GoLang password complexity

password_checker.go

package main

import (
	"errors"
	"unicode"
)

func ValidPassword(p string) error {
	if len(p) < 7 {
		return errors.New("invalid password length")
	}

	var (
		uppercasePresent   bool
		lowercasePresent   bool
		numberPresent      bool
		specialCharPresent bool
	)

	for _, r := range p {
		switch {
		case unicode.IsNumber(r):
			numberPresent = true
		case unicode.IsUpper(r):
			uppercasePresent = true
		case unicode.IsLower(r):
			lowercasePresent = true
		case unicode.IsPunct(r) || unicode.IsSymbol(r):
			specialCharPresent = true
		}
	}

	if !lowercasePresent {
		return errors.New("lowercase letter missing")
	}
	if !uppercasePresent {
		return errors.New("uppercase letter missing")
	}
	if !numberPresent {
		return errors.New("numeric character missing")
	}
	if !specialCharPresent {
		return errors.New("special character missing")
	}

	return nil
}