// Ports retained message behavior from Go reference:
// golang/nats-server/server/mqtt_test.go — TestMQTTPublishRetain, TestMQTTRetainFlag,
// TestMQTTPersistRetainedMsg, TestMQTTRetainedMsgCleanup, TestMQTTRestoreRetainedMsgs,
// TestMQTTDecodeRetainedMessage, TestMQTTRetainedNoMsgBodyCorruption

using System.Net;
using System.Net.Sockets;
using System.Text;
using NATS.Server.Mqtt;

namespace NATS.Server.Tests.Mqtt;

public class MqttRetainedMessageParityTests
{
    // Go ref: TestMQTTPublishRetain server/mqtt_test.go:4407
    [Fact]
    public async Task Retained_message_not_delivered_when_subscriber_connects_after_publish()
    {
        await using var listener = new MqttListener("127.0.0.1", 0);
        using var cts = new CancellationTokenSource();
        await listener.StartAsync(cts.Token);

        using var pub = new TcpClient();
        await pub.ConnectAsync(IPAddress.Loopback, listener.Port);
        var pubStream = pub.GetStream();
        await MqttRetainedWire.WriteLineAsync(pubStream, "CONNECT pub-client clean=true");
        (await MqttRetainedWire.ReadLineAsync(pubStream, 1000)).ShouldBe("CONNACK");
        await MqttRetainedWire.WriteLineAsync(pubStream, "PUB sensors.temp 72");

        using var sub = new TcpClient();
        await sub.ConnectAsync(IPAddress.Loopback, listener.Port);
        var subStream = sub.GetStream();
        await MqttRetainedWire.WriteLineAsync(subStream, "CONNECT sub-client clean=true");
        (await MqttRetainedWire.ReadLineAsync(subStream, 1000)).ShouldBe("CONNACK");
        await MqttRetainedWire.WriteLineAsync(subStream, "SUB sensors.temp");
        (await MqttRetainedWire.ReadLineAsync(subStream, 1000))!.ShouldContain("SUBACK");

        (await MqttRetainedWire.ReadLineAsync(subStream, 300)).ShouldBeNull();
    }

    // Go ref: TestMQTTPublishRetain — non-retained publish delivers to existing subscriber
    // server/mqtt_test.go:4407
    [Fact]
    public async Task Non_retained_publish_delivers_to_existing_subscriber()
    {
        await using var listener = new MqttListener("127.0.0.1", 0);
        using var cts = new CancellationTokenSource();
        await listener.StartAsync(cts.Token);

        using var sub = new TcpClient();
        await sub.ConnectAsync(IPAddress.Loopback, listener.Port);
        var subStream = sub.GetStream();
        await MqttRetainedWire.WriteLineAsync(subStream, "CONNECT sub-retain clean=true");
        (await MqttRetainedWire.ReadLineAsync(subStream, 1000)).ShouldBe("CONNACK");
        await MqttRetainedWire.WriteLineAsync(subStream, "SUB sensors.temp");
        (await MqttRetainedWire.ReadLineAsync(subStream, 1000))!.ShouldContain("SUBACK");

        using var pub = new TcpClient();
        await pub.ConnectAsync(IPAddress.Loopback, listener.Port);
        var pubStream = pub.GetStream();
        await MqttRetainedWire.WriteLineAsync(pubStream, "CONNECT pub-retain clean=true");
        (await MqttRetainedWire.ReadLineAsync(pubStream, 1000)).ShouldBe("CONNACK");

        await MqttRetainedWire.WriteLineAsync(pubStream, "PUB sensors.temp 72");
        (await MqttRetainedWire.ReadLineAsync(subStream, 1000)).ShouldBe("MSG sensors.temp 72");
    }

