/** 球面距离（米） */
export function haversineMeters(
  lat1: number,
  lng1: number,
  lat2: number,
  lng2: number,
): number {
  const toRad = (d: number) => (d * Math.PI) / 180;
  const R = 6371000;
  const dLat = toRad(lat2 - lat1);
  const dLng = toRad(lng2 - lng1);
  const a =
    Math.sin(dLat / 2) ** 2 +
    Math.cos(toRad(lat1)) * Math.cos(toRad(lat2)) * Math.sin(dLng / 2) ** 2;
  return 2 * R * Math.asin(Math.min(1, Math.sqrt(a)));
}

export function formatDistanceMeters(meters: number | null | undefined): string {
  if (meters == null || !Number.isFinite(meters) || meters < 0) return '—';
  if (meters < 1000) return `${Math.max(1, Math.round(meters))}m`;
  const km = meters / 1000;
  return `${km < 10 ? km.toFixed(1) : Math.round(km)}km`;
}