Period based invoice grouping

We have a customer who wants to invoice all the shipments delivered in the months should be grouped into a single invoice at the end of the month. For this, we activated the sale_invoice_grouping module until we found the following case:

  • A shipment for the customer was delivered into the first day of the next month
  • The accountant did not post the invoice before the shipment was delivered

This resulted in a wrong grouping because the invoice included shipments of two months.

I’m wondering if it will make sense to have a “period based” invoice grouping method. The objective of this method is to group the invoices based on a date (shipment date when invoice method is shipment or sale date when invoice method is order). So in case there is a draft invoice same conditions but outside of the period another draft invoice is created.

I know there is a third party module which does more or less what I need, so it seems others also have the need of such feature. I’m wondering if we should have this as part of standard.

I do not see the point to have period.
For me it is just a matter of computing and fill the invoice date of the invoice generated. The invoice_date field could be added to the _invoice_grouping_fields.
Now how would the invoice date be computed? I guess it could be managed by a kind of invoice term which could be composed of Relative Delta.
But I think this is advanced feature so it should probably be defined in its own module.

I created Issue 10931: Compute invoice date from sale - Tryton issue tracker