/*
    * Copyright 2002-2014 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.web.servlet.resource;
  
  import java.io.IOException;
  import javax.servlet.http.HttpServletRequest;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  
  import org.springframework.cache.Cache;
  import org.springframework.cache.CacheManager;
  import org.springframework.core.io.Resource;
  import org.springframework.util.Assert;
  
  /**
   * A {@link org.springframework.web.servlet.resource.ResourceTransformer} that checks a
   * {@link org.springframework.cache.Cache} to see if a previously transformed resource
   * exists in the cache and returns it if found, and otherwise delegates to the resolver
   * chain and saves the result in the cache.
   *
   * @author Rossen Stoyanchev
   * @since 4.1
   */
  public class CachingResourceTransformer implements ResourceTransformer {
  
  	private static final Log logger = LogFactory.getLog(CachingResourceTransformer.class);
  
  	private final Cache cache;
  
  	public CachingResourceTransformer(CacheManager cacheManager, String cacheName) {
  		this(cacheManager.getCache(cacheName));
  	}
  
  	public CachingResourceTransformer(Cache cache) {
  		Assert.notNull(cache, "'cache' is required");
  		this.cache = cache;
  	}
  
  
  	/**
  	 * Return the configured {@code Cache}.
  	 */
  	public Cache getCache() {
  		return this.cache;
  	}
  
  	@Override
  	public Resource transform(HttpServletRequest request, Resource resource, ResourceTransformerChain transformerChain)
  			throws IOException {
  
  		Resource transformed = this.cache.get(resource, Resource.class);
  		if (transformed != null) {
  			if (logger.isTraceEnabled()) {
  				logger.trace("Found match");
  			}
  			return transformed;
  		}
  
  		transformed = transformerChain.transform(request, resource);
  
  		if (logger.isTraceEnabled()) {
  			logger.trace("Putting transformed resource in cache");
  		}
  		this.cache.put(resource, transformed);
  
  		return transformed;
  	}
  
  }