using System;
using System.Buffers.Binary;
using System.Net;
using System.Net.Sockets;
using System.Runtime.InteropServices;
using System.Runtime.Versioning;

namespace FastGithub.Dns
{
    /// <summary>
    /// windows iphlpapi
    /// </summary>
    [SupportedOSPlatform("windows")]
    unsafe static class UdpTable
    {
        private const int ERROR_INSUFFICIENT_BUFFER = 122;

        [DllImport("iphlpapi.dll", SetLastError = true)]
        private static extern uint GetExtendedUdpTable(void* pUdpTable, ref int pdwSize, bool bOrder, AddressFamily ulAf, UDP_TABLE_CLASS tableClass, uint reserved = 0);

        /// <summary>
        /// 获取udp端口的占用进程id
        /// </summary>
        /// <param name="port"></param>
        /// <param name="processId"></param>
        /// <returns></returns>
        public static bool TryGetOwnerProcessId(int port, out int processId)
        {
            processId = 0;
            var pdwSize = 0;
            var result = GetExtendedUdpTable(null, ref pdwSize, false, AddressFamily.InterNetwork, UDP_TABLE_CLASS.UDP_TABLE_OWNER_PID);
            if (result != ERROR_INSUFFICIENT_BUFFER)
            {
                return false;
            }

            var buffer = new byte[pdwSize];
            fixed (byte* pUdpTable = &buffer[0])
            {
                result = GetExtendedUdpTable(pUdpTable, ref pdwSize, false, AddressFamily.InterNetwork, UDP_TABLE_CLASS.UDP_TABLE_OWNER_PID);
                if (result != 0)
                {
                    return false;
                }

                var table = Marshal.PtrToStructure<MIB_UDPTABLE_OWNER_PID>(new IntPtr(pUdpTable));
                foreach (var row in table.rows)
                {
                    if (row.LocalPort == port)
                    {
                        processId = row.ProcessId;
                        return true;
                    }
                }
            }

            return false;
        }


        private enum UDP_TABLE_CLASS
        {
            UDP_TABLE_BASIC,
            UDP_TABLE_OWNER_PID,
            UDP_TABLE_OWNER_MODULE
        }

        [StructLayout(LayoutKind.Sequential)]
        private struct MIB_UDPTABLE_OWNER_PID
        {
            public uint dwNumEntries;

            [MarshalAs(UnmanagedType.ByValArray, ArraySubType = UnmanagedType.Struct, SizeConst = 1)]
            public MIB_UDPROW_OWNER_PID[] rows;
        }

        [StructLayout(LayoutKind.Sequential)]
        private struct MIB_UDPROW_OWNER_PID
        {
            public uint localAddr;

            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
            public byte[] localPort;

            public int owningPid;

            public int ProcessId => owningPid;

            public IPAddress LocalAddress => new(localAddr);

            public ushort LocalPort => BinaryPrimitives.ReadUInt16BigEndian(this.localPort);
        }
    }
}