applies coupon after advance discount (i.e. inverse order)

Author: smirolo

saas/mixins.py

@@ -1,4 +1,4 @@
-# Copyright (c) 2025, DjaoDjin inc.
+# Copyright (c) 2026, DjaoDjin inc.
 # All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
@@ -179,8 +179,7 @@ def get_cart_options(subscription, created_at=None,
         coupon_discount_amount = 0
         if coupon:
             coupon_discount_amount = coupon.get_discount_amount(
-                prorated_amount=prorated_amount,
-                period_amount=plan.period_amount)
+                amount=full_amount, period_amount=plan.period_amount)
             discount_by_types[coupon.discount_type] = coupon.discount_value
         amount = max(full_amount - coupon_discount_amount, 0)
 
@@ -220,24 +219,24 @@ def get_cart_options(subscription, created_at=None,
                     prorated_amount + advance_discount.full_periods_amount)
                 advance_discount_amount = advance_discount.get_discount_amount(
                     prorated_amount=prorated_amount)
+                amount = full_amount - advance_discount_amount
                 discount_by_types = {}
                 discount_by_types[advance_discount.discount_type] = \
                     advance_discount.discount_value
-                coupon_discount_amount = 0
                 if coupon:
                     coupon_discount_amount = coupon.get_discount_amount(
-                        prorated_amount=prorated_amount,
-                        period_amount=plan.period_amount,
-                        advance_amount=(advance_discount.full_periods_amount
-                            - plan.period_amount))
+                        amount=amount, period_amount=plan.period_amount)
+                    amount = max(amount - coupon_discount_amount, 0)
                     if coupon.discount_type in discount_by_types:
-                        discount_by_types[coupon.discount_type] += \
-                            coupon.discount_value
+                        if coupon.discount_type == Coupon.PERCENTAGE:
+                            discount_by_types[coupon.discount_type] = (
+                                full_amount - amount) * 10000 // full_amount
+                        else:
+                            discount_by_types[coupon.discount_type] += \
+                                coupon.discount_value
                     else:
                         discount_by_types[coupon.discount_type] = \
                             coupon.discount_value
-                amount = (full_amount - advance_discount_amount
-                    - coupon_discount_amount)
                 if amount <= 0:
                     continue # never allow to be completely free here.
                 nb_periods = (

saas/models.py

@@ -3130,7 +3130,7 @@ def setup_price(self):
 
     def get_discounted_period_amount(self, coupon):
         return self.period_amount - coupon.get_discount_amount(
-            period_amount=self.period_amount)
+            amount=self.period_amount, period_amount=self.period_amount)
 
     def get_discounted_period_price(self, coupon):
         return Price(self.get_discounted_period_amount(coupon), self.unit)
@@ -3390,12 +3390,14 @@ def __str__(self):
     def provider(self):
         return self.organization
 
-    def get_discount_amount(self, prorated_amount=0, period_amount=0,
-                            advance_amount=0, rounding=Plan.PRICE_ROUND_NONE):
+    def get_discount_amount(self, amount=0, period_amount=0,
+                            rounding=Plan.PRICE_ROUND_NONE):
         if self.discount_type == self.CURRENCY:
             return self.discount_value
+        if self.discount_type == self.PERIOD:
+            return self.discount_value * period_amount
         # discount percentage
-        full_amount = prorated_amount + period_amount + advance_amount
+        full_amount = amount
         discount_percent = self.discount_value
         discount_amount = (full_amount * discount_percent) // 10000
         if rounding == Plan.PRICE_ROUND_WHOLE:

testsite/fixtures/170-billing.json

@@ -106,13 +106,27 @@
 },
 {
     "fields":{
-        "code": "PROMO50",
         "created_at":"2026-01-01T00:00:00+00:00",
         "discount_type": 1,
         "discount_value": 5000,
-        "organization": 170
-    },
-    "model" : "saas.Coupon", "pk": 170
+        "organization": 170,
+        "code": "PROMO50"}, "model" : "saas.Coupon", "pk": 170
+},
+{
+    "fields":{
+        "created_at":"2026-01-01T00:00:00+00:00",
+        "discount_type": 2,
+        "discount_value": 5000,
+        "organization": 170,
+        "code": "DOLLAR50"}, "model" : "saas.Coupon", "pk": 171
+},
+{
+    "fields":{
+        "created_at":"2026-01-01T00:00:00+00:00",
+        "discount_type": 3,
+        "discount_value": 1,
+        "organization": 170,
+        "code": "MONTH50"}, "model" : "saas.Coupon", "pk": 172
 },
 {
     "fields": {
@@ -351,4 +365,45 @@
       "user": 175
     },
     "model": "saas.Role", "pk": 175
-}]
+},
+
+{
+    "fields": {
+      "username": "xia176",
+      "date_joined": "2026-01-01T00:00:00+00:00",
+      "last_login": "2026-01-01T00:00:00+00:00",
+      "email": "xia+176@localhost.localdomain",
+      "first_name": "Xia176",
+      "last_name": "Subscriber",
+      "password": "pbkdf2_sha256$10000$z0MBiWn0Rlem$iZdC6uHomlE07qGK/TqfcfxNzKJtFp03c0JILF1frRc=",
+      "is_active": true,
+      "username": "xia176"}, "model": "auth.User", "pk": 176
+},
+{
+    "fields": {
+      "last_signed": "2026-01-01T00:00:00+00:00",
+      "agreement": 1,
+      "user": 176}, "model": "saas.signature", "pk": 176
+},
+{
+    "fields": {
+      "full_name": "Xia176 Subscriber",
+      "created_at": "2026-01-01T00:00:00+00:00",
+      "email": "xia+176@localhost.localdomain",
+      "phone": "555-555-5555",
+      "street_address": "1 ABC loop",
+      "locality":  "San Francisco",
+      "region": "CA",
+      "postal_code": "94102",
+      "country": "US",
+      "processor": 1,
+      "is_active": 1,
+      "slug": "xia176"}, "model": "saas.Organization", "pk": 176
+},
+{
+    "fields":{
+      "created_at": "2026-01-01T00:00:00+00:00",
+      "role_description": 1,
+      "organization": 176, "user": 176}, "model": "saas.Role", "pk": 176
+}
+]