+=item usage CLASSNUM
+
+Returns the amount of the charge associated with usage class CLASSNUM if
+CLASSNUM is defined. Otherwise returns the total charge associated with
+usage.
+
+=cut
+
+sub usage {
+ my( $self, $classnum ) = @_;
+ my $sum = 0;
+ my @values = ();
+
+ if ( $self->get('details') ) {
+
+ @values =
+ map { $_->[2] }
+ grep { ref($_) && ( defined($classnum) ? $_->[3] eq $classnum : 1 ) }
+ @{ $self->get('details') };
+
+ }else{
+
+ my $hashref = { 'billpkgnum' => $self->billpkgnum };
+ $hashref->{ 'classnum' } = $classnum if defined($classnum);
+ @values = map { $_->amount } qsearch('cust_bill_pkg_detail', $hashref);
+
+ }
+
+ foreach ( @values ) {
+ $sum += $_ if $_;
+ }
+ $sum;
+}
+
+=item usage_classes
+
+Returns a list of usage classnums associated with this invoice line's
+details.
+
+=cut
+
+sub usage_classes {
+ my( $self ) = @_;
+
+ if ( $self->get('details') ) {
+
+ my %seen = ();
+ foreach my $detail ( grep { ref($_) } @{$self->get('details')} ) {
+ $seen{ $detail->[3] } = 1;
+ }
+ keys %seen;
+
+ }else{
+
+ map { $_->classnum }
+ qsearch({ table => 'cust_bill_pkg_detail',
+ hashref => { billpkgnum => $self->billpkgnum },
+ select => 'DISTINCT classnum',
+ });
+
+ }
+
+}
+