billing: Create get_discount_for_realm function.

corporate/lib/stripe.py

@@ -450,6 +450,12 @@ def invoice_plans_as_needed(event_time: datetime) -> None:
 def attach_discount_to_realm(realm: Realm, discount: Decimal) -> None:
     Customer.objects.update_or_create(realm=realm, defaults={'default_discount': discount})
 
+def get_discount_for_realm(realm: Realm) -> Optional[Decimal]:
+    customer = Customer.objects.filter(realm=realm).first()
+    if customer is not None:
+        return customer.default_discount
+    return None
+
 def process_downgrade(user: UserProfile) -> None:  # nocoverage
     pass
 

corporate/tests/test_stripe.py

@@ -30,7 +30,7 @@ from corporate.lib.stripe import catch_stripe_errors, attach_discount_to_realm,
     compute_plan_parameters, update_or_create_stripe_customer, \
     process_initial_upgrade, add_plan_renewal_to_license_ledger_if_needed, \
     update_license_ledger_if_needed, update_license_ledger_for_automanaged_plan, \
-    invoice_plan, invoice_plans_as_needed
+    invoice_plan, invoice_plans_as_needed, get_discount_for_realm
 from corporate.models import Customer, CustomerPlan, LicenseLedger
 
 CallableT = TypeVar('CallableT', bound=Callable[..., Any])
@@ -807,6 +807,13 @@ class StripeTest(StripeTestCase):
                          [item.amount for item in stripe_invoice.lines])
         plan = CustomerPlan.objects.get(price_per_license=6000, discount=Decimal(25))
 
+    def test_get_discount_for_realm(self) -> None:
+        user = self.example_user('hamlet')
+        self.assertEqual(get_discount_for_realm(user.realm), None)
+
+        attach_discount_to_realm(user.realm, Decimal(85))
+        self.assertEqual(get_discount_for_realm(user.realm), 85)
+
     @mock_stripe()
     def test_replace_payment_source(self, *mocks: Mock) -> None:
         user = self.example_user("hamlet")