/*
 * Copyright 2002-2020 the original author or authors.
 *
 * 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
 *
 *      https://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.springframework.context.event;

import java.lang.reflect.Constructor;

import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;

import org.springframework.beans.factory.InitializingBean;
import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.context.ApplicationEventPublisherAware;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;

Interceptor that publishes an ApplicationEvent to all ApplicationListeners registered with an ApplicationEventPublisher after each successful method invocation.
Note that this interceptor is only capable of publishing stateless events configured via the "applicationEventClass" property. 
Author:
Dmitriy Kopylenko, Juergen Hoeller, Rick Evans
See Also:
setApplicationEventClass
ApplicationEvent
ApplicationListener
ApplicationEventPublisher
ApplicationContext/**
 * {@link MethodInterceptor Interceptor} that publishes an
 * {@code ApplicationEvent} to all {@code ApplicationListeners}
 * registered with an {@code ApplicationEventPublisher} after each
 * <i>successful</i> method invocation.
 *
 * <p>Note that this interceptor is only capable of publishing <i>stateless</i>
 * events configured via the
 * {@link #setApplicationEventClass "applicationEventClass"} property.
 *
 * @author Dmitriy Kopylenko
 * @author Juergen Hoeller
 * @author Rick Evans
 * @see #setApplicationEventClass
 * @see org.springframework.context.ApplicationEvent
 * @see org.springframework.context.ApplicationListener
 * @see org.springframework.context.ApplicationEventPublisher
 * @see org.springframework.context.ApplicationContext
 */
public class EventPublicationInterceptor
		implements MethodInterceptor, ApplicationEventPublisherAware, InitializingBean {

	@Nullable
	private Constructor<?> applicationEventClassConstructor;

	@Nullable
	private ApplicationEventPublisher applicationEventPublisher;


	
Set the application event class to publish.
The event class must have a constructor with a single Object argument for the event source. The interceptor will pass in the invoked object. 
Throws:
IllegalArgumentException – if the supplied Class is null or if it is not an ApplicationEvent subclass or if it does not expose a constructor that takes a single Object argument/**
	 * Set the application event class to publish.
	 * <p>The event class <b>must</b> have a constructor with a single
	 * {@code Object} argument for the event source. The interceptor
	 * will pass in the invoked object.
	 * @throws IllegalArgumentException if the supplied {@code Class} is
	 * {@code null} or if it is not an {@code ApplicationEvent} subclass or
	 * if it does not expose a constructor that takes a single {@code Object} argument
	 */
	public void setApplicationEventClass(Class<?> applicationEventClass) {
		if (ApplicationEvent.class == applicationEventClass ||
				!ApplicationEvent.class.isAssignableFrom(applicationEventClass)) {
			throw new IllegalArgumentException("'applicationEventClass' needs to extend ApplicationEvent");
		}
		try {
			this.applicationEventClassConstructor = applicationEventClass.getConstructor(Object.class);
		}
		catch (NoSuchMethodException ex) {
			throw new IllegalArgumentException("ApplicationEvent class [" +
					applicationEventClass.getName() + "] does not have the required Object constructor: " + ex);
		}
	}

	@Override
	public void setApplicationEventPublisher(ApplicationEventPublisher applicationEventPublisher) {
		this.applicationEventPublisher = applicationEventPublisher;
	}

	@Override
	public void afterPropertiesSet() throws Exception {
		if (this.applicationEventClassConstructor == null) {
			throw new IllegalArgumentException("Property 'applicationEventClass' is required");
		}
	}


	@Override
	@Nullable
	public Object invoke(MethodInvocation invocation) throws Throwable {
		Object retVal = invocation.proceed();

		Assert.state(this.applicationEventClassConstructor != null, "No ApplicationEvent class set");
		ApplicationEvent event = (ApplicationEvent)
				this.applicationEventClassConstructor.newInstance(invocation.getThis());

		Assert.state(this.applicationEventPublisher != null, "No ApplicationEventPublisher available");
		this.applicationEventPublisher.publishEvent(event);

		return retVal;
	}

}