/**
 * Small cookie helpers for the presentational choices that ride in cookies
 * (colour scheme, whether the menu shows) so the server can render them on
 * the first pass, where localStorage would only reach the page after
 * hydration and paint one layout before snapping to the other.
 */

/** A year: the merchant should not have to re-pick every session. */
const PREFERENCE_COOKIE_MAX_AGE_SECONDS = 31536000;

/**
 * Reads one cookie out of a raw Cookie header.
 *
 * @param {string | null} cookieHeader - The request's raw Cookie header
 * @param {string} name - The cookie's name
 * @returns {string | null} Its value, or null when absent
 */
export function readCookie(
  cookieHeader: string | null,
  name: string
): string | null {
  const match = new RegExp(`(?:^|;\\s*)${name}=([^;]*)(?:;|$)`).exec(
    cookieHeader ?? ''
  );
  return match ? match[1] : null;
}

/** What a preference cookie carries besides its value. */
interface PreferenceCookieOptions {
  /** Add ``Secure``; omitted on plain HTTP, where the browser would drop it. */
  secure?: boolean;
}

/**
 * The ``Set-Cookie`` value (or ``document.cookie`` assignment) that remembers
 * a preference for a year, site-wide, same-site.
 *
 * @param {string} name - The cookie's name
 * @param {string} value - The choice
 * @param {PreferenceCookieOptions} [options] - Whether to mark it Secure
 * @returns {string} The cookie string
 */
export function preferenceCookie(
  name: string,
  value: string,
  { secure = false }: PreferenceCookieOptions = {}
): string {
  return (
    `${name}=${value};Path=/;Max-Age=${PREFERENCE_COOKIE_MAX_AGE_SECONDS};SameSite=Lax` +
    (secure ? ';Secure' : '')
  );
}