use strict;
use warnings;
my $num=shift || abort("enter a number\ne.g. $0 345");
if ($num !~/^[0-9]{1,16}$/){abort('Number must be a positive integer');}
print "Number: $num\n";
my $enc=encodeBase31($num);
print "Base31: $enc\n";
my $dec=decodeBase31($enc);
print "Decoded: $dec\n";
exit;
################
sub encodeBase31{
	# Base31 encoding removes problems that may arise where a number encoded spells something not very nice
	my $decimal=shift || return "No number to encode to base31";
	my $string = '';
	my $base = 31;
	$decimal=strip($decimal);
    if ($decimal !~/^[0-9]{1,16}$/){
		return 'Value must be a positive integer';
		}
	#maximum character string is 36 characters
	my $charset = '0123456789BCDFGHJKLMNPQRSTVWXYZ';
	do {
		#get remainder after dividing by BASE
	    my $remainder = $decimal % $base;
		# get CHAR from array
	    my $char      = substr($charset, $remainder, 1);
		#prepend to output
	    $string    = "$char$string";
		$decimal   = ($decimal - $remainder) / $base;
	   }
	while ($decimal > 0);
	return $string;
	}
###############
sub decodeBase31{
	my $string=shift;
	if(!length(strip($string))){return "No base31 string to decode";}
	#uppercase the string
	$string=uc($string);
	my $decimal = 0;
	my $base=31;
	#maximum character string is 36 characters
	my $charset = '0123456789BCDFGHJKLMNPQRSTVWXYZ';
	do {
		#extract leading character
		my $char   = substr($string, 0, 1);
		#drop leading character
		$string = substr($string, 1);
		#get offset in $charset
		my $pos = index($charset, $char);
	    if ($pos == -1) {
			return "Illegal character ($char) in INPUT string";
	      }
		$decimal = ($decimal * $base) + $pos;
		} 
	while(length($string));
	return $decimal;
	}
###############
sub strip{
	#usage: $str=strip($str);
	#info: strips off beginning and endings returns, newlines, tabs, and spaces
	my $str=shift;
	if(length($str)==0){return;}
	$str=~s/^[\r\n\s\t]+//s;
	$str=~s/[\r\n\s\t]+$//s;
	return $str;
	}
###############
sub abort{
	my $msg=shift;
	print "$msg\n";
	exit;
	}