/*
    * 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.util.List;
  import javax.servlet.http.HttpServletRequest;
  
  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.ResourceResolver} that
   * resolves resources from a {@link org.springframework.cache.Cache} or otherwise
   * delegates to the resolver chain and saves the result in the cache.
   *
   * @author Rossen Stoyanchev
   * @since 4.1
   */
  public class CachingResourceResolver extends AbstractResourceResolver {
  
  	public static final String RESOLVED_RESOURCE_CACHE_KEY_PREFIX = "resolvedResource:";
  
  	public static final String RESOLVED_URL_PATH_CACHE_KEY_PREFIX = "resolvedUrlPath:";
  
  
  	private final Cache cache;
  
  	public CachingResourceResolver(CacheManager cacheManager, String cacheName) {
  		this(cacheManager.getCache(cacheName));
  	}
  
  	public CachingResourceResolver(Cache cache) {
  		Assert.notNull(cache, "'cache' is required");
  		this.cache = cache;
  	}
  
  	/**
  	 * Return the configured {@code Cache}.
  	 */
  	public Cache getCache() {
  		return this.cache;
  	}
  
  	@Override
  	protected Resource resolveResourceInternal(HttpServletRequest request, String requestPath,
  			List<? extends Resource> locations, ResourceResolverChain chain) {
  
  		String key = RESOLVED_RESOURCE_CACHE_KEY_PREFIX + requestPath;
  		Resource resource = this.cache.get(key, Resource.class);
  
  		if (resource != null) {
  			if (logger.isTraceEnabled()) {
  				logger.trace("Found match");
  			}
  			return resource;
  		}
  
  		resource = chain.resolveResource(request, requestPath, locations);
  		if (resource != null) {
  			if (logger.isTraceEnabled()) {
  				logger.trace("Putting resolved resource in cache");
  			}
  			this.cache.put(key, resource);
  		}
  
  		return resource;
  	}
  
  	@Override
  	protected String resolveUrlPathInternal(String resourceUrlPath,
  			List<? extends Resource> locations, ResourceResolverChain chain) {
  
  		String key = RESOLVED_URL_PATH_CACHE_KEY_PREFIX + resourceUrlPath;
  		String resolvedUrlPath = this.cache.get(key, String.class);
  
  		if (resolvedUrlPath != null) {
  			if (logger.isTraceEnabled()) {
  				logger.trace("Found match");
  			}
  			return resolvedUrlPath;
  		}
  
  		resolvedUrlPath = chain.resolveUrlPath(resourceUrlPath, locations);
 		if (resolvedUrlPath != null) {
 			if (logger.isTraceEnabled()) {
 				logger.trace("Putting resolved resource URL path in cache");
 			}
 			this.cache.put(key, resolvedUrlPath);
 		}
 
 		return resolvedUrlPath;
 	}
 
 }