refactor(billing): use fiat currency for invoices (#4774)

Author: turip

openmeter/app/stripe/calculator.go

@@ -12,10 +12,8 @@ import (
 )
 
 // NewStripeCalculator creates a new StripeCalculator.
-func NewStripeCalculator(currencyCode currencyx.Code) (StripeCalculator, error) {
-	currency, err := currencyx.NewCurrencyBuilder(currencyx.CurrencyTypeFiat).
-		WithCode(currencyCode).
-		Build()
+func NewStripeCalculator(currencyCode currencyx.FiatCode) (StripeCalculator, error) {
+	currency, err := currencyCode.AsFiatCurrency()
 	if err != nil {
 		return StripeCalculator{}, fmt.Errorf("failed to get stripe calculator: %w", err)
 	}

openmeter/app/stripe/client/invoice.go

@@ -144,7 +144,7 @@ type CreateInvoiceInput struct {
 	InvoiceID                    string
 	AutomaticTaxEnabled          bool
 	CollectionMethod             billing.CollectionMethod
-	Currency                     currencyx.Code
+	Currency                     currencyx.FiatCode
 	DaysUntilDue                 *int64
 	StatementDescriptor          *string
 	StripeCustomerID             string

openmeter/billing/charges/creditpurchase/service/create.go

@@ -95,9 +95,8 @@ func (s *service) buildInvoiceCreditPurchaseGatheringLine(charge creditpurchase.
 
 	// Total cost = credit amount * cost basis (e.g., 100 credits * $0.5 = $50)
 	totalCost := intent.CreditAmount.Mul(invoiceSettlement.CostBasis)
-	calc, err := currencyx.NewCurrencyBuilder(currencyx.CurrencyTypeFiat).
-		WithCode(invoiceSettlement.Currency).
-		Build()
+	invoiceCurrency := currencyx.FiatCode(invoiceSettlement.Currency)
+	calc, err := invoiceCurrency.AsFiatCurrency()
 	if err != nil {
 		return billing.GatheringLine{}, fmt.Errorf("creating currency calculator: %w", err)
 	}
@@ -134,7 +133,7 @@ func (s *service) buildInvoiceCreditPurchaseGatheringLine(charge creditpurchase.
 					},
 				),
 			),
-			Currency:      invoiceSettlement.Currency,
+			Currency:      invoiceCurrency,
 			ServicePeriod: intent.ServicePeriod,
 			InvoiceAt:     intent.CalculateEffectiveAt(),
 			TaxConfig:     lo.ToPtr(intent.TaxConfig.ToTaxConfig()),

openmeter/billing/charges/flatfee/charge.go

@@ -15,6 +15,7 @@ import (
 	"github.com/openmeterio/openmeter/openmeter/currencies"
 	"github.com/openmeterio/openmeter/openmeter/customer"
 	"github.com/openmeterio/openmeter/openmeter/productcatalog"
+	"github.com/openmeterio/openmeter/pkg/currencyx"
 	"github.com/openmeterio/openmeter/pkg/models"
 	"github.com/openmeterio/openmeter/pkg/timeutil"
 )
@@ -81,6 +82,25 @@ func (c ChargeBase) GetCurrency() currencies.Currency {
 	return c.Intent.GetCurrency()
 }
 
+func (c ChargeBase) GetInvoiceCurrency() (currencyx.FiatCode, error) {
+	currency := c.GetCurrency()
+	if currency.IsFiat() {
+		return currencyx.FiatCode(currency.GetCode()), nil
+	}
+
+	costBasisIntent := c.Intent.GetCostBasisIntent()
+	if costBasisIntent == nil {
+		return "", errors.New("cost basis intent is required for a custom-currency invoice")
+	}
+
+	fiatCurrency, err := costBasisIntent.GetFiatCurrency()
+	if err != nil {
+		return "", fmt.Errorf("getting cost basis fiat currency: %w", err)
+	}
+
+	return fiatCurrency.GetFiatCode(), nil
+}
+
 func (c ChargeBase) ErrorAttributes() models.Attributes {
 	return models.Attributes{
 		"charge_id":   c.ID,

openmeter/billing/charges/flatfee/service/create.go

@@ -195,6 +195,11 @@ func buildFlatFeeGatheringLine(input buildFlatFeeGatheringLineInput) (billing.Ga
 		managedBy = billing.ManuallyManagedLine
 	}
 
