/*
 * Copyright 2002-2012 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.interceptor;

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

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

import org.springframework.core.BridgeMethodResolver;
import org.springframework.util.ClassUtils;

/**
 * Abstract implementation of {@link CacheOperation} that caches
 * attributes for methods and implements a fallback policy: 1. specific
 * target method; 2. target class; 3. declaring method; 4. declaring
 * class/interface.
 *
 * <p>Defaults to using the target class's caching attribute if none is
 * associated with the target method. Any caching attribute associated
 * with the target method completely overrides a class caching attribute.
 * If none found on the target class, the interface that the invoked
 * method has been called through (in case of a JDK proxy) will be
 * checked.
 *
 * <p>This implementation caches attributes by method after they are
 * first used. If it is ever desirable to allow dynamic changing of
 * cacheable attributes (which is very unlikely), caching could be made
 * configurable.
 *
 * @author Costin Leau
 * @author Juergen Hoeller
 * @since 3.1
 */
public abstract class AbstractFallbackCacheOperationSource implements CacheOperationSource {

	/**
	 * 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 Collection<CacheOperation> NULL_CACHING_ATTRIBUTE = Collections.emptyList();

	/**
	 * Logger available to subclasses.
	 * <p>As this base class is not marked Serializable, the logger will be recreated
	 * after serialization - provided that the concrete subclass is Serializable.
	 */
	protected final Log logger = LogFactory.getLog(getClass());

	/**
	 * Cache of CacheOperations, keyed by {@link MethodCacheKey} (Method + target Class).
	 * <p>As this base class is not marked Serializable, the cache will be recreated
	 * after serialization - provided that the concrete subclass is Serializable.
	 */
	final Map<Object, Collection<CacheOperation>> attributeCache =
			new ConcurrentHashMap<Object, Collection<CacheOperation>>(1024);

	/**
	 * Determine the caching attribute for this method invocation.
	 * <p>Defaults to the class's caching attribute if no method attribute is found.
	 * @param method the method for the current invocation (never {@code null})
	 * @param targetClass the target class for this invocation (may be {@code null})
	 * @return {@link CacheOperation} for this method, or {@code null} if the method
	 * is not cacheable
	 */
	@Override
	public Collection<CacheOperation> getCacheOperations(Method method, Class<?> targetClass) {
		// First, see if we have a cached value.
		Object cacheKey = getCacheKey(method, targetClass);
		Collection<CacheOperation> cached = this.attributeCache.get(cacheKey);
		if (cached != null) {
			if (cached == NULL_CACHING_ATTRIBUTE) {
				return null;
			}
			// Value will either be canonical value indicating there is no caching attribute,
			// or an actual caching attribute.
			return cached;
		}
		else {
			// We need to work it out.
			Collection<CacheOperation> cacheOps = computeCacheOperations(method, targetClass);
			// Put it in the cache.
			if (cacheOps == null) {
				this.attributeCache.put(cacheKey, NULL_CACHING_ATTRIBUTE);
			}
			else {
				if (logger.isDebugEnabled()) {
					logger.debug("Adding cacheable method '" + method.getName() + "' with attribute: " + cacheOps);
				}
				this.attributeCache.put(cacheKey, cacheOps);
			}
			return cacheOps;
		}
	}

	/**
	 * Determine a cache key for the given method and target class.
	 * <p>Must not produce same key for overloaded methods.
	 * Must produce same key for different instances of the same method.
	 * @param method the method (never {@code null})
	 * @param targetClass the target class (may be {@code null})
	 * @return the cache key (never {@code null})
	 */
	protected Object getCacheKey(Method method, Class<?> targetClass) {
		return new MethodCacheKey(method, targetClass);
	}

	private Collection<CacheOperation> computeCacheOperations(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.
		Collection<CacheOperation> opDef = findCacheOperations(specificMethod);
		if (opDef != null) {
			return opDef;
		}

		// Second try is the caching operation on the target class.
		opDef = findCacheOperations(specificMethod.getDeclaringClass());
		if (opDef != null) {
			return opDef;
		}

		if (specificMethod != method) {
			// Fall back is to look at the original method.
			opDef = findCacheOperations(method);
			if (opDef != null) {
				return opDef;
			}
			// Last fall back is the class of the original method.
			return findCacheOperations(method.getDeclaringClass());
		}
		return null;
	}


	/**
	 * Subclasses need to implement this to return the caching attribute
	 * for the given method, if any.
	 * @param method the method to retrieve the attribute for
	 * @return all caching attribute associated with this method
	 * (or {@code null} if none)
	 */
	protected abstract Collection<CacheOperation> findCacheOperations(Method method);

	/**
	 * Subclasses need to implement this to return the caching attribute
	 * for the given class, if any.
	 * @param clazz the class to retrieve the attribute for
	 * @return all caching attribute associated with this class
	 * (or {@code null} if none)
	 */
	protected abstract Collection<CacheOperation> findCacheOperations(Class<?> clazz);

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