#!/usr/bin/perl

# this program figures tri-grams for a file

#  TODO:
#    1. input file on command line **DONE**
#    2. checking for case where length of file % 3 == 1 **DONE**
#    3. output to file  **DONE**

use strict;

defined($ARGV[1]) or die "Usage: my.vignere.pl <input file> <output file>\n";


my ($buf, $out, $add, $length_of_file, $count, @in_file, 
    $key, $key_length, $key_loop);

$length_of_file = 0;

open(O,">".$ARGV[1]) or die "Output file
 open failed: $!\n";

open(IN,"$ARGV[0]") || die "Sorry. Couldn't open: $!\n";

while (read (IN, $buf, 1)) { 

   if ($buf eq "\t")
   {
      $buf = "\n";
   }
         
   if ($buf ne "\n") {
      $in_file[$length_of_file] = $buf;
      $length_of_file++;
   }
}

close (IN);

$length_of_file = $length_of_file -1;

print ("key: ");
$key = <STDIN>;
chomp ($key);

$key_length = length($key);
$key_loop = 0;

for ($count = 0; $count <= $length_of_file; $count++) {

  $buf = $in_file[$count];

  $add = (substr($key,$key_loop,1));
  $out = ((ord($buf) - ord($add)) - 32) % 94;
  $key_loop = ($key_loop + 1) % $key_length;
  
  print O (chr($out + 32));
  if (($count != 0) && (($count % 70) == 0)) {
    print O ("\n")
    }
}


print("\n");

close(IN);
close(O);