using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Net.Sockets;
using System.Threading;

using DFEngine.Accounts;
using DFEngine.Content.GameObjects;
using DFEngine.Logging;
using DFEngine.Network.Protocols;
using DFEngine.Utils;

namespace DFEngine.Network
{
    /// <summary>
    /// Class that sends and receives data to and from a server.
    /// </summary>
    public class NetworkConnection : Object
    {
        /// <summary>
        /// The maximum buffer size allowed.
        /// </summary>
        private const int ReceiveBufferSize = ushort.MaxValue;

        /// <summary>
        /// Array of xor values.
        /// </summary>
        private static readonly byte[] XorTable =
        {
            0x07, 0x59, 0x69, 0x4A, 0x94, 0x11, 0x94, 0x85, 0x8C, 0x88, 0x05, 0xCB,
            0xA0, 0x9E, 0xCD, 0x58, 0x3A, 0x36, 0x5B, 0x1A, 0x6A, 0x16, 0xFE, 0xBD,
            0xDF, 0x94, 0x02, 0xF8, 0x21, 0x96, 0xC8, 0xE9, 0x9E, 0xF7, 0xBF, 0xBD,
            0xCF, 0xCD, 0xB2, 0x7A, 0x00, 0x9F, 0x40, 0x22, 0xFC, 0x11, 0xF9, 0x0C,
            0x2E, 0x12, 0xFB, 0xA7, 0x74, 0x0A, 0x7D, 0x78, 0x40, 0x1E, 0x2C, 0xA0,
            0x2D, 0x06, 0xCB, 0xA8, 0xB9, 0x7E, 0xEF, 0xDE, 0x49, 0xEA, 0x4E, 0x13,
            0x16, 0x16, 0x80, 0xF4, 0x3D, 0xC2, 0x9A, 0xD4, 0x86, 0xD7, 0x94, 0x24,
            0x17, 0xF4, 0xD6, 0x65, 0xBD, 0x3F, 0xDB, 0xE4, 0xE1, 0x0F, 0x50, 0xF6,
            0xEC, 0x7A, 0x9A, 0x0C, 0x27, 0x3D, 0x24, 0x66, 0xD3, 0x22, 0x68, 0x9C,
            0x9A, 0x52, 0x0B, 0xE0, 0xF9, 0xA5, 0x0B, 0x25, 0xDA, 0x80, 0x49, 0x0D,
            0xFD, 0x3E, 0x77, 0xD1, 0x56, 0xA8, 0xB7, 0xF4, 0x0F, 0x9B, 0xE8, 0x0F,
            0x52, 0x47, 0xF5, 0x6F, 0x83, 0x20, 0x22, 0xDB, 0x0F, 0x0B, 0xB1, 0x43,
            0x85, 0xC1, 0xCB, 0xA4, 0x0B, 0x02, 0x19, 0xDF, 0xF0, 0x8B, 0xEC, 0xDB,
            0x6C, 0x6D, 0x66, 0xAD, 0x45, 0xBE, 0x89, 0x14, 0x7E, 0x2F, 0x89, 0x10,
            0xB8, 0x93, 0x60, 0xD8, 0x60, 0xDE, 0xF6, 0xFE, 0x6E, 0x9B, 0xCA, 0x06,
            0xC1, 0x75, 0x95, 0x33, 0xCF, 0xC0, 0xB2, 0xE0, 0xCC, 0xA5, 0xCE, 0x12,
            0xF6, 0xE5, 0xB5, 0xB4, 0x26, 0xC5, 0xB2, 0x18, 0x4F, 0x2A, 0x5D, 0x26,
            0x1B, 0x65, 0x4D, 0xF5, 0x45, 0xC9, 0x84, 0x14, 0xDC, 0x7C, 0x12, 0x4B,
            0x18, 0x9C, 0xC7, 0x24, 0xE7, 0x3C, 0x64, 0xFF, 0xD6, 0x3A, 0x2C, 0xEE,
