/*
 * Copyright 2002-2016 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.aop.interceptor;

import java.lang.reflect.Method;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executor;
import java.util.concurrent.Future;

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

import org.springframework.aop.support.AopUtils;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.core.BridgeMethodResolver;
import org.springframework.core.Ordered;
import org.springframework.core.task.AsyncTaskExecutor;
import org.springframework.core.task.SimpleAsyncTaskExecutor;
import org.springframework.util.ClassUtils;

/**
 * AOP Alliance {@code MethodInterceptor} 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} or
 * {@code java.util.concurrent.Future}. 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}).
 *
 * <p>When the return type is {@code java.util.concurrent.Future}, any exception thrown
 * during the execution can be accessed and managed by the caller. With {@code void}
 * return type however, such exceptions cannot be transmitted back. In that case an
 * {@link AsyncUncaughtExceptionHandler} can be registered to process such exceptions.
 *
 * <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
 * @author Stephane Nicoll
 * @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 instance with a default {@link AsyncUncaughtExceptionHandler}.
         * @param defaultExecutor the {@link Executor} (typically a Spring {@link AsyncTaskExecutor}
         * or {@link java.util.concurrent.ExecutorService}) to delegate to;
         * as of 4.2.6, a local executor for this interceptor will be built otherwise
         */
        public AsyncExecutionInterceptor(Executor defaultExecutor) {
                super(defaultExecutor);
        }

        /**
         * Create a new {@code AsyncExecutionInterceptor}.
         * @param defaultExecutor the {@link Executor} (typically a Spring {@link AsyncTaskExecutor}
         * or {@link java.util.concurrent.ExecutorService}) to delegate to;
         * as of 4.2.6, a local executor for this interceptor will be built otherwise
         * @param exceptionHandler the {@link AsyncUncaughtExceptionHandler} to use
         */
        public AsyncExecutionInterceptor(Executor defaultExecutor, AsyncUncaughtExceptionHandler exceptionHandler) {
                super(defaultExecutor, exceptionHandler);
        }


        /**
         * 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.
         */
        @Override
        public Object invoke(final MethodInvocation invocation) throws Throwable {
                Class<?> targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null);
                Method specificMethod = ClassUtils.getMostSpecificMethod(invocation.getMethod(), targetClass);
                final Method userDeclaredMethod = BridgeMethodResolver.findBridgedMethod(specificMethod);

                AsyncTaskExecutor executor = determineAsyncExecutor(userDeclaredMethod);
                if (executor == null) {
                        throw new IllegalStateException(
                                        "No executor specified and no default executor set on AsyncExecutionInterceptor either");
                }

                Callable<Object> task = new Callable<Object>() {
                        @Override
                        public Object call() throws Exception {
                                try {
                                        Object result = invocation.proceed();
                                        if (result instanceof Future) {
                                                return ((Future<?>) result).get();
                                        }
                                }
                                catch (ExecutionException ex) {
                                        handleError(ex.getCause(), userDeclaredMethod, invocation.getArguments());
                                }
                                catch (Throwable ex) {
                                        handleError(ex, userDeclaredMethod, invocation.getArguments());
                                }
                                return null;
                        }
                };

                return doSubmit(task, executor, invocation.getMethod().getReturnType());
        }

        /**
         * 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}
         * @since 3.1.2
         * @see #determineAsyncExecutor(Method)
         */
        @Override
        protected String getExecutorQualifier(Method method) {
                return null;
        }

        /**
         * This implementation searches for a unique {@link org.springframework.core.task.TaskExecutor}
         * bean in the context, or for an {@link Executor} bean named "taskExecutor" otherwise.
         * If neither of the two is resolvable (e.g. if no {@code BeanFactory} was configured at all),
         * this implementation falls back to a newly created {@link SimpleAsyncTaskExecutor} instance
         * for local use if no default could be found.
         * @see #DEFAULT_TASK_EXECUTOR_BEAN_NAME
         */
        @Override
        protected Executor getDefaultExecutor(BeanFactory beanFactory) {
                Executor defaultExecutor = super.getDefaultExecutor(beanFactory);
                return (defaultExecutor != null ? defaultExecutor : new SimpleAsyncTaskExecutor());
        }

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

}