🤖 money

amadan.net/rastrillo/rastrillo/money

Parse decimal amounts into signed int64 minor units with money. The package uses only the Go standard library.

Install it with:

go get amadan.net/rastrillo/rastrillo/money@v0.1.0

The package is an independent nested module in the Rastrillo repository. Its release tags use the money/ prefix, such as money/v0.1.0.

package main

import (
	"fmt"

	"amadan.net/rastrillo/rastrillo/money"
)

func main() {
	minor, err := money.ParseDecimal("1.299", "BHD")
	fmt.Println(minor, err)
	fmt.Println(money.Decimal(1299, "bhd"))
}

This prints:

1299 <nil>
1.299

MinorUnits(currency string) int returns the number of decimal places: 0, 2, or 3. The lookup ignores case. Unknown and empty currencies use two places. This lookup does not validate currency codes.

CurrencyMinorUnits() map[string]int returns a new, mutable map containing the entries that do not use two places. Changes to that map do not affect later lookups.

ParseDecimal(s, currency string) (int64, error) trims surrounding whitespace and accepts a leading sign and a decimal dot. Blank input returns zero. It rejects exponents, grouping marks, commas, invalid syntax, and values outside signed int64. Extra fractional digits are allowed only when they are all zero. It uses integer arithmetic and never rounds.

Decimal(minor int64, currency string) string formats every signed int64, including math.MinInt64, without grouping.

This package does not format for a locale. In a rastrillo app, currency does. Keep price limits, tax, exchange rates and payment-provider scaling in your application.

The storage set

MinorUnits answers for any code, guessing two places for one it does not know. Rastrillo stores an amount only in a currency whose minor units ISO 4217 and this package agree on. That is 174 codes. 153 of them can be the currency of a new record; the other 21, such as HRK and SLL, stay for records that already use them.

currency.Normalize checks a code against the set. A code outside it, such as XAU, CLF or a typo like KDW, is refused rather than given a guessed scale. The set only grows: removing a code or changing its exponent fails the build.

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