/*
    * $Id: ControllerServlet.java 126 2004-11-01 20:30:33Z josem $
    *
    * Tarsis
    * Copyright (C) 2002 Talika Open Source Group
    *
    * This program is free software; you can redistribute it and/or modify
    * it under the terms of the GNU General Public License as published by
    * the Free Software Foundation; either version 2 of the License, or
   * (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
   *
   */
  
  package org.talika.tarsis.servlets;
  
  import java.io.IOException;
  
  import javax.servlet.ServletConfig;
  import javax.servlet.ServletException;
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  
  import org.talika.tarsis.command.Command;
  import org.talika.tarsis.command.Request;
  import org.talika.tarsis.command.RequestImpl;
  import org.talika.tarsis.command.Response;
  import org.talika.tarsis.command.ResponseImpl;
  import org.talika.tarsis.command.action.Action;
  import org.talika.tarsis.command.action.ActionException;
  import org.talika.tarsis.command.factory.CommandFactory;
  import org.talika.tarsis.command.view.View;
  import org.talika.tarsis.error.SystemException;
  import org.talika.tarsis.util.CommandHelper;
  
  /**
   * Implementation of controller servlet of Tarsis MVC Framework.<br>
   * <br>
   *
   * @author  Jose M. Palomar
   * @version $Revision: 126 $
   */
  public final class ControllerServlet extends AbstractServlet {
  
      // Fields
      /**
       * Command factory instance.
       */
      private CommandFactory commandFactory;
  
      /**
       * Command helper instance.
       */
      private CommandHelper commandHelper;
  
      /**
       * Called by the servlet container to indicate to a servlet that the servlet is
       * being placed into service.<br>
       * <br>
       * Initialization consits in calling super <code>init</code> method and storing
       * in a local variable command factory instance for further use.
       *
       * @param config ServletConfig the <code>ServletConfig</code> object that contains
       * configutation information for this servlet.
       * @throws ServletException if an exception occurs that interrupts the servlet's
       * normal operation.
       * @see javax.servlet.Servlet#init(javax.servlet.ServletConfig)
       */
      public void init(ServletConfig config) throws ServletException {
          super.init(config);
  
          this.commandFactory = getContext().getCommandFactory();
          this.commandHelper = CommandHelper.getInstance();
  
      }
  
      /**
       * Called by the servlet container to indicate to a servlet that the servlet is
       * being taken out of service.
       *
       * @see javax.servlet.Servlet#destroy()
       */
      public void destroy() {
  
          this.commandFactory = null;
          this.commandHelper = null;
  
          super.destroy();
  
      }
  
     /**
      * Processes requests for both HTTP GET and POST methods.<br>
      * <br>
      * Controller process requests this way:
      * <ol>
      * <li>Obtains command from request.</li>
      * <li>Process command action by calling <code>execute</code> method.</li>
      * <li>Process command view by forwarding or redirecting to it.</li>
      * </ol>
      *
      * @param request servlet object that contains the request the client has made of
      * the servlet.
      * @param response servlet object that contains the response the servlet sends to
      * the client.
      * @throws ServletException if the request could not be handled.
      * @throws IOException if an input or output error is detected when the servlet
      * handles request.
      */
     protected void process(HttpServletRequest request, HttpServletResponse response)
     throws ServletException, IOException {
 
         try {
 
             Command command = findCommand(request, response);
             View view       = processCommand(request, response, command);
                               processView(request, response, view);
 
         }
         catch (ServletException se) {
             throw se;
         }
         catch (Throwable t) {
             throw new ServletException(t);
         }
 
     }
 
     /**
      * Obtains command from client's request.
      *
      * @param request HttpServletRequest client's request.
      * @param response HttpServletResponse client's response.
      * @return Command command obtained from client's request.
      * @throws SystemException if no command is found.
      *
      * @todo Think in some kind of default command feature when no command is found.
      */
     protected Command findCommand(HttpServletRequest request, HttpServletResponse response)
     throws SystemException {
 
         // Find command
         String commandName = commandHelper.getCommand(request);
         Command command = commandFactory.findCommand(commandName);
         if (command == null) {
             throw new SystemException("Unknown command " + commandName);
         }
 
         return command;
 
     }
 
     /**
      * Process given command.
      *
      * @param request HttpServletRequest client's request.
      * @param response HttpServletResponse client's reponse.
      * @param command Command command to be processed.
      * @return View view result of processing command.
      * @throws ActionException if there is a problem executing action.
      * @throws SystemException if no view is found.
      */
     protected View processCommand(HttpServletRequest request, HttpServletResponse response,
     Command command)
     throws ActionException, SystemException {
 
         // Action
         Action action = command.getAction();
 
         // Create helper objects
         Request req = new RequestImpl(request);
         Response res = new ResponseImpl(request, response);
 
         // Execute action
         String viewName = action.execute(req, res);
 
         // Get view
         if (viewName == null) {
             viewName = View.DEFAULT_VIEW_NAME;
         }
 
         View view = command.getView(viewName);
         if (view == null) {
             throw new SystemException("Unkown view " + viewName + " in command " + command.getName());
         }
 
         return view;
 
     }
 
     /**
      * Process given view.
      *
      * @param request HttpServletRequest client's request.
      * @param response HttpServletResponse client's reponse.
      * @param view View view to be processed.
      * @throws SystemException if view's type is unkown.
      * @throws ServletException if the request could not be handled.
      * @throws IOException if an input or output error is detected when the servlet
      * handles request.
      */
     protected void processView(HttpServletRequest request, HttpServletResponse response,
     View view)
     throws SystemException, ServletException, IOException {
 
         switch(view.getType()) {
             case View.FORWARD:
                 request.getRequestDispatcher(view.getPath()).forward(request, response);
                 break;
             case View.INCLUDE:
                 request.getRequestDispatcher(view.getPath()).include(request, response);
                 break;
             case View.REDIRECT:
                 response.sendRedirect(view.getPath());
                 break;
             default:
                 throw new SystemException("Unkown view type " + view.getType() +
                                          " in view " + view.getName());
         }
 
     }
 
 }