// SPDX-License-Identifier: Apache-2.0
//
// Analysis worker: the browser's AnalysisResultsManager worker thread.
//
// Holds each loaded track's mono signal (transferred in, never copied) and runs
// one metric at a time on request, so a 10-minute spectrogram never blocks the
// page. Everything stays in this tab's memory; closing the tab frees it.
//
// Messages in:  {type: 'load', trackId, mono, sampleRate}
//               {type: 'compute', reqId, trackId, metricId}
//               {type: 'drop', trackId}
// Messages out: {type: 'result', reqId, trackId, metricId, data, ms}
//               {type: 'error', reqId, trackId, metricId, message}

import { COMPUTE, transferables } from './dsp.js';

const tracks = new Map();   // trackId -> {mono, sampleRate, memo}

self.onmessage = (event) => {
  const msg = event.data;
  if (msg.type === 'load') {
    tracks.set(msg.trackId, { mono: msg.mono, sampleRate: msg.sampleRate, memo: {} });
    return;
  }
  if (msg.type === 'drop') {
    tracks.delete(msg.trackId);
    return;
  }
  if (msg.type !== 'compute') return;

  const { reqId, trackId, metricId } = msg;
  const track = tracks.get(trackId);
  const compute = COMPUTE[metricId];
  if (!track || !compute) {
    self.postMessage({
      type: 'error', reqId, trackId, metricId,
      message: track ? `unknown metric ${metricId}` : 'track is no longer loaded',
    });
    return;
  }
  try {
    const t0 = performance.now();
    const data = compute(track.mono, track.sampleRate, track.memo);
    const ms = performance.now() - t0;
    self.postMessage({ type: 'result', reqId, trackId, metricId, data, ms }, transferables(data));
  } catch (err) {
    self.postMessage({ type: 'error', reqId, trackId, metricId, message: String((err && err.message) || err) });
  }
};