/** Haversine distance between two lat/lng points, in kilometres. */
export function distanceKm(
  lat1: number, lon1: number,
  lat2: number, lon2: number
): number {
  const R = 6371;
  const dLat = ((lat2 - lat1) * Math.PI) / 180;
  const dLon = ((lon2 - lon1) * Math.PI) / 180;
  const a =
    Math.sin(dLat / 2) ** 2 +
    Math.cos((lat1 * Math.PI) / 180) *
    Math.cos((lat2 * Math.PI) / 180) *
    Math.sin(dLon / 2) ** 2;
  return R * 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
}

export function formatDistance(km: number): string {
  return km < 1 ? `${Math.round(km * 1000)} m` : `${km.toFixed(0)} km`;
}

/** Geocode an Indian pincode to lat/lng using Nominatim (free, no key). */
export async function geocodePincode(pincode: string): Promise<{ lat: number; lng: number } | null> {
  try {
    const url = `https://nominatim.openstreetmap.org/search?postalcode=${encodeURIComponent(pincode)}&countrycodes=in&format=json&limit=1`;
    const res = await fetch(url, { headers: { "User-Agent": "PelagiaPortal/1.0" } });
    const data = await res.json();
    if (data[0]) return { lat: parseFloat(data[0].lat), lng: parseFloat(data[0].lon) };
  } catch { /* ignore */ }
  return null;
}