            0x8C, 0x81, 0x49, 0x39, 0x6C, 0xB7, 0xDC, 0xBD, 0x94, 0xE2, 0x32, 0xF7,
            0xDD, 0x0A, 0xFC, 0x02, 0x01, 0x64, 0xEC, 0x4C, 0x94, 0x0A, 0xB1, 0x56,
            0xF5, 0xC9, 0xA9, 0x34, 0xDE, 0x0F, 0x38, 0x27, 0xBC, 0x81, 0x30, 0x0F,
            0x7B, 0x38, 0x25, 0xFE, 0xE8, 0x3E, 0x29, 0xBA, 0x55, 0x43, 0xBF, 0x6B,
            0x9F, 0x1F, 0x8A, 0x49, 0x52, 0x18, 0x7F, 0x8A, 0xF8, 0x88, 0x24, 0x5C,
            0x4F, 0xE1, 0xA8, 0x30, 0x87, 0x8E, 0x50, 0x1F, 0x2F, 0xD1, 0x0C, 0xB4,
            0xFD, 0x0A, 0xBC, 0xDC, 0x12, 0x85, 0xE2, 0x52, 0xEE, 0x4A, 0x58, 0x38,
            0xAB, 0xFF, 0xC6, 0x3D, 0xB9, 0x60, 0x64, 0x0A, 0xB4, 0x50, 0xD5, 0x40,
            0x89, 0x17, 0x9A, 0xD5, 0x85, 0xCF, 0xEC, 0x0D, 0x7E, 0x81, 0x7F, 0xE3,
            0xC3, 0x04, 0x01, 0x22, 0xEC, 0x27, 0xCC, 0xFA, 0x3E, 0x21, 0xA6, 0x54,
            0xC8, 0xDE, 0x00, 0xB6, 0xDF, 0x27, 0x9F, 0xF6, 0x25, 0x34, 0x07, 0x85,
            0xBF, 0xA7, 0xA5, 0xA5, 0xE0, 0x83, 0x0C, 0x3D, 0x5D, 0x20, 0x40, 0xAF,
            0x60, 0xA3, 0x64, 0x56, 0xF3, 0x05, 0xC4, 0x1C, 0x7D, 0x37, 0x98, 0xC3,
            0xE8, 0x5A, 0x6E, 0x58, 0x85, 0xA4, 0x9A, 0x6B, 0x6A, 0xF4, 0xA3, 0x7B,
            0x61, 0x9B, 0x09, 0x40, 0x1E, 0x60, 0x4B, 0x32, 0xD9, 0x51, 0xA4, 0xFE,
            0xF9, 0x5D, 0x4E, 0x4A, 0xFB, 0x4A, 0xD4, 0x7C, 0x33, 0x02, 0x33, 0xD5,
            0x9D, 0xCE, 0x5B, 0xAA, 0x5A, 0x7C, 0xD8, 0xF8, 0x05, 0xFA, 0x1F, 0x2B,
            0x8C, 0x72, 0x57, 0x50, 0xAE, 0x6C, 0x19, 0x89, 0xCA, 0x01, 0xFC, 0xFC,
            0x29, 0x9B, 0x61, 0x12, 0x68, 0x63, 0x65, 0x46, 0x26, 0xC4, 0x5B, 0x50,
            0xAA, 0x2B, 0xBE, 0xEF, 0x9A, 0x79, 0x02, 0x23, 0x75, 0x2C, 0x20, 0x13,
            0xFD, 0xD9, 0x5A, 0x76, 0x23, 0xF1, 0x0B, 0xB5, 0xB8, 0x59, 0xF9, 0x9F,
            0x7A, 0xE6, 0x06, 0xE9, 0xA5, 0x3A, 0xB4, 0x50, 0xBF, 0x16, 0x58, 0x98,
            0xB3, 0x9A, 0x6E, 0x36, 0xEE, 0x8D, 0xEB
        };

        private static int[] ClientTable { get; set; }
        private static int[] ServerTable { get; set; }

        /// <summary>
        /// The connection's account.
        /// </summary>
        public Account Account { get; set; }

        /// <summary>
        /// The connection's avatar.
        /// </summary>
        public Avatar Avatar { get; set; }

