/*
 * NTPClient
 * Copyright (C)2001 Valer BOCAN <vbocan@dataman.ro>
 * All Rights Reserved
 * 
 * This code is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY, without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * 
 * To fully understand the concepts used herein, I strongly
 * recommend that you read the RFC 2030.
 * 
 * Borrowed from:
 * http://www.codeguru.com/Csharp/Csharp/cs_date_time/timeroutines/article.php/c4207/
 * 
 * upgraded to work in .NET V1.1
 * 
 */
using System;
using System.Net;
using System.Net.Sockets;
using System.Runtime.InteropServices;

namespace Unified.Network.SNTP
{
	// Leap indicator field values
	public enum _LeapIndicator
	{
		NoWarning,		// 0 - No warning
		LastMinute61,	// 1 - Last minute has 61 seconds
		LastMinute59,	// 2 - Last minute has 59 seconds
		Alarm			// 3 - Alarm condition (clock not synchronized)
	}

	//Mode field values
	public enum _Mode
	{
		SymmetricActive,	// 1 - Symmetric active
		SymmetricPassive,	// 2 - Symmetric pasive
		Client,				// 3 - Client
		Server,				// 4 - Server
		Broadcast,			// 5 - Broadcast
		Unknown				// 0, 6, 7 - Reserved
	}

	// Stratum field values
	public enum _Stratum
	{
		Unspecified,			// 0 - unspecified or unavailable
		PrimaryReference,		// 1 - primary reference (e.g. radio-clock)
		SecondaryReference,		// 2-15 - secondary reference (via NTP or SNTP)
		Reserved				// 16-255 - reserved
	}

	[StructLayout(LayoutKind.Sequential)]
	public struct SYSTEMTIME
	{
		public short wYear;
		public short wMonth;
		public short wDayOfWeek;
		public short wDay;
		public short wHour;
		public short wMinute;
		public short wSecond;
		public short wMilliseconds;
	}

	/// <summary>
	/// NTPClient is a C# class designed to connect to time servers on the Internet.
	/// The implementation of the protocol is based on the RFC 2030.
	/// 
	/// Public class members:
	///
	/// LeapIndicator - Warns of an impending leap second to be inserted/deleted in the last
	/// minute of the current day. (See the _LeapIndicator enum)
	/// 
	/// VersionNumber - Version number of the protocol (3 or 4).
	/// 
	/// Mode - Returns mode. (See the _Mode enum)
	/// 
	/// Stratum - Stratum of the clock. (See the _Stratum enum)
	/// 
	/// PollInterval - Maximum interval between successive messages.
	/// 
	/// Precision - Precision of the clock.
	/// 
	/// RootDelay - Round trip time to the primary reference source.
	/// 
	/// RootDispersion - Nominal error relative to the primary reference source.
	/// 
	/// ReferenceID - Reference identifier (either a 4 character string or an IP address).
	/// 
	/// ReferenceTimestamp - The time at which the clock was last set or corrected.
	/// 
	/// OriginateTimestamp - The time at which the request departed the client for the server.
	/// 
	/// ReceiveTimestamp - The time at which the request arrived at the server.
	/// 
	/// Transmit Timestamp - The time at which the reply departed the server for client.
	/// 
	/// RoundTripDelay - The time between the departure of request and arrival of reply.
	/// 
	/// LocalClockOffset - The offset of the local clock relative to the primary reference
	/// source.
	/// 
	/// Initialize - Sets up data structure and prepares for connection.
	/// 
	/// Connect - Connects to the time server and populates the data structure.
	/// 
	/// IsResponseValid - Returns true if received data is valid and if comes from
	/// a NTP-compliant time server.
	/// 
	/// ToString - Returns a string representation of the object.
	/// 
	/// -----------------------------------------------------------------------------
	/// Structure of the standard NTP header (as described in RFC 2030)
	///                       1                   2                   3
	///   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	///  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	///  |LI | VN  |Mode |    Stratum    |     Poll      |   Precision   |
	///  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	///  |                          Root Delay                           |
	///  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	///  |                       Root Dispersion                         |
	///  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	///  |                     Reference Identifier                      |
	///  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	///  |                                                               |
	///  |                   Reference Timestamp (64)                    |
	///  |                                                               |
	///  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	///  |                                                               |
	///  |                   Originate Timestamp (64)                    |
	///  |                                                               |
	///  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	///  |                                                               |
	///  |                    Receive Timestamp (64)                     |
	///  |                                                               |
	///  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	///  |                                                               |
	///  |                    Transmit Timestamp (64)                    |
	///  |                                                               |
	///  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	///  |                 Key Identifier (optional) (32)                |
	///  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	///  |                                                               |
	///  |                                                               |
	///  |                 Message Digest (optional) (128)               |
	///  |                                                               |
	///  |                                                               |
	///  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	/// 
	/// -----------------------------------------------------------------------------
	/// 
	/// NTP Timestamp Format (as described in RFC 2030)
	///                         1                   2                   3
	///     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	/// |                           Seconds                             |
	/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	/// |                  Seconds Fraction (0-padded)                  |
	/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	/// 
	/// </summary>
	public class NTPClient
	{
		[DllImport("kernel32.dll", SetLastError = true)]
		public static extern bool SetSystemTime([In] ref SYSTEMTIME st);

