/*
 * Copyright 2002-2012 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
 *
 *      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.springframework.aop.interceptor;

import java.lang.reflect.Method;

import java.util.concurrent.Callable;
import java.util.concurrent.Executor;
import java.util.concurrent.Future;

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

import org.springframework.core.Ordered;
import org.springframework.core.task.AsyncTaskExecutor;
import org.springframework.util.ReflectionUtils;

/**
 * AOP Alliance <code>MethodInterceptor</code> that processes method invocations
 * asynchronously, using a given {@link org.springframework.core.task.AsyncTaskExecutor}.
 * Typically used with the {@link org.springframework.scheduling.annotation.Async} annotation.
 *
 * <p>In terms of target method signatures, any parameter types are supported.
 * However, the return type is constrained to either <code>void</code> or
 * <code>java.util.concurrent.Future</code>. In the latter case, the Future handle
 * returned from the proxy will be an actual asynchronous Future that can be used
 * to track the result of the asynchronous method execution. However, since the
 * target method needs to implement the same signature, it will have to return
 * a temporary Future handle that just passes the return value through
 * (like Spring's {@link org.springframework.scheduling.annotation.AsyncResult}
 * or EJB 3.1's <code>javax.ejb.AsyncResult</code>).
 *
 * <p>As of Spring 3.1.2 the {@code AnnotationAsyncExecutionInterceptor} subclass is
 * preferred for use due to its support for executor qualification in conjunction with
 * Spring's {@code @Async} annotation.
 *
 * @author Juergen Hoeller
 * @author Chris Beams
 * @since 3.0
 * @see org.springframework.scheduling.annotation.Async
 * @see org.springframework.scheduling.annotation.AsyncAnnotationAdvisor
 * @see org.springframework.scheduling.annotation.AnnotationAsyncExecutionInterceptor
 */
public class AsyncExecutionInterceptor extends AsyncExecutionAspectSupport
		implements MethodInterceptor, Ordered {

	/**
	 * Create a new {@code AsyncExecutionInterceptor}.
	 * @param executor the {@link Executor} (typically a Spring {@link AsyncTaskExecutor}
	 * or {@link java.util.concurrent.ExecutorService}) to delegate to.
	 */
	public AsyncExecutionInterceptor(Executor executor) {
		super(executor);
	}


	/**
	 * Intercept the given method invocation, submit the actual calling of the method to
	 * the correct task executor and return immediately to the caller.
	 * @param invocation the method to intercept and make asynchronous
	 * @return {@link Future} if the original method returns {@code Future}; {@code null}
	 * otherwise.
	 */
	public Object invoke(final MethodInvocation invocation) throws Throwable {
		Future<?> result = this.determineAsyncExecutor(invocation.getMethod()).submit(
				new Callable<Object>() {
					public Object call() throws Exception {
						try {
							Object result = invocation.proceed();
							if (result instanceof Future) {
								return ((Future<?>) result).get();
							}
						}
						catch (Throwable ex) {
							ReflectionUtils.rethrowException(ex);
						}
						return null;
					}
				});
		if (Future.class.isAssignableFrom(invocation.getMethod().getReturnType())) {
			return result;
		}
		else {
			return null;
		}
	}

	/**
	 * {@inheritDoc}
	 * <p>This implementation is a no-op for compatibility in Spring 3.1.2. Subclasses may
	 * override to provide support for extracting qualifier information, e.g. via an
	 * annotation on the given method.
	 * @return always {@code null}
	 * @see #determineAsyncExecutor(Method)
	 * @since 3.1.2
	 */
	@Override
	protected String getExecutorQualifier(Method method) {
		return null;
	}

	public int getOrder() {
		return Ordered.HIGHEST_PRECEDENCE;
	}

}
