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

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.
 */
const calcUnionAsync = subs => new Promise((resolve, reject) => {
  const worker = new Worker(WORKER_PATH, { workerData: { subs } });
  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;