+=item decrement_months_used MONTHS
+
+Decrement months_used by the given parameter
+
+(Note: as in, extending the length of the discount. Typically only used to
+stack/extend a discount when the customer package has one active already.)
+
+=cut
+
+sub decrement_months_used {
+ my( $self, $recharged ) = @_;
+ #UPDATE cust_pkg_discount SET months_used = months_used - ?
+ #leaves no history, and billing is mutexed per-customer
+
+ #we're run from part_event/Action/referral_pkg_discount on behalf of a
+ # different customer, so we need to grab this customer's mutex.
+ # incidentally, that's some inelegant encapsulation breaking shit, and a
+ # great argument in favor of native-DB trigger history so we can trust
+ # in normal ACID like the SQL above instead of this
+ $self->cust_pkg->cust_main->select_for_update;
+
+ $self->months_used( $self->months_used - $recharged );
+ $self->replace();
+}
+