/*
 * Copyright (c) 2026 by Christian Kellner.
 * Licensed under Apache-2.0 with Commons Clause and Attribution/Naming Clause
 */

const R = 6371000; // Earth radius in meters
/**
 * Calculate the great-circle distance between two points on Earth using the Haversine formula.
 * This is to calculate the distance between the listing address & the address provided by the user. I know, it is only
 * a rough estimation as this calculates the distance as a straight line, but it's more convenient than using an external
 * service and still gives a good approximation for sorting purposes.
 * Returns distance in meters.
 *
 * @param {number} lat1
 * @param {number} lon1
 * @param {number} lat2
 * @param {number} lon2
 * @returns {number}
 */
export function distanceMeters(lat1, lon1, lat2, lon2) {
  const toRad = (deg) => (deg * Math.PI) / 180;

  const phi1 = toRad(lat1);
  const phi2 = toRad(lat2);
  const dPhi = toRad(lat2 - lat1);
  const dLambda = toRad(lon2 - lon1);

  const a =
    Math.sin(dPhi / 2) * Math.sin(dPhi / 2) +
    Math.cos(phi1) * Math.cos(phi2) * Math.sin(dLambda / 2) * Math.sin(dLambda / 2);

  const c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));

  return Math.round(R * c * 10) / 10;
}