using System;
using System.Collections.Generic;
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 readonly IReadOnlyDictionary<Guid, RSACng> _peerPublicKeyRegistry;

        private IPEndPoint _serverEndPoint;
        private RSACng _serverPublicKey;
        private SocketAsyncEventArgs _saeReceive;

        private Guid _localId;
        private RSACng _localPrivateKey;
        private Socket _localSocket;
        private IPEndPoint _localPublicEndPoint;

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

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

        public ExampleForm()
        {
            InitializeComponent();

            _peerPublicKeyRegistry = Directory.GetFiles(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "PeerPublicKey"))
                .ToDictionary(
                    s => new Guid(Path.GetFileNameWithoutExtension(s)),
                    TransferCodec.LoadKey
                );
        }

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

        private void ExampleForm_Shown(object sender, EventArgs e)
        {
            _serverPublicKey = new RSACng();
            _serverPublicKey.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;

            PeerToKnockDropDown.DataSource = _peerPublicKeyRegistry.Keys.ToArray();
        }

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

            _serverEndPoint = ServerIEndPointTextBox.Text.ParseToIpEndPointV4();

            _localId = new Guid(PeerKetyDropDown.Text);
            var peerPrivateKeyPath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "PrivateKey", PeerKetyDropDown.Text + ".txt");
            _localPrivateKey = TransferCodec.LoadKey(peerPrivateKeyPath);

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

            _saeReceive = new SocketAsyncEventArgs();
            _saeReceive.SetBuffer(new byte[ReceiveBufferSize], 0, ReceiveBufferSize);
            _saeReceive.Completed += ReceiveCompleted;
            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();
            _saeReceive?.Dispose();
            _localPrivateKey?.Dispose();

            _localSocket = null;
            _saeReceive = null;
            _localPrivateKey = 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);
            _localSocket.SendExchangeMessageTo(_serverEndPoint, _localPrivateKey, _serverPublicKey, _localId, _keepAliveMsg);
        }

        private void KnockButton_Click(object sender, EventArgs e)
        {
            var idToKnock = new Guid(PeerToKnockDropDown.Text);
            if (idToKnock == _localId)
            {
                Log("KNOCK YOUR SELF ???");
                return;
            }

            var msg = new ExchangeMessage(ExchangeMessageId.PeerKnockReq)
            {
                PeerId = idToKnock
            };

            _localSocket.SendExchangeMessageTo(_serverEndPoint, _localPrivateKey, _serverPublicKey, _localId, msg);
        }

        private void SendButton_Click(object sender, EventArgs e)
        {
            var to = SendToEndPointTextBox.Text.ParseToIpEndPointV4();
            var sendMsg = new ExchangeMessage(ExchangeMessageId.DataTransfer);
            sendMsg.PayloadBytes = Encoding.UTF8.GetBytes(SendContentTextBox.Text);
            var sendBytes = TransferCodec.Encode(_localPrivateKey, _peerPublicKeyRegistry[new Guid(PeerToKnockDropDown.Text)], _localId, sendMsg.ToBytes());
            var sent = _localSocket.SendTo(sendBytes, to);
        }

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

        private void ProcessPacket()
        {
            var peerId = TransferCodec.ReadId(_saeReceive.Buffer);
            if (_saeReceive.RemoteEndPoint.IpEndPointEqualsTo(_serverEndPoint))
            {
                if (BuildInPeerId.Invalid == peerId) throw new InvalidDataException("SERVER ERROR: FAILURE");
                if (Guid.Empty != peerId) throw new InvalidDataException("SERVER ERROR: INVALID SERVER PEER ID");

                var msgData = TransferCodec.DecodeData(_localPrivateKey, _serverPublicKey, _saeReceive.Buffer);
                var msg = new ExchangeMessage(msgData);

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

                    case ExchangeMessageId.KeepAliveAckNoChg:
                        break;

                    case ExchangeMessageId.PeerKnockReqRelay:
                        if (false == msg.PeerId.HasValue)
                        {
                            Log($"INVALID {msg.Id} was IGNORED: peer id is required");
                            break;
                        }

                        ExchangeMessage msgReply;

                        if (false == _peerPublicKeyRegistry.TryGetValue(msg.PeerId.Value, out var peerKey))
                        {
                            Log($"DENIED {msg.Id}: peer id {msg.PeerId.Value}");
                            msgReply = new ExchangeMessage(ExchangeMessageId.PeerKnockDenied);
                        }
                        else
                        {
                            Log($"ACCEPT {msg.Id}: peer id {msg.PeerId.Value} @ {msg.PeerEndPoint}");
                            msgReply = new ExchangeMessage(ExchangeMessageId.PeerKnockAck) { PeerId = msg.PeerId };

