using System;

namespace Justice.Helpers
{
    public static class GeoHelper
    {
        public static double CalculateDistance(double lat1, double lon1, double lat2, double lon2)
        {
            const double EarthRadiusKm = 6371;

            double dLat = DegreesToRadians(lat2 - lat1);
            double dLon = DegreesToRadians(lon2 - lon1);

            double a = Math.Sin(dLat / 2) * Math.Sin(dLat / 2) +
                       Math.Cos(DegreesToRadians(lat1)) * Math.Cos(DegreesToRadians(lat2)) *
                       Math.Sin(dLon / 2) * Math.Sin(dLon / 2);

            double c = 2 * Math.Atan2(Math.Sqrt(a), Math.Sqrt(1 - a));

            return EarthRadiusKm * c;
        }

        private static double DegreesToRadians(double degrees)
        {
            return degrees * Math.PI / 180;
        }
    }
}