Accounting and Formatting for Golang Shopspring decimal library

accounting.go

package quicka

import (
	"fmt"
	"strings"

	"github.com/shopspring/decimal"
)

// FormatMoneyDecimal ...
func FormatMoneyDecimal(value decimal.Decimal) string {
	return FormatNumberDecimal(value, ".", ",", 2, "$")
}

// FormatNumberDecimal ...
func FormatNumberDecimal(value decimal.Decimal, decimalStr string, thousandStr string, precision int, currencyPrefix string) string {
	if value.Equal(decimal.Zero) || value.Equal(decimal.Zero.Neg()) {
		return fmt.Sprintf("%s0%s00", currencyPrefix, decimalStr)
	}
	reFormat := value.StringFixed(int32(precision))

	// At this point we have -XXXXXXX.YY so remove neg and get our heads and trails
	isNeg := false
	if reFormat[0] == '-' {
		reFormat = strings.ReplaceAll(reFormat, "-", "")
		isNeg = true
	}
	decs := reFormat[strings.Index(reFormat, "."):]
	integral := reFormat[:strings.Index(reFormat, ".")]

	// Add the commas
	for i := len(integral) - 3; i > 0; i -= 3 {
		integral = integral[:i] + thousandStr + integral[i:]
	}

	finalValue := currencyPrefix + integral + decimalStr + decs[1:]
	if isNeg {
		finalValue = "-" + finalValue
	}

	return finalValue
}

accounting_test.go

package quicka

import (
	"testing"

	"github.com/shopspring/decimal"
)

func must(s string) decimal.Decimal {
	d, _ := decimal.NewFromString(s)
	return d
}

func TestFormatMoneyDecimal(t *testing.T) {
	tests := []struct {
		given    string
		expected string
	}{
		{"123.499", "$123.50"},
		{"3456.615", "$3,456.62"},
		{"777888.99", "$777,888.99"},
		{"-77788821412412444424.99", "-$77,788,821,412,412,444,424.99"},
		{"-5432", "-$5,432.00"},
		{"-1234567", "-$1,234,567.00"},
		{"0", "$0.00"},
		{"0.212", "$0.21"},
		{"-0.0", "$0.00"},
	}
	for _, tt := range tests {

		if got := FormatMoneyDecimal(must(tt.given)); got != tt.expected {
			t.Errorf("FormatMoneyDecimal() = %v, want %v", got, tt.expected)
		}

	}
}

func TestFormatMoneyFromDecimal(t *testing.T) {
	tests := []struct {
		given    decimal.Decimal
		expected string
	}{
		{must("123.5"), "$123.50"},
		{must("3456.615"), "$3,456.62"},
		{must("777888.99"), "$777,888.99"},
		{must("-5432"), "-$5,432.00"},
		{must("-1234567"), "-$1,234,567.00"},
		{must("0"), "$0.00"},
		{must("0.212"), "$0.21"},
		{must("-0.0"), "$0.00"},
	}
	for _, tt := range tests {

		if got := FormatMoneyDecimal(tt.given); got != tt.expected {
			t.Errorf("FormatMoneyDecimal() = %v, want %v", got, tt.expected)
		}

	}
}