Humanize numbers in go

humanize.go

package main

import (
	"fmt"
	"regexp"
	"strconv"
)

func Currency(ammount interface{}) (string, error) {
	var ok bool
	var orig string
	var err error

	if orig, ok = ammount.(string); ok {
		if ammount, err = strconv.ParseFloat(orig, 64); err != nil {
			return "", err
		}
	}

	if _, ok := ammount.(float64); ok {
		ammountInt := int(ammount.(float64))

		if ammount == float64(ammountInt) {
			ammount = ammountInt
		} else {
			orig = fmt.Sprintf("%f", ammount)
		}
	}

	if _, ok := ammount.(int); ok {
		orig = fmt.Sprintf("%d", ammount)
	}

	return comma(orig), nil
}

func comma(ammount string) string {

	re := regexp.MustCompile("^(-?[0-9]+)([0-9]{3})")
	nu := re.ReplaceAllString(ammount, "${1},${2}")

	if ammount == nu {
		fmt.Println(ammount)
		re = regexp.MustCompile("\\.([0-9]{1,2})([0-9]+)?")
		return re.ReplaceAllString(ammount, ".${1}")
	}

	return comma(nu)

}

humanize_test.go

package main

import "testing"

type testCase struct {
	currency  interface{}
	converted string
	hasErr    bool
}

func TestCurrency(t *testing.T) {
	tests := []testCase{
		testCase{
			currency:  123,
			converted: "123",
		},
		testCase{
			currency:  1123,
			converted: "1,123",
		},
		testCase{
			currency:  12312,
			converted: "12,312",
		},
		testCase{
			currency:  123123,
			converted: "123,123",
		},
		testCase{
			currency:  123123.1,
			converted: "123,123.10",
		},
		testCase{
			currency:  123123.12,
			converted: "123,123.12",
		},
		testCase{
			currency:  123123.00,
			converted: "123,123",
		},
		testCase{
			currency:  "123123",
			converted: "123,123",
		},
		testCase{
			currency:  "123123.00",
			converted: "123,123",
		},
	}

	for _, test := range tests {
		val, err := Currency(test.currency)
		if test.hasErr == false && err != nil {
			t.Error("expected: nil, got:", err)
		}

		if val != test.converted {
			t.Errorf("expected: %s got: %s", test.converted, val)
		}
	}
}