using System;
using System.Net;
using System.Net.Sockets;

public class NtpService
{
    private readonly string _ntpServer;
    private TimeSpan _timeOffset = TimeSpan.Zero;
    private DateTime _lastSync = DateTime.MinValue;

    public NtpService(string ntpServer)
    {
        _ntpServer = ntpServer;
    }

    public DateTime GetCurrentTime()
    {
        // Sync with your NTP server every 1 hour
        if ((DateTime.UtcNow - _lastSync).TotalHours > 1)
        {
            SyncWithNtp();
        }

        // Apply the offset so the clock advances smoothly between syncs
        return DateTime.Now.Add(_timeOffset);
    }

    private void SyncWithNtp()
    {
        try
        {
            var ntpData = new byte[48];
            ntpData[0] = 0x1B; // NTP request header (Client mode, Version 3)

            var addresses = Dns.GetHostEntry(_ntpServer).AddressList;
            var ipEndPoint = new IPEndPoint(addresses[0], 123);

            using (var socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp))
            {
                socket.ReceiveTimeout = 3000;
                socket.Connect(ipEndPoint);
                socket.Send(ntpData);
                socket.Receive(ntpData);
            }

            // Parse the 64-bit timestamp from the NTP response
            ulong intPart = (ulong)ntpData[40] << 24 | (ulong)ntpData[41] << 16 | (ulong)ntpData[42] << 8 | (ulong)ntpData[43];
            ulong fractPart = (ulong)ntpData[44] << 24 | (ulong)ntpData[45] << 16 | (ulong)ntpData[46] << 8 | (ulong)ntpData[47];

            var milliseconds = (intPart * 1000) + ((fractPart * 1000) / 0x100000000L);
            var networkTime = new DateTime(1900, 1, 1, 0, 0, 0, DateTimeKind.Utc).AddMilliseconds((long)milliseconds);

            // Calculate the difference between Pi's local UTC and NTP UTC
            _timeOffset = networkTime - DateTime.UtcNow;
            _lastSync = DateTime.UtcNow;

            Console.WriteLine($"NTP Sync to {_ntpServer} successful. Offset: {_timeOffset.TotalMilliseconds:F1}ms");
        }
        catch (Exception ex)
        {
            Console.WriteLine($"NTP Sync failed: {ex.Message}");
        }
    }
}