Discount on batch payments

This module adds early-payment discount handling to batch payments. When an invoice is posted, Odoo calculates a discount validity date from the payment terms and stores it on the invoice. A hidden field valid_discount_date is added to the invoice form, and a new "Discount Invoice" filter appears in the invoice search view, showing posted invoices whose discount date has not yet passed.

In the payment registration wizard, when you pick a payment date, the amounts of the selected invoice payment lines are recalculated. If the payment is made within the discount period, the discount amount is computed from the payment terms, and the difference is handled automatically: the line is set to reconcile, the discount account is used as the write-off account, and the note "Early Pay Discount" is added. If the difference is zero, the handling switches back to open.

Changing the discount days on a payment term line updates the discount date on all posted invoices using that payment term. The wizard also requires a payment date before auto-filling payments, and it recalculates the cheque amount from the invoice payment lines. The module works together with account.move, account.payment.term.line, account.payment.register and invoice.payment.line.