//
   //  ========================================================================
   //  Copyright (c) 1995-2016 Mort Bay Consulting Pty. Ltd.
   //  ------------------------------------------------------------------------
   //  All rights reserved. This program and the accompanying materials
   //  are made available under the terms of the Eclipse Public License v1.0
   //  and Apache License v2.0 which accompanies this distribution.
   //
   //      The Eclipse Public License is available at
  //      http://www.eclipse.org/legal/epl-v10.html
  //
  //      The Apache License v2.0 is available at
  //      http://www.opensource.org/licenses/apache2.0.php
  //
  //  You may elect to redistribute this code under either of these licenses.
  //  ========================================================================
  //
  
  package org.eclipse.jetty.fcgi.server.proxy;
  
  import java.io.IOException;
  import java.net.URISyntaxException;
  import java.net.URL;
  import java.nio.file.Files;
  import java.nio.file.Path;
  import java.nio.file.Paths;
  
  import javax.servlet.Filter;
  import javax.servlet.FilterChain;
  import javax.servlet.FilterConfig;
  import javax.servlet.ServletContext;
  import javax.servlet.ServletException;
  import javax.servlet.ServletRequest;
  import javax.servlet.ServletResponse;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  
  /**
   * Inspired by nginx's try_files functionality.
   * <p>
   * This filter accepts the <code>files</code> init-param as a list of space-separated
   * file URIs. The special token <code>$path</code> represents the current request URL's
   * path (the portion after the context path).
   * <p>
   * Typical example of how this filter can be configured is the following:
   * <pre>
   * &lt;filter&gt;
   *     &lt;filter-name&gt;try_files&lt;/filter-name&gt;
   *     &lt;filter-class&gt;org.eclipse.jetty.fcgi.server.proxy.TryFilesFilter&lt;/filter-class&gt;
   *     &lt;init-param&gt;
   *         &lt;param-name&gt;files&lt;/param-name&gt;
   *         &lt;param-value&gt;maintenance.html $path index.php?p=$path&lt;/param-value&gt;
   *     &lt;/init-param&gt;
   * &lt;/filter&gt;
   * </pre>
   * For a request such as <code>/context/path/to/resource.ext</code>, this filter will
   * try to serve the <code>/maintenance.html</code> file if it finds it; failing that,
   * it will try to serve the <code>/path/to/resource.ext</code> file if it finds it;
   * failing that it will forward the request to <code>index.php?p=/path/to/resource.ext</code>.
   * The last file URI specified in the list is therefore the "fallback" to which the request
   * is forwarded to in case no previous files can be found.
   * <p>
   * The files are resolved using {@link ServletContext#getResource(String)} to make sure
   * that only files visible to the application are served.
   *
   * @see FastCGIProxyServlet
   */
  public class TryFilesFilter implements Filter
  {
      public static final String FILES_INIT_PARAM = "files";
  
      private String[] files;
  
      @Override
      public void init(FilterConfig config) throws ServletException
      {
          String param = config.getInitParameter(FILES_INIT_PARAM);
          if (param == null)
              throw new ServletException(String.format("Missing mandatory parameter '%s'", FILES_INIT_PARAM));
          files = param.split(" ");
      }
  
      @Override
      public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException
      {
          HttpServletRequest httpRequest = (HttpServletRequest)request;
          HttpServletResponse httpResponse = (HttpServletResponse)response;
  
          for (int i = 0; i < files.length - 1; ++i)
          {
              String file = files[i];
              String resolved = resolve(httpRequest, file);
  
              URL url = request.getServletContext().getResource(resolved);
              if (url == null)
                  continue;
  
              if (Files.isReadable(toPath(url)))
              {
                 chain.doFilter(httpRequest, httpResponse);
                 return;
             }
         }
 
         // The last one is the fallback
         fallback(httpRequest, httpResponse, chain, files[files.length - 1]);
     }
 
     private Path toPath(URL url) throws IOException
     {
         try
         {
             return Paths.get(url.toURI());
         }
         catch (URISyntaxException x)
         {
             throw new IOException(x);
         }
     }
 
     protected void fallback(HttpServletRequest request, HttpServletResponse response, FilterChain chain, String fallback) throws IOException, ServletException
     {
         String resolved = resolve(request, fallback);
         request.getServletContext().getRequestDispatcher(resolved).forward(request, response);
     }
 
     private String resolve(HttpServletRequest request, String value)
     {
         String path = request.getServletPath();
         String info = request.getPathInfo();
         if (info != null)
             path += info;
         if (!path.startsWith("/"))
             path = "/" + path;
         return value.replaceAll("\\$path", path);
     }
 
     @Override
     public void destroy()
     {
     }
 }