#if WINDOWS_UWP
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
using System.Threading;
using System.Threading.Tasks;
using Windows.Networking;
using Windows.Networking.Sockets;
using Windows.Security.Cryptography.Certificates;
using MQTTnet.Channel;
using MQTTnet.Client;

namespace MQTTnet.Implementations
{
    public class MqttTcpChannel : IMqttChannel
    {
        // ReSharper disable once MemberCanBePrivate.Global
        // ReSharper disable once AutoPropertyCanBeMadeGetOnly.Global
        public static int BufferSize { get; set; } = 4096; // Can be changed for fine tuning by library user.

        private readonly int _bufferSize = BufferSize;
        private readonly MqttClientTcpOptions _options;

        private StreamSocket _socket;
        private Stream _readStream;
        private Stream _writeStream;

        public MqttTcpChannel(MqttClientTcpOptions options)
        {
            _options = options ?? throw new ArgumentNullException(nameof(options));

            _bufferSize = options.BufferSize;
        }

        public MqttTcpChannel(StreamSocket socket)
        {
            _socket = socket ?? throw new ArgumentNullException(nameof(socket));

            CreateStreams();
        }

        public static Func<MqttClientTcpOptions, IEnumerable<ChainValidationResult>> CustomIgnorableServerCertificateErrorsResolver { get; set; }

        public string Endpoint => _socket?.Information?.RemoteAddress?.ToString(); // TODO: Check if contains also the port.

        public async Task ConnectAsync(CancellationToken cancellationToken)
        {
            if (_socket == null)
            {
                _socket = new StreamSocket();
                _socket.Control.NoDelay = true;
                _socket.Control.KeepAlive = true;
            }

            if (!_options.TlsOptions.UseTls)
            {
                await _socket.ConnectAsync(new HostName(_options.Server), _options.GetPort().ToString());
            }
            else
            {
                _socket.Control.ClientCertificate = LoadCertificate(_options);

                foreach (var ignorableChainValidationResult in ResolveIgnorableServerCertificateErrors())
                {
                    _socket.Control.IgnorableServerCertificateErrors.Add(ignorableChainValidationResult);
                }

                await _socket.ConnectAsync(new HostName(_options.Server), _options.GetPort().ToString(), SocketProtectionLevel.Tls12);
            }

            CreateStreams();
        }

        public Task DisconnectAsync()
        {
            Dispose();
            return Task.FromResult(0);
        }

        public Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
        {
            return _readStream.ReadAsync(buffer, offset, count, cancellationToken);
        }

        public async Task WriteAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
        {
            await _writeStream.WriteAsync(buffer, offset, count, cancellationToken);
            await _writeStream.FlushAsync(cancellationToken);
        }

        public void Dispose()
        {
            TryDispose(_readStream, () => _readStream = null);
            TryDispose(_writeStream, () => _writeStream = null);
            TryDispose(_socket, () => _socket = null);
        }

        private static Certificate LoadCertificate(MqttClientTcpOptions options)
        {
            if (options.TlsOptions.Certificates == null || !options.TlsOptions.Certificates.Any())
            {
                return null;
            }

            if (options.TlsOptions.Certificates.Count > 1)
            {
                throw new NotSupportedException("Only one client certificate is supported for UWP.");
            }

            return new Certificate(options.TlsOptions.Certificates.First().AsBuffer());
        }

        private IEnumerable<ChainValidationResult> ResolveIgnorableServerCertificateErrors()
        {
            if (CustomIgnorableServerCertificateErrorsResolver != null)
            {
                return CustomIgnorableServerCertificateErrorsResolver(_options);
            }

            var result = new List<ChainValidationResult>();

            if (_options.TlsOptions.IgnoreCertificateRevocationErrors)
            {
                result.Add(ChainValidationResult.RevocationInformationMissing);
                //_socket.Control.IgnorableServerCertificateErrors.Add(ChainValidationResult.Revoked); Not supported.
                result.Add(ChainValidationResult.RevocationFailure);
            }

            if (_options.TlsOptions.IgnoreCertificateChainErrors)
            {
                result.Add(ChainValidationResult.IncompleteChain);
            }

            if (_options.TlsOptions.AllowUntrustedCertificates)
            {
                result.Add(ChainValidationResult.Untrusted);
            }

            return result;
        }

        private void CreateStreams()
        {
            _readStream = _socket.InputStream.AsStreamForRead(_bufferSize);
            _writeStream = _socket.OutputStream.AsStreamForWrite(_bufferSize);
        }

        private static void TryDispose(IDisposable disposable, Action afterDispose)
        {
            try
            {
                disposable?.Dispose();
            }
            catch (ObjectDisposedException)
            {
            }
            catch (NullReferenceException)
            {
            }
            finally
            {
                afterDispose();
            }
        }
    }
}
#endif