package util

// https://github.com/go-pg/pg/blob/7c2d9d39a5cfc18a422c88a9f5f39d8d2cd10030/internal/underscore.go

func isUpper(c byte) bool {
	return c >= 'A' && c <= 'Z'
}

func isLower(c byte) bool {
	return !isUpper(c)
}

func toLower(c byte) byte {
	return c + 32
}

// Underscore converts "CamelCasedString" to "camel_cased_string".
func Underscore(s string) string {
	r := make([]byte, 0, len(s))
	for i := 0; i < len(s); i++ {
		c := s[i]
		if isUpper(c) {
			if i > 0 && i+1 < len(s) && (isLower(s[i-1]) || isLower(s[i+1])) {
				r = append(r, '_', toLower(c))
			} else {
				r = append(r, toLower(c))
			}
		} else {
			r = append(r, c)
		}
	}
	return string(r)
}