#!/usr/bin/env perl -l

use strict;
use warnings;

if (@ARGV != 4) {
    print "Usage: $0 text encrypt/decrypt(1|0) ",
                    'right_shift/left_shift(1|0) positions_to_shift';
    print "(Note: when decrypting, '*_shift' and 'positions_to_shift' ",
                    'is what was used for the original encryption!)';
    exit;
}

my @chars = map { "\Q@{[chr]}\E" } 32 .. 126;

my ($input, $encrypt, $right, $pos) = @ARGV;
$pos %= @chars;

my $plain_chars = join '' => @chars;
my $cipher_chars = $right
    ? join('' => @chars[$pos .. $#chars, 0 .. $pos - 1]) 
    : join('' => @chars[$#chars - $pos + 1 .. $#chars, 0 .. $#chars - $pos]);

print 'Transform: ', ($encrypt ? 'encrypt' : 'decrypt'),
      '  --  Shift: ', ($right ? 'right' : 'left'),
      '  --  Positions: ', $pos;

if ($encrypt) {
    my $ciphertext;
    eval "(\$ciphertext = \$input) =~ y/$plain_chars/$cipher_chars/";
    print "Plaintext:  $input";
    print "Ciphertext: $ciphertext";
}
else {
    my $plaintext;
    eval "(\$plaintext = \$input) =~ y/$cipher_chars/$plain_chars/";
    print "Ciphertext: $input";
    print "Plaintext:  $plaintext";
}