// Plain CommonJS worker_threads entry point, NOT part of the Meteor imports
// graph (lives under private/ so `meteor build` copies it verbatim into
// programs/server/assets/app/workers/unionWorker.js instead of compiling it).
//
// Runs the CPU-heavy part of the subscriptions geo-union (circle generation +
// sequential turf.union chain) off the main thread. A single tunion() call
// against an already-complex merged polygon can itself take seconds once
// there are thousands of subscriptions — yielding between iterations on the
// main thread doesn't help when one iteration alone blocks that long, so this
// needs a real worker thread, not just cooperative scheduling.
//
// workerData.subs must already be validated (location.lat/lon/distance
// present) and decorated (addNoisy/noNoisy already applied) by the caller.
// workerData.baseUnion, if given, is an already-computed union GeoJSON that
// subs gets merged into (the incremental-add fast path) instead of starting
// from scratch — for a single new subscription this is one tunion() call
// instead of redoing the whole chain over every subscription again.
const { parentPort, workerData } = require('worker_threads');
const tcircle = require('@turf/circle').default;
const tunion = require('@turf/union').default;
const ttrunc = require('@turf/truncate').default;

const truncOptions = { precision: 6, coordinates: 2 };

const run = () => {
  const { subs, baseUnion } = workerData;
  const circles = subs.map(s => tcircle(
    [s.location.lon, s.location.lat],
    s.distance,
    { units: 'kilometers', steps: 144 }
  ));

  let unionTemp = baseUnion || null;
  let start = 0;
  if (!unionTemp && circles.length > 0) {
    unionTemp = ttrunc(circles[0], truncOptions);
    start = 1;
  }
  for (let i = start; i < circles.length; i += 1) {
    unionTemp = ttrunc(tunion(unionTemp, circles[i]), truncOptions);
  }
  return unionTemp;
};

try {
  parentPort.postMessage({ union: run() });
} catch (e) {
  parentPort.postMessage({ error: e.message });
}