#!/usr/bin/perl


$packet = "<ENTER PACKET HERE>";

$packet =~ s/1/Q/g;
$packet =~ s/0/P/g;
$packet =~ s/F/1111/g;
$packet =~ s/E/1110/g;
$packet =~ s/D/1101/g;
$packet =~ s/C/1100/g;
$packet =~ s/B/1011/g;
$packet =~ s/A/1010/g;
$packet =~ s/9/1001/g;
$packet =~ s/8/1000/g;
$packet =~ s/7/0111/g;
$packet =~ s/6/0110/g;
$packet =~ s/5/0101/g;
$packet =~ s/4/0100/g;
$packet =~ s/3/0011/g;
$packet =~ s/2/0010/g;
$packet =~ s/Q/0001/g;
$packet =~ s/P/0000/g;


$vsum = 0;

print $packet."\n\n";
($result, $leftover) = subpacket($packet);

print "VSUM: $vsum\n";
print $leftover."\n";
print $result."\n";

sub subpacket() {
        my $spacket = $_[0];
        my @stack = ();
        my $read = "";
        my $newpacket;
        my $version;
        my $type;
        my $input;
        my $ltype;
        my $plength;
        my $result;
        my $c;
        my $calcsum;
        my $val;

        $version = substr($spacket, 0, 3);
        $spacket = substr($spacket, 3, length($spacket) - 3);

        $vsum = $vsum + oct("0b".$version);

        $type = substr($spacket, 0, 3);
        $spacket = substr($spacket, 3, length($spacket) - 3);

        if ($type eq "100") {
                $read = "";
                while (substr($spacket, 0, 1) eq "1") {
                        $input = substr($spacket, 1, 4);
                        $spacket = substr($spacket, 5, length($spacket) - 5);
                        $read = $read . $input;
                }
                $input = substr($spacket, 1, 4);
                $spacket = substr($spacket, 5, length($spacket) - 5);
                $read = $read . $input;
                return (oct("0b".$read),$spacket);
        }
        else
        {
                $ltype = substr($spacket, 0, 1);
                $spacket = substr($spacket, 1, length($spacket) - 1);

                if ($ltype eq "0") {
                        $plength = substr($spacket, 0, 15);
                        $spacket = substr($spacket, 15, length($spacket) - 15);

                        $plength = oct("0b".$plength);
                        $newpacket = substr($spacket, 0, $plength);
                        $spacket = substr($spacket, $plength, length($spacket) - $plength);
                        while ($newpacket =~ m/1/) {
                                ($result, $newpacket) = subpacket($newpacket);
                                push(@stack, int($result));
                        }
                }
                else
                {

                        $plength = substr($spacket, 0, 11);
                        $spacket = substr($spacket, 11, length($spacket) - 11);
                        $plength = oct("0b".$plength);
                        for ($c = 0; $c < $plength; $c++) {
                                ($result, $spacket) = subpacket($spacket);
                                push(@stack, int($result));
                        }
                }
                $calcsum = 0;
                if ($type eq "000") {
                        foreach $val (@stack) {
                                $calcsum = $calcsum + $val;
                        }
                        return ($calcsum, $spacket);
                }
                if ($type eq "001") {
                        $calcsum = shift(@stack);
                        foreach $val (@stack) {
                                $calcsum = $calcsum * $val;
                        }
                        return ($calcsum, $spacket);
                }
                if ($type eq "010") {
                        $calcsum = 10000000000000000000;
                        foreach $val (@stack) {
                                if ($calcsum > $val) {
                                        $calcsum = $val;
                                }
                        }
                        return ($calcsum, $spacket);
                }
                if ($type eq "011") {
                        foreach $val (@stack) {
                                if ($calcsum < $val) {
                                        $calcsum = $val;
                                }
                        }
                        return ($calcsum, $spacket);
                }
                if ($type eq "101") {
                        if ($stack[0] > $stack[1]) {
                                return(1, $spacket);
                        }
                        else
                        {
                                return(0, $spacket);
                        }
                }
                if ($type eq "110") {
                        if ($stack[0] < $stack[1]) {
                                return(1, $spacket);
                        }
                        else
                        {
                                return(0, $spacket);
                        }
                }
                if ($type eq "111") {
                        if ($stack[0] == $stack[1]) {
                                return(1, $spacket);
                        }
                        else
                        {
                                return(0, $spacket);
                        }
                }
        }
}