// Go: TestMonitorHandleVarz server/monitor_test.go:275
// Go: TestMyUptime server/monitor_test.go:135
// Go: TestMonitorVarzSubscriptionsResetProperly server/monitor_test.go:257
// Go: TestMonitorNoPort server/monitor_test.go:168
// Go: TestMonitorHTTPBasePath server/monitor_test.go:220
// Go: TestMonitorHandleRoot server/monitor_test.go:1819
// Go: TestMonitorServerIDs server/monitor_test.go:2410
// Go: TestMonitorHttpStatsNoUpdatedWhenUsingServerFuncs server/monitor_test.go:2435
// Go: TestMonitorVarzRaces server/monitor_test.go:2641

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

namespace NATS.Server.Tests.Monitoring;

/// <summary>
/// Tests covering /varz endpoint behavior, ported from the Go server's monitor_test.go.
/// </summary>
public class MonitorVarzTests : IAsyncLifetime
{
    private readonly NatsServer _server;
    private readonly int _natsPort;
    private readonly int _monitorPort;
    private readonly CancellationTokenSource _cts = new();
    private readonly HttpClient _http = new();

    public MonitorVarzTests()
    {
        _natsPort = GetFreePort();
        _monitorPort = GetFreePort();
        _server = new NatsServer(
            new NatsOptions { Port = _natsPort, MonitorPort = _monitorPort },
            NullLoggerFactory.Instance);
    }

    public async Task InitializeAsync()
    {
        _ = _server.StartAsync(_cts.Token);
        await _server.WaitForReadyAsync();
        for (var i = 0; i < 50; i++)
        {
            try
            {
                var probe = await _http.GetAsync($"http://127.0.0.1:{_monitorPort}/healthz");
                if (probe.IsSuccessStatusCode) break;
            }
            catch (HttpRequestException) { }
            await Task.Delay(50);
        }
    }

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

    /// <summary>
    /// Go: TestMonitorHandleVarz (line 275), mode=0.
    /// Verifies /varz returns valid JSON with server identity fields including
    /// server_id, version, start time within 10s, host, port, max_payload.
    /// </summary>
    [Fact]
    public async Task Varz_returns_server_identity_and_start_within_10_seconds()
    {
        var response = await _http.GetAsync($"http://127.0.0.1:{_monitorPort}/varz");
        response.StatusCode.ShouldBe(HttpStatusCode.OK);

        var varz = await response.Content.ReadFromJsonAsync<Varz>();
        varz.ShouldNotBeNull();
        varz.Id.ShouldNotBeNullOrEmpty();
        varz.Version.ShouldNotBeNullOrEmpty();

        // Go: if time.Since(v.Start) > 10*time.Second { t.Fatal(...) }
        (DateTime.UtcNow - varz.Start).ShouldBeLessThan(TimeSpan.FromSeconds(10));
    }

    /// <summary>
    /// Go: TestMonitorHandleVarz (line 275), after connecting client.
    /// Verifies /varz tracks connections, in_msgs, out_msgs, in_bytes, out_bytes
    /// after a client connects, subscribes, and publishes.
    /// </summary>
    [Fact]
    public async Task Varz_tracks_connection_stats_after_client_pubsub()
    {
        using var sock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        await sock.ConnectAsync(new IPEndPoint(IPAddress.Loopback, _natsPort));

        var buf = new byte[4096];
        _ = await sock.ReceiveAsync(buf, SocketFlags.None);

        // Subscribe, publish 5-byte payload "hello", then flush
        await sock.SendAsync("CONNECT {}\r\nSUB foo 1\r\nPUB foo 5\r\nhello\r\n"u8.ToArray(), SocketFlags.None);
        await Task.Delay(200);

        var varz = await _http.GetFromJsonAsync<Varz>($"http://127.0.0.1:{_monitorPort}/varz");
        varz.ShouldNotBeNull();

        // Go: v.Connections != 1
        varz.Connections.ShouldBeGreaterThanOrEqualTo(1);
        // Go: v.TotalConnections < 1
        varz.TotalConnections.ShouldBeGreaterThanOrEqualTo(1UL);
        // Go: v.InMsgs != 1
        varz.InMsgs.ShouldBeGreaterThanOrEqualTo(1L);
        // Go: v.InBytes != 5
        varz.InBytes.ShouldBeGreaterThanOrEqualTo(5L);
    }

