ProdDash/modules/spl-meter/server.js

'use strict';

/**
 * SPL Meter server entry.
 *
 * Owns one capture child (spl-listener.js) and fans its frames out to every
 * tile over SSE. Browsers never see the audio device, only the numbers.
 *
 *   GET  /stream      → SSE, `state` events at the capture rate
 *   GET  /state       → the latest frame, for an instant first paint
 *   GET  /devices     → input devices, for the admin page's picker
 *   GET  /channels    → configured channels, for the tile gear picker
 *   POST /reset       → clear Leq and peak hold
 *   GET  /measure     → what a calibrator is reading right now, so the
 *                       admin page can tell the operator what to type
 *
 * Frames arrive 20×/s. That is the right rate for a meter to feel live and
 * the wrong rate to re-broadcast blindly, so the SSE fan-out drops a frame
 * whose numbers round to what the last one said.
 */

const path = require('path');
const { createSplListener } = require('./spl-listener');

/** Reference level of a sound level calibrator. Effectively always 94 dB. */
const CALIBRATOR_DB = 94;
/** How long /measure averages for. Long enough to ride out a wobble, short
    enough that nobody standing at the microphone gets bored. */
const MEASURE_MS = 3000;
/** SSE comment ping — keeps idle connections alive through sleepy Wi-Fi. */
const PING_MS = 15000;

/** Set by init(), read by routes() — both are rebuilt together on re-init. */
let state = null;

function parseChannels(raw) {
  return String(raw || '1')
    .split(',')
    .map((s) => Number(s.trim()))
    .filter((n) => Number.isInteger(n) && n >= 1 && n <= 64);
}

function parseCalibration(raw) {
  if (!String(raw || '').trim()) return [];
  return String(raw)
    .split(',')
    .map((s) => Number(s.trim()))
    .filter((n) => Number.isFinite(n));
}

module.exports = {
  init({ config, log }) {
    const channels = parseChannels(config.channels);
    const calibration = parseCalibration(config.calibration);
    const moduleDir = __dirname;

    state = {
      channels,
      calibrated: calibration.length === channels.length && channels.length > 0,
      frame: null,
      meta: null,
      error: '',
      streams: new Set(),
      listener: null,
      lastSent: '',
      pinger: null,
    };

    if (!config.enabled) {
      state.error = 'Sound level measurement is off — turn it on in ProdDash settings';
      return { stop() { teardown(); }, health: () => ({ status: 'error', message: state.error }) };
    }
    if (!config.device) {
      state.error = 'No audio device chosen yet';
      return { stop() { teardown(); }, health: () => ({ status: 'error', message: state.error }) };
    }
    if (!channels.length) {
      state.error = `Cannot read "${config.channels}" as a channel list — try 1, or 1,2`;
      return { stop() { teardown(); }, health: () => ({ status: 'error', message: state.error }) };
    }
    if (calibration.length && calibration.length !== channels.length) {
      state.error = `${channels.length} channel(s) but ${calibration.length} calibration offset(s) — `
        + 'give one per channel, or leave the offsets empty';
      return { stop() { teardown(); }, health: () => ({ status: 'error', message: state.error }) };
    }

    state.listener = createSplListener({
      device: config.device,
      channels,
      weighting: config.weighting || 'A',
      filter: config.filter || 'fast',
      bands: config.bands !== false,
      calibration,
      moduleDir,
      log,
      onUpdate(update) {
        if (update.error) {
          if (update.error !== state.error) log(update.error);
          state.error = update.error;
          state.frame = null;
          broadcast();
          return;
        }
        state.error = '';
        state.frame = update.frame;
        state.meta = update.meta;
        broadcast();
      },
    });

    state.pinger = setInterval(() => {
      for (const res of state.streams) {
        try { res.write(': ping\n\n'); } catch { state.streams.delete(res); }
      }
    }, PING_MS);

    return {
      stop() { teardown(); },
      health() {
        if (state.error) return { status: 'error', message: state.error };
        if (!state.frame) return { status: 'connecting', message: 'waiting for the first reading' };
        const n = state.channels.length;
        const what = `${n} channel${n === 1 ? '' : 's'} on ${config.device}`;
        return state.calibrated
          ? { status: 'ok', message: what }
          : { status: 'ok', message: `${what} — uncalibrated, reading dBFS` };
      },
    };
  },

  /**
   * Four tile kinds rather than one tile with a mode switch: an operator
   * picking "＋ SPL" wants to choose what they are putting on the wall, not
   * place a box and then configure it into being useful.
   */
  tiles() {
    return [
      { id: 'readout', name: 'SPL', description: 'The level, big',
        defaultSize: { w: 2, h: 1 }, minSize: { w: 1, h: 1 } },
      { id: 'bars', name: 'SPL Levels', description: 'One bar per channel, with peak hold',
        defaultSize: { w: 3, h: 2 }, minSize: { w: 2, h: 1 } },
      { id: 'rta', name: 'RTA', description: 'Third-octave bars',
        defaultSize: { w: 5, h: 3 }, minSize: { w: 3, h: 2 } },
      { id: 'spectrogram', name: 'Spectrogram', description: 'Third-octave bands over time',
        defaultSize: { w: 5, h: 3 }, minSize: { w: 3, h: 2 } },
    ];
  },

  routes({ config, log }) {
    return {
      'GET /state': (req, res) => {
        json(res, 200, snapshot());
      },

