using System.Buffers.Binary;
using System.Net;
using System.Net.Sockets;
using System.Security.Cryptography;
using System.Xml;

using MeWeb.Core.Net;

namespace MeWeb.Core.Router;

public enum MapVia
{
  None,
  Upnp,
  NatPmp,
  Pcp,
}

public class Mapping
{
  public MapVia Via { get; set; }
  public string Gateway { get; set; }
  public int ExternalPort { get; set; }
  public int InternalPort { get; set; }
  public string InternalClient { get; set; }
  public string Control { get; set; }
  public string Service { get; set; }
  public string Nonce { get; set; }
  public DateTimeOffset Until { get; set; }
}

public class MappingAttempt
{
  public int ExternalPort { get; set; }
  public Mapping Mapping { get; set; }
  public MapVia Via { get; set; }
  public int Error { get; set; }

  public bool Done => Mapping is not null;
}

public static class PortMapper
{
  public const int LeaseSeconds = 600;
  const int PortMappingPort = 5351;

  public static async Task<MappingAttempt> Map(RouterReport router, string localAddress, int external, int @internal, CancellationToken ct)
  {
    var attempt = new MappingAttempt { ExternalPort = external };
    if (router.UpnpControl is not null)
    {
      attempt.Via = MapVia.Upnp;
      (attempt.Mapping, attempt.Error) = await Upnp(router, localAddress, external, @internal, ct);
      if (attempt.Done) return attempt;
    }
    if (router.NatPmp == Answer.Answered)
    {
      attempt.Via = MapVia.NatPmp;
      (attempt.Mapping, attempt.Error) = await NatPmp(router.Gateway, external, @internal, ct);
      if (attempt.Done) return attempt;
    }
    if (router.Pcp != Answer.Silent)
    {
      attempt.Via = MapVia.Pcp;
      (attempt.Mapping, attempt.Error) = await Pcp(router.Gateway, localAddress, external, @internal, ct);
    }
    return attempt;
  }

  public static async Task Remove(Mapping mapping, CancellationToken ct)
  {
    try
    {
      switch (mapping.Via)
      {
        case MapVia.Upnp:
          await Gateway.Soap(new Uri(mapping.Control), mapping.Service, "DeletePortMapping",
            $"<NewRemoteHost></NewRemoteHost><NewExternalPort>{mapping.ExternalPort}</NewExternalPort><NewProtocol>TCP</NewProtocol>", ct);
          break;
        case MapVia.NatPmp:
          await Gateway.Exchange(IPAddress.Parse(mapping.Gateway), NatPmpRequest(mapping.InternalPort, 0, 0), ct);
          break;
        case MapVia.Pcp:
          await PcpExchange(mapping.Gateway, mapping.InternalClient, Convert.FromBase64String(mapping.Nonce), mapping.ExternalPort, mapping.InternalPort, 0, ct);
          break;
      }
    }
    catch (Exception ex) when (ex is HttpRequestException or XmlException or SocketException or FormatException or TaskCanceledException && !ct.IsCancellationRequested)
    {
    }
  }

  static async Task<(Mapping, int)> Upnp(RouterReport router, string localAddress, int external, int @internal, CancellationToken ct)
  {
    var control = new Uri(router.UpnpControl);
    foreach (var lease in new[] { LeaseSeconds, 0 })
    {
      try
      {
        var (answer, status) = await Gateway.Soap(control, router.UpnpService, "AddPortMapping",
          $"<NewRemoteHost></NewRemoteHost><NewExternalPort>{external}</NewExternalPort><NewProtocol>TCP</NewProtocol>" +
          $"<NewInternalPort>{@internal}</NewInternalPort><NewInternalClient>{localAddress}</NewInternalClient><NewEnabled>1</NewEnabled>" +
          $"<NewPortMappingDescription>me-web? test</NewPortMappingDescription><NewLeaseDuration>{lease}</NewLeaseDuration>", ct);
        var error = status == 200 ? 0 : Gateway.ErrorCode(answer, status);
        if (error == 0)
          return (new Mapping
          {
            Via = MapVia.Upnp,
            Gateway = router.Gateway,
            ExternalPort = external,
            InternalPort = @internal,
            InternalClient = localAddress,
            Control = router.UpnpControl,
            Service = router.UpnpService,
            Until = lease == 0 ? DateTimeOffset.MaxValue : DateTimeOffset.UtcNow.AddSeconds(lease),
          }, 0);
        if (error != 725) return (null, error);
      }
      catch (Exception ex) when (ex is HttpRequestException or XmlException or TaskCanceledException && !ct.IsCancellationRequested)
      {
        return (null, -1);
      }
    }
    return (null, 725);
  }

