Fix rendering of upsell messages for exclusive offers (#3548)

* Improve `available` method of `LineOfferConsumer` class
* Add `quantity_available_for_offer` method to `AbstractLine` class
* Improve conditions: "Get num matches" methods updated to use `quantity_available_for_offer`
method of `Line` model.
* Improve conditions: `get_upsell_message` methods updated to show upsell message only in
the cases where `delta` > 0.
* Ensure basket upsell messages are not `None`

src/oscar/apps/basket/abstract_models.py

@@ -772,6 +772,9 @@ class AbstractLine(models.Model):
     def is_available_for_offer_discount(self, offer):
         return self.consumer.available(offer) > 0
 
+    def quantity_available_for_offer(self, offer):
+        return self.quantity_without_offer_discount(offer) + self.quantity_with_offer_discount(offer)
+
     # ==========
     # Properties
     # ==========

src/oscar/apps/basket/utils.py

@@ -143,7 +143,7 @@ class LineOfferConsumer(object):
     def consumers(self):
         return [x for x in self._offers.values() if self.consumed(x)]
 
-    def available(self, offer=None) -> int:
+    def available(self, offer=None) -> int: # noqa (too complex (11))
         """
         check how many items are available for offer
 
@@ -158,13 +158,26 @@ class LineOfferConsumer(object):
 
             applied = [x for x in self.consumers if x != offer]
 
-            # find any *other* exclusive offers
-            if any([x.exclusive for x in applied]):
-                return 0
+            if offer.exclusive:
+                for a in applied:
+                    if a.exclusive:
+                        if any([
+                            a.priority > offer.priority,
+                            a.priority == offer.priority and a.id < offer.id
+                        ]):
+                            # Exclusive offers cannot be applied if any other exclusive
+                            # offer with higher priority is active already.
+                            max_affected_items = max_affected_items - self.consumed(a)
+                            if max_affected_items == 0:
+                                return 0
+
+                    else:
+                        # Exclusive offers cannot be applied if any other offers are
+                        # active already.
+                        return 0
 
-            # exclusive offers cannot be applied if any other
-            # offers are active already
-            if offer.exclusive and len(applied):
+            # find any *other* exclusive offers
+            elif any([x.exclusive for x in applied]):
                 return 0
 
             # check for applied offers allowing restricted combinations

src/oscar/apps/offer/conditions.py

@@ -57,9 +57,8 @@ class CountCondition(Condition):
             return getattr(self, '_num_matches')
         num_matches = 0
         for line in basket.all_lines():
-            if (self.can_apply_condition(line)
-                    and line.quantity_without_offer_discount(offer) > 0):
-                num_matches += line.quantity_without_offer_discount(offer)
+            if self.can_apply_condition(line):
+                num_matches += line.quantity_available_for_offer(offer)
         self._num_matches = num_matches
         return num_matches
 
@@ -70,9 +69,12 @@ class CountCondition(Condition):
     def get_upsell_message(self, offer, basket):
         num_matches = self._get_num_matches(basket, offer)
         delta = self.value - num_matches
-        return ngettext('Buy %(delta)d more product from %(range)s',
-                        'Buy %(delta)d more products from %(range)s', delta) \
-            % {'delta': delta, 'range': self.range}
+        if delta > 0:
+            return ngettext(
+                'Buy %(delta)d more product from %(range)s',
+                'Buy %(delta)d more products from %(range)s',
+                delta
+            ) % {'delta': delta, 'range': self.range}
 
     def consume_items(self, offer, basket, affected_lines):
         """
@@ -142,21 +144,21 @@ class CoverageCondition(Condition):
         return False
 
     def _get_num_covered_products(self, basket, offer):
-        covered_ids = []
+        covered_ids = set()
         for line in basket.all_lines():
-            if not line.is_available_for_offer_discount(offer):
-                continue
             product = line.product
-            if (self.can_apply_condition(line) and product.id not in
-                    covered_ids):
-                covered_ids.append(product.id)
+            if self.can_apply_condition(line) and line.quantity_available_for_offer(offer) > 0:
+                covered_ids.add(product.id)
         return len(covered_ids)
 
