// Single source of truth for "is this a plausible email address" — used
// client-side (checkout, newsletter forms) for immediate on-blur feedback
// and server-side (newsletter subscribe route) as the same check, not a
// second one that could drift out of sync.
const EMAIL_PATTERN = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;

export function isValidEmail(value: string): boolean {
  return EMAIL_PATTERN.test(value);
}

// Returns "" for valid, an error message otherwise.
export function validateEmailFormat(value: string): string {
  if (!value.trim()) return "E-Mail-Adresse ist erforderlich.";
  return isValidEmail(value) ? "" : "Bitte eine gültige E-Mail-Adresse angeben.";
}