/* Slim Uiltjies AfterCare — Express + JSON file backend
   ------------------------------------------------------------
   • Serves the PWA as static files
   • Stores all data in a single JSON file (mounted to /data on Coolify)
   • PIN-based auth, simple session tokens held in memory
   • Atomic file writes (write to .tmp, rename)
   • Write queue to prevent races between concurrent pushes

   ENV vars:
     PORT         (default 3000)
     ADMIN_PIN    (default 847291) — change before deploying
     DATA_FILE    (default ./data.json — mount a volume here in production)
*/

const express = require('express');
const fs = require('fs');
const fsp = fs.promises;
const path = require('path');
const crypto = require('crypto');

const PORT = Number(process.env.PORT) || 3000;
const ADMIN_PIN = process.env.ADMIN_PIN || '847291';
const DATA_FILE = process.env.DATA_FILE || path.join(__dirname, 'data', 'data.json');
const N8N_WEBHOOK_URL = process.env.N8N_WEBHOOK_URL || '';
const N8N_WEBHOOK_TOKEN = process.env.N8N_WEBHOOK_TOKEN || '';

const app = express();
app.disable('x-powered-by');
app.use(express.json({ limit: '2mb' }));

// CORS for local dev (when running frontend separately). In prod both
// are served from the same origin so CORS is a no-op.
app.use((req, res, next) => {
  res.setHeader('Access-Control-Allow-Origin', '*');
  res.setHeader('Access-Control-Allow-Methods', 'GET, POST, OPTIONS');
  res.setHeader('Access-Control-Allow-Headers', 'Content-Type, X-Auth-Token');
  if (req.method === 'OPTIONS') return res.sendStatus(204);
  next();
});

// ============================================================
//  Data layer
// ============================================================
function defaultState() {
  return {
    version: 1,
    business: null,
    parents: [],
    children: [],
    invoices: [],
    payments: [],
    meta: { seeded: false, nextReceipt: 1, lastUpdated: new Date().toISOString() },
    _updatedAt: new Date().toISOString(),
  };
}

async function ensureDataDir() {
  const dir = path.dirname(DATA_FILE);
  await fsp.mkdir(dir, { recursive: true });
}

async function readState() {
  try {
    const raw = await fsp.readFile(DATA_FILE, 'utf8');
    const data = JSON.parse(raw);
    // Sanity check + fill missing fields
    return Object.assign(defaultState(), data, {
      _updatedAt: data._updatedAt || new Date().toISOString(),
    });
  } catch (e) {
    if (e.code === 'ENOENT') return defaultState();
    console.error('[data] read failed:', e.message);
    throw e;
  }
}

// Serialize writes so concurrent pushes don't clobber
let writeQueue = Promise.resolve();
let writeInProgress = false;
function writeState(state) {
  const job = writeQueue.then(async () => {
    writeInProgress = true;
    try {
      state._updatedAt = new Date().toISOString();
      if (state.meta) state.meta.lastUpdated = state._updatedAt;
      const tmp = DATA_FILE + '.tmp';
      await fsp.writeFile(tmp, JSON.stringify(state, null, 2));
      await fsp.rename(tmp, DATA_FILE); // atomic on the same filesystem
      // Fire-and-forget n8n backup
      if (N8N_WEBHOOK_URL) notifyN8n(state).catch(() => {});
    } finally {
      writeInProgress = false;
    }
  });
  writeQueue = job.catch((e) => {
    console.error('[data] write failed:', e.message);
  });
  return job;
}

async function notifyN8n(state) {
  try {
    const headers = { 'Content-Type': 'application/json' };
    if (N8N_WEBHOOK_TOKEN) headers['Authorization'] = `Bearer ${N8N_WEBHOOK_TOKEN}`;
    const body = { ...state, _backupAt: new Date().toISOString() };
    const res = await fetch(N8N_WEBHOOK_URL, {
      method: 'POST',
      headers,
      body: JSON.stringify(body),
    });
    if (!res.ok) console.warn(`[n8n] webhook returned ${res.status}`);
  } catch (e) {
    console.warn('[n8n] webhook failed:', e.message);
  }
}

