/** RFC 5321 max mailbox length (no angle brackets). */
export const EMAIL_MAX_LEN = 254;

/**
 * Fallback when `HTMLInputElement.checkValidity()` is unavailable (SSR).
 * Matches the HTML living standard’s type=email pattern closely enough
 * for the save-progress field; the live input is the source of truth in
 * the browser.
 */
const EMAIL_FALLBACK_PATTERN =
  /^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$/;

/**
 * Whether a create-flow save-progress email would pass a required
 * `type="email"` input’s `checkValidity()`. Does not trim: native
 * validity rejects leading or trailing spaces.
 */
export function isValidCreateFlowSaveEmail(value: unknown): boolean {
  if (typeof value !== "string") return false;
  if (value.length === 0 || value.length > EMAIL_MAX_LEN) return false;
  // Native type=email rejects whitespace; jsdom’s checkValidity does not.
  if (/\s/.test(value)) return false;
  if (typeof document === "undefined") {
    return EMAIL_FALLBACK_PATTERN.test(value);
  }
  const input = document.createElement("input");
  input.type = "email";
  input.required = true;
  input.value = value;
  return input.checkValidity();
}