using System;
using System.Data;
using System.Data.SqlClient;
using System.Data.SqlTypes;
using System.IO;
using System.Text;
using System.Xml;
using System.Xml.Linq;
using Microsoft.SqlServer.Server;
using Neo.Afx.ComponentModel;

namespace Neo.Afx.Helpers
{
    /// <summary>
    /// A helper for geo data related functoins
    /// </summary>
    public class GeoLocationHelper
    {
        /// <summary>
        /// Does check digit validation on an RSA id number
        /// </summary>
        /// <param name="fromLongitude">The from longitude.</param>
        /// <param name="fromLatitude">The from latitude.</param>
        /// <param name="toLongitude">The to longitude.</param>
        /// <param name="toLatitude">The to latitude.</param>
        /// 
        /// <returns>True/False</returns>
        [SqlFunction(
            IsDeterministic = true,
            IsPrecise = true,
            DataAccess = DataAccessKind.Read,
            SystemDataAccess = SystemDataAccessKind.Read
            )]
        public static SqlDouble GetDistanceBetweenPoints(SqlDouble fromLongitude, SqlDouble fromLatitude, SqlDouble toLongitude, SqlDouble toLatitude)
        {
            if (fromLongitude == 0 || fromLatitude == 0 || toLongitude == 0 || toLatitude == 0)
            {
                new SqlDouble(-1);
            }

            double distance = -1; 

            try
            {                
                if ((fromLatitude.Value == toLatitude.Value) && (fromLongitude.Value == toLongitude.Value))
                {
                    return 0;
                }
                else
                {
                    //See https://www.geodatasource.com/developers/c-sharp for more info
                    double theta = fromLongitude.Value - toLongitude.Value;
                    distance = Math.Sin(deg2rad(fromLatitude.Value)) * Math.Sin(deg2rad(toLatitude.Value)) + Math.Cos(deg2rad(fromLatitude.Value)) * Math.Cos(deg2rad(toLatitude.Value)) * Math.Cos(deg2rad(theta));
                    distance = Math.Acos(distance);
                    distance = rad2deg(distance);
                    distance = distance * 60 * 1.1515;
                    distance = distance * 1.609344;                                        
                }
            }
            catch {
                distance = -1;
            }
            
            return new SqlDouble(distance);
        }

        
        //This function converts decimal degrees to radians
        private static double deg2rad(double deg)
        {
            return (deg * Math.PI / 180.0);
        }
        
        //This function converts radians to decimal degrees
        private static double rad2deg(double rad)
        {
            return (rad / Math.PI * 180.0);
        }
    }
}