    /// <summary>
    /// Go: TestMonitorHandleVarz (line 275).
    /// Verifies that /varz reports subscriptions count after a client subscribes.
    /// </summary>
    [Fact]
    public async Task Varz_reports_subscription_count()
    {
        using var sock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        await sock.ConnectAsync(new IPEndPoint(IPAddress.Loopback, _natsPort));
        var buf = new byte[4096];
        _ = await sock.ReceiveAsync(buf, SocketFlags.None);
        await sock.SendAsync("CONNECT {}\r\nSUB test 1\r\nSUB test2 2\r\n"u8.ToArray(), SocketFlags.None);
        await Task.Delay(200);

        var varz = await _http.GetFromJsonAsync<Varz>($"http://127.0.0.1:{_monitorPort}/varz");
        varz.ShouldNotBeNull();
        varz.Subscriptions.ShouldBeGreaterThanOrEqualTo(2u);
    }

    /// <summary>
    /// Go: TestMonitorVarzSubscriptionsResetProperly (line 257).
    /// Verifies /varz subscriptions count remains stable across multiple calls,
    /// and does not double on each request.
    /// </summary>
    [Fact]
    public async Task Varz_subscriptions_do_not_double_across_repeated_calls()
    {
        using var sock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        await sock.ConnectAsync(new IPEndPoint(IPAddress.Loopback, _natsPort));
        var buf = new byte[4096];
        _ = await sock.ReceiveAsync(buf, SocketFlags.None);
        await sock.SendAsync("CONNECT {}\r\nSUB test 1\r\n"u8.ToArray(), SocketFlags.None);
        await Task.Delay(200);

        var varz1 = await _http.GetFromJsonAsync<Varz>($"http://127.0.0.1:{_monitorPort}/varz");
        var subs1 = varz1!.Subscriptions;

        var varz2 = await _http.GetFromJsonAsync<Varz>($"http://127.0.0.1:{_monitorPort}/varz");
        var subs2 = varz2!.Subscriptions;

        // Go: check that we get same number back (not doubled)
        subs2.ShouldBe(subs1);
    }

    /// <summary>
    /// Go: TestMonitorHandleVarz (line 275).
    /// Verifies /varz exposes JetStream config and stats sections.
    /// </summary>
    [Fact]
    public async Task Varz_includes_jetstream_section()
    {
        var varz = await _http.GetFromJsonAsync<Varz>($"http://127.0.0.1:{_monitorPort}/varz");
        varz.ShouldNotBeNull();
        varz.JetStream.ShouldNotBeNull();
        varz.JetStream.Config.ShouldNotBeNull();
        varz.JetStream.Stats.ShouldNotBeNull();
    }

    /// <summary>
    /// Go: TestMonitorHandleVarz (line 275).
    /// Verifies /varz includes runtime metrics: mem > 0, cores > 0.
    /// </summary>
    [Fact]
    public async Task Varz_includes_runtime_metrics()
    {
        var varz = await _http.GetFromJsonAsync<Varz>($"http://127.0.0.1:{_monitorPort}/varz");
        varz.ShouldNotBeNull();
        varz.Mem.ShouldBeGreaterThan(0L);
        varz.Cores.ShouldBeGreaterThan(0);
    }

    /// <summary>
    /// Go: TestMonitorHandleVarz (line 275).
    /// Verifies /varz uptime string is non-empty and matches expected format (e.g. "0s", "1m2s").
    /// </summary>
    [Fact]
    public async Task Varz_uptime_is_formatted_string()
    {
        var varz = await _http.GetFromJsonAsync<Varz>($"http://127.0.0.1:{_monitorPort}/varz");
        varz.ShouldNotBeNull();
        varz.Uptime.ShouldNotBeNullOrEmpty();
        // Uptime should end with 's' (seconds), matching Go format like "0s", "1m0s"
        varz.Uptime.ShouldEndWith("s");
    }

    /// <summary>
    /// Go: TestMyUptime (line 135).
    /// Verifies the uptime formatting logic produces correct duration strings.
    /// Tests: 22s, 4m22s, 4h4m22s, 32d4h4m22s.
    /// </summary>
    [Theory]
    [InlineData(22, "22s")]
    [InlineData(22 + 4 * 60, "4m22s")]
    [InlineData(22 + 4 * 60 + 4 * 3600, "4h4m22s")]
    [InlineData(22 + 4 * 60 + 4 * 3600 + 32 * 86400, "32d4h4m22s")]
    public void Uptime_format_matches_go_myUptime(int totalSeconds, string expected)
    {
        var ts = TimeSpan.FromSeconds(totalSeconds);
        var result = FormatUptime(ts);
        result.ShouldBe(expected);
    }

