using System;
using Foundation;

namespace Xamarin.PropertyEditing.Mac
{
	internal static class DateExtensions
	{
		/// <summary>The NSDate from Xamarin takes a reference point form January 1, 2001, at 12:00</summary>
		/// <remarks>
		/// It also has calls for NIX reference point 1970 but appears to be problematic
		/// </remarks>
		private static DateTime _nsRef = new DateTime (2001, 1, 1, 0, 0, 0, 0, DateTimeKind.Local); // last zero is millisecond

		/// <summary>Returns the seconds interval for a DateTime from NSDate reference data of January 1, 2001</summary>
		/// <param name="dt">The DateTime to evaluate</param>
		/// <returns>The seconds since NSDate reference date</returns>
		public static double SecondsSinceNsRefenceDate (this DateTime dt)
		{
			return (dt - _nsRef).TotalSeconds;
		}

		/// <summary>Convert a DateTime to NSDate</summary>
		/// <param name="dt">The DateTime to convert</param>
		/// <returns>An NSDate</returns>
		public static NSDate ToNSDate (this DateTime dt)
		{
			return NSDate.FromTimeIntervalSinceReferenceDate (dt.SecondsSinceNsRefenceDate ());
		}

		/// <summary>Convert an NSDate to DateTime</summary>
		/// <param name="nsDate">The NSDate to convert</param>
		/// <returns>A DateTime</returns>
		public static DateTime ToDateTime (this NSDate nsDate)
		{
			try {
				// We loose granularity below millisecond range but that is probably ok
				return _nsRef.AddSeconds (nsDate.SecondsSinceReferenceDate);
			} catch (ArgumentOutOfRangeException) {
				return _nsRef;
			}
		}
	}
}