import java. io.*;
import java. net.*;
import java.math.*;
import java.util.*;


/**
  * This class is a simple server. Its port is set to 6502 on
  * the machine it is running on. It does not use threads but should.
  *
  *
  * This server reads a series of BigInteger objects from the client.
  * It is assumed that each BigInteger object was constructed on the client in the following
  * way:
  * 
  *      1)  A block of bytes was read from a file (or other location) on the
  *          client's machine. This block of bytes was of size >= 1 and <= 10.
  *      2)  The number of bytes read was prepended to this block of bytes and an 
  *          array of bytes was formed. For example, suppose the bytes we read from the
  *          input file were 65 66 67  ('A', 'B', and 'C' in ASCII). We would form the 
  *          array of bytes x formatted as follows:
  *              x[0] = 3
  *              x[1] = 65
  *              x[2] = 66
  *              x[3] = 67
  *      3)  The array of bytes was then converted to a BigInteger using Java's 
  *          BigInteger constructor that accepts an array of bytes as input.
  *      4)  The BigInteger plaintext was then enciphered using RSA with a public
  *          key.
  *
  * The server decodes each BigInteger object producing a decoded BigInteger. The 
  * resulting BigInteger is converted to an array of bytes using Java's toByteArray()
  * method for BigIntegers. The first byte of this array specifies the number of bytes
  * that follow. The server writes out each of these bytes, excluding the first, so
  * that the file is the same as that found on the client's machine.               
  *
  * Please use this class to test your client. On a later date, you will be given
  * a public key and be asked to encrypt binary and ASCII files and send them to 
  * a server on the internet.
  **/

public class Server {

// Choose a port outside of the range 1- 1024:

static final int port = 6502;

   public static void main( String[] args ) throws IOException {

         if(args.length != 1) {

              System.out.println("Usage: java Server filename");
              System.exit(-1);
         }

         KeyGen  myGen = new KeyGen();              

         Decoder myDecoder = new Decoder(myGen.getd(),myGen.getn());
   
         ServerSocket s = new ServerSocket(port);   

         int fileCtr = 0;

         try { 

            boolean flush = true;       
         
            System. out. println(" Server Started: " + s);

            while(true) {
         
               // Blocks until a connection occurs:
               Socket socket = s.accept();

        
               System. out. println(
                          "Connection accepted, socket: "+ socket);
        

               ObjectInputStream inBig = new ObjectInputStream(
                                                 socket.getInputStream());

                            
               DataOutputStream outBytes = 
                                new DataOutputStream(
                                  new BufferedOutputStream(
                                      new FileOutputStream(args[0]+fileCtr)));
            
               System.out.println("Writing to " + args[0] + fileCtr);

               try {        
                      while(true) {
                       
                              // read BigInteger c
                              BigInteger c = (BigInteger)inBig.readObject();
                              
                              // decode c to m = c^d mod n 
                              // byte 0 will have the size of live bytes

                              byte[] m = myDecoder.decode(c);                     	                                             

                              for(int index = 1; index <= m[0]; index++){
                                                         
                                 outBytes.write(m[index]);
                     
                              }
                           
                      }                  
               }

               catch(EOFException finish) {
                  System.out.println("Finished collecting BigIntegers");
            
               }

               finally {
                            System.out.println("Connection complete");
                            System.out.println("File " + args[0] + fileCtr + " written.");
                            fileCtr++;
                            outBytes.close();
                            inBig.close();
               }
           }
       }

       catch (Exception e) {
                  System.out.println("Oh No It's Crypto!");
                  e.printStackTrace();
       }
         
     }
}