converter/domain/entities.go

package domain

import (
	"errors"
	"fmt"
	"strings"
	"time"

	"github.com/shopspring/decimal"
)

// Domain-specific errors
var (
	ErrInvalidCurrency     = errors.New("invalid currency")
	ErrInvalidAmount       = errors.New("invalid amount")
	ErrNegativeAmount      = errors.New("amount cannot be negative")
	ErrInvalidRate         = errors.New("invalid exchange rate")
	ErrCurrencyMismatch    = errors.New("currency mismatch")
	ErrRateNotFound        = errors.New("exchange rate not found")
	ErrUnsupportedCurrency = errors.New("unsupported currency")
)

// Currency represents a currency with its metadata
type Currency struct {
	Code      string
	Name      string
	Precision int
}

// NewCurrency creates a new Currency with validation
func NewCurrency(code, name string, precision int) (Currency, error) {
	if strings.TrimSpace(code) == "" {
		return Currency{}, ErrInvalidCurrency
	}

	if precision < 0 {
		return Currency{}, ErrInvalidCurrency
	}

	return Currency{
		Code:      strings.ToUpper(strings.TrimSpace(code)),
		Name:      strings.TrimSpace(name),
		Precision: precision,
	}, nil
}

// String returns the currency code
func (c Currency) String() string {
	return c.Code
}

// Money represents an amount in a specific currency
type Money struct {
	Amount   decimal.Decimal
	Currency Currency
}

// NewMoney creates a new Money instance from string amount
func NewMoney(amount string, currency Currency) (Money, error) {
	if strings.TrimSpace(amount) == "" {
		return Money{}, ErrInvalidAmount
	}

	decimalAmount, err := decimal.NewFromString(strings.TrimSpace(amount))
	if err != nil {
		return Money{}, ErrInvalidAmount
	}

	if decimalAmount.IsNegative() {
		return Money{}, ErrNegativeAmount
	}

	return Money{
		Amount:   decimalAmount,
		Currency: currency,
	}, nil
}

// NewMoneyFromDecimal creates a new Money instance from decimal.Decimal
func NewMoneyFromDecimal(amount decimal.Decimal, currency Currency) (Money, error) {
	if amount.IsNegative() {
		return Money{}, ErrNegativeAmount
	}

	return Money{
		Amount:   amount,
		Currency: currency,
	}, nil
}

// String returns formatted money representation
func (m Money) String() string {
	return fmt.Sprintf("%s %s", m.Amount.StringFixed(int32(m.Currency.Precision)), m.Currency.Code)
}

// Rate represents an exchange rate between two currencies
type Rate struct {
	From      Currency
	To        Currency
	Value     decimal.Decimal
	Timestamp time.Time
	Source    string
}

// NewRate creates a new Rate with validation
func NewRate(from, to Currency, value decimal.Decimal, source string) (Rate, error) {
	if from.Code == to.Code {
		return Rate{}, ErrInvalidRate
	}

	if value.IsNegative() || value.IsZero() {
		return Rate{}, ErrInvalidRate
	}

	return Rate{
		From:      from,
		To:        to,
		Value:     value,
		Timestamp: time.Now(),
		Source:    strings.TrimSpace(source),
	}, nil
}


// String returns formatted rate representation
func (r Rate) String() string {
	return fmt.Sprintf("1 %s = %s %s",
		r.From.Code,
		r.Value.StringFixed(int32(r.To.Precision)),
		r.To.Code)
}