#! /usr/bin/perl

use CGI::Carp qw(fatalsToBrowser warningsToBrowser);
use POSIX qw(ceil);

use strict;
use warnings;

print "Content-Type: text/plain\n\n";
warningsToBrowser(1);

###########################################################

my $weight = 800;

my %postage = Postage($weight);

while (my ($location, $cost_ref) = each %postage) {
	print "$location\n";
	print "\t@$_\n" for @$cost_ref;
}

###########################################################

our %POSTAGE;
INIT {
	local $/ = "\n\n"; # Paragraph mode
	
	while (<DATA>) {
		chomp;

		# Comments begin with #
		my ($service, @rates) = grep {!/^#/} split "\n";
		
		# Eval rates
		for (@rates) {
			$_ = [split "\t"];
			$_->[1] = eval $_->[1];
			die "$service - $@" if $@;
		}
		
		$POSTAGE{$service} = \@rates;
	}
}

sub Postage {
	my $weight = shift;
	die "Invalid weight" unless $weight < 1_000_000_000;

	my %postage;

	for my $service (sort keys %POSTAGE) {
		# The Last Max
		my $max = $POSTAGE{$service}[-1][0];
		
		# Subdivide Package according to max weight
		my @weights = $weight;
		while ($max && $weights[-1] > $max) {
			unshift @weights, $max;
			$weights[-1] -= $max;
		}
		
		for my $w (@weights) {
			for my $rate (@{$POSTAGE{$service}}) {
				next if $rate->[0] && $w > $rate->[0];
				push @{$postage{$service}}, [$w, sprintf "%.2f", $rate->[1]($w)];
				last;
			}
		}
	}
	
	return %postage;
}

###########################################################

# Each section is __DATA__ is labelled by a destination
# and then by max weight and the sub that determines the cost.
# If no max weight is specified, then treat as infinate.

__DATA__
UK & Europe
	sub { 0.00 }

USA
200	sub { 2.00 }
	sub { my $w = shift; 2.00 + 1.00 * ceil(($w-200)/100) }

Australia & New Zealand
200	sub { 2.00 }
2200	sub { my $w = shift; 2.00 * (1 + 1 / 1.1) ** ceil(($w - 200) / 200) }

Other
200	sub { 2.00 }
	sub { my $w = shift; 2.00 + 1.00 * ceil(($w - 200) / 200) }

Test
100	sub { 1.00 }
200	sub { 1.00 + 0.99 }
300	sub { 1.00 + 0.99 + 0.80 }