supplierCredit method
Implementation
@action
num supplierCredit(int herderId, DateTime date) => tickets.isEmpty
? 0
: tickets
.where((t) => t.contactId == herderId)
.where((t) => t.status == true)
.where((t) => t.date.isBefore(date))
.where((t) =>
t.ticketType == TicketType.spendCovered ||
t.ticketType == TicketType.wage)
.fold(0, (prev, e) => prev + e.received);