                            Log($"SENDING CONNECTION REQ to {msg.PeerId} @ {msg.PeerEndPoint}");
                            var connMsg = new ExchangeMessage(ExchangeMessageId.PeerKnockConnectionReq);
                            _localSocket.SendExchangeMessageTo(msg.PeerEndPoint, _localPrivateKey, peerKey, _localId, connMsg);
                        }

                        _localSocket.SendExchangeMessageTo(_serverEndPoint, _localPrivateKey, _serverPublicKey, _localId, msgReply);
                        break;

                    case ExchangeMessageId.PeerKnockAckRelay:
                        if (false == msg.PeerId.HasValue)
                        {
                            Log($"INVALID RESPONSE {msg.Id} was IGNORED: peer id is required");
                            break;
                        }

                        Log($"KNOCK SUCCESS by {msg.PeerId} peer endpont is {msg.PeerEndPoint}");
                        Invoke(new Action(() =>
                        {
                            SendToEndPointTextBox.Text = msg.PeerEndPoint.ToString();
                            SendButton.Enabled = true;
                        }));

                        {
                            Log($"SENDING CONNECTION REQ to {msg.PeerId} @ {msg.PeerEndPoint}");
                            var connMsg = new ExchangeMessage(ExchangeMessageId.PeerKnockConnectionReq);
                            _localSocket.SendExchangeMessageTo(msg.PeerEndPoint, _localPrivateKey, _peerPublicKeyRegistry[msg.PeerId.Value], _localId, connMsg);
                        }
                        break;

                    case ExchangeMessageId.PeerKnockAckRelayed:
                        Log($"ACCEPT SENT {msg.PeerId}");
                        break;

                    case ExchangeMessageId.PeerKnockReqErrPeerNoAvailable:
                        Log($"KNOCK FAIL: {msg.PeerId}");
                        break;

                    case ExchangeMessageId.PeerKnockReqRelayed:
                        Log($"KNOCK SENT {msg.PeerId}");
                        break;

                    case ExchangeMessageId.PeerKnockDeniedRelay:
                        Log($"KNOCK DENIED by {msg.PeerId}");
                        break;

                    default:
                        throw new ArgumentOutOfRangeException("msg.Id", "SERVER ERROR: NO EXCEPTED MESSAGE FROM SERVER," + msg.Id);
                }
            }
            else
            {
                if (BuildInPeerId.Invalid == peerId || BuildInPeerId.Server == peerId || false == _peerPublicKeyRegistry.TryGetValue(peerId, out var peerPublicKey))
                {
                    throw new InvalidDataException("PEER ERROR: INVALID PEER ID");
                }

                var msgData = TransferCodec.DecodeData(_localPrivateKey, peerPublicKey, _saeReceive.Buffer);
                var msg = new ExchangeMessage(msgData);

                var reply = new ExchangeMessage { TimeStamp = DateTime.Now };

                if (false == msg.TimeStamp.HasValue || Math.Abs((DateTime.Now - msg.TimeStamp.Value).TotalSeconds) > 10)
                {
                    Log($"TIMESTAMP ERROR from peer {peerId}");
                    reply.Id = ExchangeMessageId.ErrTimeStamp;
                }
                else
                {
                    switch (msg.Id)
                    {
                        case ExchangeMessageId.PeerKnockConnectionReq:
                            reply.Id = ExchangeMessageId.PeerKnockConnectionAck;
                            break;

                        case ExchangeMessageId.DataTransfer:
                            reply.Id = ExchangeMessageId.DataTransferAck;
                            var payloadString = Encoding.UTF8.GetString(msg.PayloadBytes);
                            Log($"DATA FROM {peerId}:{payloadString}");
                            reply.PayloadBytes = payloadString.Length.ToLeInt16Bytes();
                            break;

                        case ExchangeMessageId.DataTransferAck:
                            Log($"DATA ACK LEN:{msg.PayloadBytes.ReadLeInt16()} FROM {peerId}");

                            return;

                        default:
                            Log($"RECV {msg.Id} FROM {peerId} @ {_saeReceive.RemoteEndPoint}");
                            return;
                    }
                }

                _localSocket.SendExchangeMessageTo(_saeReceive.RemoteEndPoint, _localPrivateKey, peerPublicKey, _localId, reply);
            }
        }

        private void ReceiveCompleted(object sender, SocketAsyncEventArgs e)
        {
            if (null == _saeReceive) return;
            if (_saeReceive.SocketError == SocketError.Success)
            {
                try
                {
                    ProcessPacket();
                }
                catch (InvalidDataException exception)
                {
                    Log($"ERROR ProcessPacket:{exception.Message}");
                }
                catch (Exception exception)
                {
                    Log($"ERROR ProcessPacket:{exception}");
                }
            }
            else
            {
                Log($"ERROR SOCKET:{_saeReceive.SocketError}");
            }

            if (null == _localSocket) return;
            if (false == _localSocket.ReceiveFromAsync(_saeReceive)) ReceiveCompleted(null, null);
        }

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

        //------------- 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();
        }
    }
}