/**
 * Auth middleware module (async).
 * 
 * Session tokens are hashed with SHA-256 for security (Punkt 4).
 * All DB calls are async (Punkt 4: PostgreSQL compatibility).
 */
const crypto = require('crypto');
const db = require('../db');
const { auditLog } = require('../auditLog');

// P6: Cookie config - defined early for use in CSRF and auth cookies
const isProduction = process.env.NODE_ENV === 'production';
const COOKIE_NAME = 'workflow_token';

function hashToken(token) {
  return crypto.createHash('sha256').update(token).digest('hex');
}

// P4: CSRF protection (Double-Submit-Cookie pattern)
const CSRF_COOKIE_NAME = 'workflow_csrf';
const CSRF_HEADER_NAME = 'x-csrf-token';

// CSRF token is derived deterministically from the session token hash (HMAC).
// Advantage: cookie and header can never drift apart (no more stale-token 403s),
// works across tabs, page reloads and re-logins. The cookie is self-healed by
// authMiddleware on every request if it is missing or out of sync.
const CSRF_SECRET = process.env.SESSION_SECRET || 'workflow-portal-csrf-v1';

function deriveCSRFToken(tokenHash) {
  return crypto.createHmac('sha256', CSRF_SECRET).update(tokenHash).digest('hex');
}

function setCSRFCookie(res, tokenHash) {
  // If a session token hash is provided, derive the CSRF token from it (deterministic).
  // Otherwise (e.g. register, no session yet) fall back to a random token.
  const csrfToken = tokenHash ? deriveCSRFToken(tokenHash) : crypto.randomBytes(32).toString('hex');
  res.cookie(CSRF_COOKIE_NAME, csrfToken, {
    httpOnly: false, // Must be readable by JS to send back in header
    secure: isProduction,
    sameSite: isProduction ? 'strict' : 'lax',
    maxAge: 24 * 60 * 60 * 1000, // 24h (re-set by authMiddleware on every request)
    path: '/',
  });
  return csrfToken;
}

function csrfMiddleware(req, res, next) {
  // Only check state-changing methods
  const stateChanging = ['POST', 'PUT', 'PATCH', 'DELETE'];
  if (!stateChanging.includes(req.method)) return next();

  const cookieToken = req.cookies?.[CSRF_COOKIE_NAME];
  const headerToken = req.headers[CSRF_HEADER_NAME];

  // Accept if header matches cookie (classic double-submit) OR if the header
  // matches the token derived from the current session (self-healing path).
  let valid = cookieToken && headerToken && cookieToken === headerToken;
  if (!valid && req.tokenHash && headerToken) {
    valid = headerToken === deriveCSRFToken(req.tokenHash);
  }
  if (!valid) {
    return res.status(403).json({ error: 'CSRF-Token ungültig oder fehlend.' });
  }
  // Self-heal: ensure the cookie always carries the correct token
  if (req.tokenHash && cookieToken !== deriveCSRFToken(req.tokenHash)) {
    res.cookie(CSRF_COOKIE_NAME, deriveCSRFToken(req.tokenHash), {
      httpOnly: false,
      secure: isProduction,
      sameSite: isProduction ? 'strict' : 'lax',
      maxAge: 24 * 60 * 60 * 1000,
      path: '/',
    });
  }
  next();
}

async function authMiddleware(req, res, next) {
  // Punkt 8: Token from HttpOnly-Cookie OR Authorization header
  const rawToken = req.cookies?.workflow_token || req.headers.authorization?.replace('Bearer ', '');
  if (!rawToken) return res.status(401).json({ error: 'Nicht authentifiziert.' });

  const tokenHash = hashToken(rawToken);
  const session = await db.prepare('SELECT s.id, s.user_id, s.expires_at, u.email, u.name, u.role, u.status, u.source, u.username FROM sessions s JOIN users u ON s.user_id = u.id WHERE s.token = ?').get(tokenHash);

  if (!session) return res.status(401).json({ error: 'Sitzung abgelaufen. Bitte erneut anmelden.' });
  if (session.status === 'inaktiv') {
    await db.prepare('DELETE FROM sessions WHERE token = ?').run(tokenHash);
    return res.status(401).json({ error: 'Konto deaktiviert.' });
  }
  if (session.expires_at && new Date(session.expires_at) < new Date()) {
    await db.prepare('DELETE FROM sessions WHERE token = ?').run(tokenHash);
    return res.status(401).json({ error: 'Sitzung abgelaufen. Bitte erneut anmelden.' });
  }

  req.user = { id: session.user_id, email: session.email, name: session.name, role: session.role, status: session.status, source: session.source, username: session.username };
  req.tokenHash = tokenHash;
  // Self-healing CSRF: on safe requests (GET/HEAD/OPTIONS), re-issue the CSRF cookie
  // derived from the current session so it can never go stale or out of sync.
  if (['GET', 'HEAD', 'OPTIONS'].includes(req.method)) {
    res.cookie(CSRF_COOKIE_NAME, deriveCSRFToken(tokenHash), {
      httpOnly: false,
      secure: isProduction,
      sameSite: isProduction ? 'strict' : 'lax',
      maxAge: 24 * 60 * 60 * 1000,
      path: '/',
    });
  }
  next();
}

