/** *****************************************************************
    calculate.java   SWE 637 servlet example.

        @author Jeff Offutt

        @version 1.0    (Nov 2006)
********************************************************************* */

// Has two faults:
// 1. If a string is submitted in the Length field, an exception will be returned.
// 2. If two negative values are entered, the result will erroneously be negative.
// Both faults have low exposure, and the second is easy to miss.

// Import Java Libraries
import java.io.*;
import java.util.*;

//Import Servlet Libraries
import javax.servlet.*;
import javax.servlet.http.*;

// calculate class
// CONSTRUCTOR: no constructor specified (default)
//
// ***************  PUBLIC OPERATIONS  **********************************
// public void doPost ()  -->
// public void doGet ()  -->
//***********************************************************************

public class calculate extends HttpServlet
{

// Location of servlet.
static String Domain  = "cs.gmu.edu:8443";
static String Path    = "/offutt/servlet/";
static String Servlet = "calculate";

// Button labels
static String OperationAdd = "Add";
static String OperationSub = "Subtract";
static String OperationMul = "Multiply";
static String OperationDiv = "Divide";
static String OperationLen = "Compute Length";

// Other strings.
static String Style ="https://www.cs.gmu.edu/~offutt/classes/637/637-style.css";

/** *****************************************************
 *  Overrides HttpServlet's doPost().
 *  Converts the values in the form, performs the operation
 *  indicated by the submit button, and sends the results
 *  back to the client.
********************************************************* */
public void doPost (HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException
{
   Float rslt    = new Float (0.0);
   Float lhsVal  = new Float (0.0);
   Float rhsVal  = new Float (0.0);
   Float rsltVal = new Float (0.0);
   int rsltLen = 0;
   String operation  = request.getParameter ("Operation");
   String lhsStr     = request.getParameter ("LHS");
   String rhsStr     = request.getParameter ("RHS");
   String rsltStr    = request.getParameter ("RSLT");
   String nameStr    = request.getParameter ("NAMESTRING");
   String rsltLenStr = request.getParameter ("RSLTLEN");

   response.setContentType ("text/html");
   PrintWriter out = response.getWriter();
   PrintHead (out);

   // Small bug .. the rsltLenStr is not used, but if a character is submitted,
   // then the servlet will crash.
   if ((rsltLenStr != null) && (rsltLenStr.length() > 0))
      rsltLen = Integer.parseInt (rsltLenStr);
   try
   {
      if ((lhsStr != null) && (lhsStr.length() > 0))
         lhsVal = new Float (lhsStr);
      if ((rhsStr != null) && (rhsStr.length() > 0))
         rhsVal = new Float (rhsStr);
      if ((rsltStr != null) && (rsltStr.length() > 0))
         rsltVal = new Float (rsltStr);
   
      if (operation.equals (OperationAdd))
         rsltVal = new Float (lhsVal.floatValue() + rhsVal.floatValue());
      else if (operation.equals (OperationSub))
         rsltVal = new Float (lhsVal.floatValue() - rhsVal.floatValue());
      else if (operation.equals (OperationMul))
{// Introduce a dumb but subtle bug. If both values are negative,
 // the value will erroneously be negative.
 // Hard to find and easy to miss.
   if ((lhsVal.floatValue() < 0.0) && (rhsVal.floatValue() < 0.0))
         rsltVal = 0 - (new Float (lhsVal.floatValue() * rhsVal.floatValue()));
   else
         rsltVal = new Float (lhsVal.floatValue() * rhsVal.floatValue());
}
      else if (operation.equals (OperationDiv))
         rsltVal = new Float (lhsVal.floatValue() / rhsVal.floatValue());
   } catch (NumberFormatException e)
   {
      // nonnumeric, ask the user to try again.
      out.println ("<DIV Style=\"font-size:115%; color:red; text-align:justify\">");
      out.println ("One or more of your entries was not numeric.");
      out.println ("Please use only integers, no characters or spaces.");
      out.println ("</DIV>");
   }

   if (operation.equals (OperationLen))
      rsltLen = nameStr.length();

   PrintBody (out, lhsStr, rhsStr, rsltVal.toString(), nameStr, rsltLen);
   PrintTail (out);

}  // End doPost

/** *****************************************************
 *  Overrides HttpServlet's doGet().
 *  Prints an HTML page with a blank form.
********************************************************* */
public void doGet (HttpServletRequest request,
                   HttpServletResponse response)
       throws ServletException, IOException
{
   response.setContentType ("text/html");
   PrintWriter out = response.getWriter();
   PrintHead (out);
   PrintBody (out);
   PrintTail (out);

