// ----------------------------------------------------------------------
// 
//  Module:          substitution_cipher.cc
//  Description:     reads plaintext and outputs it after applying 
//                   a permutation of the characters. The permutation
//                   is read from file "KEY". 
//  Contributed by:  Rene Peralta
//  Date:            2002
//  Modified by:     Michael Fischer
//  Date:            2005
//  
// ----------------------------------------------------------------------

#define BLANK 32
#define LOW_INDEX 32
#define HIGH_INDEX 126
#define ASCII_SIZE 256

#include <stdlib.h>
#include <stdio.h>
#include <iostream>
#include <fstream>
#include <ctype.h>

using namespace std;

int perm[ASCII_SIZE]; // permutation read from file "KEY"

char encrypt(char c);
void get_key(char* key_file_name);

int
main( int argc, char *argv[ ] )
{
    int i;
    char c;
    char *key_file_name;

    if ( argc==1 ) key_file_name = "KEY";
    else key_file_name = argv[1];
    get_key(key_file_name);
    while ( (i = getchar()) != EOF)
    {
      c = i;
      if ((int) c < LOW_INDEX || (int)c > HIGH_INDEX) cout << c;
      else cout << encrypt(c) ;
    }
}

char encrypt(char c)
{
        return((char) perm[(int) c]);
}

void get_key(char* key_file_name)
{
  ifstream key_file(key_file_name);
  int c_in, c_out;

  while (1)
  {
     key_file >> c_in;  // this char goes to ...
     if (c_in == -1) break; // end of key condition
     key_file >> c_out; // this char.
     
     perm[c_in] = c_out;
  }
}