/*
    * $Revision: 1.2 $
    * $Date: 2006/02/28 18:20:38 $
    *
    * ====================================================================
    * Struts back mechanism
    * Copyright (C) 2006 - Manfred Wolff
    * 
    * 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.
   *
   * created: 21-01-2006 Manfred Wolff (wolff@mwolff.org)
   */
  package org.mwolff.struts.back;
  
  import java.io.IOException;
  
  import javax.servlet.ServletException;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.struts.action.Action;
  import org.apache.struts.action.ActionForm;
  import org.apache.struts.action.ActionForward;
  import org.apache.struts.action.ActionMapping;
  import org.apache.struts.action.ActionServlet;
  import org.apache.struts.config.ModuleConfig;
  import org.apache.struts.tiles.TilesRequestProcessor;
  
  /***
   * Special RequestProcessor to process back and forward mechanism.
   * 
   * @author mwolff
   */
  public class BackRequestProcessor extends TilesRequestProcessor {
  
      /***
       * <p>
       * Commons Logging instance.
       * </p>
       */
      protected static Log log = LogFactory.getLog(BackRequestProcessor.class);
  
      /***
       * <p>
       * Initialize this request processor instance.
       * </p>
       * 
       * @param servlet The ActionServlet we are associated with
       * @param moduleConfig The ModuleConfig we are associated with.
       * @throws ServletException If an error occor during initialization
       */
      public void init(ActionServlet servlet, ModuleConfig moduleConfig)
          throws ServletException {
  
          super.init(servlet, moduleConfig);
      }
      
      public void setMarker(RingBuffer buffer, HttpServletRequest request) {
          if (buffer.isForwardPossible()) {
              request.setAttribute("org.mwolff.struts.isForward", "true"); 
          } else {
              request.setAttribute("org.mwolff.struts.isForward", "false"); 
          }
  
          if (buffer.isBackPossible()) {
              request.setAttribute("org.mwolff.struts.isBack", "true"); 
          } else {
              request.setAttribute("org.mwolff.struts.isBack", "false"); 
          }
          
      }
  
      /***
       * <p>
       * Ask the specified <code>Action</code> instance to handle this request. 
       * Return the <code>ActionForward</code> instance (if any) returned by the 
       * called <code>Action</code> for further processing.
       * </p>
       * 
       * @param request The servlet request we are processing
       * @param response The servlet response we are creating
       * @param action The Action instance to be used
       * @param form The ActionForm instance to pass to this Action
       * @param mapping The ActionMapping instance to pass to this Action
       * 
       * @return The <code>ActionForward</code> instance (if any) returned by 
       * the called <code>Action</code>.
      * 
      * @exception IOException if an input/output error occurs
      * @exception ServletException if a servlet exception occurs
      */
     protected ActionForward processActionPerform(HttpServletRequest request,
         HttpServletResponse response, Action action, ActionForm form,
         ActionMapping mapping) throws IOException, ServletException {
 
         try {
             ActionForward forward = (action.execute(mapping, form, request,
                 response));
 
             // save the appropriate QueryString for this request
             RingBuffer buffer = (RingBuffer) request.getSession().getAttribute(
                 "org.mwolff.struts.back.RingBuffer");
 
             if (buffer == null) {
                 buffer = new RingBuffer(100);
                 request.getSession().setAttribute(
                     "org.mwolff.struts.back.RingBuffer", buffer);
             }
 
             buffer.print();
             String query = calculateQueryString(request);
 
             // only push ActionForwards forward declarations not direct jsp forwards.
             if (query != null && query.indexOf(".do") != -1) {
                 
                 if (buffer.isNoPush() == true) {
                     // returns
                     buffer.setNoPush(false);
                     setMarker(buffer, request);
                     return forward;
                 }
                 if (buffer.isWereInvolved() == true) {
                     // returns
                     buffer.setWereInvolved(false);
                     setMarker(buffer, request);
                     return forward;
                 }
                 ArrayEntry entry = new ArrayEntry(query);
                 buffer.push(entry);
                 setMarker(buffer, request);
             }
 
             return forward;
 
         } catch (Exception e) {
             return (processException(request, response, e, form, mapping));
         }
 
     }
 
     /***
      * Calculate the query String out of the Reqeust.
      * 
      * @param request The actually request
      * @return The calculated string.
      */
     private String calculateQueryString(HttpServletRequest request) {
 
         String sourceURL = null;
 
         // The alternative Methode request.getRequestURL() has the side-effect
         // to do an endless loop, so we must stay by this deprecated method.
         StringBuffer url = javax.servlet.http.HttpUtils.getRequestURL(request);
 
         String queryString = request.getQueryString();
         if ((queryString != null) && (queryString.length() > 0)) {
             url.append("?");
             url.append(queryString);
         }
         sourceURL = url.toString();
         return sourceURL;
     }
 }