using System;
using System.Collections.Generic;
using System.Net;
using System.Net.Sockets;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

namespace LiteNetLib
{
    internal static class NativeSocket
    {
        static unsafe class WinSock
        {
            private const string LibName = "ws2_32.dll";

            [DllImport(LibName, SetLastError = true)]
            public static extern int recvfrom(
                IntPtr socketHandle,
                [In, Out] byte[] pinnedBuffer,
                [In] int len,
                [In] SocketFlags socketFlags,
                [Out] byte[] socketAddress,
                [In, Out] ref int socketAddressSize);

            [DllImport(LibName, SetLastError = true)]
            internal static extern int sendto(
                IntPtr socketHandle,
                byte* pinnedBuffer,
                [In] int len,
                [In] SocketFlags socketFlags,
                [In] byte[] socketAddress,
                [In] int socketAddressSize);
        }

        static unsafe class UnixSock
        {
            private const string LibName = "libc";

            [DllImport(LibName, SetLastError = true)]
            public static extern int recvfrom(
                IntPtr socketHandle,
                [In, Out] byte[] pinnedBuffer,
                [In] int len,
                [In] SocketFlags socketFlags,
                [Out] byte[] socketAddress,
                [In, Out] ref int socketAddressSize);

            [DllImport(LibName, SetLastError = true)]
            internal static extern int sendto(
                IntPtr socketHandle,
                byte* pinnedBuffer,
                [In] int len,
                [In] SocketFlags socketFlags,
                [In] byte[] socketAddress,
                [In] int socketAddressSize);
        }

        public static readonly bool IsSupported = false;
        public static readonly bool UnixMode = false;

        public const int IPv4AddrSize = 16;
        public const int IPv6AddrSize = 28;
        public const int AF_INET = 2;
        public const int AF_INET6 = 10;

        private static readonly Dictionary<int, SocketError> NativeErrorToSocketError = new()
        {
            { 13, SocketError.AccessDenied },               //EACCES
            { 98, SocketError.AddressAlreadyInUse },        //EADDRINUSE
            { 99, SocketError.AddressNotAvailable },        //EADDRNOTAVAIL
            { 97, SocketError.AddressFamilyNotSupported },  //EAFNOSUPPORT
            { 11, SocketError.WouldBlock },                 //EAGAIN
            { 114, SocketError.AlreadyInProgress },         //EALREADY
            { 9, SocketError.OperationAborted },            //EBADF
            { 125, SocketError.OperationAborted },          //ECANCELED
            { 103, SocketError.ConnectionAborted },         //ECONNABORTED
            { 111, SocketError.ConnectionRefused },         //ECONNREFUSED
            { 104, SocketError.ConnectionReset },           //ECONNRESET
            { 89, SocketError.DestinationAddressRequired }, //EDESTADDRREQ
            { 14, SocketError.Fault },                      //EFAULT
            { 112, SocketError.HostDown },                  //EHOSTDOWN
            { 6, SocketError.HostNotFound },                //ENXIO
            { 113, SocketError.HostUnreachable },           //EHOSTUNREACH
            { 115, SocketError.InProgress },                //EINPROGRESS
            { 4, SocketError.Interrupted },                 //EINTR
            { 22, SocketError.InvalidArgument },            //EINVAL
            { 106, SocketError.IsConnected },               //EISCONN
            { 24, SocketError.TooManyOpenSockets },         //EMFILE
            { 90, SocketError.MessageSize },                //EMSGSIZE
            { 100, SocketError.NetworkDown },               //ENETDOWN
            { 102, SocketError.NetworkReset },              //ENETRESET
            { 101, SocketError.NetworkUnreachable },        //ENETUNREACH
            { 23, SocketError.TooManyOpenSockets },         //ENFILE
            { 105, SocketError.NoBufferSpaceAvailable },    //ENOBUFS
            { 61, SocketError.NoData },                     //ENODATA
            { 2, SocketError.AddressNotAvailable },         //ENOENT
            { 92, SocketError.ProtocolOption },             //ENOPROTOOPT
            { 107, SocketError.NotConnected },              //ENOTCONN
            { 88, SocketError.NotSocket },                  //ENOTSOCK
            { 3440, SocketError.OperationNotSupported },    //ENOTSUP
            { 1, SocketError.AccessDenied },                //EPERM
            { 32, SocketError.Shutdown },                   //EPIPE
            { 96, SocketError.ProtocolFamilyNotSupported }, //EPFNOSUPPORT
            { 93, SocketError.ProtocolNotSupported },       //EPROTONOSUPPORT
            { 91, SocketError.ProtocolType },               //EPROTOTYPE
            { 94, SocketError.SocketNotSupported },         //ESOCKTNOSUPPORT
            { 108, SocketError.Disconnecting },             //ESHUTDOWN
            { 110, SocketError.TimedOut },                  //ETIMEDOUT
            { 0, SocketError.Success }
        };

        static NativeSocket()
        {
            if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
            {
                IsSupported = true;
                UnixMode = true;
            }
            else if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
            {
                IsSupported = true;
            }
        }

        
        public static int RecvFrom(
            IntPtr socketHandle,
            byte[] pinnedBuffer,
            int len,
            byte[] socketAddress,
            ref int socketAddressSize)
        {
            return UnixMode
                ? UnixSock.recvfrom(socketHandle, pinnedBuffer, len, 0, socketAddress, ref socketAddressSize)
                : WinSock.recvfrom(socketHandle, pinnedBuffer, len, 0, socketAddress, ref socketAddressSize);
        }

        
        public static unsafe int SendTo(
            IntPtr socketHandle,
            byte* pinnedBuffer,
            int len,
            byte[] socketAddress,
            int socketAddressSize)
        {
            return UnixMode
                ? UnixSock.sendto(socketHandle, pinnedBuffer, len, 0, socketAddress, socketAddressSize)
                : WinSock.sendto(socketHandle, pinnedBuffer, len, 0, socketAddress, socketAddressSize);
        }

        public static SocketError GetSocketError()
        {
            int error = Marshal.GetLastWin32Error();
            if (UnixMode)
                return NativeErrorToSocketError.TryGetValue(error, out var err)
                    ? err
                    : SocketError.SocketError;
            return (SocketError)error;
        }

        public static SocketException GetSocketException()
        {
            int error = Marshal.GetLastWin32Error();
            if (UnixMode)
                return NativeErrorToSocketError.TryGetValue(error, out var err)
                    ? new((int)err)
                    : new SocketException((int)SocketError.SocketError);
            return new(error);
        }

        
        public static short GetNativeAddressFamily(IPEndPoint remoteEndPoint)
        {
            return UnixMode
                ? (short)(remoteEndPoint.AddressFamily == AddressFamily.InterNetwork ? AF_INET : AF_INET6)
                : (short)remoteEndPoint.AddressFamily;
        }
    }
}
