/* 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.Expression;
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.el.NoExecutionVariableScope;

/**
 * An {@link ActivitiEventListener} implementation which resolves an expression
 * to a delegate {@link ActivitiEventListener} instance and uses this 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 DelegateExpressionActivitiEventListener extends BaseDelegateEventListener {

	protected Expression expression;
	protected boolean failOnException = true;

	public DelegateExpressionActivitiEventListener(Expression expression, Class<?> entityClass) {
		this.expression = expression;
		setEntityClass(entityClass);
	}

	@Override
	public void onEvent(ActivitiEvent event) {
		if(isValidEvent(event)) {
		  
		  Object delegate = DelegateExpressionUtil.resolveDelegateExpression(expression, new NoExecutionVariableScope());
			if (delegate instanceof ActivitiEventListener) {
				// Cache result of isFailOnException() from delegate-instance until next
				// event is received. This prevents us from having to resolve the expression twice when
				// an error occurs.
				failOnException = ((ActivitiEventListener) delegate).isFailOnException();
				
				// Call the delegate
				((ActivitiEventListener) delegate).onEvent(event);
			} else {
				
				// Force failing, since the exception we're about to throw cannot be ignored, because it
				// did not originate from the listener itself
				failOnException = true;
				throw new ActivitiIllegalArgumentException("Delegate expression " + expression
						+ " did not resolve to an implementation of " + ActivitiEventListener.class.getName());
			}
		}
	}

	@Override
	public boolean isFailOnException() {
		return failOnException;
	}

}