using System;
using System.Net;
using System.Net.Sockets;
using System.Threading.Tasks;

namespace TNet
{
    public class TcpAcceptor: IDisposable
    {
        private readonly Socket socket;
        private readonly SocketAsyncEventArgs asyncEventArgs = new SocketAsyncEventArgs();

        public TcpAcceptor(string ip, ushort port, int backLog = 100)
        {
            this.socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            this.asyncEventArgs.Completed += OnArgsCompletion;
            this.socket.Bind(new IPEndPoint(IPAddress.Parse(ip), port));
            this.socket.Listen(backLog);
        }

        public void Dispose()
        {
            this.socket.Dispose();
        }

        /// <summary>
        /// SocketAsyncEventArgs Accept回调函数,回调可能已经到了另外的线程
        /// </summary>
        /// <returns></returns>
        public Task<NetworkStream> AcceptAsync()
        {
            var tcs = new TaskCompletionSource<NetworkStream>();

            try
            {
                this.asyncEventArgs.UserToken = tcs;

                bool ret = this.socket.AcceptAsync(this.asyncEventArgs);

                if (!ret)
                {
                    if (this.asyncEventArgs.SocketError == SocketError.Success)
                    {
                        var acceptSocket = this.asyncEventArgs.AcceptSocket;
                        this.asyncEventArgs.AcceptSocket = null;
                        return Task.FromResult(new NetworkStream(acceptSocket, true));
                    }
                    tcs.TrySetException(
                                        new InvalidOperationException(
                                                this.asyncEventArgs.SocketError.ToString()));
                }
            }
            catch (Exception ex)
            {
                tcs.TrySetException(ex);
            }
            return tcs.Task;
        }

        private static void OnArgsCompletion(object sender, SocketAsyncEventArgs e)
        {
            var tcs = (TaskCompletionSource<NetworkStream>) e.UserToken;

            if (e.SocketError != SocketError.Success)
            {
                tcs.TrySetException(new InvalidOperationException(e.SocketError.ToString()));
                return;
            }
            var acceptSocket = e.AcceptSocket;
            e.AcceptSocket = null;
            tcs.SetResult(new NetworkStream(acceptSocket, true));
        }
    }
}