companion-buttons/server.js

'use strict';

/**
 * Companion Buttons — server part.
 *
 * Shows any button from Bitfocus Companion, on any page, exactly as Companion
 * draws it: colours, text, icons and live feedback included. ProdDash holds
 * one connection to Companion (companion.js) however many dashboards are open;
 * browsers only ever talk to these routes.
 *
 *   GET /pages               → every page and the buttons on it (the tile's picker)
 *   GET /image/<id>          → one button's current picture, as PNG (picker thumbnails)
 *   GET /stream/<b>/<b>/…    → SSE: `button` for each of those buttons on connect,
 *                              then again whenever one redraws or moves
 *
 * <id> is Companion's control id without its "bank:" prefix, and each <b> is
 * page.row.column.id — "19.1.4.t4bp4ZhrQblkr3bPSEBbc" — in the characters
 * ProdDash's page stream carries. A tile holds one stream for all its buttons:
 * a page carries at most 32 streams, and a status board can show more buttons
 * than that.
 *
 * Which button a tile means: the control id while Companion still has it
 * anywhere, so a button that is dragged elsewhere or a page inserted in front
 * keeps showing the same button; otherwise whatever is at the page, row and
 * column now, so a page that is re-imported (every button gets a new id) keeps
 * showing the same place. Every frame says which control and location it
 * resolved to, and the tile saves that back, so it stays current.
 *
 * Read-only by design: nothing here can press a button or change Companion.
 */

const { createLink, createPageBook } = require('./companion');

const HEARTBEAT_MS = 15000;
const LINGER_MS = 30000;      // keep a button's subscription this long after its last viewer leaves
const FIRST_FRAME_MS = 4000;  // how long /image waits for Companion's first picture
const MAX_PER_STREAM = 64;
const ID_RE = /^[A-Za-z0-9_-]{1,64}$/;
const SPOT_RE = /^(\d{1,4})\.(-?\d{1,3})\.(-?\d{1,3})\.([A-Za-z0-9_-]{1,64})$/;

let current = null;

function endpointOf(v) {
  const ep = v && typeof v === 'object' ? v : {};
  return { host: String(ep.host || '').trim(), port: Number(ep.port) || 8000 };
}

function sendJson(res, code, body) {
  res.writeHead(code, { 'Content-Type': 'application/json; charset=utf-8', 'Cache-Control': 'no-store' });
  res.end(JSON.stringify(body));
}

/** "/19.1.4.t4bp4Z…/2.0.0.QOPCk…" → [{ key, page, row, column, id }], or null if malformed. */
function spotsFrom(req) {
  const parts = String(req.wildcard || '').replace(/^\//, '').split('/');
  if (!parts.length || parts.length > MAX_PER_STREAM) return null;
  const spots = [];
  for (const key of new Set(parts)) {
    const m = SPOT_RE.exec(key);
    if (!m) return null;
    spots.push({ key, page: Number(m[1]), row: Number(m[2]), column: Number(m[3]), id: `bank:${m[4]}` });
  }
  return spots;
}

module.exports = {
  init({ config, log }) {
    const { host, port } = endpointOf(config.companion);
    const pages = createPageBook();
    const buttons = new Map(); // controlId → { image, seen, refs, waiters, linger, off }
    const viewers = new Set(); // { res, spots: [{ key, page, row, column, id, target }] }
    let link = null;
    let heartbeat = null;
    let status = host
      ? { state: 'connecting', message: `Connecting to Companion at ${host}:${port}` }
      : { state: 'error', message: "Enter Companion's address in /admin → Companion Buttons" };

    /* — following a button in Companion — */

    function watch(controlId) {
      let b = buttons.get(controlId);
      if (!b) {
        b = { image: null, seen: false, refs: 0, waiters: new Set(), linger: null, off: null };
        buttons.set(controlId, b);
        if (link) {
          b.off = link.subscribe(
            'preview.graphics.controlId',
            { controlId },
            (data) => {
              const image = typeof data === 'string' && data.startsWith('data:image/') ? data : null;
              const changed = image !== b.image || !b.seen;
              b.image = image;
              b.seen = true;
              for (const done of b.waiters) done();
              b.waiters.clear();
              // Status buttons redraw every second with the same picture; only a real change goes out.
              if (changed) sendButton(controlId);
            },
            (message) => log(`button ${controlId}: ${message}`)
          );
        }
      }
      clearTimeout(b.linger);
      b.linger = null;
      return b;
    }

    /** Let go of a button once nothing has looked at it for a while. */
    function release(controlId) {
      const b = buttons.get(controlId);
      if (!b || b.refs > 0 || b.waiters.size) return;
      clearTimeout(b.linger);
      b.linger = setTimeout(() => {
        if (b.refs > 0 || b.waiters.size) return;
        if (b.off) b.off();
        buttons.delete(controlId);
      }, LINGER_MS);
    }

    /** The control a tile's spot means right now (see the header), or null. */
    function resolve(spot) {
      if (!pages.loaded) return spot.id;
      if (pages.locate(spot.id)) return spot.id;
      return pages.at(spot.page, spot.row, spot.column);
    }

    function point(spot) {
      const target = resolve(spot);
      if (target === spot.target) return false;
      if (spot.target) {
        const old = buttons.get(spot.target);
        if (old) old.refs -= 1;
        release(spot.target);
      }
      spot.target = target;
      if (target) watch(target).refs += 1;
      return true;
    }