// ============================================================
//  Auth — PIN + session tokens
// ============================================================
const sessions = new Map();
const SESSION_TTL_MS = 1000 * 60 * 60 * 24 * 30; // 30 days

function newToken() {
  return crypto.randomBytes(24).toString('base64url');
}

function isAuthenticated(req) {
  const token = req.headers['x-auth-token'];
  if (!token) return false;
  const createdAt = sessions.get(token);
  if (!createdAt) return false;
  if (Date.now() - createdAt > SESSION_TTL_MS) {
    sessions.delete(token);
    return false;
  }
  return true;
}

// Garbage-collect expired sessions every hour
setInterval(() => {
  const now = Date.now();
  for (const [t, ts] of sessions) if (now - ts > SESSION_TTL_MS) sessions.delete(t);
}, 1000 * 60 * 60).unref();

// ============================================================
//  API routes
// ============================================================

// Public
app.get('/api/health', (_req, res) => res.json({ ok: true, ts: Date.now() }));

app.post('/api/auth', (req, res) => {
  const { pin } = req.body || {};
  if (typeof pin !== 'string' || !pin) return res.status(400).json({ error: 'PIN required' });
  if (pin !== ADMIN_PIN) return res.status(401).json({ error: 'Invalid PIN' });
  const token = newToken();
  sessions.set(token, Date.now());
  res.json({ token, ttlSeconds: SESSION_TTL_MS / 1000 });
});

// Protected
app.get('/api/state', async (req, res, next) => {
  if (!isAuthenticated(req)) return res.status(401).json({ error: 'Unauthorized' });
  try {
    const state = await readState();
    res.json(state);
  } catch (e) { next(e); }
});

app.post('/api/state', async (req, res, next) => {
  if (!isAuthenticated(req)) return res.status(401).json({ error: 'Unauthorized' });
  const state = req.body;
  if (!state || typeof state !== 'object') return res.status(400).json({ error: 'Invalid state object' });

  // Lightweight validation
  const known = ['business', 'parents', 'children', 'invoices', 'payments', 'meta', 'version'];
  const cleaned = {};
  for (const k of known) if (k in state) cleaned[k] = state[k];
  for (const k of ['parents', 'children', 'invoices', 'payments']) {
    if (cleaned[k] !== undefined && !Array.isArray(cleaned[k])) {
      return res.status(400).json({ error: `${k} must be an array` });
    }
  }
  cleaned.version = cleaned.version || 1;

  try {
    await writeState(cleaned);
    res.json({ ok: true, updatedAt: cleaned._updatedAt });
  } catch (e) { next(e); }
});

app.post('/api/logout', (req, res) => {
  const token = req.headers['x-auth-token'];
  if (token) sessions.delete(token);
  res.json({ ok: true });
});

// ============================================================
//  Static frontend (serves index.html, css, js, vendor, icons, etc.)
// ============================================================
app.use(express.static(__dirname, {
  extensions: ['html'],
  setHeaders: (res, filePath) => {
    // Don't cache HTML so updates ship immediately
    if (filePath.endsWith('.html')) res.setHeader('Cache-Control', 'no-cache');
  },
}));

// SPA fallback for client-side routing (everything else → index.html)
app.get('*', (_req, res) => res.sendFile(path.join(__dirname, 'index.html')));

// ============================================================
//  Error handler
// ============================================================
app.use((err, _req, res, _next) => {
  console.error('[server] error:', err);
  res.status(500).json({ error: err.message || 'Internal error' });
});

// ============================================================
//  Boot
// ============================================================
(async () => {
  try {
    await ensureDataDir();
    await readState(); // touch the file
    console.log(`[server] data file: ${DATA_FILE}`);
  } catch (e) {
    console.error('[server] failed to initialise data:', e.message);
    process.exit(1);
  }
  app.listen(PORT, '0.0.0.0', () => {
    console.log(`[server] Slim Uiltjies listening on :${PORT}`);
    console.log(`[server] PIN: ${ADMIN_PIN === '847291' ? '(default 847291 — change ADMIN_PIN!)' : '(custom)'}`);
  });
})();