namespace JobsMedical.Web.Services;

public static class Geo
{
    private const double EarthRadiusKm = 6371.0;

    /// <summary>Great-circle (Haversine) distance in kilometers between two lat/lng points.</summary>
    public static double DistanceKm(double lat1, double lng1, double lat2, double lng2)
    {
        double dLat = ToRad(lat2 - lat1);
        double dLng = ToRad(lng2 - lng1);
        double a = Math.Sin(dLat / 2) * Math.Sin(dLat / 2)
                 + Math.Cos(ToRad(lat1)) * Math.Cos(ToRad(lat2))
                 * Math.Sin(dLng / 2) * Math.Sin(dLng / 2);
        return EarthRadiusKm * 2 * Math.Atan2(Math.Sqrt(a), Math.Sqrt(1 - a));
    }

    private static double ToRad(double deg) => deg * Math.PI / 180.0;
}