ToSnakeCase.go

package main

import (
	"fmt"
	"regexp"
	"strings"
)

var (
	matchBeforeCap = regexp.MustCompile("([a-z])([A-Z])")
	matchAfterCap  = regexp.MustCompile("([^_])([A-Z][a-rt-z])")
)

// ToSnakeCase to to_snake_case
func ToSnakeCase(str string) string {
	str = matchBeforeCap.ReplaceAllString(str, "${1}_${2}")
	str = matchAfterCap.ReplaceAllString(str, "${1}_${2}")
	return strings.ToLower(str)
}

func main() {
	cases := map[string]string{
		"ToSnakeCase": "to_snake_case",
		"TimeSPALoad": "time_spa_load",
		"TTI":         "tti",
		"CPUs":        "cpus",
		"Action":      "action",
		"SiteID":      "site_id",
	}

	for c, e := range cases {
		if g := ToSnakeCase(c); g != e {
			fmt.Printf("ToSnakeCase(%q) should be %q but got %q\n", c, e, g)
		}
	}
}