		// NTP Data Structure Length
		private const byte NTPDataLength = 48;
		// NTP Data Structure (as described in RFC 2030)
		byte []NTPData = new byte[NTPDataLength];

		// Offset constants for timestamps in the data structure
		private const byte offReferenceID		 = 12;
		private const byte offReferenceTimestamp = 16;
		private const byte offOriginateTimestamp = 24;
		private const byte offReceiveTimestamp   = 32;
		private const byte offTransmitTimestamp  = 40;

		// Leap Indicator
		public _LeapIndicator LeapIndicator
		{
			get
			{
				// Isolate the two most significant bits
				byte val = (byte)(NTPData[0] >> 6);
				switch(val)
				{
					case 0: return _LeapIndicator.NoWarning;
					case 1: return _LeapIndicator.LastMinute61;
					case 2: return _LeapIndicator.LastMinute59;
					case 3:
					default:
						return _LeapIndicator.Alarm;
				}
			}
		}

		// Version Number
		public byte VersionNumber
		{
			get
			{
				// Isolate bits 3 - 5
				byte val = (byte)((NTPData[0] & 0x38) >> 3);
				return val;
			}
		}

		// Mode
		public _Mode Mode
		{
			get
			{
				// Isolate bits 0 - 3
				byte val = (byte)(NTPData[0] & 0x7);
				switch(val)
				{
					case 0:
					case 6:
					case 7:
					default:
						return _Mode.Unknown;
					case 1:
						return _Mode.SymmetricActive;
					case 2:
						return _Mode.SymmetricPassive;
					case 3:
						return _Mode.Client;
					case 4:
						return _Mode.Server;
					case 5:
						return _Mode.Broadcast;
				}
			}
		}

		// Stratum
		public _Stratum Stratum
		{
			get
			{
				byte val = (byte)NTPData[1];
				if(val == 0) 
					return _Stratum.Unspecified;
				else
					if(val == 1) return _Stratum.PrimaryReference;
				else
					if(val <= 15) return _Stratum.SecondaryReference;
				else
					return _Stratum.Reserved;
			}
		}

		// Poll Interval
		public uint PollInterval
		{
			get
			{
				return (uint)Math.Round(Math.Pow(2, NTPData[2]));
			}
		}

		// Precision (in milliseconds)
		public double Precision
		{
			get
			{
				return (1000 * Math.Pow(2, NTPData[3]));
			}
		}

