party-player/server/index.js

// Express serves the two frontends; a single WebSocket keeps them in sync.

import { createServer } from 'node:http';
import { dirname, join } from 'node:path';
import { fileURLToPath } from 'node:url';

import express from 'express';
import { WebSocketServer } from 'ws';

import {
  PORT,
  OVERLAP_SECONDS,
  HARD_CUT_SECONDS,
  FRAME_SCALE,
  BOUNCE_SPEED,
  CORNER_INTERVAL_SECONDS,
  CORNER_MARGIN,
  BACKGROUNDS,
} from '../config.js';
import { parseVideoId, fetchTitle } from './youtube.js';
import * as store from './state.js';

const ROOT = join(dirname(fileURLToPath(import.meta.url)), '..');

store.load();

const app = express();

// Declared before the static middleware, which would otherwise redirect
// /queue to /queue/ on its way to the directory index.
app.get('/', (_req, res) => res.sendFile(join(ROOT, 'public/player/index.html')));
app.get('/queue', (_req, res) => res.sendFile(join(ROOT, 'public/queue/index.html')));

app.use('/assets', express.static(join(ROOT, 'assets'), { maxAge: '1h' }));
app.use(express.static(join(ROOT, 'public')));

// Client-side mirror of the shared config, so the constants live in one place.
app.get('/config.js', (_req, res) => {
  res.type('application/javascript').send(
    `export const OVERLAP_SECONDS = ${OVERLAP_SECONDS};\n` +
      `export const HARD_CUT_SECONDS = ${HARD_CUT_SECONDS};\n` +
      `export const FRAME_SCALE = ${FRAME_SCALE};\n` +
      `export const BOUNCE_SPEED = ${BOUNCE_SPEED};\n` +
      `export const CORNER_INTERVAL_SECONDS = ${CORNER_INTERVAL_SECONDS};\n` +
      `export const CORNER_MARGIN = ${CORNER_MARGIN};\n` +
      `export const BACKGROUNDS = ${JSON.stringify(BACKGROUNDS)};\n`,
  );
});

const server = createServer(app);
const wss = new WebSocketServer({ server });

function broadcast(message) {
  const payload = JSON.stringify(message);
  for (const client of wss.clients) {
    if (client.readyState === client.OPEN) client.send(payload);
  }
}

function broadcastState() {
  broadcast({ type: 'state', state: store.getState() });
}

/** Persist and push in one go — every structural change ends with this. */
function commit() {
  store.save();
  broadcastState();
}

const handlers = {
  async add(_ws, msg) {
    const videoId = parseVideoId(msg.url);
    if (!videoId) throw new Error('Not a YouTube video URL');
    const title = await fetchTitle(videoId);
    store.addItem({ videoId, title });
    commit();
  },

  remove(_ws, msg) {
    if (store.removeItem(msg.id)) commit();
  },

  reorder(_ws, msg) {
    if (!Array.isArray(msg.ids)) return;
    store.reorder(msg.ids);
    commit();
  },

  jump(_ws, msg) {
    if (store.indexOf(msg.id) === -1) return;
    store.getState().currentId = msg.id;
    commit();
  },

  duration(_ws, msg) {
    if (store.setDuration(msg.id, msg.seconds)) commit();
  },

  // The player finished its crossfade and wants the pointer moved along.
  trackEnded(_ws, msg) {
    const state = store.getState();
    // Ignore stale reports from a track we already moved past.
    if (msg.id !== state.currentId) return;
    const next = store.nextItem(msg.id);
    state.currentId = next ? next.id : null;
    commit();
  },

  setBackground(_ws, msg) {
    if (!(msg.key in BACKGROUNDS)) return;
    store.getState().background = msg.key;
    commit();
  },

  // Relayed straight through: this arrives once a second and must never
  // touch the disk.
  progress(_ws, msg) {
    broadcast({ type: 'progress', id: msg.id, currentTime: msg.currentTime });
  },
};

wss.on('connection', (ws) => {
  ws.send(JSON.stringify({ type: 'state', state: store.getState() }));

  ws.on('message', async (raw) => {
    let msg;
    try {
      msg = JSON.parse(raw);
    } catch {
      return;
    }

    const handler = handlers[msg.type];
    if (!handler) return;

    try {
      await handler(ws, msg);
    } catch (err) {
      ws.send(JSON.stringify({ type: 'error', message: err.message, forType: msg.type }));
    }
  });
});

server.listen(PORT, () => {
  console.log(`\n  Player : http://localhost:${PORT}/`);
  console.log(`  Queue  : http://localhost:${PORT}/queue\n`);
});