import tcircle from '@turf/circle';
import tunion from '@turf/union';
import ttrunc from '@turf/truncate';

const truncOptions = { precision: 6, coordinates: 2 };
// How many polygons to process before yielding to the event loop once.
const YIELD_EVERY = 100;

const yieldToEventLoop = () => new Promise((resolve) => { setImmediate(resolve); });

/**
 * Circle-union of subscriptions, equivalent to map-common-utils' calcUnion(typeCircle=true),
 * but split into a `for` loop that yields to the event loop every YIELD_EVERY polygons.
 * The vendored calcUnion runs the same turf.union chain fully synchronously, which for
 * thousands of subscriptions blocks Meteor's single-threaded DDP/HTTP handling for minutes
 * (see plan-modernizacion notes on the subsUnion hang). This keeps the exact same geometry
 * output while letting other requests interleave between chunks.
 */
const calcUnionAsync = async (subs, decorated) => {
  const unionGroup = [];
  for (let i = 0; i < subs.length; i += 1) {
    const osub = subs[i];
    try {
      if (osub.location && osub.location.lat && osub.location.lon && osub.distance) {
        const dsub = decorated(osub);
        unionGroup.push(tcircle(
          [dsub.location.lon, dsub.location.lat],
          dsub.distance,
          { units: 'kilometers', steps: 144 }
        ));
      } else {
        console.info(`Wrong element to do union ${JSON.stringify(osub)}`);
      }
    } catch (e) {
      console.error(e, `Wrong element trying to make union ${JSON.stringify(osub)}`);
    }
    // Deliberate: yield to the event loop periodically instead of blocking it.
    // eslint-disable-next-line no-await-in-loop
    if (i % YIELD_EVERY === 0) await yieldToEventLoop();
  }

  let unionTemp = unionGroup.length > 0 ? ttrunc(unionGroup[0], truncOptions) : null;
  for (let i = 1; i < unionGroup.length; i += 1) {
    unionTemp = ttrunc(tunion(unionTemp, unionGroup[i]), truncOptions);
    // Deliberate: yield to the event loop periodically instead of blocking it.
    // eslint-disable-next-line no-await-in-loop
    if (i % YIELD_EVERY === 0) await yieldToEventLoop();
  }
  return unionTemp;
};

export default calcUnionAsync;