/*
    * Copyright 2002-2008 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.batch.support;
  
  import java.lang.annotation.Annotation;
  import java.lang.annotation.ElementType;
  import java.lang.annotation.Target;
  import java.lang.reflect.Method;
  import java.util.concurrent.atomic.AtomicReference;
  
  import org.springframework.aop.support.AopUtils;
  import org.springframework.core.annotation.AnnotationUtils;
  import org.springframework.util.Assert;
  import org.springframework.util.ObjectUtils;
  import org.springframework.util.ReflectionUtils;
  
  /**
   * MethodResolver implementation that finds a <em>single</em> Method on the
   * given Class that contains the specified annotation type.
   * 
   * @author Mark Fisher
   */
  public class AnnotationMethodResolver implements MethodResolver {
  
  	private Class<? extends Annotation> annotationType;
  
  
  	/**
  	 * Create a MethodResolver for the specified Method-level annotation type
  	 */
  	public AnnotationMethodResolver(Class<? extends Annotation> annotationType) {
  		Assert.notNull(annotationType, "annotationType must not be null");
  		Assert.isTrue(ObjectUtils.containsElement(
  				annotationType.getAnnotation(Target.class).value(), ElementType.METHOD),
  				"Annotation [" + annotationType + "] is not a Method-level annotation.");
  		this.annotationType = annotationType;
  	}
  
  
  	/**
  	 * Find a <em>single</em> Method on the Class of the given candidate object
  	 * that contains the annotation type for which this resolver is searching.
  	 * 
  	 * @param candidate the instance whose Class will be checked for the
  	 * annotation
  	 * 
  	 * @return a single matching Method instance or <code>null</code> if the
  	 * candidate's Class contains no Methods with the specified annotation
  	 * 
  	 * @throws IllegalArgumentException if more than one Method has the
  	 * specified annotation
  	 */
      @Override
  	public Method findMethod(Object candidate) {
  		Assert.notNull(candidate, "candidate object must not be null");
  		Class<?> targetClass = AopUtils.getTargetClass(candidate);
  		if (targetClass == null) {
  			targetClass = candidate.getClass();
  		}
  		return this.findMethod(targetClass);
  	}
  
  	/**
  	 * Find a <em>single</em> Method on the given Class that contains the
  	 * annotation type for which this resolver is searching.
  	 * 
  	 * @param clazz the Class instance to check for the annotation
  	 * 
  	 * @return a single matching Method instance or <code>null</code> if the
  	 * Class contains no Methods with the specified annotation
  	 * 
  	 * @throws IllegalArgumentException if more than one Method has the
  	 * specified annotation
  	 */
      @Override
  	public Method findMethod(final Class<?> clazz) {
  		Assert.notNull(clazz, "class must not be null");
  		final AtomicReference<Method> annotatedMethod = new AtomicReference<Method>();
  		ReflectionUtils.doWithMethods(clazz, new ReflectionUtils.MethodCallback() {
              @Override
  			public void doWith(Method method) throws IllegalArgumentException, IllegalAccessException {
  				Annotation annotation = AnnotationUtils.findAnnotation(method, annotationType);
  				if (annotation != null) {
  					Assert.isNull(annotatedMethod.get(), "found more than one method on target class ["
  							+ clazz + "] with the annotation type [" + annotationType + "]");
 					annotatedMethod.set(method);
 				}
 			}
 		});
 		return annotatedMethod.get();
 	}
 
 }