     def get_upsell_message(self, offer, basket):
         delta = self.value - self._get_num_covered_products(basket, offer)
-        return ngettext('Buy %(delta)d more product from %(range)s',
-                        'Buy %(delta)d more products from %(range)s', delta) \
-            % {'delta': delta, 'range': self.range}
+        if delta > 0:
+            return ngettext(
+                'Buy %(delta)d more product from %(range)s',
+                'Buy %(delta)d more products from %(range)s',
+                delta
+            ) % {'delta': delta, 'range': self.range}
 
     def is_partially_satisfied(self, offer, basket):
         return 0 < self._get_num_covered_products(basket, offer) < self.value
@@ -250,12 +252,9 @@ class ValueCondition(Condition):
             return getattr(self, '_value_of_matches')
         value_of_matches = D('0.00')
         for line in basket.all_lines():
-            if (self.can_apply_condition(line)
-                    and line.quantity_without_offer_discount(offer) > 0):
+            if self.can_apply_condition(line):
                 price = unit_price(offer, line)
-                value_of_matches += price * int(
-                    line.quantity_without_offer_discount(offer)
-                )
+                value_of_matches += price * int(line.quantity_available_for_offer(offer))
         self._value_of_matches = value_of_matches
         return value_of_matches
 
@@ -265,9 +264,12 @@ class ValueCondition(Condition):
 
     def get_upsell_message(self, offer, basket):
         value_of_matches = self._get_value_of_matches(offer, basket)
-        return _('Spend %(value)s more from %(range)s') % {
-            'value': currency(self.value - value_of_matches, basket.currency),
-            'range': self.range}
+        delta = self.value - value_of_matches
+        if delta > 0:
+            return _('Spend %(value)s more from %(range)s') % {
+                'value': currency(delta, basket.currency),
+                'range': self.range,
+            }
 
     def consume_items(self, offer, basket, affected_lines):
         """

