Set maximum line quantity on basket page.

docs/source/releases/v1.6.rst

  - For variant products we now display their own images on product detail page
    and fallback to parent product images if they don't have any.
 
+ - Basket line form quantity field now has "max" attribute with the maximum
+   allowed quantity in it based on product availability and basket threshold
+   (see :issue:`1412`).
+
 .. _incompatible_in_1.6:
 
 Backwards incompatible changes in Oscar 1.6

src/oscar/apps/basket/abstract_models.py

                 .order_by(self._meta.pk.name))
         return self._lines
 
-    def is_quantity_allowed(self, qty):
+    def max_allowed_quantity(self):
         """
-        Test whether the passed quantity of items can be added to the basket
+        Returns maximum product quantity, that can be added to the basket
+        with the respect to basket quantity threshold.
         """
-        # We enforce a max threshold to prevent a DOS attack via the offers
-        # system.
         basket_threshold = settings.OSCAR_MAX_BASKET_QUANTITY_THRESHOLD
         if basket_threshold:
             total_basket_quantity = self.num_items
             max_allowed = basket_threshold - total_basket_quantity
-            if qty > max_allowed:
-                return False, _(
-                    "Due to technical limitations we are not able "
-                    "to ship more than %(threshold)d items in one order.") \
-                    % {'threshold': basket_threshold}
+            return max_allowed, basket_threshold
+
+    def is_quantity_allowed(self, qty):
+        """
+        Test whether the passed quantity of items can be added to the basket
+        """
+        # We enforce a max threshold to prevent a DOS attack via the offers
+        # system.
+        max_allowed, basket_threshold = self.max_allowed_quantity()
+        if max_allowed is not None and qty > max_allowed:
+            return False, _(
+                "Due to technical limitations we are not able "
+                "to ship more than %(threshold)d items in one order.") \
+                % {'threshold': basket_threshold}
         return True, None
 
     # ============

src/oscar/apps/basket/forms.py

         super(BasketLineForm, self).__init__(*args, **kwargs)
         self.instance.strategy = strategy
 
+        max_allowed_quantity = None
+        num_available = getattr(self.instance.purchase_info.availability, 'num_available', None)
+        basket_max_allowed_quantity = self.instance.basket.max_allowed_quantity()[0]
+        if all([num_available, basket_max_allowed_quantity]):
+            max_allowed_quantity = min(num_available, basket_max_allowed_quantity)
+        else:
+            max_allowed_quantity = num_available or basket_max_allowed_quantity
+        if max_allowed_quantity:
+            self.fields['quantity'].widget.attrs['max'] = max_allowed_quantity
+
     def clean_quantity(self):
         qty = self.cleaned_data['quantity']
         if qty > 0:

tests/integration/basket/test_forms.py

 from decimal import Decimal as D
 
-from django.test import TestCase
+from django.test import TestCase, override_settings
 from django.conf import settings
 import mock
 
         form = self.build_form(quantity=invalid_qty)
         self.assertFalse(form.is_valid())
 
+    @override_settings(OSCAR_MAX_BASKET_QUANTITY_THRESHOLD=10)
     def test_enforce_max_line_quantity_for_existing_product(self):
-        settings.OSCAR_MAX_BASKET_QUANTITY_THRESHOLD = 10
         self.basket.flush()
         product = factories.create_product(num_in_stock=20)
         add_product(self.basket, D('100'), 4, product)
         form = self.build_form(quantity=11)
         self.assertFalse(form.is_valid())
 
+    def test_line_quantity_max_attribute_per_num_available(self):
+        self.basket.flush()
+        product = factories.create_product(num_in_stock=20)
+        add_product(self.basket, D('100'), 4, product)
+        self.line = self.basket.all_lines()[0]
+        form = self.build_form()
+        self.assertIn('max="20"', str(form['quantity']))
+
+    @override_settings(OSCAR_MAX_BASKET_QUANTITY_THRESHOLD=10)
+    def test_line_quantity_max_attribute_per_basket_threshold(self):
+        self.basket.flush()
+        product = factories.create_product(num_in_stock=20)
+        add_product(self.basket, D('100'), 4, product)
+        self.line = self.basket.all_lines()[0]
+        form = self.build_form()
+        self.assertIn('max="6"', str(form['quantity']))
+
     def test_basketline_formset_ordering(self):
         # when we use a unordered queryset in the Basketlineformset, the
         # discounts will be lost because django will query the database

tests/integration/basket/test_models.py

 # -*- coding: utf-8 -*-
 from decimal import Decimal as D
 
-from django.test import TestCase
+from django.test import TestCase, override_settings
 
 from oscar.apps.basket.models import Basket
 from oscar.apps.catalogue.models import Option
         self.assertEqual(self.basket.total_excl_tax_excl_discounts, 100)
         self.assertEqual(self.basket.total_incl_tax_excl_discounts, 100)
 
+    @override_settings(OSCAR_MAX_BASKET_QUANTITY_THRESHOLD=20)
+    def test_max_allowed_quantity(self):
+        self.basket.add_product(self.product, quantity=3)
+        self.assertEquals(self.basket.max_allowed_quantity()[0], 7)
+
+    @override_settings(OSCAR_MAX_BASKET_QUANTITY_THRESHOLD=20)
+    def test_is_quantity_allowed(self):
+        self.assertTrue(self.basket.is_quantity_allowed(qty=3)[0])
+        self.assertFalse(self.basket.is_quantity_allowed(qty=11)[0])
+
 
 class TestMergingTwoBaskets(TestCase):