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

namespace NATS.Server.Tests;

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

    public ServerTests()
    {
        // Use random port
        _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> ReadLineAsync(Socket sock, int bufSize = 4096)
    {
        var buf = new byte[bufSize];
        var n = await sock.ReceiveAsync(buf, SocketFlags.None);
        return Encoding.ASCII.GetString(buf, 0, n);
    }

    /// <summary>
    /// Reads from a socket until the accumulated data contains the expected substring.
    /// </summary>
    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 Server_accepts_connection_and_sends_INFO()
    {
        using var client = await ConnectClientAsync();
        var response = await ReadLineAsync(client);

        response.ShouldStartWith("INFO ");
    }

    [Fact]
    public async Task Server_basic_pubsub()
    {
        using var pub = await ConnectClientAsync();
        using var sub = await ConnectClientAsync();

        // Read INFO from both
        await ReadLineAsync(pub);
        await ReadLineAsync(sub);

        // CONNECT + SUB on subscriber, then PING to flush
        await sub.SendAsync(Encoding.ASCII.GetBytes("CONNECT {}\r\nSUB foo 1\r\nPING\r\n"));
        var pong = await ReadLineAsync(sub);
        pong.ShouldContain("PONG");

        // CONNECT + PUB on publisher
        await pub.SendAsync(Encoding.ASCII.GetBytes("CONNECT {}\r\nPUB foo 5\r\nHello\r\n"));

        // Read MSG from subscriber (may arrive across multiple TCP segments)
        var msg = await ReadUntilAsync(sub, "Hello\r\n");
        msg.ShouldContain("MSG foo 1 5\r\nHello\r\n");
    }

    [Fact]
    public async Task Server_wildcard_matching()
    {
        using var pub = await ConnectClientAsync();
        using var sub = await ConnectClientAsync();

        await ReadLineAsync(pub);
        await ReadLineAsync(sub);

        // CONNECT + SUB on subscriber, then PING to flush
        await sub.SendAsync(Encoding.ASCII.GetBytes("CONNECT {}\r\nSUB foo.* 1\r\nPING\r\n"));
        var pong = await ReadLineAsync(sub);
        pong.ShouldContain("PONG");

        await pub.SendAsync(Encoding.ASCII.GetBytes("CONNECT {}\r\nPUB foo.bar 5\r\nHello\r\n"));

        var buf = new byte[4096];
        var n = await sub.ReceiveAsync(buf, SocketFlags.None);
        var msg = Encoding.ASCII.GetString(buf, 0, n);

        msg.ShouldContain("MSG foo.bar 1 5\r\n");
    }
}