A TimeZone Aware DateTime Implementation

using System;
using NUnit.Framework;
using DateTimeZone;
using TimeZone=DateTimeZone.TimeZone;

namespace TestDateTimeZone
{
	/// <summary>
	/// Testing that local time converted to utc will be converted back to the same local time around DST changes for any time zone.
	/// </summary>
	[TestFixture]
	public class LocalToUtcToLocalTest
	{
		
		[Test]
		public void TestCetToUtcBackToCetAroundDstSummerChange()
		{
			DateTime lastSundayInMarchCet = DateUtil.GetLastSundayInMarch(2009);
			LocalDateTime beforeDst = new LocalDateTime(lastSundayInMarchCet, TimeZones.CET, false);

			// Adding 4 hours to both cet and utc representing the same time in different time zones
			for(int i=1; i<5; i++)
			{
				LocalDateTime modifiedCet = beforeDst.AddHours(i);
				UtcDateTime modifiedUtc = beforeDst.ConvertToUTC().AddHours(i);
				//Console.WriteLine("From: "+modifiedCet +" To: "+modifiedUtc);
				Assert.AreEqual(modifiedUtc, modifiedCet.ConvertToUTC());
				LocalDateTime result = modifiedUtc.AsLocalDateTime().ConvertTo(TimeZones.CET);
				//Console.WriteLine("From: "+modifiedUtc + " To: " + result);
				Assert.AreEqual(modifiedCet, result);

				//Console.WriteLine("-------------------------------------");
			}
		}

		[Test]
		public void TestCetAroundDstWinterChange()
		{
			DateTime lastSundayInOctoberCet = DateUtil.GetLastSundayInOctober(2009);
			LocalDateTime beforeDst = new LocalDateTime(lastSundayInOctoberCet.AddHours(-1), TimeZones.CET, true);

			// Adding 4 hours to both cet and utc representing the same time in different time zones
			for (int i = 2; i < 5; i++)
			{
				//Console.WriteLine("Before: " + beforeDst);
				LocalDateTime modifiedCet = beforeDst.AddHours(i);
				//Console.WriteLine("+" + i + "h: " + modifiedCet);
				
				//Console.WriteLine("-------------------------------------");
			}
		}

		[Test]
		public void TestCetAroundDstWinterChangeWithTimeSpan2h()
		{
			DateTime lastSundayInOctoberCet = DateUtil.GetLastSundayInOctober(2009);
			LocalDateTime beforeDst = new LocalDateTime(lastSundayInOctoberCet.AddHours(-1), TimeZones.CET, true);

			//Console.WriteLine("Before: " + beforeDst);
			LocalDateTime modifiedCet = beforeDst.AddTimeSpan(new TimeSpan(2, 0, 0));
			//Console.WriteLine("+2h: " + modifiedCet);
			Assert.AreEqual(new LocalDateTime(2009, 10, 25, 1, 0, 0, TimeZones.CET, true), modifiedCet);
		}

		[Test]
		public void TestCetAroundDstWinterChangeWithTimeSpan3h()
		{
			DateTime lastSundayInOctoberCet = DateUtil.GetLastSundayInOctober(2009);
			LocalDateTime beforeDst = new LocalDateTime(lastSundayInOctoberCet.AddHours(-1), TimeZones.CET, true);

			//Console.WriteLine("Before: " + beforeDst);
			LocalDateTime modifiedCet = beforeDst.AddTimeSpan(new TimeSpan(3, 0, 0));
			//Console.WriteLine("+3h: " + modifiedCet);
			Assert.AreEqual(new LocalDateTime(2009, 10, 25, 2, 0, 0, TimeZones.CET, true), modifiedCet);
		}

		[Test]
		public void TestCetAroundDstWinterChangeWithTimeSpan4hCausingFallback()
		{
			DateTime lastSundayInOctoberCet = DateUtil.GetLastSundayInOctober(2009);
			LocalDateTime beforeDst = new LocalDateTime(lastSundayInOctoberCet.AddHours(-1), TimeZones.CET, true);

			//Console.WriteLine("Before: " + beforeDst);
			LocalDateTime modifiedCet = beforeDst.AddTimeSpan(new TimeSpan(4, 0, 0));
			//Console.WriteLine("+4h: " + modifiedCet);
			Assert.AreEqual(new LocalDateTime(2009, 10, 25, 2, 0, 0, TimeZones.CET, false), modifiedCet);
		}

		[Test]
		public void TestCetToUtcBackToCetAroundDstWinterChange()
		{
			DateTime lastSundayInOctoberCet = DateUtil.GetLastSundayInOctober(2009);
			LocalDateTime beforeDst = new LocalDateTime(lastSundayInOctoberCet.AddHours(-1), TimeZones.CET, true);

