/* Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.activiti.engine.impl.bpmn.helper;

import org.activiti.engine.ActivitiIllegalArgumentException;
import org.activiti.engine.delegate.event.ActivitiEntityEvent;
import org.activiti.engine.delegate.event.ActivitiEvent;
import org.activiti.engine.delegate.event.ActivitiEventListener;
import org.activiti.engine.impl.util.ReflectUtil;

/**
 * An {@link ActivitiEventListener} implementation which uses a classname to
 * create a delegate {@link ActivitiEventListener} instance to use for event notification.
 * <br><br>
 * 
 * In case an entityClass was passed in the constructor, only events that are {@link ActivitiEntityEvent}'s
 * that target an entity of the given type, are dispatched to the delegate.
 *  
 * @author Frederik Heremans
 */
public class DelegateActivitiEventListener extends BaseDelegateEventListener {

	protected String className;
	protected ActivitiEventListener delegateInstance;
	protected boolean failOnException = true;

	public DelegateActivitiEventListener(String className, Class<?> entityClass) {
		this.className = className;
		setEntityClass(entityClass);
	}

	@Override
	public void onEvent(ActivitiEvent event) {
		if(isValidEvent(event)) {
			getDelegateInstance().onEvent(event);
		}
	}

	@Override
	public boolean isFailOnException() {
		if(delegateInstance != null) {
			return delegateInstance.isFailOnException();
		}
		return failOnException;
	}
	
	protected ActivitiEventListener getDelegateInstance() {
		if(delegateInstance == null) {
			Object instance = ReflectUtil.instantiate(className);
			if(instance instanceof ActivitiEventListener) {
				delegateInstance = (ActivitiEventListener) instance;
			} else {
				// Force failing of the listener invocation, since the delegate cannot be created
				failOnException = true;
				throw new ActivitiIllegalArgumentException("Class " + className
				    + " does not implement " + ActivitiEventListener.class.getName());
			}
		}
		return delegateInstance;
	}
}