import { randomUUID, randomBytes, scryptSync, timingSafeEqual } from 'crypto';
import { NextFunction, Request, Response } from 'express';
import { eq, lt, sql } from 'drizzle-orm';
import { db } from './db/client';
import { users, authSessions } from './db/schema';

// User-account session auth (see memory-bank/FEATURE_User_Accounts.md).
//
// Replaces the original single shared-password mode (AUTH_PASSWORD env var,
// in-memory session Set): accounts live in the `users` table, sessions in
// `auth_sessions` (so a server restart no longer signs everyone out), and the
// first account is created through POST /api/auth/setup while the users table
// is empty. Auth is always on once a user exists — there is no open mode.

const COOKIE_NAME = 'mkb_session';
const SESSION_TTL_MS = 30 * 24 * 60 * 60 * 1000; // 30 days

// Flat pause on a failed login — cheap brute-force damping without the
// bookkeeping of per-IP counters (single-family LAN app).
const FAILED_LOGIN_DELAY_MS = 350;

export interface SessionUser {
  id: number;
  username: string;
}

// requireAuth attaches the session's user here; protected routes can cast.
export interface AuthedRequest extends Request {
  user?: SessionUser;
}

// --- Password hashing (node:crypto scrypt — no native dependency) ---

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

export function verifyPassword(password: string, stored: string): boolean {
  const [scheme, saltHex, hashHex] = stored.split(':');
  if (scheme !== 'scrypt' || !saltHex || !hashHex) return false;
  const expected = Buffer.from(hashHex, 'hex');
  const actual = scryptSync(password, Buffer.from(saltHex, 'hex'), expected.length);
  return timingSafeEqual(actual, expected);
}

// --- Users ---

export function anyUsersExist(): boolean {
  return db.select({ id: users.id }).from(users).limit(1).get() !== undefined;
}

// Case-insensitive lookup: the schema's UNIQUE index is case-sensitive, so both
// login and the duplicate-username guard go through lower() instead.
export function findUserByUsername(username: string) {
  return db
    .select()
    .from(users)
    .where(sql`lower(${users.username}) = lower(${username})`)
    .get();
}

export function sleep(ms: number): Promise<void> {
  return new Promise((resolve) => setTimeout(resolve, ms));
}

export const failedLoginDelayMs = FAILED_LOGIN_DELAY_MS;

export const MIN_PASSWORD_LENGTH = 8;

// Shared by POST /api/auth/setup and POST /api/users — returns an error message
// for the 400 response, or null when the pair is acceptable.
export function validateNewCredentials(username: unknown, password: unknown): string | null {
  if (typeof username !== 'string' || username.trim().length === 0) {
    return 'Username is required';
  }
  if (username.trim().length > 64) {
    return 'Username is too long (max 64 characters)';
  }
  if (typeof password !== 'string' || password.length < MIN_PASSWORD_LENGTH) {
    return `Password must be at least ${MIN_PASSWORD_LENGTH} characters`;
  }
  return null;
}

// --- Cookie / session plumbing ---

function parseCookies(header: string | undefined): Record<string, string> {
  const out: Record<string, string> = {};
  if (!header) return out;
  for (const part of header.split(';')) {
    const eq = part.indexOf('=');
    if (eq === -1) continue;
    const key = part.slice(0, eq).trim();
    if (key) out[key] = decodeURIComponent(part.slice(eq + 1).trim());
  }
  return out;
}

export function readSessionToken(req: Request): string | undefined {
  return parseCookies(req.headers.cookie)[COOKIE_NAME];
}

export function createSession(res: Response, userId: number): void {
  const token = randomUUID();
  const expiresAt = new Date(Date.now() + SESSION_TTL_MS).toISOString();
  db.insert(authSessions).values({ token, userId, expiresAt }).run();
  res.cookie(COOKIE_NAME, token, {
    httpOnly: true,
    sameSite: 'lax',
    path: '/',
    maxAge: SESSION_TTL_MS,
  });
}

export function destroySession(req: Request, res: Response): void {
  const token = readSessionToken(req);
  if (token) db.delete(authSessions).where(eq(authSessions.token, token)).run();
  res.clearCookie(COOKIE_NAME, { path: '/' });
}

// Resolve the request's session to its user, lazily purging expired sessions.
// ISO strings compare lexicographically, so `lt` against now-ISO is correct.
export function getSessionUser(req: Request): SessionUser | null {
  const token = readSessionToken(req);
  if (!token) return null;

  db.delete(authSessions).where(lt(authSessions.expiresAt, new Date().toISOString())).run();

  const row = db
    .select({ id: users.id, username: users.username })
    .from(authSessions)
    .innerJoin(users, eq(authSessions.userId, users.id))
    .where(eq(authSessions.token, token))
    .get();
  return row ?? null;
}

export function requireAuth(req: Request, res: Response, next: NextFunction) {
  const user = getSessionUser(req);
  if (!user) {
    res.status(401).json({ error: 'Unauthorized' });
    return;
  }
  (req as AuthedRequest).user = user;
  next();
}

export function logAuthStatus() {
  if (process.env.AUTH_PASSWORD) {
    console.warn(
      'Auth: AUTH_PASSWORD is set but no longer used — auth is account-based now. ' +
        'Remove MYKINDLEBOX_PASSWORD/AUTH_PASSWORD from your environment.'
    );
  }
  if (anyUsersExist()) {
    console.log('Auth: user accounts active.');
  } else {
    console.log('Auth: no users yet — the app will show the first-run setup screen.');
  }
}