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

export function haversineKm(a: LatLng, b: LatLng): number {
  const R = 6371;
  const dLat = (b.lat - a.lat) * Math.PI / 180;
  const dLng = (b.lng - a.lng) * Math.PI / 180;
  const sinLat = Math.sin(dLat / 2);
  const sinLng = Math.sin(dLng / 2);
  const h = sinLat * sinLat +
    Math.cos(a.lat * Math.PI / 180) * Math.cos(b.lat * Math.PI / 180) * sinLng * sinLng;
  return R * 2 * Math.atan2(Math.sqrt(h), Math.sqrt(1 - h));
}

export function formatDistance(km: number): string {
  const mi = km * 0.621371;
  if (mi < 0.1) return "here";
  if (mi < 1) return `${(mi).toFixed(1)} mi`;
  return `${Math.round(mi)} mi`;
}