      'GET /stream': (req, res) => {
        res.writeHead(200, {
          'Content-Type': 'text/event-stream; charset=utf-8',
          'Cache-Control': 'no-cache, no-transform',
          Connection: 'keep-alive',
        });
        res.write('retry: 3000\n\n');
        try {
          res.write(`event: state\ndata: ${JSON.stringify(snapshot())}\n\n`);
        } catch { return; }
        state.streams.add(res);
        req.on('close', () => state.streams.delete(res));
      },

      /** Device list for the admin page. Runs the capture tool's --list,
          which is the only thing that knows what CoreAudio can see. */
      'GET /devices': async (req, res) => {
        try {
          const devices = await listDevices();
          json(res, 200, {
            options: devices.map((d) => ({
              value: d.name,
              label: `${d.name} — ${d.channels} ch @ ${Math.round(d.sampleRate)} Hz`,
            })),
          });
        } catch (err) {
          log(`device list failed: ${err.message}`);
          json(res, 200, { options: [] });   // the saved value stays selectable
        }
      },

      /** Channel list for a tile's gear popover. */
      'GET /channels': (req, res) => {
        json(res, 200, {
          options: state.channels.map((c) => ({ value: String(c), label: `Channel ${c}` })),
        });
      },

      'POST /reset': (req, res) => {
        if (state.listener) state.listener.reset();
        json(res, 200, { ok: true });
      },

      /**
       * What the microphone is hearing right now, unweighted and
       * uncalibrated, plus the offset that would make it read 94 dB.
       *
       * The module cannot write its own admin config, so this does not save
       * anything — it hands back a number for the operator to paste into the
       * Calibration box. Honest, if one step longer than it should be.
       */
      'GET /measure': (req, res) => {
        if (!state.listener || state.error) {
          json(res, 409, { error: state.error || 'not measuring' });
          return;
        }
        const wanted = Number(new URLSearchParams(req.search || '').get('channel'))
          || state.channels[0];
        const samples = [];
        const started = Date.now();
        const tick = setInterval(() => {
          const ch = state.frame && state.frame.ch.find((c) => c.i === wanted);
          if (ch && Number.isFinite(ch.dbfs) && ch.dbfs > -200) samples.push(ch.dbfs);
          if (Date.now() - started < MEASURE_MS) return;
          clearInterval(tick);
          if (samples.length < 5) {
            json(res, 200, {
              channel: wanted,
              error: 'No steady tone on that channel — check the calibrator is on and seated',
            });
            return;
          }
          // Mean of the linear powers, not of the decibels: averaging dB
          // would quietly under-read a signal that wobbles at all.
          const power = samples.reduce((s, db) => s + 10 ** (db / 10), 0) / samples.length;
          const measured = 10 * Math.log10(power);
          json(res, 200, {
            channel: wanted,
            measured: Math.round(measured * 100) / 100,
            reference: CALIBRATOR_DB,
            offset: Math.round((CALIBRATOR_DB - measured) * 100) / 100,
            samples: samples.length,
          });
        }, 100);
        req.on('close', () => clearInterval(tick));
      },
    };
  },
};

/* ── helpers ────────────────────────────────────────────────────────── */

function snapshot() {
  return {
    error: state.error,
    calibrated: state.calibrated,
    channels: state.channels,
    weighting: state.meta ? state.meta.weighting : '',
    filter: state.meta ? state.meta.filter : '',
    bandCentres: state.meta ? state.meta.bands : [],
    frame: state.frame,
  };
}

function broadcast() {
  const payload = snapshot();
  const line = JSON.stringify(payload);
  if (line === state.lastSent) return;      // nothing moved since last frame
  state.lastSent = line;
  for (const res of state.streams) {
    try { res.write(`event: state\ndata: ${line}\n\n`); } catch { state.streams.delete(res); }
  }
}

function teardown() {
  if (!state) return;
  if (state.listener) state.listener.stop();
  clearInterval(state.pinger);
  for (const res of state.streams) { try { res.end(); } catch { /* already gone */ } }
  state.streams.clear();
  state = null;
}

function listDevices() {
  return new Promise((resolve, reject) => {
    const { execFile } = require('child_process');
    execFile(path.join(__dirname, 'spl-capture'), ['--list'], { timeout: 10000 },
      (err, stdout) => {
        if (err && !stdout) { reject(err); return; }
        try { resolve(JSON.parse(stdout).devices || []); }
        catch (e) { reject(e); }
      });
  });
}

function json(res, code, body) {
  const text = JSON.stringify(body);
  res.writeHead(code, {
    'Content-Type': 'application/json; charset=utf-8',
    'Content-Length': Buffer.byteLength(text),
  });
  res.end(text);
}