using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Core.Abstractions;

namespace ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests;

/// <summary>
///     Unit tests for the per-driver diagnostic counters surfaced via
///     <see cref="DriverHealth.Diagnostics"/> for the <c>driver-diagnostics</c> RPC
///     (task #276). Counters are exercised directly through the internal helper rather
///     than via a live SDK <c>ISession</c> because the SDK requires a connected upstream
///     to publish events and we want unit-level coverage of the math + the snapshot shape.
/// </summary>
[Trait("Category", "Unit")]
public sealed class OpcUaClientDiagnosticsTests
{
    [Fact]
    public void Counters_default_to_zero()
    {
        var d = new OpcUaClientDiagnostics();
        d.PublishRequestCount.ShouldBe(0);
        d.NotificationCount.ShouldBe(0);
        d.NotificationsPerSecond.ShouldBe(0);
        d.MissingPublishRequestCount.ShouldBe(0);
        d.DroppedNotificationCount.ShouldBe(0);
        d.SessionResetCount.ShouldBe(0);
        d.LastReconnectUtc.ShouldBeNull();
    }

    [Fact]
    public void IncrementPublishRequest_bumps_total()
    {
        var d = new OpcUaClientDiagnostics();
        d.IncrementPublishRequest();
        d.IncrementPublishRequest();
        d.IncrementPublishRequest();
        d.PublishRequestCount.ShouldBe(3);
    }

    [Fact]
    public void IncrementMissingPublishRequest_bumps_total()
    {
        var d = new OpcUaClientDiagnostics();
        d.IncrementMissingPublishRequest();
        d.IncrementMissingPublishRequest();
        d.MissingPublishRequestCount.ShouldBe(2);
    }

    [Fact]
    public void IncrementDroppedNotification_bumps_total()
    {
        var d = new OpcUaClientDiagnostics();
        d.IncrementDroppedNotification();
        d.DroppedNotificationCount.ShouldBe(1);
    }

    [Fact]
    public void RecordNotification_grows_count_and_then_rate()
    {
        var d = new OpcUaClientDiagnostics();
        var t0 = new DateTime(2026, 1, 1, 0, 0, 0, DateTimeKind.Utc);
        // First sample seeds the EWMA — rate stays 0 until we have a delta.
        d.RecordNotification(t0);
        d.NotificationCount.ShouldBe(1);
        d.NotificationsPerSecond.ShouldBe(0);

        // 1 Hz steady state: 30 samples spaced 1s apart converge toward 1/s. With 5s half-life
        // and alpha=0.5^(1/5)≈0.871, the EWMA approaches 1 - alpha^N — after 30 samples that's
        // 1 - 0.871^30 ≈ 0.984.
        for (var i = 1; i <= 30; i++)
            d.RecordNotification(t0.AddSeconds(i));

        d.NotificationCount.ShouldBe(31);
        d.NotificationsPerSecond.ShouldBeInRange(0.95, 1.05, "EWMA at 5s half-life converges to ~1Hz after 30 samples");
    }

    [Fact]
    public void RecordSessionReset_bumps_count_and_sets_last_reconnect()
    {
        var d = new OpcUaClientDiagnostics();
        var t = new DateTime(2026, 4, 25, 12, 34, 56, DateTimeKind.Utc);
        d.RecordSessionReset(t);
        d.SessionResetCount.ShouldBe(1);
        d.LastReconnectUtc.ShouldBe(t);

        // Second reset overwrites timestamp + bumps count.
        var t2 = t.AddMinutes(5);
        d.RecordSessionReset(t2);
        d.SessionResetCount.ShouldBe(2);
        d.LastReconnectUtc.ShouldBe(t2);
    }

    [Fact]
    public void Snapshot_emits_well_known_keys()
    {
        var d = new OpcUaClientDiagnostics();
        d.IncrementPublishRequest();
        d.RecordNotification(new DateTime(2026, 1, 1, 0, 0, 0, DateTimeKind.Utc));
        d.IncrementMissingPublishRequest();
        d.IncrementDroppedNotification();
        d.RecordSessionReset(new DateTime(2026, 4, 25, 0, 0, 0, DateTimeKind.Utc));

        var snap = d.Snapshot();

        snap.ShouldContainKey("PublishRequestCount");
        snap["PublishRequestCount"].ShouldBe(1);
        snap.ShouldContainKey("NotificationCount");
        snap["NotificationCount"].ShouldBe(1);
        snap.ShouldContainKey("NotificationsPerSecond");
        snap.ShouldContainKey("MissingPublishRequestCount");
        snap["MissingPublishRequestCount"].ShouldBe(1);
        snap.ShouldContainKey("DroppedNotificationCount");
        snap["DroppedNotificationCount"].ShouldBe(1);
        snap.ShouldContainKey("SessionResetCount");
        snap["SessionResetCount"].ShouldBe(1);
        snap.ShouldContainKey("LastReconnectUtcTicks");
    }

    [Fact]
    public void Snapshot_omits_LastReconnectUtcTicks_when_no_reset_recorded()
    {
        var d = new OpcUaClientDiagnostics();
        d.Snapshot().ShouldNotContainKey("LastReconnectUtcTicks");
    }

    [Fact]
    public void Driver_GetHealth_includes_diagnostics_dictionary()
    {
        // GetHealth must expose the snapshot to the RPC consumer even before any session
        // has been opened — operators call it during startup to check counters baseline.
        using var drv = new OpcUaClientDriver(new OpcUaClientDriverOptions(), "diag-test");
        var health = drv.GetHealth();
        health.Diagnostics.ShouldNotBeNull();
        health.Diagnostics!.ShouldContainKey("PublishRequestCount");
        health.Diagnostics["PublishRequestCount"].ShouldBe(0);
        health.Diagnostics.ShouldContainKey("NotificationCount");
        health.Diagnostics.ShouldContainKey("SessionResetCount");
    }

    [Fact]
    public void Driver_health_diagnostics_reflect_internal_counters_after_increment()
    {
        using var drv = new OpcUaClientDriver(new OpcUaClientDriverOptions(), "diag-test-2");

        // Drive a counter through the test seam to prove the GetHealth snapshot is live,
        // not a one-shot at construction.
        drv.DiagnosticsForTest.IncrementPublishRequest();
        drv.DiagnosticsForTest.IncrementPublishRequest();

        var health = drv.GetHealth();
        health.Diagnostics!["PublishRequestCount"].ShouldBe(2);
    }

    [Fact]
    public void DriverHealth_default_diagnostics_is_null_but_DiagnosticsOrEmpty_is_empty()
    {
        // Back-compat: pre-existing call sites that construct DriverHealth with the
        // 3-arg overload must keep working — the 4th param defaults to null.
        var h = new DriverHealth(DriverState.Healthy, DateTime.UtcNow, null);
        h.Diagnostics.ShouldBeNull();
        h.DiagnosticsOrEmpty.ShouldBeEmpty();
    }
}