require('dotenv').config();

const crypto     = require('crypto');
const express    = require('express');
const { createServer } = require('http');
const { Server } = require('socket.io');

const EMIT_SECRET = process.env.EMIT_SECRET || '';
if (!EMIT_SECRET) {
    // Without a secret anyone could call /emit and sign socket tokens.
    console.error('EMIT_SECRET is not set — refusing to start.');
    process.exit(1);
}

// Socket tokens are signed with a key derived from EMIT_SECRET, so a token can
// never double as the /emit secret. Must match socket_token() in include_ending.php.
const SOCKET_KEY = crypto.createHmac('sha256', EMIT_SECRET).update('socket-token').digest();

function safeEqual(a, b) {
    const x = Buffer.from(String(a));
    const y = Buffer.from(String(b));
    return x.length === y.length && crypto.timingSafeEqual(x, y);
}

// Token = base64url(JSON {c, u, r, exp}) + "." + base64url(HMAC-SHA256(payload)).
// Returns the claims, or null when the token is missing, forged or expired.
function verifySocketToken(token) {
    if (typeof token !== 'string' || token.indexOf('.') < 1) return null;
    const [payload, sig] = token.split('.', 2);
    const expected = crypto.createHmac('sha256', SOCKET_KEY).update(payload).digest('base64url');
    if (!safeEqual(sig, expected)) return null;
    let claims;
    try { claims = JSON.parse(Buffer.from(payload, 'base64url').toString('utf8')); }
    catch (e) { return null; }
    if (!claims || !Number.isInteger(claims.c) || claims.c <= 0) return null;
    if (!Number.isInteger(claims.exp) || claims.exp < Math.floor(Date.now() / 1000)) return null;
    return claims;
}

const app        = express();
const httpServer = createServer(app);
const io         = new Server(httpServer, {
    cors: { origin: process.env.ALLOWED_ORIGIN || 'http://localhost' }
});

app.use(express.json());

// ── /emit ─────────────────────────────────────────────────────────────────────
// PHP calls this after any significant action.
// Body: { event, data, company_id }
//
app.post('/emit', (req, res) => {
    const secret = req.headers['x-emit-secret'] || '';
    if (!safeEqual(secret, EMIT_SECRET)) {
        return res.status(403).json({ ok: false, message: 'Forbidden' });
    }

    const { event, data, company_id, target, user_id } = req.body;
    if (!event || !company_id) {
        return res.status(400).json({ ok: false, message: 'event and company_id required' });
    }

    if (target === 'user' && user_id) {
        // Notify the acting user on all their tabs + all admins (excluding the acting user to avoid duplicates)
        io.to(`user_${user_id}`).emit(event, data);
        io.to(`admin_${company_id}`).except(`user_${user_id}`).emit(event, data);
        console.log(`[emit] company=${company_id} user=${user_id} event=${event}`, data);
    } else if (target === 'admin') {
        // Admins and owners only
        io.to(`admin_${company_id}`).emit(event, data);
        console.log(`[emit] company=${company_id} admin-only event=${event}`, data);
    } else {
        // Company-wide — stock events, GL events, scheduler alerts
        io.to(`company_${company_id}`).emit(event, data);
        console.log(`[emit] company=${company_id} event=${event}`, data);
    }

    res.json({ ok: true });
});

// ── /health ───────────────────────────────────────────────────────────────────
// Deliberately public (used by uptime checks); reports status only.
app.get('/health', (req, res) => {
    res.json({ status: 'ok' });
});

// ── WebSocket connections ─────────────────────────────────────────────────────
// Each browser tab connects here on page load with a token PHP signed for the
// signed-in user (include_ending.php). Rooms come only from the verified token —
// never from values the browser chooses — so a visitor cannot listen to another
// company's events.
//
io.use((socket, next) => {
    const claims = verifySocketToken(socket.handshake.auth && socket.handshake.auth.token);
    if (!claims) return next(new Error('unauthorized'));
    socket.data.claims = claims;
    next();
});

io.on('connection', (socket) => {
    const { c: company_id, u: user_id, r: role } = socket.data.claims;

    socket.join(`company_${company_id}`);

    if (user_id) {
        socket.join(`user_${user_id}`);
    }

    if (role === 'admin' || role === 'owner') {
        socket.join(`admin_${company_id}`);
    }

    console.log(`[connect] socket=${socket.id} company=${company_id} user=${user_id} role=${role}`);

    socket.on('disconnect', () => {
        console.log(`[disconnect] socket=${socket.id}`);
    });
});

// ── Start ─────────────────────────────────────────────────────────────────────
const PORT = process.env.PORT || 3000;
httpServer.listen(PORT, () => {
    console.log(`Node.js real-time server running on port ${PORT}`);
});