Fix non-exclusive offers with count condition

Issue: https://github.com/django-oscar/django-oscar/issues/3162

* Checking of `offer.benefit.max_affected_items` removed from the
`available` method of `LineOfferConsumer` class - available items should
not be limited by related benefit (it should be considered when applying
the offer).
* Improved `apply` method of `PercentageDiscountBenefit` - affected
items must include "quantities with discount applied".
* `is_satisfied` method of `CountCondition` updated to pass `offer`
instead of `None` to `line.quantity_without_offer_discount` - this
change is required to fix the initial issue.
* Updated `test_available_with_offer` test - initially this test was
added to check the lines that we removed from the `available` method of
`LineOfferConsumer` class (See fda27a183d/).
* Added tests to confirm that the initial issue is fixed.

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: # noqa (too complex (11))
+    def available(self, offer=None) -> int:
         """
         check how many items are available for offer
 
@@ -186,8 +186,4 @@ class LineOfferConsumer(object):
                 if check and offer not in x.combined_offers:
                     return 0
 
-            # respect max_affected_items
-            if offer.benefit.max_affected_items:
-                max_affected_items = min(offer.benefit.max_affected_items, max_affected_items)
-
         return max_affected_items - self.consumed(offer)

src/oscar/apps/offer/benefits.py

@@ -66,6 +66,7 @@ class PercentageDiscountBenefit(Benefit):
         affected_items = 0
         max_affected_items = self._effective_max_affected_items()
         for price, line in line_tuples:
+            affected_items += line.quantity_with_offer_discount(offer)
             if affected_items >= max_affected_items:
                 break
             if discount_amount_available == 0:

src/oscar/apps/offer/conditions.py

@@ -47,7 +47,7 @@ class CountCondition(Condition):
         num_matches = 0
         for line in basket.all_lines():
             if self.can_apply_condition(line):
-                num_matches += line.quantity_without_offer_discount(None)
+                num_matches += line.quantity_without_offer_discount(offer)
             if num_matches >= self.value:
                 return True
         return False

tests/integration/basket/test_utils.py

@@ -76,7 +76,7 @@ class TestLineOfferConsumer:
         offer1 = ConditionalOfferFactory(name='offer1', benefit=benefit)
         lines = basket.all_lines()
         assert lines[0].consumer.available(offer1) == 1
-        assert lines[1].consumer.available(offer1) == 5
+        assert lines[1].consumer.available(offer1) == 10
 
     def test_consumed_with_offer(self, filled_basket):
         offer1 = ConditionalOfferFactory(name='offer1')

tests/integration/offer/test_condition.py

@@ -3,13 +3,17 @@ from unittest import mock
 
 import pytest
 from django.test import TestCase
+from django.utils.timezone import now
 
 from oscar.apps.basket.models import Basket
-from oscar.apps.offer import custom, models
+from oscar.apps.offer import applicator, custom, models
+from oscar.core.loading import get_class
 from oscar.test import factories
 from oscar.test.basket import add_product
 from tests._site.model_tests_app.models import BasketOwnerCalledBarry
 
+Selector = get_class('partner.strategy', 'Selector')
+
 
 @pytest.fixture
 def products_some():
@@ -329,3 +333,47 @@ class TestCustomCondition(TestCase):
     def test_is_satisfied_by_match(self):
         self.basket.owner = factories.UserFactory(first_name="Barry")
         assert self.offer.is_condition_satisfied(self.basket)
+
+
+class TestOffersWithCountCondition(TestCase):
+
+    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 a non-exclusive offer #1.
+        condition1 = factories.ConditionFactory(range=rng, value=D('1'))
+        benefit1 = factories.BenefitFactory(range=rng, value=D('10'))
+        self.offer1 = factories.ConditionalOfferFactory(
+            condition=condition1, benefit=benefit1, start_datetime=now(),
+            name='Test offer #1', exclusive=False,
+        )
+
+        # Create a non-exclusive offer #2.
+        condition2 = factories.ConditionFactory(range=rng, value=D('1'))
+        benefit2 = factories.BenefitFactory(range=rng, value=D('5'))
+        self.offer2 = factories.ConditionalOfferFactory(
+            condition=condition2, benefit=benefit2, start_datetime=now(),
+            name='Test offer #2', exclusive=False,
+        )
+
+    def add_product(self):
+        self.basket.add_product(self.product)
+        self.basket.strategy = Selector().strategy()
+        applicator.Applicator().apply(self.basket)
+
+    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_both_non_exclusive_offers_are_applied(self):
+        self.add_product()
+        self.assertOffersApplied([self.offer1, self.offer2])