using System;
using System.Collections.Generic;
using System.IO;
using System.IO.Pipelines;
using System.Net;
using System.Net.Sockets;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Connections;
using Microsoft.AspNetCore.Connections.Features;
using Microsoft.AspNetCore.Http.Features;

namespace ClientSample
{
    public class TcpConnection : ConnectionContext, IConnectionInherentKeepAliveFeature
    {
        private readonly Socket _socket;
        private volatile bool _aborted;
        private readonly EndPoint _endPoint;
        private IDuplexPipe _application;
        private readonly SocketSender _sender;
        private readonly SocketReceiver _receiver;

        public TcpConnection(EndPoint endPoint)
        {
            _socket = new Socket(SocketType.Stream, ProtocolType.Tcp);
            _endPoint = endPoint;

            _sender = new SocketSender(_socket, PipeScheduler.ThreadPool);
            _receiver = new SocketReceiver(_socket, PipeScheduler.ThreadPool);

            // Add IConnectionInherentKeepAliveFeature to the tcp connection impl since Kestrel doesn't implement
            // the IConnectionHeartbeatFeature
            Features.Set<IConnectionInherentKeepAliveFeature>(this);
        }

        public override IDuplexPipe Transport { get; set; }

        public override IFeatureCollection Features { get; } = new FeatureCollection();
        public override string ConnectionId { get; set; } = Guid.NewGuid().ToString();
        public override IDictionary<object, object> Items { get; set; } = new ConnectionItems();

        // We claim to have inherent keep-alive so the client doesn't kill the connection when it hasn't seen ping frames.
        public bool HasInherentKeepAlive { get; } = true;

        public Task DisposeAsync()
        {
            Transport?.Output.Complete();
            Transport?.Input.Complete();

            _socket?.Dispose();

            return Task.CompletedTask;
        }

        public async Task<ConnectionContext> StartAsync()
        {
            await _socket.ConnectAsync(_endPoint);

            var pair = DuplexPipe.CreateConnectionPair(PipeOptions.Default, PipeOptions.Default);

            Transport = pair.Transport;
            _application = pair.Application;

            _ = ExecuteAsync();

            return this;
        }

        private async Task ExecuteAsync()
        {
            Exception sendError = null;
            try
            {
                // Spawn send and receive logic
                var receiveTask = DoReceive();
                var sendTask = DoSend();

                // If the sending task completes then close the receive
                // We don't need to do this in the other direction because the kestrel
                // will trigger the output closing once the input is complete.
                if (await Task.WhenAny(receiveTask, sendTask) == sendTask)
                {
                    // Tell the reader it's being aborted
                    _socket.Dispose();
                }

                // Now wait for both to complete
                await receiveTask;
                sendError = await sendTask;

                // Dispose the socket(should noop if already called)
                _socket.Dispose();
            }
            catch (Exception ex)
            {
                Console.WriteLine($"Unexpected exception in {nameof(TcpConnection)}.{nameof(StartAsync)}: " + ex);
            }
            finally
            {
                // Complete the output after disposing the socket
                _application.Input.Complete(sendError);
            }
        }
        private async Task DoReceive()
        {
            Exception error = null;

            try
            {
                await ProcessReceives();
            }
            catch (SocketException ex) when (ex.SocketErrorCode == SocketError.ConnectionReset)
            {
                error = new ConnectionResetException(ex.Message, ex);
            }
            catch (SocketException ex) when (ex.SocketErrorCode == SocketError.OperationAborted ||
                                             ex.SocketErrorCode == SocketError.ConnectionAborted ||
                                             ex.SocketErrorCode == SocketError.Interrupted ||
                                             ex.SocketErrorCode == SocketError.InvalidArgument)
            {
                if (!_aborted)
                {
                    // Calling Dispose after ReceiveAsync can cause an "InvalidArgument" error on *nix.
                    error = new ConnectionAbortedException();
                }
            }
            catch (ObjectDisposedException)
            {
                if (!_aborted)
                {
                    error = new ConnectionAbortedException();
                }
            }
            catch (IOException ex)
            {
                error = ex;
            }
            catch (Exception ex)
            {
                error = new IOException(ex.Message, ex);
            }
            finally
            {
                if (_aborted)
                {
                    error = error ?? new ConnectionAbortedException();
                }

                _application.Output.Complete(error);
            }
        }

        private async Task ProcessReceives()
        {
            while (true)
            {
                // Ensure we have some reasonable amount of buffer space
                var buffer = _application.Output.GetMemory();

                var bytesReceived = await _receiver.ReceiveAsync(buffer);

                if (bytesReceived == 0)
                {
                    // FIN
                    break;
                }

                _application.Output.Advance(bytesReceived);

                var flushTask = _application.Output.FlushAsync();

                if (!flushTask.IsCompleted)
                {
                    await flushTask;
                }

                var result = flushTask.GetAwaiter().GetResult();
                if (result.IsCompleted)
                {
                    // Pipe consumer is shut down, do we stop writing
                    break;
                }
            }
        }

        private async Task<Exception> DoSend()
        {
            Exception error = null;

            try
            {
                await ProcessSends();
            }
            catch (SocketException ex) when (ex.SocketErrorCode == SocketError.OperationAborted)
            {
                error = null;
            }
            catch (ObjectDisposedException)
            {
                error = null;
            }
            catch (IOException ex)
            {
                error = ex;
            }
            catch (Exception ex)
            {
                error = new IOException(ex.Message, ex);
            }
            finally
            {
                _aborted = true;
                _socket.Shutdown(SocketShutdown.Both);
            }

            return error;
        }

        private async Task ProcessSends()
        {
            while (true)
            {
                // Wait for data to write from the pipe producer
                var result = await _application.Input.ReadAsync();
                var buffer = result.Buffer;

                if (result.IsCanceled)
                {
                    break;
                }

                var end = buffer.End;
                var isCompleted = result.IsCompleted;
                if (!buffer.IsEmpty)
                {
                    await _sender.SendAsync(buffer);
                }

                _application.Input.AdvanceTo(end);

                if (isCompleted)
                {
                    break;
                }
            }
        }

        public Task StartAsync(TransferFormat transferFormat)
        {
            // Transfer format is irrelevant
            return StartAsync();
        }
    }
}