select all records from staffingtable between startDate and endDate

for each distinct staffid:
    Create invoice header:
        InvoiceRef = autonumber
        InvoiceDate = today()
        StaffID = distinct staffid from staffingtable
        InvoicePayDate = supplied_date_parameter
        InvoiceSortCode = value from staff table
        InvoiceAccount = value from staff table

Insert into InvoiceLineItem
    LineID = autonumber
    InvoiceRef = invoiceheader that was just created
    JobType = PTS/EVENT based on populated ID field or lookup to event header table
    JobDate = date of job from staffing table
    JobName = value from event header table
    JobPaid (currency amount) = job hours * payrate from staffgrade table