/*
 * Copyright 2014-2016 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
 *
 *      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.data.util;

import java.lang.annotation.Annotation;
import java.lang.reflect.Method;

import org.springframework.core.annotation.AnnotatedElementUtils;
import org.springframework.util.Assert;
import org.springframework.util.ReflectionUtils.MethodCallback;

/**
 * {@link MethodCallback} to find annotations of a given type.
 * 
 * @author Oliver Gierke
 * @author Christoph Strobl
 */
public class AnnotationDetectionMethodCallback<A extends Annotation> implements MethodCallback {

	private static final String MULTIPLE_FOUND = "Found annotation %s both on %s and %s! Make sure only one of them is annotated with it!";

	private final boolean enforceUniqueness;
	private final Class<A> annotationType;

	private Method foundMethod;
	private A annotation;

	/**
	 * Creates a new {@link AnnotationDetectionMethodCallback} for the given annotation type.
	 * 
	 * @param annotationType must not be {@literal null}.
	 */
	public AnnotationDetectionMethodCallback(Class<A> annotationType) {
		this(annotationType, false);
	}

	/**
	 * Creates a new {@link AnnotationDetectionMethodCallback} for the given annotation type.
	 * 
	 * @param annotationType must not be {@literal null}.
	 * @param enforceUniqueness whether to fail if multiple methods with the annotation are found.
	 */
	public AnnotationDetectionMethodCallback(Class<A> annotationType, boolean enforceUniqueness) {

		Assert.notNull(annotationType, "Annotation type must not be null!");

		this.annotationType = annotationType;
		this.enforceUniqueness = enforceUniqueness;
	}

	/**
	 * @return the method
	 */
	public Method getMethod() {
		return foundMethod;
	}

	/**
	 * @return the annotation
	 */
	public A getAnnotation() {
		return annotation;
	}

	/**
	 * Returns whether an annotation was found.
	 * 
	 * @return
	 */
	public boolean hasFoundAnnotation() {
		return annotation != null;
	}

	/* 
	 * (non-Javadoc)
	 * @see org.springframework.util.ReflectionUtils.MethodCallback#doWith(java.lang.reflect.Method)
	 */
	@Override
	public void doWith(Method method) throws IllegalArgumentException, IllegalAccessException {

		if (foundMethod != null && !enforceUniqueness) {
			return;
		}

		A foundAnnotation = AnnotatedElementUtils.findMergedAnnotation(method, annotationType);

		if (foundAnnotation != null) {

			if (foundMethod != null && enforceUniqueness) {
				throw new IllegalStateException(String.format(MULTIPLE_FOUND, foundAnnotation.getClass().getName(), foundMethod,
						method));
			}

			this.annotation = foundAnnotation;
			this.foundMethod = method;
		}
	}
}