using System.Reflection;
using System.Security.Claims;
using Bunit;
using Microsoft.AspNetCore.Components.Authorization;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Logging.Abstractions;
using Microsoft.Extensions.Options;
using NSubstitute;
using ZB.MOM.WW.ScadaBridge.Commons.Entities.Instances;
using ZB.MOM.WW.ScadaBridge.Commons.Entities.Sites;
using ZB.MOM.WW.ScadaBridge.Commons.Entities.Templates;
using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Repositories;
using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Services;
using ZB.MOM.WW.ScadaBridge.Commons.Entities.Deployment;
using ZB.MOM.WW.ScadaBridge.Communication;
using ZB.MOM.WW.ScadaBridge.DeploymentManager;
using ZB.MOM.WW.ScadaBridge.Security;
using ZB.MOM.WW.ScadaBridge.TemplateEngine.Services;
using TopologyPage = ZB.MOM.WW.ScadaBridge.CentralUI.Components.Pages.Deployment.Topology;

namespace ZB.MOM.WW.ScadaBridge.CentralUI.Tests;

/// <summary>
/// Regression tests for register row 103 (the P6-6 lesser instance in
/// <c>Topology</c>). <c>OnInitializedAsync</c> awaits <c>LoadDataAsync</c> and only then
/// calls <c>StartLiveUpdatesTimer</c>. If the circuit was torn down inside that await
/// (user navigates away during the initial page load), the pre-fix <c>Dispose</c> would
/// have already run and found <c>_liveUpdatesTimer</c> still null — a no-op — so the
/// timer <c>StartLiveUpdatesTimer</c> creates once the await resumes is never disposed:
/// it ticks against a torn-down component every 15s until process restart. The fix
/// (mirroring <c>DebugView</c>'s P6-6 fix and <c>TransportImport</c>'s row-103 sibling
/// fix) creates/replaces the timer and observes disposal atomically under
/// <c>_timerLock</c>, so a (re)start that resumes after <c>Dispose</c> already ran
/// refuses to create a new timer instead of leaking one.
///
/// <para>
/// The race is reproduced deterministically by driving the exact call ORDER the async
/// gap allows — <c>Dispose()</c> then a late-arriving <c>StartLiveUpdatesTimer()</c> —
/// rather than by gating I/O and sleeping: <c>StartLiveUpdatesTimer</c> itself is
/// synchronous, so once we control ordering there is nothing left to wait on. This is
/// the "deterministic observation, never sleep-then-assert" style the shared plan
/// constraints require: the assertion is a direct field-state check, not a timer tick.
/// </para>
/// </summary>
public class TopologyLiveUpdatesTimerDisposeRaceTests : BunitContext
{
    private readonly ITemplateEngineRepository _repo = Substitute.For<ITemplateEngineRepository>();
    private readonly ISiteRepository _siteRepo = Substitute.For<ISiteRepository>();
    private readonly IDeploymentManagerRepository _deployRepo = Substitute.For<IDeploymentManagerRepository>();
    private readonly IAuditService _audit = Substitute.For<IAuditService>();

    public TopologyLiveUpdatesTimerDisposeRaceTests()
    {
        Services.AddSingleton(_repo);
        Services.AddSingleton(_siteRepo);
        Services.AddSingleton(_deployRepo);
        Services.AddSingleton(Substitute.For<ZB.MOM.WW.ScadaBridge.DeploymentManager.IFlatteningPipeline>());
        // DeploymentService takes IStaleInstanceProbe since the Low-wave P7-6 pre-filter (T13).
        Services.AddSingleton(Substitute.For<ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Transport.IStaleInstanceProbe>());
        Services.AddSingleton(_audit);

        var comms = new CommunicationService(
            Options.Create(new CommunicationOptions()),
            NullLogger<CommunicationService>.Instance);
        Services.AddSingleton(comms);

        Services.AddSingleton(new OperationLockManager());
        Services.AddSingleton(Options.Create(new DeploymentManagerOptions
        {
            OperationLockTimeout = TimeSpan.FromSeconds(5)
        }));
        Services.AddSingleton(Options.Create(new CommunicationOptions()));
        Services.AddSingleton<ILogger<DeploymentService>>(NullLogger<DeploymentService>.Instance);
        Services.AddScoped<ZB.MOM.WW.ScadaBridge.TemplateEngine.Flattening.DiffService>();
        Services.AddScoped<ZB.MOM.WW.ScadaBridge.TemplateEngine.Flattening.RevisionHashService>();
        Services.AddSingleton<IDeploymentStatusNotifier>(
            new DeploymentStatusNotifier(NullLogger<DeploymentStatusNotifier>.Instance));
        Services.AddScoped<DeploymentService>();
        Services.AddScoped<AreaService>();
        Services.AddScoped<InstanceService>();

        AddTestAuth();

        Services.AddScoped<ZB.MOM.WW.ScadaBridge.CentralUI.Components.Shared.IDialogService,
            ZB.MOM.WW.ScadaBridge.CentralUI.Components.Shared.DialogService>();
        Services.AddScoped<ZB.MOM.WW.ScadaBridge.CentralUI.Auth.SiteScopeService>();

        JSInterop.Setup<string?>("treeviewStorage.load", _ => true).SetResult(null);
        JSInterop.SetupVoid("treeviewStorage.save", _ => true);