tests/integration/offer/test_upsell_messages.py

@@ -0,0 +1,140 @@
+from decimal import Decimal as D
+
+from django.test.client import RequestFactory
+from django.urls import reverse
+from django.utils.timezone import now
+
+from oscar.apps.basket.views import BasketView
+from oscar.apps.offer.applicator import Applicator
+from oscar.core.loading import get_class
+from oscar.test import factories
+from oscar.test.testcases import WebTestCase
+
+Selector = get_class('partner.strategy', 'Selector')
+
+
+class TestUpsellMessages(WebTestCase):
+
+    def setUp(self):
+        super().setUp()
+
+        self.basket = factories.create_basket(empty=True)
+
+        # Create range and add one product to it.
+        rng = factories.RangeFactory(name='All products', includes_all_products=True)
+        self.product = factories.ProductFactory()
+        rng.add_product(self.product)
+
+        # Create offer #1.
+        condition1 = factories.ConditionFactory(
+            range=rng, type=factories.ConditionFactory._meta.model.COUNT, value=D('2'),
+        )
+        benefit1 = factories.BenefitFactory(
+            range=rng, type=factories.BenefitFactory._meta.model.MULTIBUY, value=None,
+        )
+        self.offer1 = factories.ConditionalOfferFactory(
+            condition=condition1, benefit=benefit1,
+            slug='offer-1',
+            start_datetime=now(),
+            name='Test offer #1',
+            priority=1,
+        )
+
+        # Create offer #2.
+        condition2 = factories.ConditionFactory(
+            range=rng, type=factories.ConditionFactory._meta.model.VALUE, value=D('1.99'),
+        )
+        benefit2 = factories.BenefitFactory(
+            range=rng, type=factories.BenefitFactory._meta.model.MULTIBUY, value=None,
+        )
+        self.offer2 = factories.ConditionalOfferFactory(
+            condition=condition2,
+            benefit=benefit2,
+            slug='offer-2',
+            start_datetime=now(),
+            name='Test offer #2',
+        )
+
+        # Create offer #3.
+        condition3 = factories.ConditionFactory(
+            range=rng, type=factories.ConditionFactory._meta.model.COVERAGE, value=1,
+        )
+        benefit3 = factories.BenefitFactory(
+            range=rng, type=factories.BenefitFactory._meta.model.MULTIBUY, value=None,
+        )
+        self.offer3 = factories.ConditionalOfferFactory(
+            condition=condition3,
+            benefit=benefit3,
+            slug='offer-3',
+            start_datetime=now(),
+            name='Test offer #3',
+        )
+
+        # Prepare `BasketView` to use `get_upsell_messages` method in tests.
+        self.view = BasketView()
+        self.view.request = RequestFactory().get(reverse('basket:summary'))
+        self.view.request.user = factories.UserFactory()
+        self.view.args = []
+        self.view.kwargs = {}
+
+    def add_product(self):
+        self.basket.add_product(self.product)
+        self.basket.strategy = Selector().strategy()
+        Applicator().apply(self.basket)
+
+        self.assertBasketUpsellMessagesAreNotNone()
+
+    def assertBasketUpsellMessagesAreNotNone(self):
+        messages = self.view.get_upsell_messages(self.basket)
+        for message_data in messages:
+            # E.g. message data:
+            # {
+            #     'message': 'Buy 1 more product from All products',
+            #     'offer': <ConditionalOffer: Test offer #1>
+            # }.
+            self.assertIsNotNone(message_data['message'])
+            self.assertIsNotNone(message_data['offer'])
+
+    def assertOffersApplied(self, offers):
+        applied_offers = self.basket.applied_offers()
+        self.assertEqual(len(offers), len(applied_offers))
+        for offer in offers:
+            self.assertIn(offer.id, applied_offers, msg=offer)
+
+    def test_upsell_messages(self):
+        # The basket is empty. No offers are applied.
+        self.assertEqual(self.offer1.get_upsell_message(self.basket), 'Buy 2 more products from All products')
+        self.assertEqual(self.offer2.get_upsell_message(self.basket), 'Spend £1.99 more from All products')
+        self.assertEqual(self.offer3.get_upsell_message(self.basket), 'Buy 1 more product from All products')
+
+        self.add_product()
+
+        # 1 product in the basket. Offer #2 is applied.
+        self.assertOffersApplied([self.offer2])
+        self.assertEqual(self.offer1.get_upsell_message(self.basket), 'Buy 1 more product from All products')
+        self.assertIsNone(self.offer2.get_upsell_message(self.basket))
+        self.assertEqual(self.offer3.get_upsell_message(self.basket), 'Buy 1 more product from All products')
+
+        self.add_product()
+
+        # 2 products in the basket. Offers #1 is applied.
+        self.assertOffersApplied([self.offer1])
+        self.assertIsNone(self.offer1.get_upsell_message(self.basket))
+        self.assertEqual(self.offer2.get_upsell_message(self.basket), 'Spend £1.99 more from All products')
+        self.assertEqual(self.offer3.get_upsell_message(self.basket), 'Buy 1 more product from All products')
+
+        self.add_product()
+
+        # 3 products in the basket. Offers #1 and #2 are applied.
+        self.assertOffersApplied([self.offer1, self.offer2])
+        self.assertIsNone(self.offer1.get_upsell_message(self.basket))
+        self.assertIsNone(self.offer2.get_upsell_message(self.basket))
+        self.assertEqual(self.offer3.get_upsell_message(self.basket), 'Buy 1 more product from All products')
+
+        self.add_product()
+
+        # 4 products in the basket. All offers are applied.
+        self.assertOffersApplied([self.offer1, self.offer2, self.offer3])
+        self.assertIsNone(self.offer1.get_upsell_message(self.basket))
+        self.assertIsNone(self.offer2.get_upsell_message(self.basket))
+        self.assertIsNone(self.offer3.get_upsell_message(self.basket))