package PackageEncryptDecrypt;

/*-------------------------------------------------------------------*
 * NTU Student: Java With Engineering Applications, Spring 1999
 * Assignment # 1 - Java How To Program 2nd edition, Deitel & Deitel
 * Problem 2.31 on page 223
 *
 * Michael Kusmierz
 * Xerox Corporation
 * Rev 1.0	Apr 9, 1999 
 *
 * This code represents a students work in progress 
 * and is not to be used beyond that purpose.
 *-------------------------------------------------------------------*/ 

import java.applet.*;
import java.awt.*;
import java.awt.event.*;	//import the event pkg
/**
 * Decryption Applet for four digit numbers.	
 * This type was created in VisualAge. All other code added manually
 * without the help of the GUI "Composition" editor.
 */
public class Decrypt extends Applet implements ActionListener {
	Label lblPrompt;
	TextField txtInput;
	String strInput;		//Input text from user filled by actionPerformed
	int iNumberInput;		//number to store input value to decrypt
	int iNumberTemp;		//temporary parse buffer			
	int iDig1000, iDig100, iDig10, iDig1;	//four Parsed digits
	String strNumberDecrypted;	//result of Decryption
	int iErr;				//error during decryption = -1 otherwise 0
	public void actionPerformed( ActionEvent e )
	{	//--- get the text entered
		strInput = e.getActionCommand();
		showStatus( " Entered Integer Data = " + strInput);
		
		//--- text must be four characters
		if (strInput.length() == 4) {
			DecryptInputData();
			iErr = 0;
		}	
		else {
		    showStatus( "ERROR-USE FOUR CHARACTERS.");
		    strInput = "";
		    iErr = -1;
		}    
		repaint();	
	
	}
	public void DecryptInputData()
	{
		int iNumberDecrypted;      //Result of decryption
		
		//--- get the number equivalent to the input string
		iNumberInput = Integer.parseInt(strInput);

		//--- 4 integers assumed, no negative numbers allowed
		if (iNumberInput < 0) {
			showStatus( "ERROR-USE POSITIVE NUMBERS.");
		    iNumberInput = 0;
		    strNumberDecrypted = "";
		    iErr = -1;
		}    
		else {    
			//--- parse the number into four digits
	 		iDig1000 = (iNumberInput / 1000);
			iNumberTemp = iNumberInput - (iDig1000 * 1000);
			iDig100  = (iNumberTemp / 100);
			iNumberTemp = iNumberTemp - (iDig100 * 100);
			iDig10   = (iNumberTemp / 10);
			iNumberTemp = iNumberTemp - (iDig10 * 10);
			iDig1  = iNumberTemp;
			//--- Decrypt: Swap 1st and 3rd digits, 2nd and 4th
			iNumberTemp = iDig1000;
			iDig1000 = iDig10;
			iDig10   = iNumberTemp;
		
			iNumberTemp = iDig100;
			iDig100  = iDig1;
			iDig1    = iNumberTemp;
			//--- Decrypt: continued:( Num + 3 ) % 10
			iDig1000 = (iDig1000 + 3) % 10;
			iDig100  = (iDig100 + 3) % 10;
			iDig10   = (iDig10 + 3) % 10;
			iDig1    = (iDig1 + 3) % 10;
	
			//--- Assemble digits into a single encrypted number.
			iNumberDecrypted = iDig1000*1000 + iDig100*100 + iDig10*10 + iDig1;

			//--- Must have leading zero's filled
			if (iNumberDecrypted > 999)
				strNumberDecrypted = Integer.toString(iNumberDecrypted);
			else if (iNumberDecrypted > 99)
				strNumberDecrypted = "0" + Integer.toString(iNumberDecrypted);
			else if (iNumberDecrypted > 9)
				strNumberDecrypted = "00" + Integer.toString(iNumberDecrypted);
			else 
				strNumberDecrypted = "000" + Integer.toString(iNumberDecrypted);
		}
	}
	public void init()
	{
		//--- Add items to applet
		lblPrompt = new Label( "Enter a four digit integer, press Enter:" );
		add( lblPrompt );
		txtInput = new TextField( 10);
		add( txtInput );
		
		//--- Initialize variables
		iErr = 1;	//Idicator of fresh start...Waiting for input
		
		//--- This applet handles action events for TextFields
		txtInput.addActionListener( this );
	}
/**
 * This method was created in VisualAge.
 * @param g java.awt.Graphics
 */
public void paint(Graphics g) {
	g.drawString("Decrypted Value = " + strNumberDecrypted, 60, 100 );
	switch (iErr) {
		case -1:
			g.drawString("Error",60,120);
			break;
		case 0:
			g.drawString("Done",60,120);
			break;
		case 1:
			g.drawString("...Waiting for input",60,120);
			break;
	} //---end switch on iErr		

}
}