package cpa.app.vip;

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.lang.reflect.*;
import java.util.StringTokenizer;


/*************************************************************************
 * This servlet controller (CLT) class handles HTTP requests and
 * uses the extra path information in a URL to call an object
 * and/or method.  If both object and method are provided the servlet
 * calls the the method in the target object residing
 * in session.  If only one element is in the extra path information
 * is provided only the method defined within the servlet is called.
 *
 * This class was created based on the article in the December 2000
 * JavaWorld "Servlet Reflection - Untagle your servlet code with
 * reflection."  The servlet uses relflection to call the the designated
 * method based on paramaters in the "extra path" information in the
 * passed URL.  The benefit of this approach is to help simplify
 * servlet code, ability to centralize repeated methods in the abstract
 * class, and a better ability to use an object-oriented style in
 * servlet programming.
 *
 * Example in: /ecpa/vip/StateToVendorPaymentCTL/handleStateAgencyMaint/
 *
 * The handleStateAgencyMaint method will be called from the
 * StateToVendorPaymentCTL controller servlet.  
 *
 * @author Paul McKinney
 *************************************************************************/
abstract public class ServletCTL extends HttpServlet
{


   /************************************************************************
    * Handles HTTP POST resquest.
    *
    * @param request  object used to provide the servlet information about
    *                 the request
    * @param response response that the servlet provides back to the
    *                 client
    ************************************************************************/
   public void doPost(HttpServletRequest request, HttpServletResponse response)
                      throws ServletException, IOException
   {
      doGetOrPost(request, response);
   }


   /************************************************************************
    * Handles HTTP GET resquest.
    *
    * @param request  object used to provide the servlet information about
    *                 the request
    * @param response response that the servlet provides back to the
    *                 client
    ************************************************************************/
   public void doGet(HttpServletRequest request, HttpServletResponse response) 
                      throws ServletException, IOException
   {
      doGetOrPost(request, response);
   }


   /************************************************************************
    * Takes the request from the POST or GET, parses out the object name
    * and method name (if any) and calls the dispatch method.
    *
    * @param request  object used to provide the servlet information about
    *                 the request
    * @param response response that the servlet provides back to the
    *                 client
    ************************************************************************/
   private void doGetOrPost(HttpServletRequest request, 
                            HttpServletResponse response)
   {
      try
      {
         ParsedPathInfo ppi = new ParsedPathInfo(request);
         dispatch(getController(ppi.object,ppi.methodName),
                  ppi.object,
                  request,
                  response);
      }
      catch (ControllerNotFoundException e)
      {
         handleControllerNotFound(request, response);
      }
   }


   /************************************************************************
    * Called if a problem with calling the method.
    *
    * @param request  object used to provide the servlet information about
    *                 the request
    * @param response response that the servlet provides back to the
    *                 client
    ************************************************************************/
   abstract protected void handleControllerNotFound(HttpServletRequest request, 
                                                 HttpServletResponse response);


   /************************************************************************
    * Called if the method is not found.
    *
    * @param request  object used to provide the servlet information about
    *                 the request
    * @param response response that the servlet provides back to the
    *                 client
    ************************************************************************/
   abstract protected void handleRequest(HttpServletRequest request, 
                                         HttpServletResponse response);


   /***********************************************************************
    * Invokes a method against a target object using the request and
    * response objects as paramaters.
    *
    * @param method   method to dispatch
    * @param target   object in which the method is run against
    * @param request  object used to provide the servlet information about
    *                 the request
    * @param response response that the servlet provides back to the
    *                 client
    ***********************************************************************/
   protected void dispatch(Method method, Object target, 
                           HttpServletRequest request, 
                           HttpServletResponse response) 
                throws ControllerNotFoundException
   {
      try
      {
         method.invoke(target, new Object[] {request, response});
      }
      catch (IllegalAccessException ex)
      {
         throw new ControllerNotFoundException("Error:ServletCTL:IAE:" +
             "couldn't access method");
      }
      catch (InvocationTargetException ex)
      {
         ex.printStackTrace();
         throw new ControllerNotFoundException("Error:ServletCTL:ITE:" +
             "object doesn't have method");
      }
   }


   //gets classes of Class for HttpServletRequest and HttpServletResponse 
   //using class literals
   static final Class[] sFormalArgs = {HttpServletRequest.class, 
                                       HttpServletResponse.class};


   protected Method getController(Object target, String methodName)
                                    throws ControllerNotFoundException
   {
      try
      {
         return target.getClass().getMethod(methodName,sFormalArgs);
      }
      catch (NoSuchMethodException e)
      {
         throw new ControllerNotFoundException("Error:ServletCTL:" +
             "getController:couldn't get method");
      }
   }


   class ControllerNotFoundException extends ServletException
   {
      ControllerNotFoundException(String reason)
      {
         super(reason);
      }
   }


   protected Object getDefaultObject()
   {
      return this;
   }


   /*************************************************************
    * Encapsulates the methods and properties used to parse out
    * the object and method in the extra path information
    * in a URL.
    *************************************************************/
   public class ParsedPathInfo
   {
      String methodName;
      Object object;
      private String firstPart;
      private String secondPart;

      /************************************************************************
       * Takes the extra path info in a URL and returns an object or
       * default object if none specified and method or default method
       * if none specified.
       *
       * @param request  object used to provide the servlet information about
       *                 the request
       * @param response response that the servlet provides back to the
       *                 client
       ************************************************************************/
      public ParsedPathInfo(HttpServletRequest request) 
                   throws ServletCTL.ControllerNotFoundException
      {
         String pathInfo = normalize(request.getPathInfo());
         parsePath(pathInfo);
         if (secondPart == null && firstPart == null)
         {
            object = getDefaultObject();
            methodName = "handleRequest";
         }
         else if (secondPart == null)
         {
            object = getDefaultObject();
            methodName = firstPart;
         }
         else
         {
            object = request.getSession().getValue(firstPart);
            methodName = secondPart;
            if (object == null) 
            {
               throw new ControllerNotFoundException(
                         "Error:ServletCTL:ParsedPathInfo:ParsedPathInfo:" + 
                         "missing object");
            }
         }
      }


      private String normalize(String pathInfo)
      {
         return (pathInfo != null) ? pathInfo : "/";
      }


      private void parsePath(String pathInfo)
      {
         StringTokenizer tokens = new StringTokenizer(pathInfo,"/");
         if (tokens.hasMoreTokens())
         {
            firstPart = tokens.nextToken();
         }
         if (tokens.hasMoreTokens())
         {
            secondPart = tokens.nextToken();
         }
      }
   } //class ParsedInfoPath

}