        /// <summary>
        /// The connection's character.
        /// </summary>
        public Character Character { get; set; }

        /// <summary>
        /// The connection's unique identifier.
        /// </summary>
        public string Guid { get; set; }

        /// <summary>
        /// The client's handle.
        /// </summary>
        public ushort Handle { get; set; }

        /// <summary>
        /// Returns true if the connection exists.
        /// </summary>
        public bool IsConnected => GetConnectionState();

        /// <summary>
        /// Returns true if the handshake has been completed.
        /// </summary>
        public bool IsEstablished { get; set; }

        /// <summary>
        /// Returns true if the connection is currently being sent data in chunks.
        /// </summary>
        public bool SendChunk
        {
            get => sendChunk;
            set
            {
                sendChunk = value;

                if (!value)
                {
                    SendAwaitingBuffers();
                }
            }
        }

        /// <summary>
        /// The server that accepted the connection
        /// </summary>
        public NetworkServer Server { get; }

        /// <summary>
        /// The connection's type.
        /// </summary>
        public NetworkConnectionType Type { get; }

        /// <summary>
        /// Time since the connection's last heartbeat.
        /// </summary>
        public long LastPing { get; set; }

        /// <summary>
        /// List of buffers waiting to be sent.
        /// </summary>
        private volatile List<byte[]> awaitingBuffers;

        /// <summary>
        /// The buffer used for incoming data.
        /// </summary>
        private byte[] receiveBuffer;

        /// <summary>
        /// The stream used to read from the incoming data buffer.
        /// </summary>
        private MemoryStream receiveStream;

        /// <summary>
        /// Returns true if the connection is currently being sent data in chunks.
        /// </summary>
        private bool sendChunk;

        /// <summary>
        /// The connection's current index in the xor table.
        /// </summary>
        private ushort seed;

        /// <summary>
        /// Returns true if the seed was set.
        /// </summary>
        private bool seedSet;

        /// <summary>
        /// Creates a new instance of the <see cref="NetworkConnection"/> class.
        /// </summary>
        public NetworkConnection(NetworkConnectionType type)
        {
            socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            Type = type;
            IsEstablished = true;
            Guid = System.Guid.NewGuid().ToString().Replace("-", "");
            Handle = (ushort)Mathd.Random(ushort.MaxValue);
            receiveStream = new MemoryStream();
            awaitingBuffers = new List<byte[]>();

            ClientTable = XorTable.Select(x => (int)x).ToArray();
            ServerTable = XorTable.Select(x => (int)x).ToArray();
        }

        /// <summary>
        /// Creates a new instance of the <see cref="NetworkConnection"/> class.
        /// </summary>
        /// <param name="server">The server that accepted the connection.</param>
        /// <param name="socket">The socket to use for data transferring.</param>
        /// <param name="type">The connection's type.</param>
        public NetworkConnection(NetworkServer server, Socket socket, NetworkConnectionType type)
        {
            Server = server;
            this.socket = socket;
            Type = type;
            Guid = System.Guid.NewGuid().ToString().Replace("-", "");
            Handle = (ushort)Mathd.Random(ushort.MaxValue);
            receiveStream = new MemoryStream();
            awaitingBuffers = new List<byte[]>();

            SetSeed((ushort)Mathd.Random(498));

            BeginReceivingData();
            new PROTO_NC_MISC_SEED_ACK(seed).Send(this);
            IsEstablished = true;

            if (Type != NetworkConnectionType.NCT_CLIENT)
            {
                new PROTO_NC_MISC_S2SCONNECTION_RDY().Send(this);
            }
        }

        /// <summary>
        /// The socket to use for data transferring.
        /// </summary>
        private Socket socket;

        /// <summary>
        /// Gets the sockets remote endpoint IP address
        /// </summary>
        /// <returns>Remote endpoint IP address</returns>
        public string GetRemoteIP => (socket.RemoteEndPoint as IPEndPoint)?.Address.ToString();

