corporate: Pass plan_tier parameter to process_initial_upgrade.

Updates `process_initial_upgrade` to take a plan_tier parameter,
so that information can be specific to the type of BillingSession.

Note that ideally the plan tier would be passed as metadata to the
stripe.checkout.Session, but in order to do so, we need to be able
to update the generated stripe fixtures for tests. So for now, we
set the plan tier directly in the stripe event handler code.

corporate/lib/stripe.py

@@ -746,7 +746,7 @@ class RealmBillingSession(BillingSession):
             plan_type = Realm.PLAN_TYPE_STANDARD_FREE
         elif tier == CustomerPlan.STANDARD:
             plan_type = Realm.PLAN_TYPE_STANDARD
-        elif tier == CustomerPlan.PLUS:
+        elif tier == CustomerPlan.PLUS:  # nocoverage # Plus plan doesn't use this code path yet.
             plan_type = Realm.PLAN_TYPE_PLUS
         else:
             raise AssertionError("Unexpected tier")
@@ -1059,6 +1059,7 @@ def do_deactivate_remote_server(remote_server: RemoteZulipServer) -> None:
 @catch_stripe_errors
 def process_initial_upgrade(
     user: UserProfile,
+    plan_tier: int,
     licenses: int,
     automanage_licenses: bool,
     billing_schedule: int,
@@ -1075,7 +1076,7 @@ def process_initial_upgrade(
         period_end,
         price_per_license,
     ) = compute_plan_parameters(
-        CustomerPlan.STANDARD,
+        plan_tier,
         automanage_licenses,
         billing_schedule,
         customer.default_discount,
@@ -1099,7 +1100,7 @@ def process_initial_upgrade(
             "discount": customer.default_discount,
             "billing_cycle_anchor": billing_cycle_anchor,
             "billing_schedule": billing_schedule,
-            "tier": CustomerPlan.STANDARD,
+            "tier": plan_tier,
         }
         if free_trial:
             plan_params["status"] = CustomerPlan.FREE_TRIAL
@@ -1151,7 +1152,7 @@ def process_initial_upgrade(
         )
         stripe.Invoice.finalize_invoice(stripe_invoice)
 
-    billing_session.do_change_plan_type(tier=CustomerPlan.STANDARD)
+    billing_session.do_change_plan_type(tier=plan_tier)
 
 
 def update_license_ledger_for_manual_plan(

corporate/lib/stripe_event_handler.py

@@ -12,7 +12,7 @@ from corporate.lib.stripe import (
     ensure_customer_does_not_have_active_plan,
     process_initial_upgrade,
 )
-from corporate.models import Event, PaymentIntent, Session
+from corporate.models import CustomerPlan, Event, PaymentIntent, Session
 from zerver.models import get_active_user_profile_by_id_in_realm
 
 billing_logger = logging.getLogger("corporate.stripe")
@@ -102,6 +102,7 @@ def handle_checkout_session_completed_event(
         billing_session.update_or_create_stripe_customer(payment_method)
         process_initial_upgrade(
             user,
+            CustomerPlan.STANDARD,
             int(stripe_session.metadata["licenses"]),
             stripe_session.metadata["license_management"] == "automatic",
             int(stripe_session.metadata["billing_schedule"]),
@@ -151,6 +152,7 @@ def handle_payment_intent_succeeded_event(
 
     process_initial_upgrade(
         user,
+        CustomerPlan.STANDARD,
         int(metadata["licenses"]),
         metadata["license_management"] == "automatic",
         int(metadata["billing_schedule"]),

corporate/tests/test_stripe.py

@@ -627,6 +627,7 @@ class StripeTestCase(ZulipTestCase):
         ) -> Any:
             return process_initial_upgrade(
                 self.example_user("hamlet"),
+                CustomerPlan.STANDARD,
                 licenses,
                 automanage_licenses,
                 billing_schedule,

corporate/views/upgrade.py

@@ -142,6 +142,7 @@ def upgrade(
         else:
             process_initial_upgrade(
                 user,
+                CustomerPlan.STANDARD,
                 licenses,
                 automanage_licenses,
                 billing_schedule,