using System;
using System.Net;
using System.Net.Security;
using System.Net.Sockets;
using System.Security.Authentication;
using System.Security.Cryptography.X509Certificates;
using System.Threading;
using System.Threading.Tasks;
using MQTTnet.Core.Adapter;
using MQTTnet.Core.Diagnostics;
using MQTTnet.Core.Serializer;
using MQTTnet.Core.Server;

namespace MQTTnet.Implementations
{
    public class MqttServerAdapter : IMqttServerAdapter, IDisposable
    {
        private CancellationTokenSource _cancellationTokenSource;
        private Socket _defaultEndpointSocket;
        private Socket _tlsEndpointSocket;
        private X509Certificate2 _tlsCertificate;

        private bool _isRunning;

        public event EventHandler<MqttClientConnectedEventArgs> ClientConnected;

        public void Start(MqttServerOptions options)
        {
            if (options == null) throw new ArgumentNullException(nameof(options));

            if (_isRunning) throw new InvalidOperationException("Server is already started.");
            _isRunning = true;

            _cancellationTokenSource = new CancellationTokenSource();

            if (options.DefaultEndpointOptions.IsEnabled)
            {
                _defaultEndpointSocket = new Socket(SocketType.Stream, ProtocolType.Tcp);
                _defaultEndpointSocket.Bind(new IPEndPoint(IPAddress.Any, options.GetDefaultEndpointPort()));
                _defaultEndpointSocket.Listen(options.ConnectionBacklog);

                Task.Run(() => AcceptDefaultEndpointConnectionsAsync(_cancellationTokenSource.Token), _cancellationTokenSource.Token);
            }

            if (options.TlsEndpointOptions.IsEnabled)
            {
                if (options.TlsEndpointOptions.Certificate == null)
                {
                    throw new ArgumentException("TLS certificate is not set.");
                }

                _tlsCertificate = new X509Certificate2(options.TlsEndpointOptions.Certificate);

                _tlsEndpointSocket = new Socket(SocketType.Stream, ProtocolType.Tcp);
                _tlsEndpointSocket.Bind(new IPEndPoint(IPAddress.Any, options.GetTlsEndpointPort()));
                _tlsEndpointSocket.Listen(options.ConnectionBacklog);

                Task.Run(() => AcceptTlsEndpointConnectionsAsync(_cancellationTokenSource.Token), _cancellationTokenSource.Token);
            }
        }

        public void Stop()
        {
            _isRunning = false;

            _cancellationTokenSource?.Cancel(false);
            _cancellationTokenSource?.Dispose();
            _cancellationTokenSource = null;

            _defaultEndpointSocket?.Dispose();
            _defaultEndpointSocket = null;

            _tlsEndpointSocket?.Dispose();
            _tlsEndpointSocket = null;
        }

        public void Dispose()
        {
            Stop();
        }

        private async Task AcceptDefaultEndpointConnectionsAsync(CancellationToken cancellationToken)
        {
            while (!cancellationToken.IsCancellationRequested)
            {
                try
                {
                    var clientSocket = await Task.Factory.FromAsync(_defaultEndpointSocket.BeginAccept, _defaultEndpointSocket.EndAccept, null).ConfigureAwait(false);
                    var clientAdapter = new MqttChannelCommunicationAdapter(new MqttTcpChannel(clientSocket, null), new MqttPacketSerializer());
                    ClientConnected?.Invoke(this, new MqttClientConnectedEventArgs(clientSocket.RemoteEndPoint.ToString(), clientAdapter));
                }
                catch (Exception exception) when (!(exception is ObjectDisposedException))
                {
                    MqttTrace.Error(nameof(MqttServerAdapter), exception, "Error while accepting connection at default endpoint.");

                    //excessive CPU consumed if in endless loop of socket errors
                    await Task.Delay(TimeSpan.FromSeconds(1), cancellationToken).ConfigureAwait(false);
                }
            }
        }

        private async Task AcceptTlsEndpointConnectionsAsync(CancellationToken cancellationToken)
        {
            while (!cancellationToken.IsCancellationRequested)
            {
                try
                {
                    var clientSocket = await Task.Factory.FromAsync(_tlsEndpointSocket.BeginAccept, _tlsEndpointSocket.EndAccept, null).ConfigureAwait(false);

                    var sslStream = new SslStream(new NetworkStream(clientSocket));
                    await sslStream.AuthenticateAsServerAsync(_tlsCertificate, false, SslProtocols.Tls12, false).ConfigureAwait(false);
                    
                    var clientAdapter = new MqttChannelCommunicationAdapter(new MqttTcpChannel(clientSocket, sslStream), new MqttPacketSerializer());
                    ClientConnected?.Invoke(this, new MqttClientConnectedEventArgs(clientSocket.RemoteEndPoint.ToString(), clientAdapter));
                }
                catch (Exception exception)
                {
                    MqttTrace.Error(nameof(MqttServerAdapter), exception, "Error while accepting connection at TLS endpoint.");

                    //excessive CPU consumed if in endless loop of socket errors
                    await Task.Delay(TimeSpan.FromSeconds(1), cancellationToken).ConfigureAwait(false);
                }
            }
        }
    }
}