		// Root Delay (in milliseconds)
		public double RootDelay
		{
			get
			{
				int temp = 0;
				temp = 256 * (256 * (256 * NTPData[4] + NTPData[5]) + NTPData[6]) + NTPData[7];
				return 1000 * (((double)temp) / 0x10000);
			}
		}

		// Root Dispersion (in milliseconds)
		public double RootDispersion
		{
			get
			{
				int temp = 0;
				temp = 256 * (256 * (256 * NTPData[8] + NTPData[9]) + NTPData[10]) + NTPData[11];
				return 1000 * (((double)temp) / 0x10000);
			}
		}

		// Reference Identifier
		public string ReferenceID
		{
			get
			{
				string val = "";
				
				switch(Stratum)
				{
					case _Stratum.Unspecified:
					case _Stratum.PrimaryReference:
						val += System.Convert.ToChar(NTPData[offReferenceID + 0]);
						val += System.Convert.ToChar(NTPData[offReferenceID + 1]);
						val += System.Convert.ToChar(NTPData[offReferenceID + 2]);
						val += System.Convert.ToChar(NTPData[offReferenceID + 3]);
						break;

					case _Stratum.SecondaryReference:
						switch(VersionNumber)
						{
							case 3:	// Version 3, Reference ID is an IPv4 address
								string Address = NTPData[offReferenceID + 0].ToString() + "." +
									NTPData[offReferenceID + 1].ToString() + "." +
									NTPData[offReferenceID + 2].ToString() + "." +
									NTPData[offReferenceID + 3].ToString();
								try
								{
								
									IPAddress RefAddr = System.Net.IPAddress.Parse(Address);
									//IPHostEntry Host = Dns.GetHostByAddress(RefAddr);
									IPHostEntry Host = Dns.GetHostEntry(RefAddr);
									val = Host.HostName + " (" + Address + ")";
								}
								catch(Exception)
								{
									val = "N/A";
								}

								break;

							case 4: // Version 4, Reference ID is the timestamp of last update
								DateTime time = ComputeDate(GetMilliSeconds(offReferenceID));
								// Take care of the time zone
								long offset = TimeZone.CurrentTimeZone.GetUtcOffset(DateTime.Now).Ticks;
								TimeSpan offspan = TimeSpan.FromTicks(offset);
								val = (time + offspan).ToString();
								break;

							default:
								val = "N/A";
								break;
						}

						break;
				}

				return val;
			}
		}

		// Reference Timestamp
		public DateTime ReferenceTimestamp
		{
			get
			{
				DateTime time = ComputeDate(GetMilliSeconds(offReferenceTimestamp));
				// Take care of the time zone
				long offset = TimeZone.CurrentTimeZone.GetUtcOffset(DateTime.Now).Ticks;
				TimeSpan offspan = TimeSpan.FromTicks(offset);
				return time + offspan;
			}
		}

		// Originate Timestamp
		public DateTime OriginateTimestamp
		{
			get
			{
				return ComputeDate(GetMilliSeconds(offOriginateTimestamp));
			}
		}

		// Receive Timestamp
		public DateTime ReceiveTimestamp
		{
			get
			{
				DateTime time = ComputeDate(GetMilliSeconds(offReceiveTimestamp));
				// Take care of the time zone
				long offset = TimeZone.CurrentTimeZone.GetUtcOffset(DateTime.Now).Ticks;
				TimeSpan offspan = TimeSpan.FromTicks(offset);
				return time + offspan;
			}
		}

		// Transmit Timestamp
		public DateTime TransmitTimestamp
		{
			get
			{
				DateTime time = ComputeDate(GetMilliSeconds(offTransmitTimestamp));
				// Take care of the time zone
				long offset = TimeZone.CurrentTimeZone.GetUtcOffset(DateTime.Now).Ticks;
				TimeSpan offspan = TimeSpan.FromTicks(offset);
				return time + offspan;
			}

			set
			{
				SetDate(offTransmitTimestamp, value);
			}
		}

		// Reception Timestamp
		public DateTime ReceptionTimestamp;
		