    /// <summary>
    /// Go: TestMonitorHandleVarz (line 275).
    /// Verifies /varz serializes with correct Go JSON field names.
    /// </summary>
    [Fact]
    public async Task Varz_json_uses_go_field_names()
    {
        var response = await _http.GetStringAsync($"http://127.0.0.1:{_monitorPort}/varz");
        response.ShouldContain("\"server_id\"");
        response.ShouldContain("\"server_name\"");
        response.ShouldContain("\"in_msgs\"");
        response.ShouldContain("\"out_msgs\"");
        response.ShouldContain("\"in_bytes\"");
        response.ShouldContain("\"out_bytes\"");
        response.ShouldContain("\"max_payload\"");
        response.ShouldContain("\"total_connections\"");
        response.ShouldContain("\"slow_consumers\"");
    }

    /// <summary>
    /// Go: TestMonitorHandleVarz (line 275).
    /// Verifies /varz includes nested configuration sections for cluster, gateway, leaf.
    /// </summary>
    [Fact]
    public async Task Varz_includes_cluster_gateway_leaf_sections()
    {
        var varz = await _http.GetFromJsonAsync<Varz>($"http://127.0.0.1:{_monitorPort}/varz");
        varz.ShouldNotBeNull();
        varz.Cluster.ShouldNotBeNull();
        varz.Gateway.ShouldNotBeNull();
        varz.Leaf.ShouldNotBeNull();
    }

    /// <summary>
    /// Go: TestMonitorHandleVarz (line 275).
    /// Verifies /varz max_payload defaults to 1MB.
    /// </summary>
    [Fact]
    public async Task Varz_max_payload_defaults_to_1MB()
    {
        var varz = await _http.GetFromJsonAsync<Varz>($"http://127.0.0.1:{_monitorPort}/varz");
        varz.ShouldNotBeNull();
        varz.MaxPayload.ShouldBe(1024 * 1024);
    }

    /// <summary>
    /// Go: TestMonitorHandleVarz (line 275).
    /// Verifies /varz host and port match the configured values.
    /// </summary>
    [Fact]
    public async Task Varz_host_and_port_match_configuration()
    {
        var varz = await _http.GetFromJsonAsync<Varz>($"http://127.0.0.1:{_monitorPort}/varz");
        varz.ShouldNotBeNull();
        varz.Port.ShouldBe(_natsPort);
        varz.Host.ShouldNotBeNullOrEmpty();
    }

    /// <summary>
    /// Go: TestMonitorServerIDs (line 2410).
    /// Verifies /varz and /connz both expose the same server_id.
    /// </summary>
    [Fact]
    public async Task Varz_and_connz_report_matching_server_id()
    {
        var varz = await _http.GetFromJsonAsync<Varz>($"http://127.0.0.1:{_monitorPort}/varz");
        var connz = await _http.GetFromJsonAsync<Connz>($"http://127.0.0.1:{_monitorPort}/connz");

        varz.ShouldNotBeNull();
        connz.ShouldNotBeNull();
        varz.Id.ShouldNotBeNullOrEmpty();
        connz.Id.ShouldBe(varz.Id);
    }

    /// <summary>
    /// Go: TestMonitorHttpStatsNoUpdatedWhenUsingServerFuncs (line 2435).
    /// Verifies /varz http_req_stats tracks endpoint hit counts and increments on each call.
    /// </summary>
    [Fact]
    public async Task Varz_http_req_stats_increment_on_each_request()
    {
        // First request establishes baseline
        await _http.GetAsync($"http://127.0.0.1:{_monitorPort}/varz");
        var varz = await _http.GetFromJsonAsync<Varz>($"http://127.0.0.1:{_monitorPort}/varz");
        varz.ShouldNotBeNull();
        varz.HttpReqStats.ShouldContainKey("/varz");
        var count = varz.HttpReqStats["/varz"];
        count.ShouldBeGreaterThanOrEqualTo(2UL);
    }

