//  Encrypt.java  Copyright (c) 2005 Kari Laitinen

//  http://www.naturalprogramming.com

//  2005-05-09   File created.
//  2005-11-19   Last modification.

//  The encryption/decryption algorithm used by this program is
//  explained in "A Natural Introduction to Computer Programming
//  with C++"

//  The best way to execute this program is to run it in a
//  command prompt window where command line parameters can
//  be given. It may be difficult, and even impossible, to
//  supply the command line parameters if this program is 
//  executed with a modern development tool such as JCreator
//  or Eclipse.

import java.util.* ;
import java.io.* ;    // Classes for file handling.

class Encrypt
{
   public static void main( String[] command_line_parameters )
   {
      if ( command_line_parameters.length  ==  2 )
      {
         try
         {
            FileInputStream original_file  =
                   new  FileInputStream( command_line_parameters[ 0 ] ) ;

            PrintWriter encrypted_file  = new PrintWriter( 
                           new  FileWriter( command_line_parameters[ 1 ] ) ) ;

            int number_of_blocks_encrypted  =  0 ;


            byte[]  bytes_from_file  =  new  byte[ 30 ] ;

            int number_of_bytes_read  ;

            while (( number_of_bytes_read  =
                       original_file.read( bytes_from_file, 0,
                                           bytes_from_file.length ))  >  0 )
            {
               StringBuilder encrypted_bytes  =  new  StringBuilder() ;

               for ( int byte_index  =  0 ;
                         byte_index  <  number_of_bytes_read ;
                         byte_index  ++ )
               {
                  encrypted_bytes.append(
                    (char) ( ( bytes_from_file[ byte_index ] & 0xF )
                              + 0x20 + byte_index ) ) ;

                  encrypted_bytes.append(
                    (char) ( ( bytes_from_file[ byte_index ] >> 4 )
                              + 0x20 + byte_index ) ) ;
               }

               encrypted_file.println( encrypted_bytes ) ;

               number_of_blocks_encrypted  ++  ;
            }

            original_file.close() ;
            encrypted_file.close() ;

            System.out.print( "\n "  +  number_of_blocks_encrypted
                           +  " blocks were encrypted. \n" ) ;
         }
         catch ( FileNotFoundException caught_file_not_found_exception )
         {
            System.out.print( "\n Cannot open file "
                        +  command_line_parameters[ 0 ] ) ;
         }
         catch ( Exception caught_exception )
         {
            System.out.print( "\n File error. Probably cannot write to "
                        +  command_line_parameters[ 1 ] ) ;
         }
      }
      else
      {
         System.out.print( "\n You have to command this program as: \n"
                    +  "\n  java Encrypt originalfile.ext ecryptedfile.ext\n") ;
      }
   }
}