wangjia
90 lines
2.2 KiB
Go
90 lines
2.2 KiB
Go
// Package money represents amounts as int64 minor units + a currency code.
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// CNY/USD = 分 (1e-2), USDT = micro (1e-6). No float, no "元 string" (v2).
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package money
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import (
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"errors"
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"fmt"
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"math"
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"strconv"
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"strings"
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)
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var ErrUnknownCurrency = errors.New("money: unknown currency")
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var exponents = map[string]int{
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"CNY": 2,
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"USD": 2,
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"USDT": 6,
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}
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// Exponent returns the number of decimal places for a currency.
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func Exponent(currency string) (int, bool) {
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e, ok := exponents[strings.ToUpper(currency)]
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return e, ok
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}
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// Format renders minor units as a decimal string, trailing zeros trimmed.
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func Format(minor int64, currency string) (string, error) {
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exp, ok := Exponent(currency)
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if !ok {
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return "", ErrUnknownCurrency
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}
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if exp == 0 {
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return strconv.FormatInt(minor, 10), nil
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}
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neg := minor < 0
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if neg {
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minor = -minor
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}
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div := int64(math.Pow10(exp))
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whole := minor / div
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frac := minor % div
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s := fmt.Sprintf("%d.%0*d", whole, exp, frac)
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s = strings.TrimRight(s, "0")
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s = strings.TrimRight(s, ".")
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if neg {
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s = "-" + s
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}
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return s, nil
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}
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// Parse converts a decimal string to minor units for the currency. It rejects
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// values with more fractional digits than the currency allows.
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func Parse(s, currency string) (int64, error) {
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exp, ok := Exponent(currency)
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if !ok {
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return 0, ErrUnknownCurrency
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}
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s = strings.TrimSpace(s)
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neg := strings.HasPrefix(s, "-")
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s = strings.TrimPrefix(s, "-")
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intPart, fracPart := s, ""
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if i := strings.IndexByte(s, '.'); i >= 0 {
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intPart, fracPart = s[:i], s[i+1:]
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}
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if len(fracPart) > exp {
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return 0, fmt.Errorf("money.Parse: %q exceeds %d dp for %s", s, exp, currency)
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}
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if intPart == "" && fracPart == "" {
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return 0, fmt.Errorf("money.Parse: empty %q", s)
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}
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whole, err := strconv.ParseInt("0"+intPart, 10, 64)
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if err != nil {
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return 0, fmt.Errorf("money.Parse int %q: %w", s, err)
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}
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fracPart += strings.Repeat("0", exp-len(fracPart))
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var frac int64
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if fracPart != "" {
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frac, err = strconv.ParseInt(fracPart, 10, 64)
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if err != nil {
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return 0, fmt.Errorf("money.Parse frac %q: %w", s, err)
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}
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}
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minor := whole*int64(math.Pow10(exp)) + frac
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if neg {
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minor = -minor
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}
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return minor, nil
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}
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