function adminMiddleware(req, res, next) {
  if (req.user.role !== 'admin') return res.status(403).json({ error: 'Admin-Rechte erforderlich.' });
  next();
}

async function createSession(userId, oldRawToken) {
  // V6: Session-Rotation - invalidate old session on new login (prevents session fixation)
  if (oldRawToken) {
    const oldHash = hashToken(oldRawToken);
    await db.prepare('DELETE FROM sessions WHERE token = ?').run(oldHash);
  }

  const rawToken = crypto.randomBytes(32).toString('hex');
  const tokenHash = hashToken(rawToken);
  const ttlHours = parseInt(process.env.SESSION_TTL_HOURS) || 168;
  const expiresAt = new Date(Date.now() + ttlHours * 60 * 60 * 1000).toISOString();
  
  // Punkt 9: Session-Limitierung - max sessions per user
  const maxSessions = parseInt(process.env.SESSION_MAX_PER_USER) || 5;
  const existingSessions = await db.prepare('SELECT id FROM sessions WHERE user_id = ? ORDER BY created_at ASC').all(userId);
  if (existingSessions.length >= maxSessions) {
    const toDelete = existingSessions.slice(0, existingSessions.length - maxSessions + 1);
    const deleteIds = toDelete.map(s => s.id).filter(id => Number.isInteger(id));
    if (deleteIds.length > 0) {
      const placeholders = deleteIds.map(() => '?').join(',');
      await db.prepare(`DELETE FROM sessions WHERE id IN (${placeholders})`).run(...deleteIds);
    }
  }
  
  await db.prepare('INSERT INTO sessions (user_id, token, expires_at) VALUES (?, ?, ?)').run(userId, tokenHash, expiresAt);
  return rawToken;
}

async function deleteSession(rawToken) {
  if (!rawToken) return;
  const tokenHash = hashToken(rawToken);
  const session = await db.prepare('SELECT user_id FROM sessions WHERE token = ?').get(tokenHash);
  if (session) {
    auditLog(session.user_id, 'logout', 'user', session.user_id, null);
  }
  await db.prepare('DELETE FROM sessions WHERE token = ?').run(tokenHash);
}

async function invalidateUserSessions(userId) {
  await db.prepare('DELETE FROM sessions WHERE user_id = ?').run(userId);
}

// Punkt 12: Account-Lockout functions
const MAX_ATTEMPTS = parseInt(process.env.LOGIN_MAX_ATTEMPTS) || 5;
const LOCKOUT_MINUTES = parseInt(process.env.LOGIN_LOCKOUT_MINUTES) || 15;

async function isAccountLocked(userId) {
  const user = await db.prepare('SELECT locked_until FROM users WHERE id = ?').get(userId);
  if (!user || !user.locked_until) return false;
  if (new Date(user.locked_until) > new Date()) return true;
  await db.prepare('UPDATE users SET failed_login_attempts = 0, locked_until = NULL WHERE id = ?').run(userId);
  return false;
}

async function recordFailedLogin(userId) {
  if (!userId) return;
  const user = await db.prepare('SELECT failed_login_attempts FROM users WHERE id = ?').get(userId);
  if (!user) return;
  const attempts = (user.failed_login_attempts || 0) + 1;
  if (attempts >= MAX_ATTEMPTS) {
    const lockedUntil = new Date(Date.now() + LOCKOUT_MINUTES * 60 * 1000).toISOString();
    await db.prepare('UPDATE users SET failed_login_attempts = ?, locked_until = ? WHERE id = ?').run(attempts, lockedUntil, userId);
  } else {
    await db.prepare('UPDATE users SET failed_login_attempts = ? WHERE id = ?').run(attempts, userId);
  }
}

async function recordSuccessfulLogin(userId) {
  if (!userId) return;
  await db.prepare('UPDATE users SET failed_login_attempts = 0, locked_until = NULL WHERE id = ?').run(userId);
}

// Punkt 8: Cookie helpers
function setAuthCookie(res, token) {
  const ttlHours = parseInt(process.env.SESSION_TTL_HOURS) || 168;
  res.cookie(COOKIE_NAME, token, {
    httpOnly: true,
    secure: isProduction,
    sameSite: isProduction ? 'strict' : 'lax',
    maxAge: ttlHours * 60 * 60 * 1000,
    path: '/',
  });
}

function clearAuthCookie(res) {
  res.clearCookie(COOKIE_NAME, { path: '/' });
}

module.exports = { 
  authMiddleware, adminMiddleware, createSession, deleteSession, invalidateUserSessions, hashToken,
  isAccountLocked, recordFailedLogin, recordSuccessfulLogin,
  setAuthCookie, clearAuthCookie, COOKIE_NAME,
  setCSRFCookie, csrfMiddleware, CSRF_COOKIE_NAME, CSRF_HEADER_NAME
};