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The Amazon Web Services SDK for Java provides Java APIs for building software on AWS' cost-effective, scalable, and reliable infrastructure products. The AWS Java SDK allows developers to code against APIs for all of Amazon's infrastructure web services (Amazon S3, Amazon EC2, Amazon SQS, Amazon Relational Database Service, Amazon AutoScaling, etc).

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/*
 * Copyright 2012-2014 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 *  http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file 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 com.amazonaws.services.simpleworkflow.flow.aspectj;

import java.lang.annotation.Annotation;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.Signature;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.reflect.MethodSignature;

import com.amazonaws.services.simpleworkflow.flow.annotations.Asynchronous;
import com.amazonaws.services.simpleworkflow.flow.annotations.NoWait;
import com.amazonaws.services.simpleworkflow.flow.annotations.Wait;
import com.amazonaws.services.simpleworkflow.flow.core.AndPromise;
import com.amazonaws.services.simpleworkflow.flow.core.Promise;

@Aspect
public class AsynchronousAspect {

    @SuppressWarnings({ "rawtypes", "unchecked" })
    @Around("call(@com.amazonaws.services.simpleworkflow.flow.annotations.Asynchronous * *(..)) && @annotation(asynchronousAnnotation)")
    public Object makeAsynchronous(ProceedingJoinPoint pjp, Asynchronous asynchronousAnnotation) throws Throwable {
        final Signature signature = pjp.getStaticPart().getSignature();
        if (signature instanceof MethodSignature) {
            final MethodSignature methodSignature = (MethodSignature) signature;
            int i = 0;
            Object[] methodArguments = pjp.getArgs();
            Annotation[][] parameterAnnotations = methodSignature.getMethod().getParameterAnnotations();
            List valueParams = new ArrayList();
            for (final Class parameterType : methodSignature.getParameterTypes()) {
                if ((isPromise(parameterType) || isPromiseArray(parameterType) || (isCollection(parameterType) && hasWaitAnnotation(parameterAnnotations[i])))
                        && !hasNoWaitAnnotation(parameterAnnotations[i])) {
                    Object param = methodArguments[i];
                    if (isPromise(parameterType)) {
                        valueParams.add((Promise) param);
                    }
                    else if (isCollection(parameterType)) {
                        valueParams.add(new AndPromise((Collection) param));
                    }
                    else {
                        valueParams.add(new AndPromise((Promise[]) param));
                    }
                } else {
                    valueParams.add(null);
                }
                i++;
            }

            Promise[] values = valueParams.toArray(new Promise[0]);
            Boolean daemon = asynchronousAnnotation.daemon() ? true : null;
            AsynchronousAspectTask task = new AsynchronousAspectTask(daemon, pjp, values);
            return task.getReturnValue();
        }

        return pjp.proceed();
    }

    private static boolean isPromise(Class clazz) {
        return Promise.class.isAssignableFrom(clazz);
    }

    private static boolean isCollection(Class clazz) {
        return Collection.class.isAssignableFrom(clazz);
    }

    private static boolean isPromiseArray(Class clazz) {
        if (!clazz.isArray()) {
            return false;
        }
        Class elementType = clazz.getComponentType();
        return isPromise(elementType);
    }

    private static boolean hasWaitAnnotation(Annotation[] annotations) {
        for (Annotation annotation : annotations) {
            if (annotation.annotationType().equals(Wait.class)) {
                return true;
            }
        }

        return false;
    }

    private static boolean hasNoWaitAnnotation(Annotation[] annotations) {
        for (Annotation annotation : annotations) {
            if (annotation.annotationType().equals(NoWait.class)) {
                return true;
            }
        }

        return false;
    }
}