    /* — what a tile is sent — */

    function frame(spot) {
      const b = spot.target ? buttons.get(spot.target) : null;
      const location = spot.target ? pages.locate(spot.target) : null;
      const body = {
        key: spot.key,
        controlId: spot.target,
        status: status.state,
        message: status.message,
        image: b ? b.image : null,
        // A spot with nothing there is as answered as it will get.
        seen: b ? b.seen : pages.loaded,
        location,
      };
      return `event: button\ndata: ${JSON.stringify(body)}\n\n`;
    }

    function write(viewer, chunk) {
      try {
        viewer.res.write(chunk);
      } catch {
        drop(viewer);
      }
    }

    function sendButton(controlId) {
      for (const v of viewers) for (const spot of v.spots) if (spot.target === controlId) write(v, frame(spot));
    }

    function sendAll() {
      for (const v of viewers) {
        for (const spot of v.spots) {
          point(spot);
          write(v, frame(spot));
        }
      }
    }

    function drop(viewer) {
      if (!viewers.delete(viewer)) return;
      for (const spot of viewer.spots) {
        if (!spot.target) continue;
        const b = buttons.get(spot.target);
        if (b) b.refs -= 1;
        release(spot.target);
      }
    }

    function addViewer(res, spots) {
      const viewer = { res, spots: spots.map((s) => ({ ...s, target: null })) };
      viewers.add(viewer);
      for (const spot of viewer.spots) {
        point(spot);
        write(viewer, frame(spot));
      }
      return viewer;
    }

    if (host) {
      link = createLink({
        host,
        port,
        onStatus(next) {
          status = next.state === 'ok' && !pages.loaded
            ? { state: 'connecting', message: 'Connected — reading pages' }
            : next;
          if (next.state !== 'ok') log(next.message);
          sendAll();
        },
      });
      link.subscribe('pages.watch', undefined, (change) => {
        pages.apply(change);
        if (change && change.type === 'init') {
          status = { state: 'ok', message: `Companion at ${host}:${port} · ${pages.count} pages` };
          log(`connected to Companion at ${host}:${port} (${pages.count} pages)`);
        }
        // A page renamed, a button moved or a page re-imported changes what tiles show.
        sendAll();
      });
    }

    heartbeat = setInterval(() => {
      for (const v of viewers) write(v, ': ping\n\n');
    }, HEARTBEAT_MS);

    current = {
      get status() {
        return status;
      },
      pages,
      watch,
      release,
      addViewer,
      drop,
      linked: Boolean(link),
    };
    const self = current;

    return {
      stop() {
        clearInterval(heartbeat);
        for (const v of viewers) {
          try {
            v.res.end();
          } catch {
            /* gone */
          }
        }
        viewers.clear();
        for (const b of buttons.values()) {
          clearTimeout(b.linger);
          for (const done of b.waiters) done();
        }
        buttons.clear();
        if (link) link.close();
        if (current === self) current = null;
      },
      health() {
        const shown = new Set();
        for (const v of viewers) for (const spot of v.spots) if (spot.target) shown.add(spot.target);
        const suffix = status.state === 'ok' && shown.size ? ` · showing ${shown.size} button${shown.size === 1 ? '' : 's'}` : '';
        return { status: status.state, message: status.message + suffix };
      },
    };
  },

  routes() {
    return {
      'GET /pages': (req, res) => {
        if (!current) return sendJson(res, 503, { error: 'Companion Buttons is not running' });
        const { state, message } = current.status;
        return sendJson(res, 200, { status: state, message, pages: current.pages.list() });
      },

      'GET /image/*': (req, res) => {
        const raw = String(req.wildcard || '').replace(/^\//, '');
        if (!ID_RE.test(raw)) return sendJson(res, 400, { error: 'Not a Companion button id' });
        if (!current || !current.linked) return sendJson(res, 503, { error: current ? current.status.message : 'Not running' });
        const id = `bank:${raw}`;
        const app = current;
        const b = app.watch(id);
        const reply = () => {
          if (!b.image) {
            res.writeHead(b.seen ? 404 : 504, { 'Cache-Control': 'no-store' });
            res.end();
          } else {
            const png = Buffer.from(b.image.slice(b.image.indexOf(',') + 1), 'base64');
            res.writeHead(200, { 'Content-Type': 'image/png', 'Cache-Control': 'no-store', 'Content-Length': png.length });
            res.end(png);
          }
          app.release(id);
        };
        if (b.seen) return reply();
        let done = false;
        const finish = () => {
          if (done) return;
          done = true;
          clearTimeout(timer);
          b.waiters.delete(finish);
          reply();
        };
        const timer = setTimeout(finish, FIRST_FRAME_MS);
        b.waiters.add(finish);
        req.on('close', () => {
          if (done) return;
          done = true;
          clearTimeout(timer);
          b.waiters.delete(finish);
          app.release(id);
        });
      },

      'GET /stream/*': (req, res) => {
        const spots = spotsFrom(req);
        if (!spots) return sendJson(res, 400, { error: 'Not a list of Companion buttons' });
        res.writeHead(200, {
          'Content-Type': 'text/event-stream; charset=utf-8',
          'Cache-Control': 'no-cache, no-transform',
          Connection: 'keep-alive',
          'X-Accel-Buffering': 'no',
        });
        res.write('retry: 3000\n\n');
        if (!current) {
          for (const s of spots) {
            const body = { key: s.key, controlId: null, status: 'error', message: 'Companion Buttons is not running', image: null, seen: false, location: null };
            res.write(`event: button\ndata: ${JSON.stringify(body)}\n\n`);
          }
          return void res.end();
        }
        const app = current;
        const viewer = app.addViewer(res, spots);
        try {
          req.socket.setKeepAlive(true, HEARTBEAT_MS);
        } catch {
          /* gone */
        }
        req.on('close', () => app.drop(viewer));
      },
    };
  },
};