feat(invoice): commitment charge

openmeter/app/stripe/entity/app/invoice.go

@@ -509,10 +509,19 @@ func getStripeAddLinesLineParams(isInteger bool, line *billing.Line, calculator
 		}
 	}
 
+	amount := line.Totals.Amount
+
+	// Handle usage based commitments like minimum spend
+	if amount.IsZero() {
+		// ChargesTotal is the amount of value of the line that are due to additional charges.
+		// If the line is a commitment we use the total charges.
+		amount = line.Totals.ChargesTotal
+	}
+
 	// Otherwise we add the calculated total with with quantity one
 	return &stripe.InvoiceAddLinesLineParams{
 		Description: lo.ToPtr(name),
-		Amount:      lo.ToPtr(calculator.RoundToAmount(line.Totals.Amount)),
+		Amount:      lo.ToPtr(calculator.RoundToAmount(amount)),
 		Quantity:    lo.ToPtr(int64(1)),
 		Period:      period,
 		Metadata: map[string]string{

test/app/stripe/invoice_test.go

@@ -580,8 +580,7 @@ func (s *StripeInvoiceTestSuite) TestComplexInvoice() {
 				},
 			},
 			{
-				// FIXME(pmarton): should be 162300
-				Amount:      lo.ToPtr(int64(0)),
+				Amount:      lo.ToPtr(int64(162300)),
 				Description: lo.ToPtr("UBP - Tiered volume: minimum spend"),
 				Period: &stripe.InvoiceAddLinesLinePeriodParams{
 					// TODO: check rounding