/**
 * Sort/geo helpers shared across pages. Kept out of SortDropdown.tsx so that
 * component file exports only a component (React Fast Refresh).
 */
import ngeohash from 'ngeohash';

interface LatLng {
  lat: number;
  lng: number;
}

/**
 * Distance in km from `from` to a listing's own geohash, or null when the
 * listing carries no location. Used for the marketplace "Near me" sort + badges.
 */
export function itemDistanceKm(item: { geohash?: string }, from: LatLng): number | null {
  if (!item.geohash) return null;
  try {
    const { latitude, longitude } = ngeohash.decode(item.geohash);
    if (!Number.isFinite(latitude) || !Number.isFinite(longitude)) return null;
    return calculateDistance(from.lat, from.lng, latitude, longitude);
  } catch {
    return null;
  }
}

/** Weighted popularity score: comments 3x, reactions 1x, zaps 5x. */
export function calculatePopularity(
  commentCount = 0,
  reactionCount = 0,
  zapCount = 0,
): number {
  return commentCount * 3 + reactionCount * 1 + zapCount * 5;
}

/** Great-circle distance between two coordinates, in kilometres (Haversine). */
export function calculateDistance(
  lat1: number,
  lon1: number,
  lat2: number,
  lon2: number,
): number {
  const R = 6371; // Earth's radius in km
  const dLat = toRad(lat2 - lat1);
  const dLon = toRad(lon2 - lon1);

  const a =
    Math.sin(dLat / 2) * Math.sin(dLat / 2) +
    Math.cos(toRad(lat1)) * Math.cos(toRad(lat2)) * Math.sin(dLon / 2) * Math.sin(dLon / 2);

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

function toRad(degrees: number): number {
  return degrees * (Math.PI / 180);
}