using System;
using System.Runtime.InteropServices;
using SQLite;

namespace Touchin.SQLiteExtensions
{
	public static partial class SQLite3Extensions
	{
		public static void CreateDistanceFunction (this SQLiteConnection connection)
		{
			connection.CreateFunction ("DISTANCE", 4, DistanceBody);
		}

		private static double Distance (double latitude1, double longitude1, double latitude2, double longitude2)
		{
			const double earthRadius = 6378.1;

			double lat1 =  latitude1 * Math.PI / 180;
			double lon1 = longitude1 * Math.PI / 180;
			double lat2 =  latitude2 * Math.PI / 180;
			double lon2 = longitude2 * Math.PI / 180;

			return earthRadius * Math.Acos (Math.Sin (lat1) * Math.Sin (lat2) + Math.Cos (lat1) * Math.Cos (lat2) * Math.Cos (lon2 - lon1));
		}

#if __IOS__
		// https://bugzilla.novell.com/show_bug.cgi?id=576775
		[MonoTouch.MonoPInvokeCallback (typeof (Action<IntPtr, int, IntPtr>))]
#endif
		private static void DistanceBody (IntPtr ctx, int argc, IntPtr argv)
		{
			IntPtr[] args = ExtractArgs (argc, argv);

			if (ValueType (args [0]) != SQLite3.ColType.Float ||
				ValueType (args [1]) != SQLite3.ColType.Float ||
				ValueType (args [2]) != SQLite3.ColType.Float ||
				ValueType (args [3]) != SQLite3.ColType.Float)
			{
				ResultNull (ctx);
			}
			else
			{
				double  latitude1 = ValueDouble (args [0]);
				double longitude1 = ValueDouble (args [1]);
				double  latitude2 = ValueDouble (args [2]);
				double longitude2 = ValueDouble (args [3]);
				double result = Distance (latitude1, longitude1, latitude2, longitude2);
				ResultDouble (ctx, result);
			}
		}
	}
}