		// Round trip delay (in milliseconds)
		public int RoundTripDelay
		{
			get
			{
				TimeSpan span = (ReceiveTimestamp - OriginateTimestamp) + (ReceptionTimestamp - TransmitTimestamp);
				return (int)span.TotalMilliseconds;
			}
		}

		// Local clock offset (in milliseconds)
		public int LocalClockOffset
		{
			get
			{
				TimeSpan span = (ReceiveTimestamp - OriginateTimestamp) - (ReceptionTimestamp - TransmitTimestamp);
				return (int)(span.TotalMilliseconds / 2);
			}
		}

		// Compute date, given the number of milliseconds since January 1, 1900
		private DateTime ComputeDate(ulong milliseconds)
		{
			TimeSpan span = TimeSpan.FromMilliseconds((double)milliseconds);
			DateTime time = new DateTime(1900, 1, 1);
			time += span;
			return time;
		}

		// Compute the number of milliseconds, given the offset of a 8-byte array
		private ulong GetMilliSeconds(byte offset)
		{
			ulong intpart = 0, fractpart = 0;

			for(int i = 0; i <= 3; i++)
			{
				intpart = 256 * intpart + NTPData[offset + i];	
			}

			for(int i = 4; i<=7; i++)
			{
				fractpart = 256 * fractpart + NTPData[offset + i];
			}

			ulong milliseconds = intpart * 1000 + (fractpart * 1000) / 0x100000000L;
			return milliseconds;
		}

		// Compute the 8-byte array, given the date
		private void SetDate(byte offset, DateTime date)
		{
			ulong intpart = 0, fractpart = 0;
			DateTime StartOfCentury = new DateTime(1900, 1, 1, 0, 0, 0);	// January 1, 1900 12:00 AM

			ulong milliseconds = (ulong)(date - StartOfCentury).TotalMilliseconds;
			intpart = milliseconds / 1000;
			fractpart=((milliseconds % 1000) * 0x100000000L) / 1000;

			ulong temp = intpart;
			for(int i = 3; i >= 0; i--)
			{
				NTPData[offset + i] = (byte) (temp % 256);
				temp = temp / 256;
			}

			temp = fractpart;
			for(int i = 7; i >=4; i--)
			{
				NTPData[offset + i] = (byte) (temp % 256);
				temp = temp / 256;
			}
		}

		// Initialize the NTPClient data
		private void Initialize()
		{
			// Set version number to 4 and Mode to 3 (client)
			NTPData[0] = 0x1B;
			// Initialize all other fields with 0
			for(int i = 1; i < 48; i++)
			{
				NTPData[i] = 0;
			}

			// Initialize the transmit timestamp
			TransmitTimestamp = DateTime.Now;
		}

		public NTPClient(string host)
		{
			TimeServer = host;
		}

		// Connect to the time server
		public void Connect()
		{
			try
			{
				//IPHostEntry hostadd = System.Net.Dns.Resolve(TimeServer);
				IPHostEntry hostadd = System.Net.Dns.GetHostEntry(TimeServer);
				IPEndPoint EPhost = new IPEndPoint(hostadd.AddressList[0], 123);
				UdpClient TimeSocket = new UdpClient();
				TimeSocket.Client.ReceiveTimeout = 1000;
				TimeSocket.Connect(EPhost);
				System.Threading.Thread.Sleep(1000);
				Initialize();
				TimeSocket.Send(NTPData, NTPData.Length);
				System.Threading.Thread.Sleep(1000);
				NTPData = TimeSocket.Receive(ref EPhost);
				if(!IsResponseValid())
				{
					//throw new Exception("Invalid response from " + TimeServer);
				}

				ReceptionTimestamp = DateTime.Now;
			}
			catch (SocketException)
			{
				//throw new Exception(e.Message);
			}
		}

