import { createHmac, timingSafeEqual } from "node:crypto";
import { cookies } from "next/headers";
import { NextRequest } from "next/server";

/* ============================================================================
 * TV dashboard session — signed-cookie auth.
 *
 * The TV is more visible than the 3 counter phones (anyone walking past
 * can glance at it), so the operator gets a PIN-gated shell instead of
 * the fully-open kiosk model the counter PWA uses.
 *
 * Storage: a single httpOnly cookie `tv_session` holding a base64url
 * payload of `{ exp: number }` HMAC-signed with TV_SESSION_SECRET. The
 * whole cookie is `payload.signature`; the cookie helpers below
 * assemble and verify it.
 *
 * Rotation: change TV_SESSION_SECRET + restart → all existing cookies
 * fail verify and the TV goes back to the PIN screen.
 *
 * `assertTvSession` returns true when the cookie is present AND valid;
 * `false` when it's missing OR expired OR tampered. The caller decides
 * whether to bounce to /pin (redirect 307) or just render an "unauth"
 * placeholder.
 *
 * NOTE: this is intentionally not a JWT library — we don't need the
 * header/payload/3-segment shape, alg/version negotiation, or the rest
 * of the spec. A minimal HMAC over a single number is enough.
 * ========================================================================= */

const COOKIE_NAME = "tv_session";
const DEFAULT_TTL_HOURS = 12;

function secret(): string {
  const s = process.env.TV_SESSION_SECRET;
  if (!s) {
    throw new Error(
      "TV_SESSION_SECRET is not configured. Set it in .env.local — generate with: node -e \"console.log(require('crypto').randomBytes(48).toString('base64'))\"",
    );
  }
  return s;
}

function ttlHours(): number {
  const raw = process.env.TV_SESSION_HOURS;
  const parsed = raw ? Number.parseInt(raw, 10) : DEFAULT_TTL_HOURS;
  return Number.isFinite(parsed) && parsed > 0 ? parsed : DEFAULT_TTL_HOURS;
}

function b64urlEncode(buf: Buffer): string {
  return buf.toString("base64url");
}

function b64urlDecode(input: string): Buffer {
  return Buffer.from(input, "base64url");
}

function sign(payload: string): string {
  return b64urlEncode(
    createHmac("sha256", secret()).update(payload).digest(),
  );
}

function timingSafeStringEqual(a: string, b: string): boolean {
  const ab = Buffer.from(a);
  const bb = Buffer.from(b);
  if (ab.length !== bb.length) return false;
  return timingSafeEqual(ab, bb);
}

export async function issueTvSession(): Promise<string> {
  const exp = Date.now() + ttlHours() * 60 * 60 * 1000;
  const payload = b64urlEncode(Buffer.from(JSON.stringify({ exp })));
  const signature = sign(payload);
  return `${payload}.${signature}`;
}

/**
 * Cookie options for the auth cookie. httpOnly so JS can't read it,
 * sameSite=lax so the TV's same-origin fetch (auto-refresh) carries
 * it normally, secure only when we know we're on https (Coolify in
 * prod is HTTPS; dev on http://localhost stays non-secure).
 *
 * `secure` is left as a default that the runtime infers from the
 * request protocol when available.
 */
export function tvCookieOptions() {
  return {
    name: COOKIE_NAME,
    httpOnly: true,
    sameSite: "lax" as const,
    path: "/",
    maxAge: ttlHours() * 60 * 60,
  };
}

export async function verifyTvToken(token: string | undefined): Promise<boolean> {
  if (!token) return false;
  const dot = token.indexOf(".");
  if (dot < 0) return false;
  const payload = token.slice(0, dot);
  const providedSig = token.slice(dot + 1);
  const expectedSig = sign(payload);
  if (!timingSafeStringEqual(providedSig, expectedSig)) return false;
  let parsed: { exp?: unknown };
  try {
    parsed = JSON.parse(b64urlDecode(payload).toString("utf8"));
  } catch {
    return false;
  }
  if (typeof parsed.exp !== "number" || !Number.isFinite(parsed.exp)) {
    return false;
  }
  return parsed.exp > Date.now();
}

/**
 * Read the cookie from a route-handler `NextRequest` (API routes).
 * Returns true when the cookie is present AND valid.
 */
export async function assertTvSession(req: NextRequest): Promise<boolean> {
  const raw = req.cookies.get(COOKIE_NAME)?.value;
  return verifyTvToken(raw);
}

/**
 * Read the cookie from a Server Component via `next/headers`. Same
 * return semantics as `assertTvSession`.
 */
export async function isTvAuthed(): Promise<boolean> {
  const jar = await cookies();
  const raw = jar.get(COOKIE_NAME)?.value;
  return verifyTvToken(raw);
}

export const TV_SESSION_COOKIE_NAME = COOKIE_NAME;