/* Encrypted file transfer protocol, by Chuck Liang */
/* server */

import java.io.*;
import java.net.*;

public class eftp
{

static String instring, outstring;
static final int eport = 1902;
static ServerSocket ssocket;  // listening, passive socket

public static void main(String[] args)
{ try {  
    ssocket = new ServerSocket(eport);  
    System.out.println("eftp server running ...");
    while (true)
      {
        Socket csocket = ssocket.accept();  //  wait for client
        csocket.setSoTimeout(30000);  // 30 second timeout on reads
        ethread newthread = new ethread(csocket);
        newthread.start();
      }  // end while
    } catch (Exception E) { System.err.println(E.toString()); }
} // end main

} // end eftp

class ethread extends Thread
{ Socket csocket;
    ethread(Socket s) { super(); csocket = s; }  // constructor

    /* encryption routines: */
    static char scramble2(char c, char previous)
    {  int pval = (int) previous;
       int cval = (int) c;
       int ciphercode = 0;  // code for ciphertext
       if ((pval%2) == 0)                   // pval is even
          ciphercode = cval + 2;
       else                                 // pval is odd
          ciphercode = cval + 3;  
       return (char) ciphercode;
    }
     
    static String encryptString2(String A)
    { String Newstring = "";
      char previous = (char) 32;
      int length = A.length();
      for(int i=0;i<length;i++)
        { 
          Newstring = Newstring + scramble2(A.charAt(i),previous);
          previous = A.charAt(i);
        }
      return Newstring;
    }

    /* server thread method */
 public void run()
 { try {  
    InetAddress me, you;
    InputStreamReader isr;  OutputStreamWriter osw;
    BufferedReader br;  PrintWriter pw;
    BufferedReader filer;
    me = InetAddress.getLocalHost();
    you = csocket.getInetAddress();

    // set up IO objects br and pw
    isr = new InputStreamReader(csocket.getInputStream());
    br = new BufferedReader(isr);  // reads from socket
    osw = new OutputStreamWriter(csocket.getOutputStream());
    pw = new PrintWriter(osw,true);  // writes to socket; true for autoflush
    BufferedReader keyboard;    // reads from keyboard;
    keyboard = new BufferedReader(new InputStreamReader(System.in));
    String outstring, instring, filename;
    outstring = "ddd";  instring = "dddd";  // make sure strings not null

    // connnection to pop3 server for password authentication
    Socket popsocket = new Socket(me,110);  // 110 = pop3 port
    BufferedReader poprd = 
     new BufferedReader(new InputStreamReader(popsocket.getInputStream()));
    PrintWriter popwr = 
     new PrintWriter(new OutputStreamWriter(popsocket.getOutputStream()),true);

    String popin, popout;
    popin = poprd.readLine();  // discard initial greeting from pop3
  System.out.println("from pop: " + popin);
    pw.println("Username: ");  // prompt client for authentication info
    instring = br.readLine();
    popwr.println("user " + instring);  // forward info to pop3 server    
    popin = poprd.readLine();  //  get response from pop3
  System.out.println("from pop: " + popin);
    if (popin.charAt(0) == '+') // username recognized
    {
      pw.println("Password: ");
      instring = br.readLine();
      popwr.println("pass " + instring);  // give password to pop3
      popin = poprd.readLine();
  System.out.println("from pop: " + popin);
    } // if
    if (popin.charAt(0) != '+')
       { pw.println("login refused"); }  // deny access 
    else   // authentication complete
    {
      popwr.println("quit");  // logoff from pop3

      pw.println("Which file do you want?");
      filename = br.readLine();   // wait for response indicating filename
      try {   // sets up filer - file reader
      filer = 
       new BufferedReader(new InputStreamReader(new FileInputStream(filename)));
      }  catch (Exception E) { pw.println("Problem opening file."); throw E; }

      if (filename.charAt(0) == 'm') // don't just transmit any file!
      {
        pw.println("ready to transmit file");  // tell client to get ready
        while (!(instring.equals("ready to receive")))
               instring = br.readLine();
        int lines = Integer.parseInt(filer.readLine());  
        pw.println(lines);   // tell client how many lines to expect
        for (int i=0;i<lines;i++)                   
            { outstring = encryptString2(filer.readLine());
              pw.println(outstring);
            }
      } // if
      pw.println("bye!");
    } // else
      popsocket.close();
      csocket.close();
  }      catch (Exception E) { System.err.println(E.toString()); }
 } // end main

} // end ethread