#!/usr/bin/perl
use strict;
use Getopt::Std;

# name:     transpos-decipher
# author:   ap0calypse (ap0calypse@agitatio.org)
# version:  0.1     (2008-06-17)
# license:  DO WHATEVER YOU WANT!
# purpose:  reads a sentence from STDIN an returns a
#           (probably) deciphered sentence. It depends on how high
#           the cipher-sentence-fence-height was, so you maybe have to try
#           very often to get results.

our ($opt_c, $opt_h);

getopt('hc:');

sub usage {
    print << "EOUSAGE";
usage:
======
    echo "im akenose nse" | transpos-decipher -c NUM
     - NUM must be a numeric value which represents
       the "height" of the "fence"
example:
========
    echo "io apion vtnotnglerssii" | transpos-decipher -c 3
    will result in following output:
    [i love transpositioning]
explanation:
============
    This is because the ciphered sentence was transformed like this:
    [i] [o] [ ] [a] [p] [i] [o] [n] -> line 1
    [ ] [v] [t] [n] [o] [t] [n] [g] -> line 2
    [l] [e] [r] [s] [s] [i] [i]     -> line 3
    =========================================================================
    For further information search the web for transposition or visit my blog:
    http://ap0calypse.agitatio.org
    Have fun!
EOUSAGE
}

if ($opt_h) {
    &usage;
    exit 2;
}
if ($opt_c !~ m/^\d+$/) {
   &usage;
   exit 1;
}

chomp (my $input =  <>);
my @a_input = split //, $input;

my $fenceheight = $opt_c;

my $str_len = length $input;
my $overhead = $str_len % $fenceheight;
my $std_len = ($str_len - $overhead) / $fenceheight;
my $parts = ($str_len - $overhead) / $std_len;

my $AoA = [[]];
my ($i, $j, @final_array) = (0, 0, qw());

for (1 .. $parts) {
    for (1 .. $overhead) {
        for (0 .. $std_len) {
            push @{$AoA->[$i]}, shift @a_input;
        }
        $i++;
    }
    for (0 .. $std_len-1) {
        push @{$AoA->[$i]}, shift @a_input;
    }
    $i++;
}

while ($j < $str_len) {
    for (0 .. $parts-1) {
        $final_array[$j] = shift @{$AoA->[$_]};
        $j++;
    }
}
print "[";
print join "", @final_array;
print "]\n";