        SeedEmptyRepos();
    }

    private void AddTestAuth()
    {
        var claims = new[]
        {
            new Claim(JwtTokenService.UsernameClaimType, "tester"),
            new Claim(JwtTokenService.RoleClaimType, "Deployer")
        };
        var user = new ClaimsPrincipal(new ClaimsIdentity(claims, "TestAuth"));
        Services.AddSingleton<AuthenticationStateProvider>(new TestAuthStateProvider(user));
        Services.AddAuthorizationCore();
    }

    private void SeedEmptyRepos()
    {
        _siteRepo.GetAllSitesAsync(Arg.Any<CancellationToken>())
            .Returns(Task.FromResult<IReadOnlyList<Site>>(new List<Site>()));
        _repo.GetAllTemplatesAsync(Arg.Any<CancellationToken>())
            .Returns(Task.FromResult<IReadOnlyList<Template>>(new List<Template>()));
        _repo.GetAllInstancesAsync(Arg.Any<CancellationToken>())
            .Returns(Task.FromResult<IReadOnlyList<Instance>>(new List<Instance>()));
        _repo.GetAreasBySiteIdAsync(Arg.Any<int>(), Arg.Any<CancellationToken>())
            .Returns(Task.FromResult<IReadOnlyList<Area>>(new List<Area>()));
    }

    private static void InvokePrivate(object obj, string name) =>
        obj.GetType().GetMethod(name, BindingFlags.Instance | BindingFlags.NonPublic)!
            .Invoke(obj, null);

    private static T? GetField<T>(object obj, string name) =>
        (T?)obj.GetType().GetField(name, BindingFlags.Instance | BindingFlags.NonPublic)!.GetValue(obj);

    [Fact]
    public void Render_StartsALiveTimer_Sanity()
    {
        // Baseline: the normal init path (fast/empty repos complete synchronously) leaves
        // a running timer, so the race tests below start from a known non-null state.
        var cut = Render<TopologyPage>();
        Assert.NotNull(GetField<Timer?>(cut.Instance, "_liveUpdatesTimer"));
        cut.Instance.Dispose();
    }

    [Fact]
    public void StartLiveUpdatesTimer_ResumingAfterDispose_LeavesNoLiveTimer()
    {
        // Simulates: OnInitializedAsync is suspended awaiting LoadDataAsync; the user
        // navigates away, so Dispose() runs (and, since no timer exists yet, has nothing
        // to stop); the await then resumes and calls StartLiveUpdatesTimer() — the exact
        // shape register row 103 flags for Topology (the P6-6 lesser instance).
        var cut = Render<TopologyPage>();

        // The normal init path already started a timer; dispose it first so the field is
        // null going into the race exactly as it would be if OnInitializedAsync's await
        // was still pending when Dispose ran (no timer created yet).
        cut.Instance.Dispose();
        Assert.Null(GetField<Timer?>(cut.Instance, "_liveUpdatesTimer"));

        // The late-arriving continuation's call, happening strictly AFTER Dispose().
        InvokePrivate(cut.Instance, "StartLiveUpdatesTimer");

        // Post-fix: refuses to create a timer once disposed — nothing is leaked.
        // Pre-fix: this assignment is unconditional, so the field would be non-null here
        // (a live Timer nothing will ever dispose).
        Assert.Null(GetField<Timer?>(cut.Instance, "_liveUpdatesTimer"));
    }

    [Fact]
    public void Dispose_StopsTheLiveTimer_ExactlyOnce()
    {
        var cut = Render<TopologyPage>();
        Assert.NotNull(GetField<Timer?>(cut.Instance, "_liveUpdatesTimer"));

        cut.Instance.Dispose();
        Assert.Null(GetField<Timer?>(cut.Instance, "_liveUpdatesTimer"));

        // A second Dispose (bUnit tears the component down again at test end) must not
        // throw (e.g. from double-disposing the same Timer) and must leave the slot null.
        var ex = Record.Exception(() => cut.Instance.Dispose());
        Assert.Null(ex);
        Assert.Null(GetField<Timer?>(cut.Instance, "_liveUpdatesTimer"));
    }

    [Fact]
    public void OnLiveUpdatesToggled_Off_ThenDispose_LeavesNoLiveTimer()
    {
        var cut = Render<TopologyPage>();
        Assert.NotNull(GetField<Timer?>(cut.Instance, "_liveUpdatesTimer"));

        // Turn live updates off via the toolbar handler (StopLiveUpdatesTimer path).
        var toggleMethod = typeof(TopologyPage).GetMethod(
            "OnLiveUpdatesToggled", BindingFlags.Instance | BindingFlags.NonPublic)!;
        var changeArgsType = typeof(Microsoft.AspNetCore.Components.ChangeEventArgs);
        var changeArgs = (Microsoft.AspNetCore.Components.ChangeEventArgs)Activator.CreateInstance(changeArgsType)!;
        changeArgs.Value = false;
        toggleMethod.Invoke(cut.Instance, new object?[] { changeArgs });

        Assert.Null(GetField<Timer?>(cut.Instance, "_liveUpdatesTimer"));

        var ex = Record.Exception(() => cut.Instance.Dispose());
        Assert.Null(ex);
        Assert.Null(GetField<Timer?>(cut.Instance, "_liveUpdatesTimer"));
    }
}