/*
 * Copyright 2002-2015 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.cache.jcache.interceptor;

import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.context.expression.AnnotatedElementKey;
import org.springframework.core.BridgeMethodResolver;
import org.springframework.util.ClassUtils;

/**
 * Abstract implementation of {@link JCacheOperationSource} that caches
 * attributes for methods and implements a fallback policy: 1. specific
 * target method; 2. declaring method.
 *
 * <p>This implementation caches attributes by method after they are
 * first used.
 *
 * @author Stephane Nicoll
 * @since 4.1
 * @see org.springframework.cache.interceptor.AbstractFallbackCacheOperationSource
 */
public abstract class AbstractFallbackJCacheOperationSource
		implements JCacheOperationSource {

	/**
	 * Canonical value held in cache to indicate no caching attribute was
	 * found for this method and we don't need to look again.
	 */
	private final static Object NULL_CACHING_ATTRIBUTE = new Object();

	protected final Log logger = LogFactory.getLog(getClass());

	private final Map<Object, Object> cache =
			new ConcurrentHashMap<Object, Object>(1024);

	@Override
	public JCacheOperation<?> getCacheOperation(Method method, Class<?> targetClass) {
		// First, see if we have a cached value.
		Object cacheKey = new AnnotatedElementKey(method, targetClass);
		Object cached = this.cache.get(cacheKey);
		if (cached != null) {
			if (cached == NULL_CACHING_ATTRIBUTE) {
				return null;
			}
			return (JCacheOperation<?>) cached;
		}
		else {
			JCacheOperation<?> operation = computeCacheOperation(method, targetClass);
			if (operation == null) {
				this.cache.put(cacheKey, NULL_CACHING_ATTRIBUTE);
			}
			else {
				if (logger.isDebugEnabled()) {
					logger.debug("Adding cacheable method '" + method.getName()
							+ "' with operation: " + operation);
				}
				this.cache.put(cacheKey, operation);
			}
			return operation;
		}
	}

	private JCacheOperation<?> computeCacheOperation(Method method, Class<?> targetClass) {
		// Don't allow no-public methods as required.
		if (allowPublicMethodsOnly() && !Modifier.isPublic(method.getModifiers())) {
			return null;
		}

		// The method may be on an interface, but we need attributes from the target class.
		// If the target class is null, the method will be unchanged.
		Method specificMethod = ClassUtils.getMostSpecificMethod(method, targetClass);
		// If we are dealing with method with generic parameters, find the original method.
		specificMethod = BridgeMethodResolver.findBridgedMethod(specificMethod);

		// First try is the method in the target class.
		JCacheOperation<?> operation = findCacheOperation(specificMethod, targetClass);
		if (operation != null) {
			return operation;
		}
		if (specificMethod != method) {
			// Fall back is to look at the original method.
			operation = findCacheOperation(method, targetClass);
			if (operation != null) {
				return operation;
			}
		}
		return null;
	}

	/**
	 * Subclasses need to implement this to return the caching operation
	 * for the given method, if any.
	 * @param method the method to retrieve the operation for
	 * @param targetType the target class
	 * @return the cache operation associated with this method
	 * (or {@code null} if none)
	 */
	protected abstract JCacheOperation<?> findCacheOperation(Method method, Class<?> targetType);

	/**
	 * Should only public methods be allowed to have caching semantics?
	 * <p>The default implementation returns {@code false}.
	 */
	protected boolean allowPublicMethodsOnly() {
		return false;
	}

}
