import { cookies } from "next/headers";
import { redirect } from "next/navigation";
import { createHmac, timingSafeEqual, randomBytes, scryptSync } from "crypto";
import { getDb } from "./db";

const SESSION_SECRET = process.env.SESSION_SECRET!;
const COOKIE_NAME = "session";
const MAX_AGE = 60 * 60 * 24 * 7; // 7 dagen

// impersonatorId: admin die via "Inloggen als" de pagina van een expert bekijkt (alleen lezen)
type SessionPayload = { userId: number; email: string; name: string; impersonatorId?: number };

function sign(payload: SessionPayload): string {
  const data = JSON.stringify(payload);
  const encoded = Buffer.from(data).toString("base64url");
  const sig = createHmac("sha256", SESSION_SECRET).update(encoded).digest("base64url");
  return `${encoded}.${sig}`;
}

function verify(token: string): SessionPayload | null {
  const [encoded, sig] = token.split(".");
  if (!encoded || !sig) return null;
  const expected = createHmac("sha256", SESSION_SECRET).update(encoded).digest("base64url");
  try {
    if (!timingSafeEqual(Buffer.from(sig), Buffer.from(expected))) return null;
  } catch {
    return null;
  }
  return JSON.parse(Buffer.from(encoded, "base64url").toString());
}

export async function getSession(): Promise<SessionPayload | null> {
  const jar = await cookies();
  const token = jar.get(COOKIE_NAME)?.value;
  if (!token) return null;
  return verify(token);
}

export async function createSession(payload: SessionPayload) {
  const jar = await cookies();
  jar.set(COOKIE_NAME, sign(payload), {
    httpOnly: true,
    secure: process.env.NODE_ENV === "production",
    sameSite: "lax",
    maxAge: MAX_AGE,
    path: "/",
  });
}

export async function destroySession() {
  const jar = await cookies();
  jar.delete(COOKIE_NAME);
}

export function hashPassword(password: string): string {
  const salt = randomBytes(16).toString("hex");
  const hash = scryptSync(password, salt, 64).toString("hex");
  return `${salt}:${hash}`;
}

export function verifyPassword(password: string, stored: string): boolean {
  // Uitgenodigde experts hebben nog geen wachtwoord (lege hash) en kunnen niet inloggen
  if (!stored || !stored.includes(":")) return false;
  const [salt, hash] = stored.split(":");
  const attempt = scryptSync(password, salt, 64).toString("hex");
  return timingSafeEqual(Buffer.from(hash, "hex"), Buffer.from(attempt, "hex"));
}

export function getUserByEmail(email: string) {
  const db = getDb();
  return db.prepare("SELECT * FROM users WHERE email = ?").get(email) as
    | { id: number; email: string; name: string; password_hash: string; role: string }
    | undefined;
}

export type Role = "admin" | "expert";
export type CurrentUser = {
  id: number;
  email: string;
  name: string;
  role: Role;
  // Gezet als een admin via "Inloggen als" meekijkt; alleen geldig als die gebruiker nog admin is
  impersonator: { id: number; email: string; name: string } | null;
};

// Ingelogde gebruiker met zijn rol uit de database (niet uit de cookie), zodat een
// gewijzigde of verwijderde gebruiker direct geen toegang meer heeft.
export async function getCurrentUser(): Promise<CurrentUser | null> {
  const session = await getSession();
  if (!session) return null;
  const user = getDb().prepare("SELECT id, email, name, role FROM users WHERE id = ?").get(session.userId) as
    | { id: number; email: string; name: string; role: string }
    | undefined;
  if (!user) return null;
  let impersonator: CurrentUser["impersonator"] = null;
  if (session.impersonatorId) {
    const admin = getDb()
      .prepare("SELECT id, email, name FROM users WHERE id = ? AND role = 'admin'")
      .get(session.impersonatorId) as { id: number; email: string; name: string } | undefined;
    // Een meekijk-sessie van een gebruiker die geen admin (meer) is, is ongeldig
    if (!admin) return null;
    impersonator = { id: admin.id, email: admin.email, name: admin.name };
  }
  return {
    id: user.id,
    email: user.email,
    name: user.name,
    role: user.role === "expert" ? "expert" : "admin",
    impersonator,
  };
}

export function homeForRole(role: Role): string {
  return role === "expert" ? "/expert" : "/tenants";
}

// Voor alle beheerpagina's en -acties: alleen admins. Experts gaan naar hun eigen pagina.
export async function requireAdmin(): Promise<CurrentUser> {
  const user = await getCurrentUser();
  if (!user) redirect("/login");
  if (user.role !== "admin") redirect(homeForRole(user.role));
  return user;
}

// Voor de expertpagina: alleen experts.
export async function requireExpert(): Promise<CurrentUser> {
  const user = await getCurrentUser();
  if (!user) redirect("/login");
  if (user.role !== "expert") redirect(homeForRole(user.role));
  return user;
}