+=sub _items_usage_class_summary OPTIONS
+
+Returns a list of detail items summarizing the usage charges on this
+invoice. Each one will have 'amount', 'description' (the usage charge name),
+and 'usage_classnum'.
+
+OPTIONS can include 'escape' (a function to escape the descriptions).
+
+=cut
+
+sub _items_usage_class_summary {
+ my $self = shift;
+ my %opt = @_;
+
+ my $escape = $opt{escape} || sub { $_[0] };
+ my $invnum = $self->invnum;
+ my @classes = qsearch({
+ 'table' => 'usage_class',
+ 'select' => 'classnum, classname, SUM(amount) AS amount',
+ 'addl_from' => ' LEFT JOIN cust_bill_pkg_detail USING (classnum)' .
+ ' LEFT JOIN cust_bill_pkg USING (billpkgnum)',
+ 'extra_sql' => " WHERE cust_bill_pkg.invnum = $invnum".
+ ' GROUP BY classnum, classname, weight'.
+ ' HAVING (usage_class.disabled IS NULL OR SUM(amount) > 0)'.
+ ' ORDER BY weight ASC',
+ });
+ my @l;
+ my $section = {
+ description => &{$escape}($self->mt('Usage Summary')),
+ no_subtotal => 1,
+ usage_section => 1,
+ };
+ foreach my $class (@classes) {
+ push @l, {
+ 'description' => &{$escape}($class->classname),
+ 'amount' => sprintf('%.2f', $class->amount),
+ 'usage_classnum' => $class->classnum,
+ 'section' => $section,
+ };
+ }
+ return @l;
+}
+