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

namespace DhcpServer
{
    internal class DhcpProgram
    {
        private static bool _isRunning;

        private static void Main(string[] args)
        {
            Console.WriteLine("Starting...");

            if (AppConfigs.CreateDefaultClientEntryIfNoExist()) Console.WriteLine("Default client entry config created.");

            var tWorker = new Thread(Working);
            _isRunning = true;
            tWorker.Start();

            Console.WriteLine("Press ENTER to Stop.");
            Console.ReadLine();

            Console.Write("Shutting down...");
            _isRunning = false;
            tWorker.Join();

            Console.Write("Stopped.");

            Console.WriteLine();
            Console.Write("Press ENTER to Exit.");
            Console.ReadLine();
        }

        private static void Working(object obj)
        {
            var listenEndPoint = new IPEndPoint(IPAddress.Parse(Properties.Settings.Default.ListenOn), 67);

            var socket = new Socket(listenEndPoint.AddressFamily, SocketType.Dgram, ProtocolType.Udp)
            {
                EnableBroadcast = true,
                SendBufferSize = 65536,
                ReceiveBufferSize = 65536
            };
            socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReuseAddress, 1);
            socket.Bind(listenEndPoint);

            var upTime = DateTime.Now;

            Console.WriteLine($"DHCP Server started, listing on: {listenEndPoint}");

            var buffer = new byte[65536];
            EndPoint remoteEndPoint = new IPEndPoint(IPAddress.Any, 68);
            var polling = DateTime.Now;
            while (_isRunning)
            {
                Console.CursorLeft = 0;
                if (false == socket.Poll(500 * 1000, SelectMode.SelectRead))
                {
                    var timeSpan = DateTime.Now - polling;
                    var up = DateTime.Now - upTime;
                    Console.Write($"Polling..." +
                                  $" {timeSpan.Days:00}D {timeSpan.Hours:00}H {timeSpan.Minutes:00}M {timeSpan.Seconds:00}S {timeSpan.Milliseconds:000}" +
                                  $" / UP {up.Days:00}D {up.Hours:00}H {up.Minutes:00}M {up.Seconds:00}S {up.Milliseconds:000}");
                }
                else
                {
                    polling = DateTime.Now;
                    Console.WriteLine();

                    var bytes = socket.ReceiveFrom(buffer, 0, buffer.Length, SocketFlags.None, ref remoteEndPoint);
                    Console.Write($"Receive {bytes} byte From {remoteEndPoint}");

                    try
                    {
                        var packet = new DhcpPacket(buffer);

                        var mac = packet.ClientMacAddressHex;
                        Console.Write($" {packet.MessageType} by {mac}");

                        var entry = AppConfigs.GetClientEntry(mac);
                        if (entry.Enable == false)
                        {
                            Console.WriteLine(" ** No enabled, please edit config file.");
                        }
                        else
                        {
                            packet.OpCode = DhcpOpCode.BootReply;
                            DhcpMessageType reply;
                            switch (packet.MessageType)
                            {
                                default:
                                    reply = DhcpMessageType.Unknown;
                                    break;

                                case DhcpMessageType.Discover:
                                    reply = DhcpMessageType.Offer;
                                    break;

                                case DhcpMessageType.Request:
                                    reply = DhcpMessageType.Ack;
                                    break;
                            }

                            if (reply != DhcpMessageType.Unknown)
                            {
                                packet.Options.Clear();
                                packet.DhcpServerIdentifier = listenEndPoint.Address;
                                packet.MessageType = reply;
                                packet.LoadClientEntry(AppConfigs.GetDefaultClientEntry());
                                packet.LoadClientEntry(entry);

                                bytes = packet.WriteToBuffer(buffer);
                                var to = new IPEndPoint(IPAddress.Broadcast, 68);
                                Console.WriteLine();
                                Console.WriteLine($"Send {bytes} bytes to {to} {packet.MessageType} by {mac}");
                                socket.SendTo(buffer, 0, bytes, SocketFlags.None, to);
                            }
                        }
                    }
                    catch (Exception e)
                    {
                        Console.WriteLine(e);
                    }
                }
            }

            socket.Close();
        }
    }
}