cashless2ecash

amount.go (5420B)

---

 // This file is part of taler-go, the Taler Go implementation.
 // Copyright (C) 2022 Martin Schanzenbach
 // Copyright (C) 2024 Joel Häberli
 //
 // Taler Go is free software: you can redistribute it and/or modify it
 // under the terms of the GNU Affero General Public License as published
 // by the Free Software Foundation, either version 3 of the License,
 // or (at your option) any later version.
 //
 // Taler Go is distributed in the hope that it will be useful, but
 // WITHOUT ANY WARRANTY; without even the implied warranty of
 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 // Affero General Public License for more details.
 //
 // You should have received a copy of the GNU Affero General Public License
 // along with this program.  If not, see <http://www.gnu.org/licenses/>.
 //
 // SPDX-License-Identifier: AGPL3.0-or-later
 
 package main
 
 import (
 	"errors"
 	"fmt"
 	"math"
 	"strconv"
 	"strings"
 )
 
 // The GNU Taler Amount object
 type Amount struct {
 
 	// The type of currency, e.g. EUR
 	Currency string `json:"currency"`
 
 	// The value (before the ".")
 	Value uint64 `json:"value"`
 
 	// The fraction (after the ".", optional)
 	Fraction uint64 `json:"fraction"`
 }
 
 func FormatAmount(amount *Amount, fractionalDigits int) string {
 
 	if amount == nil {
 		return ""
 	}
 
 	if amount.Currency == "" && amount.Value == 0 && amount.Fraction == 0 {
 		return ""
 	}
 
 	if amount.Fraction <= 0 {
 		return fmt.Sprintf("%s:%d", amount.Currency, amount.Value)
 	}
 
 	fractionStr := toFractionStr(int(amount.Fraction), fractionalDigits)
 	return fmt.Sprintf("%s:%d.%s", amount.Currency, amount.Value, fractionStr)
 }
 
 // The maximim length of a fraction (in digits)
 const FractionalLength = 8
 
 // The base of the fraction.
 const FractionalBase = 1e8
 
 // The maximum value
 var MaxAmountValue = uint64(math.Pow(2, 52))
 
 // Create a new amount from value and fraction in a currency
 func NewAmount(currency string, value uint64, fraction uint64) Amount {
 	return Amount{
 		Currency: currency,
 		Value:    value,
 		Fraction: fraction,
 	}
 }
 
 func toFractionStr(frac int, fractionalDigits int) string {
 
 	if fractionalDigits > 8 {
 		return ""
 	}
 
 	leadingZerosStr := ""
 	strLengthTens := int(math.Pow10(fractionalDigits - 1))
 	strLength := int(math.Log10(float64(strLengthTens)))
 	leadingZeros := 0
 	if strLengthTens > frac {
 		for i := 0; i < strLength; i++ {
 			if strLengthTens > frac {
 				leadingZeros++
 				strLengthTens = strLengthTens / 10
 			}
 		}
 		for i := 0; i < leadingZeros; i++ {
 			leadingZerosStr += "0"
 		}
 	}
 
 	return leadingZerosStr + strconv.Itoa(frac)
 }
 
 // Subtract the amount b from a and return the result.
 // a and b must be of the same currency and a >= b
 func (a *Amount) Sub(b Amount) (*Amount, error) {
 	if a.Currency != b.Currency {
 		return nil, errors.New("currency mismatch")
 	}
 	v := a.Value
 	f := a.Fraction
 	if a.Fraction < b.Fraction {
 		v -= 1
 		f += FractionalBase
 	}
 	f -= b.Fraction
 	if v < b.Value {
 		return nil, errors.New("amount overflow")
 	}
 	v -= b.Value
 	r := Amount{
 		Currency: a.Currency,
 		Value:    v,
 		Fraction: f,
 	}
 	return &r, nil
 }
 
 // Add b to a and return the result.
 // Returns an error if the currencies do not match or the addition would
 // cause an overflow of the value
 func (a *Amount) Add(b Amount) (*Amount, error) {
 	if a.Currency != b.Currency {
 		return nil, errors.New("currency mismatch")
 	}
 	v := a.Value +
 		b.Value +
 		uint64(math.Floor((float64(a.Fraction)+float64(b.Fraction))/FractionalBase))
 
 	if v >= MaxAmountValue {
 		return nil, fmt.Errorf("amount overflow (%d > %d)", v, MaxAmountValue)
 	}
 	f := uint64((a.Fraction + b.Fraction) % FractionalBase)
 	r := Amount{
 		Currency: a.Currency,
 		Value:    v,
 		Fraction: f,
 	}
 	return &r, nil
 }
 
 // Parses an amount string in the format <currency>:<value>[.<fraction>]
 func ParseAmount(s string, fractionDigits int) (*Amount, error) {
 
 	if s == "" {
 		return &Amount{"", 0, 0}, nil
 	}
 
 	if !strings.Contains(s, ":") {
 		return nil, fmt.Errorf("invalid amount: %s", s)
 	}
 
 	currencyAndAmount := strings.Split(s, ":")
 	if len(currencyAndAmount) != 2 {
 		return nil, fmt.Errorf("invalid amount: %s", s)
 	}
 
 	currency := currencyAndAmount[0]
 	valueAndFraction := strings.Split(currencyAndAmount[1], ".")
 	if len(valueAndFraction) < 1 && len(valueAndFraction) > 2 {
 		return nil, fmt.Errorf("invalid value and fraction part in amount %s", s)
 	}
 	value, err := strconv.Atoi(valueAndFraction[0])
 	if err != nil {
 		return nil, fmt.Errorf("invalid value in amount %s", s)
 	}
 
 	fraction := 0
 	if len(valueAndFraction) == 2 {
 		if len(valueAndFraction[1]) > fractionDigits {
 			return nil, fmt.Errorf("invalid amount: %s expected at max %d fractional digits", s, fractionDigits)
 		}
 		fractionInt, err := strconv.Atoi(valueAndFraction[1])
 		if err != nil {
 			return nil, fmt.Errorf("invalid fraction in amount %s", s)
 		}
 		fraction = fractionInt
 	}
 
 	a := NewAmount(currency, uint64(value), uint64(fraction))
 	return &a, nil
 }
 
 // Check if this amount is zero
 func (a *Amount) IsZero() bool {
 	return (a.Value == 0) && (a.Fraction == 0)
 }
 
 // Returns the string representation of the amount: <currency>:<value>[.<fraction>]
 // Omits trailing zeroes.
 func (a *Amount) String() string {
 	v := strconv.FormatUint(a.Value, 10)
 	if a.Fraction != 0 {
 		f := strconv.FormatUint(a.Fraction, 10)
 		f = strings.TrimRight(f, "0")
 		v = fmt.Sprintf("%s.%s", v, f)
 	}
 	return fmt.Sprintf("%s:%s", a.Currency, v)
 }