/**
 * Digital twin demo server.
 *
 * Owns the telemetry source, broadcasts frames over WebSocket at 2 Hz, exposes a
 * small control API for the what-if panel, and proxies the copilot so the API key
 * never reaches the browser.
 */

import fs from 'node:fs';
import path from 'node:path';
import { fileURLToPath } from 'node:url';
import dotenv from 'dotenv';
import http from 'node:http';
import express from 'express';
import { WebSocketServer } from 'ws';

// Load .env from the repo root explicitly. `dotenv/config` resolves relative to
// process.cwd(), and `npm run dev -w server` sets cwd to server/, so the root
// .env was silently ignored - the symptom being a copilot that quietly falls back
// to a different provider than the one you configured.
const HERE = path.dirname(fileURLToPath(import.meta.url));
dotenv.config({ path: path.join(HERE, '..', '.env') });
dotenv.config({ path: path.join(HERE, '.env') });

import { STATION_SPECS, BUFFER_CAPACITY } from './sim/stations.js';
import { FAULT_PROFILES } from './sim/faults.js';
import { KPI_WINDOW_SEC } from './sim/kpi.js';
import { SimulatedSource, SPEEDS } from './ingest/simulatedSource.js';
import { MqttSource } from './ingest/mqttSource.js';
import { OpcUaSource } from './ingest/opcuaSource.js';
import { Copilot } from './ai/copilot.js';

const PORT = Number(process.env.PORT || 8787);
const SOURCE_KIND = (process.env.TELEMETRY_SOURCE || 'simulated').toLowerCase();

function createSource() {
  switch (SOURCE_KIND) {
    case 'mqtt':
      return new MqttSource({
        url: process.env.MQTT_URL,
        username: process.env.MQTT_USERNAME,
        password: process.env.MQTT_PASSWORD,
      });
    case 'opcua':
      return new OpcUaSource({
        endpoint: process.env.OPCUA_ENDPOINT,
        username: process.env.OPCUA_USERNAME,
        password: process.env.OPCUA_PASSWORD,
      });
    case 'simulated':
      return new SimulatedSource({
        seed: process.env.SIM_SEED ? Number(process.env.SIM_SEED) : undefined,
      });
    default:
      throw new Error(`Unknown TELEMETRY_SOURCE "${SOURCE_KIND}". Use simulated, mqtt or opcua.`);
  }
}

const source = createSource();
const copilot = new Copilot();

const app = express();
app.use(express.json({ limit: '256kb' }));

// --- static metadata the UI needs once, not on every frame -------------------

app.get('/api/meta', (_req, res) => {
  res.json({
    lineId: 'LINE-1',
    stations: STATION_SPECS,
    faults: FAULT_PROFILES,
    bufferCapacity: BUFFER_CAPACITY,
    kpiWindowSec: KPI_WINDOW_SEC,
    speeds: SPEEDS,
    source: { kind: source.name, capabilities: source.capabilities },
    copilot: copilot.status(),
  });
});

app.get('/api/health', (_req, res) => {
  res.json({
    ok: true,
    source: source.name,
    hasFrame: Boolean(source.latest),
    simTime: source.latest ? source.latest.t : 0,
    copilot: copilot.status(),
  });
});

app.get('/api/state', (_req, res) => {
  if (!source.latest) return res.status(503).json({ error: 'No telemetry yet.' });
  res.json(source.latest);
});

// --- control surface --------------------------------------------------------

/** Wrap a control action so an unsupported source returns 400, not a 500. */
function control(handler) {
  return (req, res) => {
    try {
      const result = handler(req);
      res.json({ ok: true, result });
    } catch (err) {
      res.status(400).json({ ok: false, error: err.message });
    }
  };
}

app.post('/api/control/speed', control((req) => source.setSpeed(req.body.speed)));
app.post('/api/control/setpoint', control((req) => source.setSetpoint(req.body.value)));
app.post('/api/control/line-speed', control((req) => source.setLineSpeed(req.body.value)));
app.post('/api/control/tool-change', control(() => source.toolChange()));
app.post('/api/control/reset', control(() => source.reset()));

app.post('/api/control/fault', control((req) => {
  const { id, action } = req.body;
  if (!FAULT_PROFILES.some((f) => f.id === id)) throw new Error(`Unknown fault "${id}".`);
  return action === 'clear' ? source.clearFault(id) : source.injectFault(id);
}));

// --- copilot ---------------------------------------------------------------

app.get('/api/copilot/status', async (_req, res) => {
  res.json(await copilot.detect());
});

