using System;
using System.IO;
using System.Linq;
using System.Net;
using System.Net.Sockets;
using System.Security.Cryptography;
using System.Text;
using System.Windows.Forms;

namespace UdPunching.ExampleW
{
    public partial class ExampleForm : Form
    {
        private const int ReceiveBufferSize = 1500;

        private static readonly IPEndPoint AnyEndPoint = new IPEndPoint(IPAddress.Any, 0);

        private IPEndPoint _serverEndPoint;
        private RSACryptoServiceProvider _serverRsa;
        private SocketAsyncEventArgs _saeRecv;

        private Guid _localId;
        private RSACryptoServiceProvider _localRsa;

        private Socket _localSocket;
        private IPEndPoint _publicEndPoint;
        private IPEndPoint _peerEndPoint;

        private readonly byte[] _keepAliveBuf = new byte[7];// 1flag,1count,1section,4timestamp
        private readonly ExchangeMessage _keepAliveMsg = new ExchangeMessage { Id = ExchangeMessageId.KeepAliveReq };

        //------------- ctor -------------

        public ExampleForm()
        {
            InitializeComponent();
            //------------- ui event -------------
        }

        //------------- ui event -------------

        private void ExampleForm_Shown(object sender, EventArgs e)
        {
            _serverRsa = new RSACryptoServiceProvider();
            _serverRsa.FromXmlString(File.ReadAllText(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "ServerPublicKey.txt")));

            var privateKeys = Directory
                .GetFiles(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "PrivateKey"))
                .Select(Path.GetFileNameWithoutExtension)
                .ToArray();

            PeerKetyDropDown.DataSource = privateKeys;

            var peerPubKeys = Directory
                .GetFiles(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "PeerPublicKey"))
                .Select(Path.GetFileNameWithoutExtension)
                .ToArray();

            PeerToKonckDropDown.DataSource = peerPubKeys;
        }

        private void StartButton_Click(object sender, EventArgs e)
        {
            Log("Starting...");

            _serverEndPoint = ServerIEndPointTextBox.Text.ParseToIpEndPointV4();

            _localId = new Guid(PeerKetyDropDown.Text);
            _localRsa = new RSACryptoServiceProvider();
            var peerPrivateKeyPath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "PrivateKey", PeerKetyDropDown.Text + ".txt");
            _localRsa.FromXmlString(
                File.ReadAllText(
                    peerPrivateKeyPath
                )
            );

            _localSocket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
            _localSocket.Bind(AnyEndPoint);

            _saeRecv = new SocketAsyncEventArgs();
            _saeRecv.SetBuffer(new byte[ReceiveBufferSize], 0, ReceiveBufferSize);
            _saeRecv.Completed += RecvCompleted;
            BeginRecv();

            KeepAliveTimer.Start();
            KeepAliveTimer_Tick(null, null);

            PeerKetyDropDown.Enabled = false;
            StartButton.Enabled = false;
            StopButton.Enabled = true;
            KnockButton.Enabled = true;

            Log("Started...");
        }

        private void StopButton_Click(object sender, EventArgs e)
        {
            Log("Stopping...");

            KeepAliveTimer.Stop();

            _localSocket?.Dispose();
            _saeRecv?.Dispose();
            _localRsa?.Dispose();

            _localSocket = null;
            _saeRecv = null;
            _localRsa = null;

            PeerKetyDropDown.Enabled = true;
            StartButton.Enabled = true;
            StopButton.Enabled = false;
            KnockButton.Enabled = false;
            SendButton.Enabled = false;

            Log("Stopped");
        }

        private void KeepAliveTimer_Tick(object sender, EventArgs e)
        {
            _keepAliveMsg.TimeStamp = DateTime.Now;
            _keepAliveMsg.WriteToBuffer(_keepAliveBuf);
            var encode = TransferCodec.Encode(_serverRsa, _localId, _keepAliveBuf);
            _localSocket.SendTo(encode, _serverEndPoint);
        }

        private void KnockButton_Click(object sender, EventArgs e)
        {
            //TODO:
            SendButton.Enabled = true;
        }

        private void SendButton_Click(object sender, EventArgs e)
        {
            //TODO: use datatransfer message
            var to = SendToEndPointTextBox.Text.ParseToIpEndPointV4();
            var sent = _localSocket.SendTo(Encoding.UTF8.GetBytes(SendContentTextBox.Text), to);
        }

        //------------- logic -------------

        private void ProcessPacket()
        {
            var peerId = TransferCodec.ReadId(_saeRecv.Buffer);
            if (_saeRecv.RemoteEndPoint.IpEndPointEqualsTo(_serverEndPoint))
            {
                if (BuildInPeerId.Invalid == peerId)
                {
                    Log("ERROR SERVER FAILURE");
                }
                else if (Guid.Empty == peerId)
                {
                    var msgData = TransferCodec.DecodeData(_localRsa, _saeRecv.Buffer);

                    var msg = new ExchangeMessage(msgData);

                    switch (msg.Id)
                    {
                        case ExchangeMessageId.KeepAliveAckSessionCreated:
                            _publicEndPoint = msg.PeerEndPoint;
                            Log($"Session Created, public endpoint {_publicEndPoint}");
                            Invoke(new Action(() =>
                            {
                                PublicEndPointTextBox.Text = msg.PeerEndPoint.ToString();
                            }));
                            break;

                        case ExchangeMessageId.KeepAliveAckNoChg:
                            break;

                        default:
                            throw new ArgumentOutOfRangeException();
                    }
                }
            }
            else
            {
                if (BuildInPeerId.Invalid == peerId || BuildInPeerId.Server == peerId)
                {
                    return; //Ignore invalid message
                }

                Invoke(new Action(() =>
                {
                    Log($"RECV FROM {_saeRecv.RemoteEndPoint},{Encoding.UTF8.GetString(_saeRecv.Buffer, 0, _saeRecv.BytesTransferred)}");
                }));
            }
        }

        private void RecvCompleted(object sender, SocketAsyncEventArgs e)
        {
            if (e.SocketError == SocketError.Success)
            {
                try
                {
                    ProcessPacket();
                }
                catch (Exception exception)
                {
                    Log($"ERROR ProcessPacket:{exception}");
                    Invoke(new Action(() => { StopButton_Click(null, null); }));
                }
            }
            else
            {
                Log($"ERROR SOCKET:{e.SocketError}");
            }

            if (null == _localSocket) return;
            if (false == _localSocket.ReceiveFromAsync(_saeRecv)) RecvCompleted(null, null);
        }

        private void BeginRecv()
        {
            _saeRecv.RemoteEndPoint = AnyEndPoint;
            if (false == _localSocket.ReceiveFromAsync(_saeRecv))
            {
                RecvCompleted(null, _saeRecv);
            }
        }

        //------------- util -------------

        private void Log(string content)
        {
            if (InvokeRequired)
            {
                Invoke(new Action<string>(Log), content);
                return;
            }

            RecvTextBox.Text =
                $"{DateTime.Now:yyyy-MM-dd HH:mm:ss} {content}"
                + $"{Environment.NewLine}"
                + RecvTextBox.Text;

            RecvTextBox.Refresh();
        }
    }
}