import path from 'path';
import { Worker } from 'worker_threads';

// Meteor only bundles the npm packages it sees imported/required somewhere in
// its own compiled module graph. The actual usage of these three is inside
// private/workers/unionWorker.js, a plain asset file Meteor's bundler never
// traces (it's loaded at runtime via new Worker(), not import/require here).
// Without this, `meteor build` drops them from programs/server/node_modules
// and the worker fails at startup with "Cannot find module '@turf/circle'".
import '@turf/circle';
import '@turf/union';
import '@turf/truncate';

const WORKER_PATH = path.resolve(process.cwd(), 'assets/app/workers/unionWorker.js');

/**
 * Circle-union of already-validated, already-decorated subscriptions, run in a
 * worker thread so the main event loop (DDP/HTTP) stays free regardless of
 * how long any single turf.union call takes. subs must be an array of plain
 * { location: { lat, lon }, distance } objects. If baseUnion is given, subs
 * are merged into it instead of a union computed from scratch.
 */
const calcUnionAsync = (subs, baseUnion = null) => new Promise((resolve, reject) => {
  const worker = new Worker(WORKER_PATH, { workerData: { subs, baseUnion } });
  worker.once('message', (msg) => {
    worker.terminate();
    if (msg.error) {
      reject(new Error(msg.error));
    } else {
      resolve(msg.union);
    }
  });
  worker.once('error', (err) => {
    worker.terminate();
    reject(err);
  });
});

export default calcUnionAsync;