#!/usr/bin/perl -w
#

#####
# Provides fuctions for bencoding/decoding
###

# Decodes a bencoded string to a hash/array reference
sub bDecode {
	my $dictref = $_[0];
	my $retref = undef;
	
	if (substr(${$dictref},0,1) eq "d") {
#		print Dumper($dictref);
		$retref = {};
		${$dictref} = substr(${$dictref},1);
		PROCDICTHASH: while (substr(${$dictref},0,1) ne 'e') {
			my ($key, $value);
			
			${$dictref} =~ /^(-?[\d]+)/;
			$key = substr(${$dictref}, length($1)+1, $1);
			${$dictref} = substr(${$dictref}, length($1)+$1+1);
			if (${$dictref} =~ /^[ldi\d]/) {
				$value = bDecode(\${$dictref});
				if (!defined($value)) {
					return undef;
				}
			} else {
				return undef;
			}
			
			$retref->{$key} = $value;
		}
		${$dictref} = substr(${$dictref},1);
	} elsif (substr(${$dictref},0,1) eq "l") {
#		print Dumper($dictref);
		$retref = [];
		${$dictref} = substr(${$dictref},1);
		PROCDICTARR: while (substr(${$dictref},0,1) ne 'e') {
			if (${$dictref} =~ /^[ldi\d]/) {
				my $value = bDecode(\${$dictref});
				if (!defined($value)) {
					return undef;
				}
				push (@$retref, $value);
			} else {
				return undef;
			}
		}
		${$dictref} = substr(${$dictref},1);
	} elsif (${$dictref} =~ /^i(-?[\d]+)e/) {
		${$dictref} = substr(${$dictref}, length($1)+2);
		return $1;
	} elsif (${$dictref} =~ /^([\d]+):/) {
		$retref = substr(${$dictref}, length($1)+1, $1);
		${$dictref} = substr(${$dictref}, length($1)+$1+1);
		return $retref;
	} else {
		return undef;
	}

	return $retref;
}

#Encodes a hash/array ref to a bencoded string
sub bEncode {
	my $dictref = $_[0];
	my $retval = '';
	if (ref($dictref) eq 'HASH') {
		$retval = 'd';
		for my $key (sort keys %$dictref) {
			$retval .= length($key).':'.$key;
			$retval .= bEncode($dictref->{$key});
		}
		$retval .= 'e';
	} elsif (ref($dictref) eq 'ARRAY') {
		$retval = 'l';
		for (my $i = 0; $i <= $#{$dictref}; $i++) {
			$retval .= bEncode($dictref->[$i]);
		}
		$retval .= 'e';
	} elsif ($dictref =~ /^-?[\d]+$/) {
		$retval = 'i'.$dictref.'e';
	} else {
		$retval = length($dictref).':'.$dictref;
	}
	return $retval;
};