all the refactor

pkg/cart/tax.go

@@ -1,58 +1,24 @@
 package cart
 
+import (
+	"git.k6n.net/mats/platform/money"
+	"git.k6n.net/mats/platform/tax"
+)
+
 // TaxProvider computes taxes for orders and line items.
-// It mirrors the PaymentProvider and ShippingProvider seam patterns: one
-// interface, interchangeable implementations.
-//
-// All tax rates are expressed as raw percent (e.g. 25 = 25 %). This matches the
-// OrderLine.tax_rate proto convention.
-type TaxProvider interface {
-	// Name returns the provider name for identification (logging, metrics).
-	Name() string
+// The canonical definition is now in platform/tax; this is a type alias
+// for backward compatibility.
+type TaxProvider = tax.Provider
 
-	// ComputeTax computes the tax portion from a gross (inc-VAT) total and tax
-	// rate. Both total and return value are in minor currency units (ore).
-	// taxRate is expressed as raw percent (e.g. 25 = 25 %).
-	//
-	// Formula: tax = total x rate / (100 + rate)
-	//
-	// When taxRate <= 0 the result is 0 (untaxed / zero-rated items).
-	ComputeTax(total int64, taxRate int) int64
-
-	// DefaultTaxRate returns the default VAT rate for a country, expressed as
-	// raw percent (e.g. 25 = 25 %). Used for deliveries and items where no
-	// explicit rate was recorded at add-to-cart time.
-	//
-	// Return 0 if the country is unknown or untaxed.
-	DefaultTaxRate(country string) int
+// ComputeTax returns the VAT portion of an inc-VAT total. rateBp is basis points
+// (2500 = 25%). Re-exported from platform/tax.
+func ComputeTax(total money.Cents, rateBp int) money.Cents {
+	return money.Cents(tax.Compute(total.Int64(), rateBp))
 }
 
-// ComputeTax is the shared tax formula: tax = total x rate / (100 + rate).
-// taxRate is raw percent (e.g. 25 = 25 %). When taxRate <= 0 the result is 0.
-//
-// This differs from GetTaxAmount which uses the CartItem convention
-// (percent x 100, e.g. 2500 = 25.00 %) with formula total x rate / (10000 + rate).
-func ComputeTax(total int64, taxRate int) int64 {
-	if taxRate <= 0 {
-		return 0
-	}
-	return total * int64(taxRate) / int64(100+taxRate)
-}
+// StaticTaxProvider is a stateless, always-available TaxProvider.
+// Re-exported from platform/tax for backward compatibility.
+type StaticTaxProvider = tax.Static
 
-// StaticTaxProvider is a stateless, always-available TaxProvider that simply
-// runs the formula without any country-specific rates. Use for local dev,
-// tests, and as a no-dependency default.
-type StaticTaxProvider struct{}
-
-var _ TaxProvider = (*StaticTaxProvider)(nil)
-
-func NewStaticTaxProvider() *StaticTaxProvider { return &StaticTaxProvider{} }
-
-func (p *StaticTaxProvider) Name() string { return "static" }
-
-func (p *StaticTaxProvider) ComputeTax(total int64, taxRate int) int64 {
-	return ComputeTax(total, taxRate)
-}
-
-// DefaultTaxRate returns 0 for any country (no awareness).
-func (p *StaticTaxProvider) DefaultTaxRate(_ string) int { return 0 }
+// NewStaticTaxProvider returns a new StaticTaxProvider.
+func NewStaticTaxProvider() *StaticTaxProvider { return tax.NewStatic() }