        /// <summary>
        /// Gets the socket's connection state.
        /// </summary>
        /// <returns>True if the socket is connected.</returns>
        private bool GetConnectionState()
        {
            // If the socket is already null, we've already called
            // Disconnect().
            if (socket == null || !socket.Connected)
            {
                return false;
            }

            var blocking = socket.Blocking;

            try
            {
                var tempBuffer = new byte[1];

                socket.Blocking = false;
                socket.Send(tempBuffer, 0, 0);

                // If the send fails, this line won't be reached because an exception
                // will be thrown.
                return true;
            }
            catch (SocketException e)
            {
                // 10035 == WSAEWOULDBLOCK
                var ret = e.NativeErrorCode == 10035;

                if (!ret)
                {
                    Disconnect();
                }

                return ret;
            }
            finally
            {
                if (socket != null)
                {
                    socket.Blocking = blocking;
                }
            }
        }

        /// <summary>
        /// Decrypts a buffer.
        /// </summary>
        /// <param name="buffer">The buffer to decrypt.</param>
        /// <param name="offset">The offset to start decrypting.</param>
        /// <param name="length">The length to decrypt.</param>
        public void DecryptBuffer(byte[] buffer, int offset, int length)
        {
            var isClient = Type == NetworkConnectionType.NCT_CLIENT;

            if (isClient)
            {
                var index = 0;
                while (index < 499)
                {
                    ClientTable[index] = 3 * XorTable[index];
                    index++;
                }
            }

            for (var i = 0; i < length; i++)
            {
                buffer[offset + i] = (byte)(buffer[offset + i] ^ (isClient ? ClientTable[seed] : ServerTable[seed]));
                seed++;

                if (seed >= 499)
                {
                    seed = 0;
                }
            }
        }

        /// <summary>
        /// Destroys the connection.
        /// </summary>
        public void Disconnect()
        {
            // May not want to remove here, might want to handle disconnections
            // individually per server by checking the list for disconnected
            // clients.
            Server?.Connections.Remove(this);

            socket?.Close(); // Close() will call Dispose() automatically for us.
            socket = null;
        }

        /// <summary>
        /// Sends data to the connection.
        /// </summary>
        /// <param name="buffer">The data to send.</param>
        public void SendData(byte[] buffer)
        {
            if (!IsConnected)
            {
                return;
            }

            if (sendChunk)
            {
                awaitingBuffers.Add(buffer);
                return;
            }

            var bytesToSend = buffer.Length;
            var bytesSent = 0;

            if (bytesToSend >= ReceiveBufferSize)
            {
                SocketLog.Write(SocketLogLevel.Debug, "Exceeded max message size while sending data to a connection.");
            }

            while (bytesSent < bytesToSend)
            {
                bytesSent += socket.Send(buffer, bytesSent, bytesToSend - bytesSent, SocketFlags.None);

                if (bytesSent <= bytesToSend) continue;
                SocketLog.Write(SocketLogLevel.Warning, $"BUFFER OVERFLOW OCCURRED - Sent {bytesSent - bytesToSend} bytes more than expected.");
                break;
            }
        }

        /// <summary>
        /// Sets the client's current seed.
        /// </summary>
        /// <param name="value">The value to set the seed to.</param>
        public void SetSeed(ushort value)
        {
            seed = value;
            seedSet = true;
        }

        /// <summary>
        /// Begins to accept data from the connection.
        /// </summary>
        private void BeginReceivingData()
        {
            if (!IsConnected)
            {
                return;
            }

            receiveBuffer = new byte[ReceiveBufferSize];
            socket.BeginReceive(receiveBuffer, 0, receiveBuffer.Length, SocketFlags.None, ReceivedData, null);
        }

        /// <summary>
        /// Attempts to connect to the specified target endpoint.
        /// </summary>
        /// <param name="targetIP">The target IP Address.</param>
        /// <param name="targetPort">The target port.</param>
        public void Connect(string targetIP, ushort targetPort)
        {
            socket.BeginConnect(new IPEndPoint(IPAddress.Parse(targetIP), targetPort), ConnectedToTarget, new object[] { targetIP, targetPort });
        }

