sub _read_vat {
	my %vat;
	for my $line (slurp "revbank.vat") {
		my ($match, $vataccount, $pct) = split " ", $line;
		$vat{$match} = { user => $vataccount, pct => $pct };
	}
	return \%vat;
}

sub hook_checkout_prepare($class, $cart, $username, $transaction_id, @) {
	my $vat = _read_vat;

	for my $entry ($cart->entries) {
		my @contras = $entry->contras;

		for my $contra ($entry->contras) {
			my $vat = $vat->{ $contra->{user} } or next;

			my $amount = RevBank::Amount->new(
				$contra->{amount}->cents * $vat->{pct} / (100 + $vat->{pct})
			);

			$entry->add_contra($contra->{user}, -$amount, "$vat->{pct}% VAT");
			$entry->add_contra($vat->{user},    +$amount, "$vat->{pct}% VAT");
		}
	}
}