/*
 * 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.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;

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

import org.springframework.web.filter.OncePerRequestFilter;

/**
 * A filter that wraps the {@link HttpServletResponse} and overrides its
 * {@link HttpServletResponse#encodeURL(String) encodeURL} method in order to
 * translate internal resource request URLs into public URL paths for external
 * use.
 *
 * @author Jeremy Grelle
 * @author Rossen Stoyanchev
 * @author Sam Brannen
 * @since 4.1
 */
public class ResourceUrlEncodingFilter extends OncePerRequestFilter {

	private static Log logger = LogFactory.getLog(ResourceUrlEncodingFilter.class);


	@Override
	protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
			throws ServletException, IOException {

		filterChain.doFilter(request, new ResourceUrlEncodingResponseWrapper(request, response));
	}


	private static class ResourceUrlEncodingResponseWrapper extends HttpServletResponseWrapper {

		private HttpServletRequest request;


		private ResourceUrlEncodingResponseWrapper(HttpServletRequest request, HttpServletResponse wrapped) {
			super(wrapped);
			this.request = request;
		}

		@Override
		public String encodeURL(String url) {
			String name = PublicResourceUrlProviderExposingInterceptor.RESOURCE_URL_PROVIDER_ATTR;
			PublicResourceUrlProvider urlProvider = (PublicResourceUrlProvider) this.request.getAttribute(name);
			if (urlProvider != null) {
				String translatedUrl = urlProvider.getForRequestUrl(this.request, url);
				if (translatedUrl != null) {
					return super.encodeURL(translatedUrl);
				}
			}
			else {
				logger.debug("Request attribute exposing PublicResourceUrlProvider not found under name: " + name);
			}
			return super.encodeURL(url);
		}
	}

}