfigurationElement _configurationElement;

		/**
		 * Constructor.
		 * 
		 * @param configurationElement
		 *            required
		 */
		public PropertyDescriptorFactoryContribution(final IConfigurationElement configurationElement) {
			assert configurationElement != null;
			_configurationElement = configurationElement;
		}

		/**
		 * Returns a new instance of the PropertyDescriptorFactory.
		 * 
		 * @return A new property descriptor factory.
		 */
		public IPropertyDescriptorFactory createPropertyDescriptorFactory() {
			IPropertyDescriptorFactory factory = null;
			try {
				factory = (IPropertyDescriptorFactory) _configurationElement
						.createExecutableExtension("class"); //$NON-NLS-1$
			} catch (CoreException e) {
				LOG.error(e.toString());
			}
			return factory;
		}
	}

	/**
	 * Holds reference to the singleton instance of this class.
	 */
	private static PropertyDescriptorFactoryService _instance;
	
	/**
	 * Contributions to this extension points.
	 */
	private Map<PropertyTypesEnum, PropertyDescriptorFactoryContribution> _contributions;

	/**
	 * @return The singleton instance of this service.
	 */
	public static PropertyDescriptorFactoryService getInstance() {
		if (_instance == null) {
			_instance = new PropertyDescriptorFactoryService();
		}
		return _instance;
	}
	
	/**
	 * Private contructor because of singleton. 
	 * Use {@link PropertyDescriptorFactoryService#getInstance()}.
	 */
	private PropertyDescriptorFactoryService() {
		lookup();
	}

	/**
	 * Looks up all extensions from the extension registry and creates the
	 * corresponding descriptor objects.
	 */
	private void lookup() {
		_contributions = new HashMap<PropertyTypesEnum, PropertyDescriptorFactoryContribution>();

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

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

			
			PropertyTypesEnum typeId;
			try {
				typeId = PropertyTypesEnum
						.createFromPortable(typeIdString);
			} catch (Exception e) {
				// apply String as default
				typeId = PropertyTypesEnum.STRING;
			}

			
			if (_contributions.containsKey(typeId)) {
				throw new IllegalArgumentException(
						"Only one property descriptor factory for the type >>" + typeId //$NON-NLS-1$
								+ "<< should be registered."); //$NON-NLS-1$
			}

			if (typeId != null) {
				_contributions.put(typeId, new PropertyDescriptorFactoryContribution(element));
			}
		}
	}
	
	/**
	 * @param typeId The typeId of the factory.
	 * @return <code>true</code> if the requested factory could be found in the extension point registry.
	 */
	public boolean hasPropertyDescriptorFactory(final PropertyTypesEnum typeId) {
		return _contributions.containsKey(typeId);
	}
	
	/**
	 * @param typeId The typeId of the factory. Must be a valid factory id.
	 * @return The factory corresponding to the ID.
	 */
	public IPropertyDescriptorFactory getPropertyDescriptorFactory(final PropertyTypesEnum typeId) {
		assert hasPropertyDescriptorFactory(typeId) : "Precondition violated: hasPropertyDescriptor(type)"; //$NON-NLS-1$
		
		PropertyDescriptorFactoryContribution contribution = _contributions.get(typeId);
		return contribution.createPropertyDescriptorFactory();
	}

}