feat: pick the most recently start plan as auto-applicable

ENT-9734

license_manager/apps/subscriptions/forms.py

@@ -46,7 +46,13 @@ class SubscriptionPlanForm(forms.ModelForm):
         choices=SubscriptionPlanShouldAutoApplyLicensesChoices.CHOICES,
         required=False,
         label="Should auto apply licenses",
-        help_text="Whether licenses from this Subscription Plan should be auto applied."
+        help_text=(
+            """
+            Whether licenses from this Subscription Plan should be auto applied.
+            It it possible and acceptable for more than one plan in a single
+            customer agreement to have this field enabled.
+            """
+        )
     )
 
     # Extra form field to specify the number of licenses to be associated with the subscription plan
@@ -292,8 +298,17 @@ def populate_subscription_for_auto_applied_licenses_choices(self, instance):
             choices=choices,
             required=False,
             initial=empty_choice if not current_plan else (current_plan.uuid, current_plan.title),
-            help_text="The subscription plan to be associated with auto apply licenses. Selecting a license"
-            " will automatically enable the \"Should auto apply licenses\" field on the subscription plan"
+            help_text=(
+                """
+                The subscription plan from which licenses will be auto-applied, if any.
+                If you do not manually modify this field, it will be automatically set, chosen as the
+                most recently started plan that is active, current, and has 'should_auto_apply_licenses'
+                set to true. Manually selecting/modifying the plan for this field will have two effects:
+                It will automatically enable the \"Should auto apply licenses\" field on the selected plan,
+                and it will automatically *disable* that field on all other plans
+                associated with this customer agreement.
+                """
+            ),
         )
         self.fields['subscription_for_auto_applied_licenses'] = choice_field
 

license_manager/apps/subscriptions/models.py

@@ -237,7 +237,7 @@ def auto_applicable_subscription(self):
             is_active=True,
             start_date__lte=now,
             expiration_date__gte=now
-        ).first()
+        ).order_by('-start_date').first()
 
         return plan
 

license_manager/apps/subscriptions/tests/test_models.py

@@ -117,6 +117,55 @@ def test_is_locked_for_renewal_processing(self, is_locked_for_renewal_processing
                 renewed_subscription_plan.is_locked_for_renewal_processing, is_locked_for_renewal_processing,
             )
 
+    def test_auto_applicable_subscription(self):
+        """
+        Tests that we pick the most recent auto-applicable plan for a CustomerAgreement.
+        """
+        agreement = CustomerAgreementFactory.create()
+        SubscriptionPlanFactory.create(
+            customer_agreement=agreement,
+            start_date=localized_datetime(2020, 1, 1),
+            should_auto_apply_licenses=True,
+        )
+        SubscriptionPlanFactory.create(
+            customer_agreement=agreement,
+            start_date=localized_datetime(2020, 4, 1),
+            should_auto_apply_licenses=True,
+        )
+        plan_3 = SubscriptionPlanFactory.create(
+            customer_agreement=agreement,
+            start_date=localized_datetime(2020, 12, 1),
+            should_auto_apply_licenses=True,
+        )
+        # make one plan that hasn't started yet
+        SubscriptionPlanFactory.create(
+            customer_agreement=agreement,
+            start_date=localized_utcnow() + timedelta(days=1),
+            should_auto_apply_licenses=True,
+        )
+        self.assertEqual(agreement.auto_applicable_subscription, plan_3)
+
+    def test_auto_applicable_subscription_none_available(self):
+        """
+        Tests that when no current, auto-applicable plan is available,
+        CustomerAgreement.auto_applicable_subscription evaluates to null.
+        """
+        agreement = CustomerAgreementFactory.create()
+        # make a plan that's expired
+        SubscriptionPlanFactory.create(
+            customer_agreement=agreement,
+            start_date=localized_datetime(2020, 1, 1),
+            expiration_date=localized_utcnow() + timedelta(days=-1),
+            should_auto_apply_licenses=True,
+        )
+        # make one plan that hasn't started yet
+        SubscriptionPlanFactory.create(
+            customer_agreement=agreement,
+            start_date=localized_utcnow() + timedelta(days=1),
+            should_auto_apply_licenses=True,
+        )
+        self.assertIsNone(agreement.auto_applicable_subscription)
+
     def test_auto_apply_licenses_turned_on_at(self):
         """
         Tests that auto_apply_licenses_turned_on_at returns the correct time.