  static async Task<(Mapping, int)> NatPmp(string gateway, int external, int @internal, CancellationToken ct)
  {
    var answer = await Gateway.Exchange(IPAddress.Parse(gateway), NatPmpRequest(@internal, external, LeaseSeconds), ct);
    if (answer is null || answer.Length < 16 || answer[0] != 0 || answer[1] != 130) return (null, -1);
    var result = BinaryPrimitives.ReadUInt16BigEndian(answer.AsSpan(2));
    if (result != 0) return (null, result);
    var mapped = BinaryPrimitives.ReadUInt16BigEndian(answer.AsSpan(10));
    var lifetime = BinaryPrimitives.ReadUInt32BigEndian(answer.AsSpan(12));
    return (new Mapping
    {
      Via = MapVia.NatPmp,
      Gateway = gateway,
      ExternalPort = mapped,
      InternalPort = @internal,
      Until = DateTimeOffset.UtcNow.AddSeconds(lifetime),
    }, 0);
  }

  static async Task<(Mapping, int)> Pcp(string gateway, string localAddress, int external, int @internal, CancellationToken ct)
  {
    var nonce = RandomNumberGenerator.GetBytes(12);
    var answer = await PcpExchange(gateway, localAddress, nonce, external, @internal, LeaseSeconds, ct);
    if (answer is null || answer.Length < 60 || answer[0] != 2 || answer[1] != 0x81) return (null, -1);
    if (answer[3] != 0) return (null, answer[3]);
    var lifetime = BinaryPrimitives.ReadUInt32BigEndian(answer.AsSpan(4));
    var mapped = BinaryPrimitives.ReadUInt16BigEndian(answer.AsSpan(42));
    return (new Mapping
    {
      Via = MapVia.Pcp,
      Gateway = gateway,
      ExternalPort = mapped,
      InternalPort = @internal,
      InternalClient = localAddress,
      Nonce = Convert.ToBase64String(nonce),
      Until = DateTimeOffset.UtcNow.AddSeconds(lifetime),
    }, 0);
  }

  static byte[] NatPmpRequest(int @internal, int external, uint lifetime)
  {
    var request = new byte[12];
    request[1] = 2;
    BinaryPrimitives.WriteUInt16BigEndian(request.AsSpan(4), (ushort)@internal);
    BinaryPrimitives.WriteUInt16BigEndian(request.AsSpan(6), (ushort)external);
    BinaryPrimitives.WriteUInt32BigEndian(request.AsSpan(8), lifetime);
    return request;
  }

  static async Task<byte[]> PcpExchange(string gateway, string localAddress, byte[] nonce, int external, int @internal, uint lifetime, CancellationToken ct)
  {
    var request = new byte[60];
    request[0] = 2;
    request[1] = 1;
    BinaryPrimitives.WriteUInt32BigEndian(request.AsSpan(4), lifetime);
    (Addresses.Parse(localAddress) ?? IPAddress.Any).MapToIPv6().GetAddressBytes().CopyTo(request, 8);
    nonce.CopyTo(request, 24);
    request[36] = 6;
    BinaryPrimitives.WriteUInt16BigEndian(request.AsSpan(40), (ushort)@internal);
    BinaryPrimitives.WriteUInt16BigEndian(request.AsSpan(42), (ushort)external);
    IPAddress.Any.MapToIPv6().GetAddressBytes().CopyTo(request, 44);
    return await Gateway.Exchange(IPAddress.Parse(gateway), request, ct);
  }
}