// RootNode Academy — Lab Host Router (Phase 4.1).
//
// Runs on the SAME Docker host as student Labs (rn-lab-host-01 in production). Its only job:
// take a request from the Platform Gateway carrying an opaque routing token, find the ONE
// local container labeled with that token, and reverse-proxy the request to it. See
// docs/PHASE4_1_PREPRODUCTION_HARDENING.md §1-3 and docs/PRODUCTION_NETWORK_SECURITY.md.
//
// Deliberately narrow:
//   - Never talks to Postgres, the Provisioner, or anything off this host — it resolves purely
//     from local `docker ps` state (containers are labeled by the Provisioner at creation time,
//     see provisioner lifecycle.js), so a destroyed/reset environment's old token simply has no
//     matching container anymore. No separate "is this token still valid" check is needed.
//   - Only one route exists: proxy-by-token. No container listing, no Docker-API passthrough,
//     no endpoint that echoes back a container id, IP, or network name to the caller.
//   - Requires mTLS — the Node https server itself rejects any connection that doesn't present
//     a certificate signed by the configured CA (requestCert + rejectUnauthorized), so an
//     unauthenticated caller never reaches route-resolution logic at all. This is the ONLY
//     authentication; there is no bearer-token/API-key fallback (mTLS or nothing).
//   - Binds to an internal address only — this process has no idea what "public" means, that's
//     enforced by the firewall (infra/firewall/rn-lab-host-01.rules) and by never being given a
//     public-facing port mapping in the production Compose file. Defense in depth: even if the
//     firewall were misconfigured, mTLS still blocks anyone without the Gateway's client cert.

const fs = require('fs');
const https = require('https');
const httpProxy = require('http-proxy');
const Docker = require('dockerode');
const { resolveTarget, tokenFingerprint } = require('./resolve');

const PORT = Number(process.env.LAB_ROUTER_PORT) || 8443;
const TLS_CA = process.env.LAB_ROUTER_TLS_CA;
const TLS_CERT = process.env.LAB_ROUTER_TLS_CERT;
const TLS_KEY = process.env.LAB_ROUTER_TLS_KEY;
const ROUTE_TOKEN_HEADER = 'x-rootnode-route-token';

if (!TLS_CA || !TLS_CERT || !TLS_KEY) {
  console.error('FATAL: LAB_ROUTER_TLS_CA/CERT/KEY are not set. Refusing to start an unauthenticated Lab Host Router.');
  process.exit(1);
}

// Always the local socket — the Router only ever inspects containers on ITS OWN host, never a
// remote Docker daemon (that's the Provisioner's job, over a completely separate mTLS
// connection — see docs/PHASE4_1_PREPRODUCTION_HARDENING.md §10 "control plane vs data plane").
const docker = new Docker({ socketPath: process.env.DOCKER_SOCKET || '/var/run/docker.sock' });

const proxy = httpProxy.createProxyServer({ ws: true });
proxy.on('error', (err, req, res) => {
  console.error('[lab-router] proxy error:', err.message);
  if (res && res.writeHead && !res.headersSent) {
    res.writeHead(502, { 'Content-Type': 'application/json' });
    res.end(JSON.stringify({ error: 'lab_unreachable' }));
  } else if (res && res.destroy) {
    res.destroy();
  }
});

async function handleRequest(req, res) {
  const token = req.headers[ROUTE_TOKEN_HEADER];
  let target;
  try {
    target = await resolveTarget(docker, token);
  } catch (e) {
    console.error('[lab-router] docker lookup failed:', e.message);
    res.writeHead(502, { 'Content-Type': 'application/json' });
    return res.end(JSON.stringify({ error: 'router_internal_error' }));
  }
  if (!target) {
    console.log(`[lab-router] unknown/stale token ${tokenFingerprint(token)} -> 404`);
    res.writeHead(404, { 'Content-Type': 'application/json' });
    return res.end(JSON.stringify({ error: 'unknown_environment' }));
  }
  proxy.web(req, res, { target });
}

async function handleUpgrade(req, socket, head) {
  const token = req.headers[ROUTE_TOKEN_HEADER];
  let target;
  try {
    target = await resolveTarget(docker, token);
  } catch (e) {
    console.error('[lab-router] docker lookup failed (ws):', e.message);
    return socket.destroy();
  }
  if (!target) {
    console.log(`[lab-router] unknown/stale token ${tokenFingerprint(token)} -> ws rejected`);
    return socket.destroy();
  }
  proxy.ws(req, socket, head, { target });
}

const tlsOptions = {
  ca: fs.readFileSync(TLS_CA),
  cert: fs.readFileSync(TLS_CERT),
  key: fs.readFileSync(TLS_KEY),
  requestCert: true,
  rejectUnauthorized: true, // the entire authentication mechanism — see file header
};

const server = https.createServer(tlsOptions, handleRequest);
server.on('upgrade', handleUpgrade);
server.on('tlsClientError', (err) => console.warn('[lab-router] rejected unauthenticated/invalid TLS client:', err.message));

server.listen(PORT, () => console.log(`Lab Host Router listening on :${PORT} (mTLS required)`));