billing: Separate initial upgrade logic to another function.

zilencer/lib/stripe.py

@@ -9,6 +9,7 @@ from django.conf import settings
 from django.db import transaction
 from django.utils.translation import ugettext as _
 from django.core.signing import Signer
+from django.core import signing
 import stripe
 
 from zerver.lib.exceptions import JsonableError
@@ -177,3 +178,27 @@ def do_subscribe_customer_to_plan(stripe_customer: stripe.Customer, stripe_plan_
                 event_time=timestamp_to_datetime(stripe_subscription.created),
                 requires_billing_update=True,
                 extra_data=ujson.dumps({'quantity': current_seat_count}))
+
+def process_initial_upgrade(user: UserProfile, plan: str, signed_seat_count: str,
+                            salt: str, stripe_token: str) -> Optional[str]:
+    if plan not in [Plan.CLOUD_ANNUAL, Plan.CLOUD_MONTHLY]:
+        billing_logger.warning("Tampered plan during realm upgrade. user: %s, realm: %s (%s)."
+                               % (user.id, user.realm.id, user.realm.string_id))
+        return "Something went wrong. Please contact support@zulipchat.com"
+    try:
+        seat_count = int(unsign_string(signed_seat_count, salt))
+    except signing.BadSignature:
+        billing_logger.warning("Tampered seat count during realm upgrade. user: %s, realm: %s (%s)."
+                               % (user.id, user.realm.id, user.realm.string_id))
+        return "Something went wrong. Please contact support@zulipchat.com"
+
+    stripe_customer = do_create_customer_with_payment_source(user, stripe_token)
+    do_subscribe_customer_to_plan(
+        stripe_customer=stripe_customer,
+        stripe_plan_id=Plan.objects.get(nickname=plan).stripe_plan_id,
+        seat_count=seat_count,
+        # TODO: billing address details are passed to us in the request;
+        # use that to calculate taxes.
+        tax_percent=0)
+    # TODO: check for errors and raise/send to frontend
+    return None