/**
 * Reine Hilfsfunktionen der Flash-Meldungen (siehe lib/flash.ts) ohne
 * next/headers — damit auch der Proxy (src/proxy.ts) und Route Handler sie
 * nutzen koennen.
 */
export const FLASH_COOKIE = "wh_flash";
export const MAX_FLASH_MESSAGE_LENGTH = 300;
/** Ohne JavaScript loescht niemand das Cookie — dann verfaellt es von selbst. */
const FLASH_MAX_AGE_SECONDS = 60;

const FLASH_KINDS = ["success", "error", "info"] as const;
export type FlashKind = (typeof FLASH_KINDS)[number];

export interface Flash {
  id: string;
  kind: FlashKind;
  message: string;
}

export function serializeFlash(flash: Flash): string {
  return encodeURIComponent(JSON.stringify({ ...flash, message: flash.message.slice(0, MAX_FLASH_MESSAGE_LENGTH) }));
}

export function parseFlash(raw: string | undefined): Flash | null {
  if (!raw) return null;
  let value: unknown;
  try {
    value = JSON.parse(decodeURIComponent(raw));
  } catch {
    return null;
  }
  if (typeof value !== "object" || value === null) return null;
  const { id, kind, message } = value as Record<string, unknown>;
  if (typeof id !== "string" || typeof message !== "string" || message.trim() === "") return null;
  if (!(FLASH_KINDS as readonly unknown[]).includes(kind)) return null;
  return { id: id.slice(0, 64), kind: kind as FlashKind, message: message.slice(0, MAX_FLASH_MESSAGE_LENGTH) };
}

export function flashCookieOptions() {
  return {
    path: "/",
    maxAge: FLASH_MAX_AGE_SECONDS,
    sameSite: "lax" as const,
    secure: process.env.NODE_ENV === "production",
    httpOnly: false,
  };
}

/**
 * Fuer Route Handler, die selbst eine NextResponse zurueckgeben (z.B. der
 * Link aus der Bestaetigungs-E-Mail): haengt die Meldung direkt an die
 * Weiterleitung.
 */
export function withFlash<T extends { cookies: { set: (name: string, value: string, options: object) => unknown } }>(
  response: T,
  kind: FlashKind,
  message: string
): T {
  response.cookies.set(FLASH_COOKIE, serializeFlash({ id: crypto.randomUUID(), kind, message }), flashCookieOptions());
  return response;
}