# 🤖 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:

```sh
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`.

```go
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:

```text
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`](/docs/reference/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.