+	invoiceCurrency, err := flatFee.GetInvoiceCurrency()
+	if err != nil {
+		return billing.GatheringLine{}, fmt.Errorf("getting invoice currency: %w", err)
+	}
+
 	gatheringLine := billing.GatheringLine{
 		GatheringLineBase: billing.GatheringLineBase{
 			ManagedResource: models.NewManagedResource(models.ManagedResourceInput{
@@ -217,7 +222,7 @@ func buildFlatFeeGatheringLine(input buildFlatFeeGatheringLineInput) (billing.Ga
 			),
 			FeatureKey: lo.FromPtr(lineIntent.FeatureKey),
 
-			Currency:      lineIntent.Currency.GetCode(),
+			Currency:      invoiceCurrency,
 			ServicePeriod: lineIntent.ServicePeriod,
 			InvoiceAt:     lineIntent.InvoiceAt,
 

openmeter/billing/charges/flatfee/service/linemapper.go

@@ -8,13 +8,10 @@ import (
 
 	"github.com/openmeterio/openmeter/openmeter/billing"
 	"github.com/openmeterio/openmeter/openmeter/billing/charges/flatfee"
-	"github.com/openmeterio/openmeter/pkg/currencyx"
 )
 
 func populateFlatFeeStandardLineFromRun(stdLine *billing.StandardLine, run flatfee.RealizationRun) error {
-	currency, err := currencyx.NewCurrencyBuilder(currencyx.CurrencyTypeFiat).
-		WithCode(stdLine.Currency).
-		Build()
+	currency, err := stdLine.Currency.AsFiatCurrency()
 	if err != nil {
 		return fmt.Errorf("creating currency calculator: %w", err)
 	}

openmeter/billing/charges/flatfee/service/manualedit.go

@@ -78,10 +78,11 @@ func intentFromManualCreatedLine(
 		return flatfee.Intent{}, fmt.Errorf("line id is required")
 	}
 
-	currency, err := currencies.NewFiatCurrency(line.GetCurrency())
+	fiatCurrency, err := line.GetCurrency().AsFiatCurrency()
 	if err != nil {
 		return flatfee.Intent{}, fmt.Errorf("resolving fiat currency %q: %w", line.GetCurrency(), err)
 	}
+	currency := currencies.Currency{Currency: fiatCurrency}
 
 	if chargeID := line.GetChargeID(); chargeID != nil && *chargeID != "" {
 		return flatfee.Intent{}, fmt.Errorf("line[%s]: charge id must be empty for manual create", line.GetID())

openmeter/billing/charges/invoiceupdater/invoiceupdate.go

@@ -320,7 +320,7 @@ func (u *updater) provisionUpcomingLines(ctx context.Context, customerID custome
 		return nil
 	}
 
-	linesByCurrency := lo.GroupBy(lines, func(l billing.GatheringLine) currencyx.Code {
+	linesByCurrency := lo.GroupBy(lines, func(l billing.GatheringLine) currencyx.FiatCode {
 		return l.Currency
 	})
 

openmeter/billing/charges/models/costbasis/intent.go

@@ -130,6 +130,36 @@ func (i Intent) AsDynamic() (DynamicIntent, error) {
 	return *i.dynamic, nil
 }
 
+// GetFiatCurrency returns the fiat currency in which the custom-currency cost
+// basis is expressed, regardless of the selected resolution mode.
+func (i Intent) GetFiatCurrency() (*currencyx.FiatCurrency, error) {
+	switch i.kind {
+	case ModeDynamic:
+		intent, err := i.AsDynamic()
+		if err != nil {
+			return nil, err
+		}
+
+		return intent.FiatCurrency, nil
+	case ModePinned:
+		intent, err := i.AsPinned()
+		if err != nil {
+			return nil, err
+		}
+
+		return intent.FiatCurrency, nil
+	case ModeManual:
+		intent, err := i.AsManual()
+		if err != nil {
+			return nil, err
+		}
+
+		return intent.FiatCurrency, nil
+	default:
+		return nil, models.NewGenericValidationError(fmt.Errorf("invalid intent kind: %s", i.kind))
+	}
+}
+
 type DynamicIntent struct {
 	FiatCurrency *currencyx.FiatCurrency
 }

openmeter/billing/charges/service/create.go

@@ -394,7 +394,7 @@ type currencyAndCustomerID struct {
 }
 
 type currencyCodeAndCustomerID struct {
-	currency   currencyx.Code
+	currency   currencyx.FiatCode
 	customerID customer.CustomerID
 }