using System.Net;
using System.Net.Sockets;
using System.Text;
using Microsoft.Extensions.Logging.Abstractions;
using NATS.Server;

namespace NATS.Server.Tests;

public class NoRespondersTests : IAsyncLifetime
{
    private readonly NatsServer _server;
    private readonly int _port;
    private readonly CancellationTokenSource _cts = new();

    public NoRespondersTests()
    {
        _port = GetFreePort();
        _server = new NatsServer(new NatsOptions { Port = _port }, NullLoggerFactory.Instance);
    }

    public async Task InitializeAsync()
    {
        _ = _server.StartAsync(_cts.Token);
        await _server.WaitForReadyAsync();
    }

    public async Task DisposeAsync()
    {
        await _cts.CancelAsync();
        _server.Dispose();
    }

    private static int GetFreePort()
    {
        using var sock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        sock.Bind(new IPEndPoint(IPAddress.Loopback, 0));
        return ((IPEndPoint)sock.LocalEndPoint!).Port;
    }

    private async Task<Socket> ConnectClientAsync()
    {
        var sock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        await sock.ConnectAsync(IPAddress.Loopback, _port);
        return sock;
    }

    private static async Task<string> ReadUntilAsync(Socket sock, string expected, int timeoutMs = 5000)
    {
        using var cts = new CancellationTokenSource(timeoutMs);
        var sb = new StringBuilder();
        var buf = new byte[4096];
        while (!sb.ToString().Contains(expected))
        {
            var n = await sock.ReceiveAsync(buf, SocketFlags.None, cts.Token);
            if (n == 0) break;
            sb.Append(Encoding.ASCII.GetString(buf, 0, n));
        }
        return sb.ToString();
    }

    [Fact]
    public async Task NoResponders_without_headers_closes_connection()
    {
        using var client = await ConnectClientAsync();

        // Read INFO
        await ReadUntilAsync(client, "\r\n");

        // Send CONNECT with no_responders:true but headers:false
        await client.SendAsync(Encoding.ASCII.GetBytes(
            "CONNECT {\"no_responders\":true,\"headers\":false}\r\n"));

        // Should receive -ERR and connection should close
        var response = await ReadUntilAsync(client, "-ERR");
        response.ShouldContain("-ERR");
        response.ShouldContain("No Responders Requires Headers Support");
    }

    [Fact]
    public async Task NoResponders_with_headers_accepted()
    {
        using var client = await ConnectClientAsync();

        // Read INFO
        await ReadUntilAsync(client, "\r\n");

        // Send CONNECT with both no_responders and headers true, then PING
        await client.SendAsync(Encoding.ASCII.GetBytes(
            "CONNECT {\"no_responders\":true,\"headers\":true}\r\nPING\r\n"));

        // Should receive PONG (connection stays alive)
        var response = await ReadUntilAsync(client, "PONG\r\n");
        response.ShouldContain("PONG\r\n");
    }

    [Fact]
    public async Task NoResponders_sends_503_when_no_subscribers()
    {
        using var client = await ConnectClientAsync();

        // Read INFO
        await ReadUntilAsync(client, "\r\n");

        // CONNECT with no_responders and headers enabled
        // SUB to the reply inbox so we can receive the 503
        // PUB to a subject with no subscribers, using a reply-to subject
        await client.SendAsync(Encoding.ASCII.GetBytes(
            "CONNECT {\"no_responders\":true,\"headers\":true}\r\n" +
            "SUB _INBOX.reply 1\r\n" +
            "PUB no.subscribers _INBOX.reply 5\r\nHello\r\n"));

        // Should receive HMSG with 503 status on the reply subject
        var response = await ReadUntilAsync(client, "HMSG");
        response.ShouldContain("HMSG _INBOX.reply 1");
        response.ShouldContain("503");
    }
}