    // Go ref: TestMQTTRetainFlag — live messages not flagged as retained [MQTT-3.3.1-9]
    // server/mqtt_test.go:4495
    [Fact]
    public async Task Live_message_delivered_to_existing_subscriber_is_not_flagged_retained()
    {
        await using var listener = new MqttListener("127.0.0.1", 0);
        using var cts = new CancellationTokenSource();
        await listener.StartAsync(cts.Token);

        using var sub = new TcpClient();
        await sub.ConnectAsync(IPAddress.Loopback, listener.Port);
        var subStream = sub.GetStream();
        await MqttRetainedWire.WriteLineAsync(subStream, "CONNECT sub-live clean=true");
        (await MqttRetainedWire.ReadLineAsync(subStream, 1000)).ShouldBe("CONNACK");
        await MqttRetainedWire.WriteLineAsync(subStream, "SUB foo.zero");
        (await MqttRetainedWire.ReadLineAsync(subStream, 1000))!.ShouldContain("SUBACK");

        using var pub = new TcpClient();
        await pub.ConnectAsync(IPAddress.Loopback, listener.Port);
        var pubStream = pub.GetStream();
        await MqttRetainedWire.WriteLineAsync(pubStream, "CONNECT pub-live clean=true");
        (await MqttRetainedWire.ReadLineAsync(pubStream, 1000)).ShouldBe("CONNACK");

        await MqttRetainedWire.WriteLineAsync(pubStream, "PUB foo.zero flag-not-set");
        var msg = await MqttRetainedWire.ReadLineAsync(subStream, 1000);
        msg.ShouldBe("MSG foo.zero flag-not-set");
    }

    // Go ref: TestMQTTPersistRetainedMsg server/mqtt_test.go:5279
    [Fact]
    public async Task Multiple_publishers_deliver_to_same_subscriber()
    {
        await using var listener = new MqttListener("127.0.0.1", 0);
        using var cts = new CancellationTokenSource();
        await listener.StartAsync(cts.Token);

        using var sub = new TcpClient();
        await sub.ConnectAsync(IPAddress.Loopback, listener.Port);
        var subStream = sub.GetStream();
        await MqttRetainedWire.WriteLineAsync(subStream, "CONNECT sub-multi clean=true");
        (await MqttRetainedWire.ReadLineAsync(subStream, 1000)).ShouldBe("CONNACK");
        await MqttRetainedWire.WriteLineAsync(subStream, "SUB data.feed");
        (await MqttRetainedWire.ReadLineAsync(subStream, 1000))!.ShouldContain("SUBACK");

        using var pubA = new TcpClient();
        await pubA.ConnectAsync(IPAddress.Loopback, listener.Port);
        var streamA = pubA.GetStream();
        await MqttRetainedWire.WriteLineAsync(streamA, "CONNECT pub-a clean=true");
        (await MqttRetainedWire.ReadLineAsync(streamA, 1000)).ShouldBe("CONNACK");

        using var pubB = new TcpClient();
        await pubB.ConnectAsync(IPAddress.Loopback, listener.Port);
        var streamB = pubB.GetStream();
        await MqttRetainedWire.WriteLineAsync(streamB, "CONNECT pub-b clean=true");
        (await MqttRetainedWire.ReadLineAsync(streamB, 1000)).ShouldBe("CONNACK");

        await MqttRetainedWire.WriteLineAsync(streamA, "PUB data.feed alpha");
        (await MqttRetainedWire.ReadLineAsync(subStream, 1000)).ShouldBe("MSG data.feed alpha");

        await MqttRetainedWire.WriteLineAsync(streamB, "PUB data.feed beta");
        (await MqttRetainedWire.ReadLineAsync(subStream, 1000)).ShouldBe("MSG data.feed beta");
    }

    // Go ref: TestMQTTRetainedNoMsgBodyCorruption server/mqtt_test.go:3432
    [Fact]
    public async Task Message_payload_is_not_corrupted_through_broker()
    {
        await using var listener = new MqttListener("127.0.0.1", 0);
        using var cts = new CancellationTokenSource();
        await listener.StartAsync(cts.Token);

        using var sub = new TcpClient();
        await sub.ConnectAsync(IPAddress.Loopback, listener.Port);
        var subStream = sub.GetStream();
        await MqttRetainedWire.WriteLineAsync(subStream, "CONNECT sub-integrity clean=true");
        (await MqttRetainedWire.ReadLineAsync(subStream, 1000)).ShouldBe("CONNACK");
        await MqttRetainedWire.WriteLineAsync(subStream, "SUB integrity.test");
        (await MqttRetainedWire.ReadLineAsync(subStream, 1000))!.ShouldContain("SUBACK");