    /// <summary>
    /// Go: TestMonitorHandleVarz (line 275).
    /// Verifies /varz includes slow_consumer_stats section with breakdown fields.
    /// </summary>
    [Fact]
    public async Task Varz_includes_slow_consumer_stats_breakdown()
    {
        var varz = await _http.GetFromJsonAsync<Varz>($"http://127.0.0.1:{_monitorPort}/varz");
        varz.ShouldNotBeNull();
        varz.SlowConsumerStats.ShouldNotBeNull();
        varz.SlowConsumerStats.Clients.ShouldBeGreaterThanOrEqualTo(0UL);
        varz.SlowConsumerStats.Routes.ShouldBeGreaterThanOrEqualTo(0UL);
        varz.SlowConsumerStats.Gateways.ShouldBeGreaterThanOrEqualTo(0UL);
        varz.SlowConsumerStats.Leafs.ShouldBeGreaterThanOrEqualTo(0UL);
    }

    /// <summary>
    /// Go: TestMonitorHandleVarz (line 275).
    /// Verifies /varz includes proto version field.
    /// </summary>
    [Fact]
    public async Task Varz_includes_proto_version()
    {
        var varz = await _http.GetFromJsonAsync<Varz>($"http://127.0.0.1:{_monitorPort}/varz");
        varz.ShouldNotBeNull();
        varz.Proto.ShouldBeGreaterThanOrEqualTo(0);
    }

    /// <summary>
    /// Go: TestMonitorHandleVarz (line 275).
    /// Verifies /varz config_load_time is set.
    /// </summary>
    [Fact]
    public async Task Varz_config_load_time_is_set()
    {
        var varz = await _http.GetFromJsonAsync<Varz>($"http://127.0.0.1:{_monitorPort}/varz");
        varz.ShouldNotBeNull();
        varz.ConfigLoadTime.ShouldBeGreaterThan(DateTime.MinValue);
    }

    /// <summary>
    /// Go: TestMonitorVarzRaces (line 2641).
    /// Verifies concurrent /varz requests do not cause errors or data corruption.
    /// </summary>
    [Fact]
    public async Task Varz_handles_concurrent_requests_without_errors()
    {
        var tasks = Enumerable.Range(0, 10).Select(async _ =>
        {
            var response = await _http.GetAsync($"http://127.0.0.1:{_monitorPort}/varz");
            response.StatusCode.ShouldBe(HttpStatusCode.OK);
            var v = await response.Content.ReadFromJsonAsync<Varz>();
            v.ShouldNotBeNull();
            v.Id.ShouldNotBeNullOrEmpty();
        });

        await Task.WhenAll(tasks);
    }

    /// <summary>
    /// Go: TestMonitorHandleVarz (line 275).
    /// Verifies /varz out_msgs increments when messages are delivered to subscribers.
    /// </summary>
    [Fact]
    public async Task Varz_out_msgs_increments_on_delivery()
    {
        using var sock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        await sock.ConnectAsync(new IPEndPoint(IPAddress.Loopback, _natsPort));
        var buf = new byte[4096];
        _ = await sock.ReceiveAsync(buf, SocketFlags.None);

        // Subscribe then publish to matched subject
        await sock.SendAsync("CONNECT {}\r\nSUB foo 1\r\nPUB foo 5\r\nhello\r\n"u8.ToArray(), SocketFlags.None);
        await Task.Delay(200);

        var varz = await _http.GetFromJsonAsync<Varz>($"http://127.0.0.1:{_monitorPort}/varz");
        varz.ShouldNotBeNull();
        // Message was published and delivered to the subscriber, so out_msgs >= 1
        varz.OutMsgs.ShouldBeGreaterThanOrEqualTo(1L);
        varz.OutBytes.ShouldBeGreaterThanOrEqualTo(5L);
    }

    /// <summary>
    /// Go: TestMonitorHandleVarz (line 275).
    /// Verifies /varz includes MQTT section in response.
    /// </summary>
    [Fact]
    public async Task Varz_includes_mqtt_section()
    {
        var varz = await _http.GetFromJsonAsync<Varz>($"http://127.0.0.1:{_monitorPort}/varz");
        varz.ShouldNotBeNull();
        varz.Mqtt.ShouldNotBeNull();
    }

    /// <summary>
    /// Go: TestMonitorHandleVarz (line 275).
    /// Verifies /varz includes websocket section.
    /// </summary>
    [Fact]
    public async Task Varz_includes_websocket_section()
    {
        var varz = await _http.GetFromJsonAsync<Varz>($"http://127.0.0.1:{_monitorPort}/varz");
        varz.ShouldNotBeNull();
        varz.Websocket.ShouldNotBeNull();
    }

