bililng: Fix incorrect price per license on billing page.

There is a discrepancy between price per license shown on billing
and upgrade page for annual billing frequency due to difference
in methods used to calculate the amount.

To fix it, we use the same method on both the pages.

I didn't use the helpers.format_money directly here since that would
create a visual delay in showing the price per license which will
not be nice considering that will be the only thing on this page
being updated that way.

The stripe fixture used is same as
free_trial_upgrade_by_card--Customer.retrieve.3.json

corporate/lib/stripe.py

@@ -68,6 +68,20 @@ STRIPE_API_VERSION = "2020-08-27"
 stripe.api_version = STRIPE_API_VERSION
 
 
+# This function imitates the behavior of the format_money in billing/helpers.ts
+def format_money(cents: float) -> str:
+    # allow for small floating point errors
+    cents = math.ceil(cents - 0.001)
+    if cents % 100 == 0:
+        precision = 0
+    else:
+        precision = 2
+
+    dollars = cents / 100
+    # Format the number as a string with the correct number of decimal places
+    return f"{dollars:.{precision}f}"
+
+
 def get_latest_seat_count(realm: Realm) -> int:
     return get_seat_count(realm, extra_non_guests_count=0, extra_guests_count=0)
 

corporate/tests/test_stripe.py

@@ -1208,6 +1208,16 @@ class StripeTest(StripeTestCase):
             invoice_plans_as_needed(add_months(free_trial_end_date, 12))
             [invoice0, invoice1, invoice2] = stripe.Invoice.list(customer=stripe_customer.id)
 
+        # Check /billing/ has correct information for fixed price customers.
+        plan.fixed_price = 127
+        plan.price_per_license = None
+        plan.save(update_fields=["fixed_price", "price_per_license"])
+        with patch("corporate.views.billing_page.timezone_now", return_value=self.now):
+            response = self.client_get("/billing/")
+        self.assert_in_success_response(["$1.27"], response)
+        # Don't show price breakdown
+        self.assert_not_in_success_response(["{self.seat_count} x"], response)
+
     @mock_stripe(tested_timestamp_fields=["created"])
     def test_free_trial_upgrade_by_card_from_onboarding_page(self, *mocks: Mock) -> None:
         user = self.example_user("hamlet")

corporate/views/billing_page.py

@@ -14,6 +14,7 @@ from corporate.lib.stripe import (
     do_change_plan_status,
     downgrade_at_the_end_of_billing_cycle,
     downgrade_now_without_creating_additional_invoices,
+    format_money,
     get_latest_seat_count,
     make_end_of_cycle_updates_if_needed,
     renewal_amount,
@@ -194,15 +195,13 @@ def billing_home(
             )
 
             billing_frequency = CustomerPlan.BILLING_SCHEDULES[plan.billing_schedule]
-            price_per_license_int = plan.price_per_license
-            if price_per_license_int is not None and billing_frequency == "Annual":
-                price_per_license_int = int(price_per_license_int / 12)
 
-            price_per_license = (
-                cents_to_dollar_string(price_per_license_int)
-                if price_per_license_int is not None
-                else None
-            )
+            if plan.price_per_license is None:
+                price_per_license = ""
+            elif billing_frequency == "Annual":
+                price_per_license = format_money(plan.price_per_license / 12)
+            else:
+                price_per_license = format_money(plan.price_per_license)
 
             context.update(
                 plan_name=plan.name,

web/src/billing/helpers.ts

@@ -89,6 +89,7 @@ export function create_ajax_request(
     });
 }
 
+// This function imitates the behavior of the format_money in views/billing_page.py
 export function format_money(cents: number): string {
     // allow for small floating point errors
     cents = Math.ceil(cents - 0.001);