using System.Net;
using System.Net.Sockets;
using System.Text;
using NATS.Server.Gateways;
using NATS.Server.Subscriptions;

namespace NATS.Server.Gateways.Tests.Gateways;

public class GatewayInterestIdempotencyTests
{
    [Fact]
    public async Task Duplicate_RSplus_or_reconnect_replay_does_not_double_count_remote_interest()
    {
        using var listener = new TcpListener(IPAddress.Loopback, 0);
        listener.Start();

        var port = ((IPEndPoint)listener.LocalEndpoint).Port;
        using var remoteSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        await remoteSocket.ConnectAsync(IPAddress.Loopback, port);
        using var gatewaySocket = await listener.AcceptSocketAsync();
        await using var gateway = new GatewayConnection(gatewaySocket);
        using var timeout = new CancellationTokenSource(TimeSpan.FromSeconds(5));

        var handshakeTask = gateway.PerformOutboundHandshakeAsync("LOCAL", timeout.Token);
        (await ReadLineAsync(remoteSocket, timeout.Token)).ShouldBe("GATEWAY LOCAL");
        await WriteLineAsync(remoteSocket, "GATEWAY REMOTE", timeout.Token);
        await handshakeTask;

        using var subList = new SubList();
        var remoteAdded = 0;
        subList.InterestChanged += change =>
        {
            if (change.Kind == InterestChangeKind.RemoteAdded)
                remoteAdded++;
        };

        gateway.RemoteSubscriptionReceived = sub =>
        {
            subList.ApplyRemoteSub(sub);
            return Task.CompletedTask;
        };
        gateway.StartLoop(timeout.Token);

        await WriteLineAsync(remoteSocket, "A+ A orders.*", timeout.Token);
        await WaitForAsync(() => subList.HasRemoteInterest("A", "orders.created"), timeout.Token);

        await WriteLineAsync(remoteSocket, "A+ A orders.*", timeout.Token);
        await Task.Delay(100, timeout.Token);

        subList.MatchRemote("A", "orders.created").Count.ShouldBe(1);
        remoteAdded.ShouldBe(1);
    }

    private static async Task<string> ReadLineAsync(Socket socket, CancellationToken ct)
    {
        var bytes = new List<byte>(64);
        var single = new byte[1];
        while (true)
        {
            var read = await socket.ReceiveAsync(single, SocketFlags.None, ct);
            if (read == 0)
                break;
            if (single[0] == (byte)'\n')
                break;
            if (single[0] != (byte)'\r')
                bytes.Add(single[0]);
        }

        return Encoding.ASCII.GetString([.. bytes]);
    }

    private static Task WriteLineAsync(Socket socket, string line, CancellationToken ct)
        => socket.SendAsync(Encoding.ASCII.GetBytes($"{line}\r\n"), SocketFlags.None, ct).AsTask();

    private static async Task WaitForAsync(Func<bool> predicate, CancellationToken ct)
    {
        while (!ct.IsCancellationRequested)
        {
            if (predicate())
                return;

            await Task.Delay(20, ct);
        }

        throw new TimeoutException("Timed out waiting for condition.");
    }
}