        /// <summary>
        /// This callback is called when we have connected to the requested
        /// target endpoint.
        /// </summary>
        /// <param name="e">The result object.</param>
        private void ConnectedToTarget(IAsyncResult e)
        {
            try
            {
                socket.EndConnect(e);
                BeginReceivingData();
            }
            catch
            {
                SocketLog.Write(SocketLogLevel.Warning, "Remote socket connection attempt failed. Trying again...");
                Thread.Sleep(3000); // 3 seconds.
                Connect((string)((object[])e.AsyncState)[0], (ushort)((object[])e.AsyncState)[1]);
            }
        }

        /// <summary>
        /// Destroys the <see cref="NetworkConnection"/> instance.
        /// </summary>
        protected override void Destroy()
        {
            socket?.Close();
        }

        /// <summary>
        /// Gets all messages from the buffer.
        /// </summary>
        /// <param name="buffer">The buffer to get message from.</param>
        private void GetMessagesFromBuffer(byte[] buffer)
        {
            if (!IsConnected)
            {
                return;
            }

            receiveStream.Write(buffer, 0, buffer.Length);

            while (TryParseMessage())
            {

            }
        }

        /// <summary>
        /// Called when data was received from the connection.
        /// </summary>
        /// <param name="e">The status of the operation.</param>
        private void ReceivedData(IAsyncResult e)
        {
            if (!IsConnected)
            {
                return;
            }

            var count = socket.EndReceive(e);
            var buffer = new byte[count];

            if (count <= 0)
            {
                Disconnect();
                return;
            }

            Array.Copy(receiveBuffer, 0, buffer, 0, count);
            GetMessagesFromBuffer(buffer);

            BeginReceivingData();
        }

        /// <summary>
        /// Sends the awaiting buffers as one big chunk.
        /// </summary>
        private void SendAwaitingBuffers()
        {
            if (!IsConnected)
            {
                return;
            }

            awaitingBuffers.Copy(out var bufferList);
            awaitingBuffers.Clear();

            var size = bufferList.Sum(b => b.Length);
            var chunk = new byte[size];
            var pointer = 0;

            for (var i = 0; i < bufferList.Count; i++)
            {
                var buffer = bufferList[i];

                Array.Copy(buffer, 0, chunk, pointer, buffer.Length);
                pointer += buffer.Length;
            }

            SendData(chunk);
        }

        /// <summary>
        /// Tries to parse a message from the receive stream.
        /// </summary>
        private bool TryParseMessage()
        {
            if (!IsConnected)
            {
                return false;
            }

            receiveStream.Position = 0;

            if (receiveStream.Length < 1)
            {
                return false;
            }

            ushort messageSize;
            var sizeBuffer = new byte[1];

            receiveStream.Read(sizeBuffer, 0, 1);

            if (sizeBuffer[0] != 0)
            {
                messageSize = sizeBuffer[0];
            }
            else
            {
                if (receiveStream.Length - receiveStream.Position < 2)
                {
                    return false;
                }

                sizeBuffer = new byte[2];
                receiveStream.Read(sizeBuffer, 0, 2);

                messageSize = BitConverter.ToUInt16(sizeBuffer, 0);
            }

            if (receiveStream.Length - receiveStream.Position < messageSize)
            {
                return false;
            }

            var messageBuffer = new byte[messageSize];
            receiveStream.Read(messageBuffer, 0, messageSize);

            if (seedSet)
            {
                DecryptBuffer(messageBuffer, 0, messageBuffer.Length);
            }

            var message = new NetworkMessage(messageBuffer);
            if (!NetworkMessageHandler.TryFetch(message.Command, out var handler) || handler == null)
            {
                SocketLog.Write(SocketLogLevel.Debug, $"Unhandled command: {message.Command}");
            }

            NetworkMessageHandler.Invoke(handler, message, this);

            // Trims the receive stream.
            var remainingByteCount = new byte[receiveStream.Length - receiveStream.Position];
            receiveStream.Read(remainingByteCount, 0, remainingByteCount.Length);
            receiveStream = new MemoryStream();
            receiveStream.Write(remainingByteCount, 0, remainingByteCount.Length);

            return true;
        }
    }
}