Add a way to register custom currencies

register.go

@@ -0,0 +1,91 @@
+package currency
+
+import (
+	"fmt"
+)
+
+// EmptyCurrencyCodeError indicates that the currency code was empty.
+type EmptyCurrencyCodeError struct{}
+
+func (e EmptyCurrencyCodeError) Error() string {
+	return "register currency error: empty currency code"
+}
+
+// CurrencyAlreadyExistsError indicates that the currency code already exists in the ISO list.
+type CurrencyAlreadyExistsError struct {
+	Code string
+}
+
+func (e CurrencyAlreadyExistsError) Error() string {
+	return fmt.Sprintf("register currency error: code %q already exists in ISO list", e.Code)
+}
+
+// RegisterCurrencyOptions defines parameters for registering a new or custom currency.
+type RegisterCurrencyOptions struct {
+	// NumericCode is usually a three-digit code, for example "999".
+	NumericCode string
+
+	// Digits is the number of decimal fraction digits.
+	Digits uint8
+
+	// SymbolData is a list of possible symbols and the locales
+	// in which each symbol is used.
+	//
+	// Example:
+	//    []SymbolData{
+	//       {Symbol: "₿", Locales: []string{"en"}},
+	//       {Symbol: "BTC", Locales: []string{"uk"}},
+	//    }
+	SymbolData []SymbolData
+}
+
+// SymbolData describes one symbol and the set of locales
+// for which that symbol applies.
+type SymbolData struct {
+	Symbol  string
+	Locales []string
+}
+
+// RegisterCurrency adds a non-ISO currency to the global structures:
+//   - currencies
+//   - currencyCodes
+//   - currencySymbols
+//
+// It returns an error if the code already exists in the ISO list, or if the code is empty.
+func RegisterCurrency(code string, opts RegisterCurrencyOptions) error {
+	if code == "" {
+		return EmptyCurrencyCodeError{}
+	}
+	if _, isoExists := currencies[code]; isoExists {
+		return CurrencyAlreadyExistsError{Code: code}
+	}
+
+	// Insert into the global `currencies` map.
+	currencies[code] = currencyInfo{
+		numericCode: opts.NumericCode,
+		digits:      opts.Digits,
+	}
+
+	// Also append to currencyCodes, so that GetCurrencyCodes() is aware of it.
+	currencyCodes = append(currencyCodes, code)
+
+	// If SymbolData is provided, insert symbols into currencySymbols.
+	if len(opts.SymbolData) > 0 {
+		// Ensure there's a slice for 'code' in currencySymbols.
+		if _, ok := currencySymbols[code]; !ok {
+			currencySymbols[code] = []symbolInfo{}
+		}
+		// Add each entry from opts.SymbolData.
+		for _, s := range opts.SymbolData {
+			currencySymbols[code] = append(
+				currencySymbols[code],
+				symbolInfo{
+					symbol:  s.Symbol,
+					locales: s.Locales,
+				},
+			)
+		}
+	}
+
+	return nil
+}

register_test.go

@@ -0,0 +1,51 @@
+package currency
+
+import (
+	"testing"
+)
+
+func TestRegisterCurrencyBTC(t *testing.T) {
+	err := RegisterCurrency("BTC", RegisterCurrencyOptions{
+		NumericCode: "1000",
+		Digits:      8,
+		SymbolData: []SymbolData{
+			{
+				Symbol:  "₿",
+				Locales: []string{"en"},
+			},
+			{
+				Symbol:  "BTC",
+				Locales: []string{"uk"},
+			},
+		},
+	})
+	if err != nil {
+		t.Errorf("RegisterCurrency returned an error for BTC: %v", err)
+	}
+
+	if !IsValid("BTC") {
+		t.Error("Expected 'BTC' to be valid after registration, but IsValid returned false.")
+	}
+
+	d, ok := GetDigits("BTC")
+	if !ok {
+		t.Error("Expected 'BTC' to be found, but GetDigits says not ok.")
+	} else if d != 8 {
+		t.Errorf("Expected 'BTC' digits=8, got %d", d)
+	}
+
+	symEN, _ := GetSymbol("BTC", NewLocale("en")) // "₿"
+	if symEN != "₿" {
+		t.Errorf("Expected '₿' for locale 'en', got '%s'", symEN)
+	}
+
+	symRU, _ := GetSymbol("BTC", NewLocale("uk")) // "BTC"
+	if symRU != "BTC" {
+		t.Errorf("Expected 'BTC' for locale 'uk', got '%s'", symRU)
+	}
+
+	err = RegisterCurrency("BTC", RegisterCurrencyOptions{})
+	if err == nil {
+		t.Error("Expected an error when re-registering code 'BTC', but got nil.")
+	}
+}