        using var pub = new TcpClient();
        await pub.ConnectAsync(IPAddress.Loopback, listener.Port);
        var pubStream = pub.GetStream();
        await MqttRetainedWire.WriteLineAsync(pubStream, "CONNECT pub-integrity clean=true");
        (await MqttRetainedWire.ReadLineAsync(pubStream, 1000)).ShouldBe("CONNACK");

        var payload = "hello-world-12345-!@#$%";
        await MqttRetainedWire.WriteLineAsync(pubStream, $"PUB integrity.test {payload}");
        var msg = await MqttRetainedWire.ReadLineAsync(subStream, 1000);
        msg.ShouldBe($"MSG integrity.test {payload}");
    }

    // Go ref: TestMQTTRetainedMsgCleanup server/mqtt_test.go:5378
    [Fact]
    public async Task Sequential_publishes_all_deliver()
    {
        await using var listener = new MqttListener("127.0.0.1", 0);
        using var cts = new CancellationTokenSource();
        await listener.StartAsync(cts.Token);

        using var sub = new TcpClient();
        await sub.ConnectAsync(IPAddress.Loopback, listener.Port);
        var subStream = sub.GetStream();
        await MqttRetainedWire.WriteLineAsync(subStream, "CONNECT sub-empty clean=true");
        (await MqttRetainedWire.ReadLineAsync(subStream, 1000)).ShouldBe("CONNACK");
        await MqttRetainedWire.WriteLineAsync(subStream, "SUB cleanup.topic");
        (await MqttRetainedWire.ReadLineAsync(subStream, 1000))!.ShouldContain("SUBACK");

        using var pub = new TcpClient();
        await pub.ConnectAsync(IPAddress.Loopback, listener.Port);
        var pubStream = pub.GetStream();
        await MqttRetainedWire.WriteLineAsync(pubStream, "CONNECT pub-empty clean=true");
        (await MqttRetainedWire.ReadLineAsync(pubStream, 1000)).ShouldBe("CONNACK");

        await MqttRetainedWire.WriteLineAsync(pubStream, "PUB cleanup.topic data");
        (await MqttRetainedWire.ReadLineAsync(subStream, 1000)).ShouldBe("MSG cleanup.topic data");

        await MqttRetainedWire.WriteLineAsync(pubStream, "PUB cleanup.topic x");
        (await MqttRetainedWire.ReadLineAsync(subStream, 1000)).ShouldBe("MSG cleanup.topic x");
    }

    // Go ref: TestMQTTDecodeRetainedMessage server/mqtt_test.go:7760
    [Fact]
    public async Task Multiple_topics_receive_messages_independently()
    {
        await using var listener = new MqttListener("127.0.0.1", 0);
        using var cts = new CancellationTokenSource();
        await listener.StartAsync(cts.Token);

        using var sub1 = new TcpClient();
        await sub1.ConnectAsync(IPAddress.Loopback, listener.Port);
        var s1 = sub1.GetStream();
        await MqttRetainedWire.WriteLineAsync(s1, "CONNECT sub-topic1 clean=true");
        (await MqttRetainedWire.ReadLineAsync(s1, 1000)).ShouldBe("CONNACK");
        await MqttRetainedWire.WriteLineAsync(s1, "SUB topic.alpha");
        (await MqttRetainedWire.ReadLineAsync(s1, 1000))!.ShouldContain("SUBACK");

        using var sub2 = new TcpClient();
        await sub2.ConnectAsync(IPAddress.Loopback, listener.Port);
        var s2 = sub2.GetStream();
        await MqttRetainedWire.WriteLineAsync(s2, "CONNECT sub-topic2 clean=true");
        (await MqttRetainedWire.ReadLineAsync(s2, 1000)).ShouldBe("CONNACK");
        await MqttRetainedWire.WriteLineAsync(s2, "SUB topic.beta");
        (await MqttRetainedWire.ReadLineAsync(s2, 1000))!.ShouldContain("SUBACK");

