[FIX] l10n_ke_edi_tremol: fix price and quantity negative scenario

When both the price and quantity are negative, this creates a few
problems that the serialisation code does not handle appropriately.

Firstly, the device does not accept negative values for price or
quantity. Price and quantity should therefore always be positive. In the
case where both the price and the quantity are negative, the line is
positive, and we must therefore processes it in the same manner as
positive lines.

A line with both negative and price and quantity should qualify as a
line that, when negative lines are present, can be subtracted from in
order to represent a discount.

This commit adapts the serialisation function in order to correctly
represent a negative price and quantity line as positive (by using the
absolute values of each). It also adapts the discount line code in order
to recognize these lines as candidate lines for discount.

X-original-commit: db774ac144e760e23d4a032971c64e2010486325
Part-of: odoo/odoo#116615

addons/l10n_ke_edi_tremol/models/account_move.py

@@ -129,7 +129,7 @@ class AccountMove(models.Model):
                   in order to add a line to the opened invoice.
         """
         def is_discount_line(line):
-            return line.price_unit < 0.0
+            return line.price_subtotal < 0.0
 
         def is_candidate(discount_line, other_line):
             """ If the of one line match those of the discount line, the discount can be distributed accross that line """
@@ -166,7 +166,7 @@ class AccountMove(models.Model):
         msgs = []
         for line in self.invoice_line_ids.filtered(lambda l: l.display_type == 'product' and l.quantity and l.price_total > 0 and not discount_dict.get(l.id) >= 100):
             # Here we use the original discount of the line, since it the distributed discount has not been applied in the price_total
-            price = round(line.price_total / line.quantity * 100 / (100 - line.discount), 2) * currency_rate
+            price = round(line.price_total / abs(line.quantity) * 100 / (100 - line.discount), 2) * currency_rate
             percentage = line.tax_ids[0].amount
 
             # Letter to classify tax, 0% taxes are handled conditionally, as the tax can be zero-rated or exempt
@@ -194,7 +194,7 @@ class AccountMove(models.Model):
                 str(percentage).encode('cp1251')[:5]            # up to 5 symbols for vat rate
             ])
             # 1 to 10 symbols for quantity
-            line_data += b'*' + str(line.quantity).encode('cp1251')[:10]
+            line_data += b'*' + str(abs(line.quantity)).encode('cp1251')[:10]
             if discount_dict.get(line.id):
                 # 1 to 7 symbols for percentage of discount/addition
                 discount_sign = b'-' if discount_dict[line.id] > 0 else b'+'