/*
 * Copyright 2002-2018 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
 *
 *      https://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.core.MethodClassKey;
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 static final 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 method on a specific 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.
         */
        private 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) {
                if (method.getDeclaringClass() == Object.class) {
                        return null;
                }

                Object cacheKey = getCacheKey(method, targetClass);
                Collection<CacheOperation> cached = this.attributeCache.get(cacheKey);

                if (cached != null) {
                        return (cached != NULL_CACHING_ATTRIBUTE ? cached : null);
                }
                else {
                        Collection<CacheOperation> cacheOps = computeCacheOperations(method, targetClass);
                        if (cacheOps != null) {
                                if (logger.isDebugEnabled()) {
                                        logger.debug("Adding cacheable method '" + method.getName() + "' with attribute: " + cacheOps);
                                }
                                this.attributeCache.put(cacheKey, cacheOps);
                        }
                        else {
                                this.attributeCache.put(cacheKey, NULL_CACHING_ATTRIBUTE);
                        }
                        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 MethodClassKey(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 && ClassUtils.isUserLevelMethod(method)) {
                        return opDef;
                }

                if (specificMethod != method) {
                        // Fallback is to look at the original method.
                        opDef = findCacheOperations(method);
                        if (opDef != null) {
                                return opDef;
                        }
                        // Last fallback is the class of the original method.
                        opDef = findCacheOperations(method.getDeclaringClass());
                        if (opDef != null && ClassUtils.isUserLevelMethod(method)) {
                                return opDef;
                        }
                }

                return null;
        }


        /**
         * 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);

        /**
         * 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);

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

}