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

namespace TcpEcho
{
    internal class Program
    {
        private static async Task Main()
        {
            CancellationTokenSource cts = new();

            Console.CancelKeyPress += (_, e) => {
                cts.Cancel();
                e.Cancel = true;
            };

            Console.WriteLine("Press Ctl-C to exit.");

            try
            {
                await Run(cts.Token).ConfigureAwait(false);
            }
            catch (Exception e) when (
                e is SocketException || e is IOException)
            {
                Console.WriteLine("Server stopped.");
            }
        }

        private static async Task Run(CancellationToken ct)
        {
            TcpListener tcpListener = new(IPAddress.Parse("127.0.0.1"), 3737);
            using var stopListener = ct.Register(tcpListener.Stop);
            tcpListener.Start();

            while (true)
            {
                using var client = await tcpListener.AcceptTcpClientAsync().ConfigureAwait(false);
                using var closeClient = ct.Register(client.Close);
                using var stream = client.GetStream();
                using var tr = new StreamReader(stream);
                using var tw = new StreamWriter(stream);
                var line = await tr.ReadLineAsync().ConfigureAwait(false);
                await tw.WriteLineAsync($"Hello, {line}").ConfigureAwait(false);
            }
        }
    }
}