[stripe] Finalized invoce debits, do not set credits to negative when…

… updating

components/usage/pkg/apiv1/billing.go

@@ -108,7 +108,8 @@ func (s *BillingService) FinalizeInvoice(ctx context.Context, in *v1.FinalizeInv
 		ID:            uuid.New(),
 		AttributionID: attributionID,
 		Description:   fmt.Sprintf("Invoice %s finalized in Stripe", invoice.ID),
-		CreditCents:   db.NewCreditCents(float64(creditsOnInvoice)),
+		// Apply negative value of credits to reduce accrued credit usage
+		CreditCents:   db.NewCreditCents(float64(-creditsOnInvoice)),
 		EffectiveTime: db.NewVarcharTime(finalizedAt),
 		Kind:          db.InvoiceUsageKind,
 		Draft:         false,

components/usage/pkg/stripe/stripe.go

@@ -131,6 +131,16 @@ func (c *Client) findCustomers(ctx context.Context, query string) ([]*stripe.Cus
 }
 
 func (c *Client) updateUsageForCustomer(ctx context.Context, customer *stripe.Customer, credits int64) (*UsageRecord, error) {
+	if credits < 0 {
+		log.WithField("customer_id", customer.ID).
+			WithField("customer_name", customer.Name).
+			WithField("credits", credits).
+			Infof("Received request to update customer %s usage to negative value, updating to 0 instead.", customer.ID)
+
+		// nullify any existing usage, but do not set it to negative value - negative invoice doesn't make sense...
+		credits = 0
+	}
+
 	subscriptions := customer.Subscriptions.Data
 	if len(subscriptions) != 1 {
 		return nil, fmt.Errorf("customer has an unexpected number of subscriptions %v (expected 1, got %d)", subscriptions, len(subscriptions))