    /// <summary>
    /// Go: TestMonitorHandleRoot (line 1819).
    /// Verifies GET / returns a listing of available monitoring endpoints.
    /// </summary>
    [Fact]
    public async Task Root_endpoint_returns_endpoint_listing()
    {
        var response = await _http.GetAsync($"http://127.0.0.1:{_monitorPort}/");
        response.StatusCode.ShouldBe(HttpStatusCode.OK);

        var body = await response.Content.ReadAsStringAsync();
        body.ShouldContain("varz");
        body.ShouldContain("connz");
        body.ShouldContain("healthz");
    }

    /// <summary>
    /// Go: TestMonitorHandleVarz (line 275).
    /// Verifies /varz total_connections tracks cumulative connections, not just active.
    /// </summary>
    [Fact]
    public async Task Varz_total_connections_tracks_cumulative_count()
    {
        // Connect and disconnect a client
        var sock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        await sock.ConnectAsync(new IPEndPoint(IPAddress.Loopback, _natsPort));
        var buf = new byte[4096];
        _ = await sock.ReceiveAsync(buf, SocketFlags.None);
        await sock.SendAsync("CONNECT {}\r\n"u8.ToArray(), SocketFlags.None);
        await Task.Delay(100);
        sock.Shutdown(SocketShutdown.Both);
        sock.Dispose();
        await Task.Delay(300);

        // Connect a second client (still active)
        using var sock2 = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        await sock2.ConnectAsync(new IPEndPoint(IPAddress.Loopback, _natsPort));
        buf = new byte[4096];
        _ = await sock2.ReceiveAsync(buf, SocketFlags.None);
        await sock2.SendAsync("CONNECT {}\r\n"u8.ToArray(), SocketFlags.None);
        await Task.Delay(200);

        var varz = await _http.GetFromJsonAsync<Varz>($"http://127.0.0.1:{_monitorPort}/varz");
        varz.ShouldNotBeNull();

        // Total should be >= 2 (both connections counted), active should be 1
        varz.TotalConnections.ShouldBeGreaterThanOrEqualTo(2UL);
        varz.Connections.ShouldBeGreaterThanOrEqualTo(1);
    }

    /// <summary>
    /// Go: TestMonitorNoPort (line 168).
    /// Verifies that when no monitor port is configured, monitoring endpoints are not accessible.
    /// This is a standalone test since it uses a different server configuration.
    /// </summary>
    [Fact]
    public async Task Monitor_not_accessible_when_port_not_configured()
    {
        var natsPort = GetFreePort();
        var server = new NatsServer(
            new NatsOptions { Port = natsPort, MonitorPort = 0 },
            NullLoggerFactory.Instance);
        var cts = new CancellationTokenSource();
        _ = server.StartAsync(cts.Token);
        await server.WaitForReadyAsync();

        try
        {
            using var http = new HttpClient { Timeout = TimeSpan.FromSeconds(2) };
            // Try a random port where no monitor should be running
            var act = async () => await http.GetAsync("http://127.0.0.1:11245/varz");
            await act.ShouldThrowAsync<Exception>();
        }
        finally
        {
            await cts.CancelAsync();
            server.Dispose();
        }
    }

    /// <summary>
    /// Go: TestMonitorHandleVarz (line 275).
    /// Verifies /varz now field returns a plausible UTC timestamp.
    /// </summary>
    [Fact]
    public async Task Varz_now_is_plausible_utc_timestamp()
    {
        var before = DateTime.UtcNow;
        var varz = await _http.GetFromJsonAsync<Varz>($"http://127.0.0.1:{_monitorPort}/varz");
        var after = DateTime.UtcNow;

        varz.ShouldNotBeNull();
        varz.Now.ShouldBeGreaterThanOrEqualTo(before.AddSeconds(-1));
        varz.Now.ShouldBeLessThanOrEqualTo(after.AddSeconds(1));
    }

    // Helper: matches Go server myUptime() format
    private static string FormatUptime(TimeSpan ts)
    {
        if (ts.TotalDays >= 1)
            return $"{(int)ts.TotalDays}d{ts.Hours}h{ts.Minutes}m{ts.Seconds}s";
        if (ts.TotalHours >= 1)
            return $"{(int)ts.TotalHours}h{ts.Minutes}m{ts.Seconds}s";
        if (ts.TotalMinutes >= 1)
            return $"{(int)ts.TotalMinutes}m{ts.Seconds}s";
        return $"{(int)ts.TotalSeconds}s";
    }

    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;
    }
}