			// Adding 4 hours to both cet and utc representing the same time in different time zones
			for (int i = 1; i < 5; i++)
			{
				//Console.WriteLine("Before: " + beforeDst);
				//Console.WriteLine("Before: " + beforeDst.ConvertToUTC());
				//Console.WriteLine("--");
				LocalDateTime modifiedCet = beforeDst.AddHours(i);
				UtcDateTime modifiedUtc = beforeDst.ConvertToUTC().AddHours(i);
				//Console.WriteLine("+"+i+"h: " + modifiedCet);
				//Console.WriteLine("+" + i + "h: " + modifiedUtc);
				Assert.AreEqual(modifiedUtc, modifiedCet.ConvertToUTC());

				//Console.WriteLine("-------------------------------------");
			}
		}

		[Test]
		public void TestCetToUtcBackToCetAroundDstSummerChange01_59_59()
		{
			DateTime lastSundayInMarchCet = DateUtil.GetLastSundayInMarch(2009).AddHours(-1).AddMinutes(-1);
			LocalDateTime beforeDst = new LocalDateTime(lastSundayInMarchCet, TimeZones.CET, false);

			// Adding 4 hours to both cet and utc representing the same time in different time zones
			for (int i = 1; i < 5; i++)
			{
				LocalDateTime modifiedCet = beforeDst.AddHours(i);
				UtcDateTime modifiedUtc = beforeDst.ConvertToUTC().AddHours(i);
				//Console.WriteLine("From: " + modifiedCet + " To: " + modifiedUtc);
				Assert.AreEqual(modifiedUtc, modifiedCet.ConvertToUTC());
				LocalDateTime result = modifiedUtc.AsLocalDateTime().ConvertTo(TimeZones.CET);
				//Console.WriteLine("From: " + modifiedUtc + " To: " + result);
				Assert.AreEqual(modifiedCet, result);

				//Console.WriteLine("-------------------------------------");
			}
		}

		[Test]
		public void TestCetToUtcBackToNewYorkAroundDstSummerChange01_59_59()
		{
			TimeZone tz = TimeZones.America__New_York;
			DateTime beforeDstStart = tz.GetDSTStart(2009).AddHours(-1).AddMinutes(-1);
			LocalDateTime beforeDst = new LocalDateTime(beforeDstStart, tz, false);

			// Adding 4 hours to both cet and utc representing the same time in different time zones
			for (int i = 1; i < 5; i++)
			{
				LocalDateTime modifiedCet = beforeDst.AddHours(i);
				UtcDateTime modifiedUtc = beforeDst.ConvertToUTC().AddHours(i);
				//Console.WriteLine("From: " + modifiedCet + " To: " + modifiedUtc);
				Assert.AreEqual(modifiedUtc, modifiedCet.ConvertToUTC());
				LocalDateTime result = modifiedUtc.AsLocalDateTime().ConvertTo(tz);
				//Console.WriteLine("From: " + modifiedUtc + " To: " + result);
				Assert.AreEqual(modifiedCet, result);

				//Console.WriteLine("-------------------------------------");
			}


		}

		/// <summary>
		/// Testing that UTC time jut before winter change will find the correct 2 hour in CET
		/// In this test, the UTC time is 12am and should then be adjusten to 2am CET summer time.
		/// </summary>
		[Test]
		public void TestUtc_2510_2009_00_ToCet()
		{
			DateTime expected = new DateTime(2009, 10, 25, 2,0,0);
			UtcDateTime utc = new UtcDateTime(2009, 10, 25);
			TimeZone toTimeZone = TimeZones.CET;
			
			LocalDateTime local = utc.AsLocalDateTime().ConvertTo(toTimeZone);
			//Console.WriteLine(local);
			Assert.AreEqual(expected, local.GetDateTime());
		}

		/// <summary>
		/// Testing that UTC time jut before winter change will find the correct 2 hour in CET
		/// In this test, the UTC time is 1am and should then be adjusten to 2am CET winter time.
		/// </summary>
		[Test]
		public void TestUtc_2510_2009_01_ToCet()
		{
			DateTime expected = new DateTime(2009, 10, 25, 2, 0, 0);
			UtcDateTime utc = new UtcDateTime(2009, 10, 25, 1,0,0);
			TimeZone toTimeZone = TimeZones.CET;

			LocalDateTime local = utc.AsLocalDateTime().ConvertTo(toTimeZone);
			//Console.WriteLine(local);
			Assert.AreEqual(expected, local.GetDateTime());
		}
	}
}