billing: Note applied discount on upgrade and billing pages.

Fixes #27526

corporate/lib/stripe.py

@@ -99,6 +99,19 @@ def format_money(cents: float) -> str:
     return f"{dollars:.{precision}f}"
 
 
+def format_discount_percentage(discount: Optional[Decimal]) -> Optional[str]:
+    if type(discount) is not Decimal:
+        return None
+
+    # Even though it looks like /activity/support only finds integers valid,
+    # this will look good for any custom discounts that we apply.
+    if discount * 100 % 100 == 0:
+        precision = 0
+    else:
+        precision = 2  # nocoverage
+    return f"{discount:.{precision}f}"
+
+
 def get_latest_seat_count(realm: Realm) -> int:
     return get_seat_count(realm, extra_non_guests_count=0, extra_guests_count=0)
 
@@ -1215,6 +1228,7 @@ class BillingSession(ABC):
                     "fixed_price": fixed_price,
                     "price_per_license": price_per_license,
                     "is_sponsorship_pending": customer.sponsorship_pending,
+                    "discount_percent": format_discount_percentage(customer.default_discount),
                 }
         return context
 
@@ -1256,6 +1270,7 @@ class BillingSession(ABC):
                 "monthly_price": get_price_per_license(tier, CustomerPlan.MONTHLY, percent_off),
             },
             "manual_license_management": initial_upgrade_request.manual_license_management,
+            "discount_percent": format_discount_percentage(percent_off),
         }
 
         # Check if user was successful in adding a card and we are rendering the page again.

templates/corporate/billing.html

@@ -169,6 +169,11 @@
                                 {% else %}
                                     {{ "1 month" if billing_frequency == "Monthly" else "12 months" }}
                                 {% endif %})
+                                {% if discount_percent %}
+                                <br />
+                                <i class="billing-page-discount">(includes {{ discount_percent }}% discount)</i>
+                                {% endif %}
+
                             {% endif %}
                             {% endif %}
                         {% else %}

templates/corporate/upgrade.html

@@ -87,6 +87,9 @@
                                 {{ 'user' if seat_count == 1 else 'users' }}
                             </span> x
                             <span class="due-today-duration"></span>
+                            {% if discount_percent %}
+                            <i class="billing-page-discount">(includes {{ discount_percent }}% discount)</i>
+                            {% endif %}
                             <h1>$<span class="due-today-price"></span></h1>
                         </div>
                     </div>

web/styles/portico/billing.css

@@ -647,3 +647,8 @@ input[name="licenses"] {
 #sponsorship-form #sponsorship-button {
     width: 100%;
 }
+
+.billing-page-discount {
+    opacity: 0.8;
+    font-weight: 400;
+}