use v6;

my @alphabet = 'A' .. 'Z';

multi sub MAIN(Str $mode, Int $n, Str $filename) {
  given $mode {
    when $_ eq 'enc' {
      my $message = prepare(slurp($filename));
      my $encrypt = encrypt($n, $message);
      say $encrypt;
    }
    when $_ eq 'dec' {
      my $message = slurp($filename);
      my $decrypt = decrypt($n, $message);
      say $decrypt;
    }
    default {
      say 'Invalid !';
    }
  }
}

multi sub prepare(Str $message) {
  return $message.subst(/<-:L>+/,'',:g).uc;
}

multi sub encrypt ($key where 1..25, $message) {
  $message.trans(@alphabet Z=> @alphabet.rotate($key));
}

multi sub decrypt ($key where 1..25, $message) {
  $message.trans(@alphabet.rotate($key) Z=> @alphabet);
}