/*
    * Copyright 2005-2008 The Kuali Foundation
    * 
    * 
    * Licensed under the Educational Community 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.opensource.org/licenses/ecl2.php
   * 
   * 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.kuali.rice.core.web;
  
  import java.io.IOException;
  import java.text.MessageFormat;
  import java.util.Enumeration;
  import java.util.LinkedHashMap;
  import java.util.Map;
  import java.util.regex.Matcher;
  import java.util.regex.Pattern;
  
  import javax.servlet.RequestDispatcher;
  import javax.servlet.ServletConfig;
  import javax.servlet.ServletException;
  import javax.servlet.http.HttpServlet;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  
  /**
   * Servlet that forwards requests via the RequestDispatcher based on regular expression
   * matching and replacement on the URI
   * @author Kuali Rice Team (rice.collab@kuali.org)
   */
  public class RequestForwardingServlet extends HttpServlet {
      private LinkedHashMap<Pattern, MessageFormat> forwardTable = new LinkedHashMap<Pattern, MessageFormat>();
  
      @Override
      public void init() throws ServletException {
          super.init();
  
          ServletConfig cfg = getServletConfig();
          Enumeration paramNames = cfg.getInitParameterNames(); 
          while (paramNames.hasMoreElements()) {
              String name = (String) paramNames.nextElement();
              Pattern pattern = Pattern.compile(name);
              String forwardPath = cfg.getInitParameter(name);
              MessageFormat messageFormat = new MessageFormat(forwardPath);
              forwardTable.put(pattern, messageFormat);
          }
      }
  
      @Override
      protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
          String requestURI = request.getRequestURI();
          for (Map.Entry<Pattern, MessageFormat> entry: forwardTable.entrySet()) {
              Pattern pattern = entry.getKey();
              Matcher matcher = pattern.matcher(requestURI);
              if (matcher.matches()) {
                  Object[] params = new Object[matcher.groupCount()];
                  for (int i = 0; i < params.length; i++) {
                      params[i] = matcher.group(i + 1); // offset by 1 because group at index 0 denotes the "entire pattern" 
                  }
                  String forwardPath = entry.getValue().format(params);
                  RequestDispatcher rd = request.getRequestDispatcher(forwardPath);
                  if (rd == null) {
                      response.sendError(HttpServletResponse.SC_NOT_FOUND, "Internal resource '" + forwardPath + "' not found");
                  } else {
                      rd.forward(request, response);
                  }
                  return;
              }
          }
          
      }
  }