} // End doGet

/** *****************************************************
 *  Prints the <HEAD> of the HTML page, no <BODY>.
********************************************************* */
private void PrintHead (PrintWriter out)
{
   out.println ("<HTML>");
   out.println ("");

   out.println ("<HEAD>");
   out.println ("<TITLE>637 Servlet Homework</TITLE>");
   out.println (" <LINK Rel=\"stylesheet\" Type=\"text/css\" Href=\"" + Style + "\">");
   out.println ("</HEAD>");
   out.println ("");
} // End PrintHead

/** *****************************************************
 *  Prints the <BODY> of the HTML page with the form data
 *  values from the parameters.
********************************************************* */
private void PrintBody (PrintWriter out, String lhs, String rhs, String rslt, String namestring, int rsltlen)
{
   out.println ("<BODY>");
   out.println ("<P>");
   out.println ("A servlet to compute arithmetic operations on numbers and strings.");
   out.println ("</P>");
   out.print ("<FORM Method=\"POST\"");
   out.println ("Action=\"https://" + Domain + Path + Servlet + "\">");
   out.println ("");

   out.println ("<center>");
   out.println ("<table border=1><!-- outer table -->");
   out.println ("<tr>");
   out.println ("<td>");
   out.println (" <TABLE>");
   out.println ("  <TR>");
   out.println ("   <TD>First val:");
   out.println ("   <TD><INPUT Type=\"text\" Name=\"LHS\" Value=\"" + lhs + "\" Size=5>");
   out.println ("  </TR>");
   out.println ("  <TR>");
   out.println ("   <TD>Second val:");
   out.println ("   <TD><INPUT Type=\"text\" Name=\"RHS\" Value=\"" + rhs + "\" Size=5>");
   out.println ("  </TR>");
   out.println ("  <TR>");
   out.println ("   <TD>Result:");
   out.println ("   <TD><INPUT Type=\"text\" Name=\"RSLT\" Value=\"" + rslt + "\" Size=6>");
   out.println ("  </TR>");
   out.println (" </TABLE>");
   out.println ("  <td>");
   out.println ("  <table>");
   out.println ("  <tr>");
   out.println ("  <td>Enter a name:");
   out.println ("  <td><INPUT Type=\"text\" Name=\"NAMESTRING\" Value=\"" + namestring + "\" Size=20>");
   out.println ("  </tr>");
   out.println ("  <tr>");
   out.println ("  <TD>Length:");
   if (rsltlen==0)
      out.println ("  <TD><INPUT Type=\"text\" Name=\"RSLTLEN\" Size=6>");
   else
      out.println ("  <TD><INPUT Type=\"text\" Name=\"RSLTLEN\" Value=\"" + rsltlen + "\" Size=6>");
   out.println ("  </tr>");
   out.println ("  </table>");

   out.println ("  <tr>");
   out.println ("  <tr>");
   out.println ("  <tr><td>");
   out.println (" <table>");
   out.println (" <tr>");
   out.println ("  <td><INPUT Type=\"submit\" Value=\"" + OperationAdd + "\" Name=\"Operation\">");
   out.println ("  <td><INPUT Type=\"submit\" Value=\"" + OperationSub + "\" Name=\"Operation\">");
   out.println ("  <td><INPUT Type=\"submit\" Value=\"" + OperationMul + "\" Name=\"Operation\">");
   out.println ("  <td><INPUT Type=\"submit\" Value=\"" + OperationDiv + "\" Name=\"Operation\">");
   out.println (" </table>");
   out.println ("  <td align=center><INPUT Type=\"submit\" Value=\"" + OperationLen + "\" Name=\"Operation\">");
   out.println (" <tr>");
   out.println ("  <td colspan=2 align=center><INPUT Type=\"reset\" Value=\"Reset\" Name=\"reset\">");
   out.println ("  </table><!-- outer table -->");
   out.println ("</center>");

   out.println ("</FORM>");
   out.println ("");

   out.println ("</BODY>");
} // End PrintBody

/** *****************************************************
 *  Overloads PrintBody(out,lhs,rhs,rslt,namestring) to print a page
 *  with blanks in the form fields.
********************************************************* */
private void PrintBody (PrintWriter out)
{
   PrintBody (out, "", "", "", "", 0);
}

/** *****************************************************
 *  Prints the bottom of the HTML page.
********************************************************* */
private void PrintTail (PrintWriter out)
{
   out.println ("");

   out.println ("<P><FONT Size=-1><I>");
   out.println ("Jeff Offutt, November 2006");
   out.println ("</P></FONT></I>");
   out.println ("</HTML>");
} // End PrintTail

}  // End calculate