/*
 * 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.annotation;

import java.util.Collection;

import javax.annotation.PostConstruct;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cache.CacheManager;
import org.springframework.cache.interceptor.KeyGenerator;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.ImportAware;
import org.springframework.core.annotation.AnnotationAttributes;
import org.springframework.core.type.AnnotationMetadata;
import org.springframework.util.Assert;
import org.springframework.util.CollectionUtils;

/**
 * Abstract base {@code @Configuration} class providing common structure for enabling
 * Spring's annotation-driven cache management capability.
 *
 * @author Chris Beams
 * @since 3.1
 * @see EnableCaching
 */
@Configuration
public abstract class AbstractCachingConfiguration implements ImportAware {

	protected AnnotationAttributes enableCaching;
	protected CacheManager cacheManager;
	protected KeyGenerator keyGenerator;

	@Autowired(required=false)
	private Collection<CacheManager> cacheManagerBeans;
	@Autowired(required=false)
	private Collection<CachingConfigurer> cachingConfigurers;

	public void setImportMetadata(AnnotationMetadata importMetadata) {
		this.enableCaching = AnnotationAttributes.fromMap(
				importMetadata.getAnnotationAttributes(EnableCaching.class.getName(), false));
		Assert.notNull(this.enableCaching,
				"@EnableCaching is not present on importing class " +
				importMetadata.getClassName());
	}

	/**
	 * Determine which {@code CacheManager} bean to use. Prefer the result of
	 * {@link CachingConfigurer#cacheManager()} over any by-type matching. If none, fall
	 * back to by-type matching on {@code CacheManager}.
	 * @throws IllegalArgumentException if no CacheManager can be found; if more than one
	 * CachingConfigurer implementation exists; if multiple CacheManager beans and no
	 * CachingConfigurer exists to disambiguate.
	 */
	@PostConstruct
	protected void reconcileCacheManager() {
		if (!CollectionUtils.isEmpty(cachingConfigurers)) {
			int nConfigurers = cachingConfigurers.size();
			if (nConfigurers > 1) {
				throw new IllegalStateException(nConfigurers + " implementations of " +
						"CachingConfigurer were found when only 1 was expected. " +
						"Refactor the configuration such that CachingConfigurer is " +
						"implemented only once or not at all.");
			}
			CachingConfigurer cachingConfigurer = cachingConfigurers.iterator().next();
			this.cacheManager = cachingConfigurer.cacheManager();
			this.keyGenerator = cachingConfigurer.keyGenerator();
		}
		else if (!CollectionUtils.isEmpty(cacheManagerBeans)) {
			int nManagers = cacheManagerBeans.size();
			if (nManagers > 1) {
				throw new IllegalStateException(nManagers + " beans of type CacheManager " +
						"were found when only 1 was expected. Remove all but one of the " +
						"CacheManager bean definitions, or implement CachingConfigurer " +
						"to make explicit which CacheManager should be used for " +
						"annotation-driven cache management.");
			}
			CacheManager cacheManager = cacheManagerBeans.iterator().next();
			this.cacheManager = cacheManager;
			// keyGenerator remains null; will fall back to default within CacheInterceptor
		}
		else {
			throw new IllegalStateException("No bean of type CacheManager could be found. " +
					"Register a CacheManager bean or remove the @EnableCaching annotation " +
					"from your configuration.");
		}
	}
}
