const EMAIL_REGEX = /^[^\s@]+@[^\s@]+\.[^\s@]+$/

/**
 * Validates an email address.
 * @param value - The email address to validate
 * @returns An error message if invalid, null if valid or empty
 */
export function validateEmail(value: string): string | null {
  if (!value) {
    return null
  }
  if (!EMAIL_REGEX.test(value)) {
    return "Please enter a valid email address"
  }
  return null
}

/**
 * Validates a Telegram handle.
 * @param value - The Telegram handle to validate (with or without @ prefix)
 * @returns An error message if invalid, null if valid or empty
 */
export function validateTelegram(value: string): string | null {
  if (!value) {
    return null
  }
  const handle = value.startsWith("@") ? value.slice(1) : value
  if (handle.length < 5) {
    return "Telegram handle must be at least 5 characters"
  }
  if (!/^[a-zA-Z0-9_]+$/.test(handle)) {
    return "Telegram handle can only contain letters, numbers, and underscores"
  }
  return null
}