[FW][FIX] sale_coupon: free product quantity in promotion

Create a promotion program with conditions:
- Minimum purchase in currency (ex 100$ tax excluded)
- Auto apply
- On current order
- Unlimited use

And reward:
- Free product
- 1 Quantity

Go to website shop. Fill an order with amount above the minimum
required by the program. The promo will apply and add the free
product.
Increasing the order amount will eventually make the free product
quantity increase, eventually overcoming the reward product
quantity.

Fixing by calculating the reward quantity using both minimum quantity
and minimum amount and using as cap the to reward product quantity
currently in cart

opw-2246138

closes odoo/odoo#51680

X-original-commit: 02331a34cf66117b27cfa1e96078b4721cbd1e70
Related: odoo/enterprise#10722
Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

addons/sale_coupon/models/sale_order.py

@@ -86,6 +86,11 @@ class SaleOrder(models.Model):
             program_in_order = max_product_qty // (program.rule_min_quantity + program.reward_product_quantity)
             # multipled by the reward qty
             reward_product_qty = program.reward_product_quantity * program_in_order
+            # do not give more free reward than products
+            reward_product_qty = min(reward_product_qty, self.order_line.filtered(lambda x: x.product_id == program.reward_product_id).product_uom_qty)
+            if program.rule_minimum_amount:
+                order_total = sum(line.price_total for line in order_lines.filtered(lambda x: x.product_id != program.reward_product_id))
+                reward_product_qty = min(reward_product_qty, order_total // program.rule_minimum_amount)
         else:
             reward_product_qty = min(max_product_qty, self.order_line.filtered(lambda x: x.product_id == program.reward_product_id).product_uom_qty)