#! /usr/bin/perl -w

use strict;

my %lookup;
my %invert;

my @base = qw(a c g t);

my $count = 0;
for my $x1 (@base) {
for my $x2 (@base) {
for my $x3 (@base) {
for my $x4 (@base) {
    my $key   = chr($count++);
    my $chunk = "$x1$x2$x3$x4";
    $invert{$key} = $chunk;
    $lookup{$chunk} = $key;
} } } }

for my $seq (@ARGV) {
    print "squeeze   => ", squeeze($seq), "\n";
    print "unsqueeze => ", unsqueeze($seq), "\n";
}

sub squeeze {
    my $seq = shift;
    my $out = '';
    $out .= $lookup{lc $1} while ($seq =~ /(....)/g);
    return $out;
}

sub unsqueeze {
    my $seq = shift;
    my $out = '';
    $out .= $invert{$_} for split //, $seq;
    return $out;
}