// --- settings ---------------------------------------------------------------

app.get('/api/settings', (_req, res) => {
  res.json({ settings: copilot.publicSettings(), status: copilot.status() });
});

app.post('/api/settings', async (req, res) => {
  const result = await copilot.configure(req.body || {});
  // A rejected patch changes nothing, so report it as a client error.
  res.status(result.ok ? 200 : 400).json(result);
});

app.post('/api/settings/reset', async (_req, res) => {
  res.json(await copilot.reset());
});

app.get('/api/copilot/models', async (req, res) => {
  const provider = String(req.query.provider || '').toLowerCase();
  if (provider !== 'openrouter' && provider !== 'ollama') {
    return res.status(400).json({ error: 'provider must be openrouter or ollama' });
  }
  res.json(await copilot.listModels(provider, { force: req.query.force === '1' }));
});

app.post('/api/copilot/test', async (req, res) => {
  const { provider, model } = req.body || {};
  res.json(await copilot.testProvider({ provider, model }));
});

app.post('/api/copilot/chat', async (req, res) => {
  const { question, history, provider } = req.body || {};

  res.writeHead(200, {
    'Content-Type': 'text/event-stream',
    'Cache-Control': 'no-cache, no-transform',
    Connection: 'keep-alive',
    'X-Accel-Buffering': 'no',
  });

  const send = (obj) => res.write(`data: ${JSON.stringify(obj)}\n\n`);

  // Detect client disconnect on the RESPONSE, not the request. Express has
  // already consumed the POST body by this point, which ends the request stream
  // and fires req 'close' immediately - watching that aborts the stream before
  // the first token is ever written.
  let closed = false;
  res.on('close', () => { closed = true; });

  try {
    for await (const chunk of copilot.stream(question, history, source.latest, provider)) {
      if (closed) break;
      send(chunk);
    }
  } catch (err) {
    // copilot.stream() degrades internally, so reaching here means something
    // unexpected broke. Still return prose rather than a broken stream.
    console.error('[copilot] unexpected failure:', err);
    if (!closed) send({ type: 'token', text: `The copilot failed unexpectedly: ${err.message}` });
  }
  if (!res.writableEnded) {
    send({ type: 'end' });
    res.end();
  }
});

// --- built front end -------------------------------------------------------

/**
 * Serve web/dist when it exists, so `npm run build` plus this process is a
 * complete, single-port deployment with no dev server and no second origin.
 *
 * This is what makes the "one Node process, works with no internet" claim true.
 * In development Vite serves the front end on :5173 and proxies here instead, so
 * this block simply finds no dist directory and does nothing.
 */
const DIST = path.join(HERE, '..', 'web', 'dist');
if (fs.existsSync(path.join(DIST, 'index.html'))) {
  app.use(express.static(DIST));

  // SPA fallback for anything that is not an API call. Registered as middleware
  // rather than app.get('*') because Express 5 rejects a bare '*' path.
  app.use((req, res, next) => {
    if (req.method !== 'GET' || req.path.startsWith('/api/')) return next();
    res.sendFile(path.join(DIST, 'index.html'));
  });
  console.log(`[server] serving built front end from ${DIST}`);
} else {
  console.log('[server] no web/dist found - run "npm run build" for single-port mode');
}

// --- websocket broadcast ---------------------------------------------------

const server = http.createServer(app);
const wss = new WebSocketServer({ server, path: '/ws' });

wss.on('connection', (ws) => {
  // Replay recent history first so the trend charts are populated on load, then
  // the current frame so the dashboard renders without waiting for the next tick.
  if (source.replay.length) {
    ws.send(JSON.stringify({ type: 'history', frames: source.replay }));
  }
  if (source.latest) {
    ws.send(JSON.stringify({ type: 'frame', frame: source.latest }));
  }
  ws.on('error', (err) => console.error('[ws] client error:', err.message));
});

source.onFrame((frame) => {
  const msg = JSON.stringify({ type: 'frame', frame });
  for (const client of wss.clients) {
    if (client.readyState === 1) client.send(msg);
  }
});

// --- startup ---------------------------------------------------------------

async function main() {
  const status = await copilot.detect();
  console.log(`[copilot] ${status.label} - ${status.detail}`);

  try {
    await source.start();
    console.log(`[source] ${source.name} started`);
  } catch (err) {
    // A stub source throws a long explanatory message. Print it and stop, rather
    // than serving a dashboard with no data behind it.
    console.error(`\n[source] failed to start "${SOURCE_KIND}":\n${err.message}\n`);
    process.exit(1);
  }

  server.listen(PORT, () => {
    console.log(`[server] http://localhost:${PORT}  (ws://localhost:${PORT}/ws)`);
  });
}

for (const sig of ['SIGINT', 'SIGTERM']) {
  process.on(sig, async () => {
    await source.stop();
    server.close(() => process.exit(0));
  });
}

main();