Tweak subscriptions some more

svelte/src/lib/NovaAPI.ts

@@ -208,6 +208,20 @@ export const subscription_periods: SubscriptionPeriod[] = [
 // same value the server divides the monthly fee by
 export const days_per_month = 365.25 / 12
 
+// The price of the subscription period the user is in. This is also how far
+// the balance can go below zero before usage above the plan is refused
+export const period_price = (u: User) => {
+	const period = subscription_periods.find(p => p.months === u.subscription_months)
+	return period === undefined ? 0 :
+		u.subscription.monthly_fee * period.months * period.discount
+}
+
+// Whether usage above a limit of the plan is billed instead of refused. price
+// is what the plan charges for that usage. The server does the same check in
+// billsExtra
+export const bills_extra = (u: User, price: number) =>
+	u.usage_based_billing && price > 0 && u.balance_micro_eur >= -period_price(u)
+
 export const get_misc_subscriptions = async () => {
 	return await check_response(
 		await fetch(get_endpoint() + "/misc/subscriptions")