		// Check if the response from server is valid
		public bool IsResponseValid()
		{
			if (NTPData.Length < NTPDataLength || Mode != _Mode.Server)
			{
				return false;
			}
			else
			{
				return true;
			}
		}

		// Converts the object to string
		public override string ToString()
		{
			string str;

			str = "Leap Indicator: ";
			switch(LeapIndicator)
			{
				case _LeapIndicator.NoWarning:
					str += "No warning";
					break;
				case _LeapIndicator.LastMinute61:
					str += "Last minute has 61 seconds";
					break;
				case _LeapIndicator.LastMinute59:
					str += "Last minute has 59 seconds";
					break;
				case _LeapIndicator.Alarm:
					str += "Alarm Condition (clock not synchronized)";
					break;
			}

			str += "\r\nVersion number: " + VersionNumber.ToString() + "\r\n";
			str += "Mode: ";
			switch(Mode)
			{
				case _Mode.Unknown:
					str += "Unknown";
					break;
				case _Mode.SymmetricActive:
					str += "Symmetric Active";
					break;
				case _Mode.SymmetricPassive:
					str += "Symmetric Pasive";
					break;
				case _Mode.Client:
					str += "Client";
					break;
				case _Mode.Server:
					str += "Server";
					break;
				case _Mode.Broadcast:
					str += "Broadcast";
					break;
			}

			str += "\r\nStratum: ";
			switch(Stratum)
			{
				case _Stratum.Unspecified:
				case _Stratum.Reserved:
					str += "Unspecified";
					break;
				case _Stratum.PrimaryReference:
					str += "Primary Reference";
					break;
				case _Stratum.SecondaryReference:
					str += "Secondary Reference";
					break;
			}

			str += "\r\nLocal time: " + TransmitTimestamp.ToString();
			str += "\r\nPrecision: " + Precision.ToString() + " ms";
			str += "\r\nPoll Interval: " + PollInterval.ToString() + " s";
			str += "\r\nReference ID: " + ReferenceID.ToString();
			str += "\r\nRoot Dispersion: " + RootDispersion.ToString() + " ms";
			str += "\r\nRound Trip Delay: " + RoundTripDelay.ToString() + " ms";
			str += "\r\nLocal Clock Offset: " + LocalClockOffset.ToString() + " ms";
			str += "\r\n";

			return str;
		}

		// The URL of the time server we're connecting to
		private string TimeServer;

		public static Unified.Network.SNTP.NTPClient GetTime(string TimeServer)
		{
			Unified.Network.SNTP.NTPClient client = new Unified.Network.SNTP.NTPClient(TimeServer);
			client.Connect();
			return client;
		}

		public static Unified.Network.SNTP.NTPClient GetTime()
		{
			return GetTime(DefaultTimeServer);
		}

		public static string DefaultTimeServer="time.nist.gov";
		public static Unified.Network.SNTP.NTPClient GetAndSetTime()
		{
			return GetAndSetTime(DefaultTimeServer);
		}

		public static Unified.Network.SNTP.NTPClient GetAndSetTime(string TimeServer)
		{
			Unified.Network.SNTP.NTPClient client = GetTime(TimeServer);	
			System.DateTime setTime =TimeZone.CurrentTimeZone.ToUniversalTime(System.DateTime.Now.AddMilliseconds(client.LocalClockOffset));

			SYSTEMTIME st = new SYSTEMTIME();
			st.wYear = (short)setTime.Year; // must be short 
			st.wMonth = (short)setTime.Month;
			st.wDay = (short)setTime.Day;
			st.wHour = (short)setTime.Hour;
			st.wMinute = (short)setTime.Minute;
			st.wSecond = (short)setTime.Second;
			st.wMilliseconds = (short)setTime.Millisecond;

			SetSystemTime(ref st);

			//int val = Unified.LocalSystem.CurrentSystem.SetSystemTime(setTime);
			return client;
		}
	}
}
