plumber/internal/store/email.go

package store

import (
	"fmt"
	"net/mail"
	"strings"
	"unicode/utf8"
)

const (
	minEmailLen = 3
	maxEmailLen = 254
)

// NormalizeEmail trims and lowercases an address for storage/comparison.
func NormalizeEmail(s string) string {
	return strings.ToLower(strings.TrimSpace(s))
}

// ValidateEmail returns a normalized address or an error message suitable for UI.
func ValidateEmail(raw string) (normalized string, errMsg string) {
	normalized = NormalizeEmail(raw)
	if normalized == "" {
		return "", "Email is required."
	}
	n := utf8.RuneCountInString(normalized)
	if n < minEmailLen || len(normalized) > maxEmailLen {
		return "", "Enter a valid email address."
	}
	addr, err := mail.ParseAddress(normalized)
	if err != nil || addr.Address != normalized {
		return "", "Enter a valid email address."
	}
	at := strings.LastIndex(normalized, "@")
	if at < 1 || at == len(normalized)-1 {
		return "", "Enter a valid email address."
	}
	domain := normalized[at+1:]
	if !strings.Contains(domain, ".") || strings.HasPrefix(domain, ".") || strings.HasSuffix(domain, ".") {
		return "", "Enter a valid email address."
	}
	return normalized, ""
}

// MustValidateEmail is like ValidateEmail but returns a Go error.
func MustValidateEmail(raw string) (string, error) {
	n, msg := ValidateEmail(raw)
	if msg != "" {
		return "", fmt.Errorf("%s", msg)
	}
	return n, nil
}