using System;

namespace Algorithms.Other
{
    public static class GeoLocation
    {
        private const double EarthRadiusKm = 6371.01d;

        /// <summary>
        ///     Calculates spherical distance between 2 points given their latitude, longitude coordinates.
        ///     https://www.movable-type.co.uk/scripts/latlong.html.
        /// </summary>
        /// <param name="lat1">Latitude of point A.</param>
        /// <param name="lng1">Longitude of point A.</param>
        /// <param name="lat2">Latitude of point B.</param>
        /// <param name="lng2">Longitude of point B.</param>
        /// <returns>Spherical distance between A and B.</returns>
        public static double CalculateDistanceFromLatLng(double lat1, double lng1, double lat2, double lng2)
        {
            var pi180 = Math.PI / 180d;
            var lat1Radian = lat1 * pi180;
            var lng1Radian = lng1 * pi180;
            var lat2Radian = lat2 * pi180;
            var lng2Radian = lng2 * pi180;

            var diffLat = lat2Radian - lat1Radian;
            var diffLng = lng2Radian - lng1Radian;

            var haversine =
                Math.Sin(diffLat / 2) * Math.Sin(diffLat / 2)
                + Math.Cos(lat1Radian) * Math.Cos(lat2Radian) * Math.Sin(diffLng / 2) * Math.Sin(diffLng / 2);
            var distance = EarthRadiusKm * (2d * Math.Atan2(Math.Sqrt(haversine), Math.Sqrt(1 - haversine)));

            return distance * 1000; // Convert from km -> m
        }
    }
}