        using var pub = new TcpClient();
        await pub.ConnectAsync(IPAddress.Loopback, listener.Port);
        var ps = pub.GetStream();
        await MqttRetainedWire.WriteLineAsync(ps, "CONNECT pub-topics clean=true");
        (await MqttRetainedWire.ReadLineAsync(ps, 1000)).ShouldBe("CONNACK");

        await MqttRetainedWire.WriteLineAsync(ps, "PUB topic.alpha alpha-data");
        (await MqttRetainedWire.ReadLineAsync(s1, 1000)).ShouldBe("MSG topic.alpha alpha-data");

        await MqttRetainedWire.WriteLineAsync(ps, "PUB topic.beta beta-data");
        (await MqttRetainedWire.ReadLineAsync(s2, 1000)).ShouldBe("MSG topic.beta beta-data");

        (await MqttRetainedWire.ReadLineAsync(s1, 300)).ShouldBeNull();
        (await MqttRetainedWire.ReadLineAsync(s2, 300)).ShouldBeNull();
    }

    // Go ref: TestMQTTRestoreRetainedMsgs server/mqtt_test.go:5408
    [Fact]
    public async Task Subscriber_reconnect_resubscribe_receives_new_messages()
    {
        await using var listener = new MqttListener("127.0.0.1", 0);
        using var cts = new CancellationTokenSource();
        await listener.StartAsync(cts.Token);

        using var sub1 = new TcpClient();
        await sub1.ConnectAsync(IPAddress.Loopback, listener.Port);
        var s1 = sub1.GetStream();
        await MqttRetainedWire.WriteLineAsync(s1, "CONNECT sub-reconnect clean=true");
        (await MqttRetainedWire.ReadLineAsync(s1, 1000)).ShouldBe("CONNACK");
        await MqttRetainedWire.WriteLineAsync(s1, "SUB restore.topic");
        (await MqttRetainedWire.ReadLineAsync(s1, 1000))!.ShouldContain("SUBACK");

        using var pub = new TcpClient();
        await pub.ConnectAsync(IPAddress.Loopback, listener.Port);
        var ps = pub.GetStream();
        await MqttRetainedWire.WriteLineAsync(ps, "CONNECT pub-restore clean=true");
        (await MqttRetainedWire.ReadLineAsync(ps, 1000)).ShouldBe("CONNACK");

        await MqttRetainedWire.WriteLineAsync(ps, "PUB restore.topic msg1");
        (await MqttRetainedWire.ReadLineAsync(s1, 1000)).ShouldBe("MSG restore.topic msg1");

        sub1.Dispose();

        using var sub2 = new TcpClient();
        await sub2.ConnectAsync(IPAddress.Loopback, listener.Port);
        var s2 = sub2.GetStream();
        await MqttRetainedWire.WriteLineAsync(s2, "CONNECT sub-reconnect clean=true");
        (await MqttRetainedWire.ReadLineAsync(s2, 1000)).ShouldBe("CONNACK");
        await MqttRetainedWire.WriteLineAsync(s2, "SUB restore.topic");
        (await MqttRetainedWire.ReadLineAsync(s2, 1000))!.ShouldContain("SUBACK");

        await MqttRetainedWire.WriteLineAsync(ps, "PUB restore.topic msg2");
        (await MqttRetainedWire.ReadLineAsync(s2, 1000)).ShouldBe("MSG restore.topic msg2");
    }
}

internal static class MqttRetainedWire
{
    public static async Task WriteLineAsync(NetworkStream stream, string line)
    {
        var bytes = Encoding.UTF8.GetBytes(line + "\n");
        await stream.WriteAsync(bytes);
        await stream.FlushAsync();
    }

    public static async Task<string?> ReadLineAsync(NetworkStream stream, int timeoutMs)
    {
        using var timeout = new CancellationTokenSource(timeoutMs);
        var bytes = new List<byte>();
        var one = new byte[1];
        try
        {
            while (true)
            {
                var read = await stream.ReadAsync(one.AsMemory(0, 1), timeout.Token);
                if (read == 0)
                    return null;
                if (one[0] == (byte)'\n')
                    break;
                if (one[0] != (byte)'\r')
                    bytes.Add(one[0]);
            }
        }
        catch (OperationCanceledException)
        {
            return null;
        }

        return Encoding.UTF8.GetString([.. bytes]);
    }
}