using System.Reflection;
using System.Security.Claims;
using Bunit;
using Microsoft.AspNetCore.Components.Authorization;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging.Abstractions;
using NSubstitute;
using ZB.MOM.WW.ScadaBridge.CentralUI.Auth;
using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Repositories;
using ZB.MOM.WW.ScadaBridge.Commons.Types.Deployment;
using ZB.MOM.WW.ScadaBridge.Commons.Types.Enums;
using ZB.MOM.WW.ScadaBridge.DeploymentManager;
using DeploymentsPage = ZB.MOM.WW.ScadaBridge.CentralUI.Components.Pages.Deployment.Deployments;

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

/// <summary>
/// Regression tests for arch-review 2026-08-19 P6-11. Three independent initiators —
/// search, paging, and the push/coalesce reload — can each have a
/// <c>LoadDataAsync</c> flight in flight on the Deployment Status page at once. Every
/// flight awaits its own round-trip to central MS SQL, so COMPLETION order is not
/// CALL order: a slow flight that started first can resolve LAST and overwrite a
/// newer grid the operator is already looking at.
///
/// <para>
/// Separately, the filter-debounce timer used to write <c>_currentPage = 1</c>
/// directly on its raw <see cref="System.Threading.Timer"/> callback thread — a
/// Blazor threading violation, since component state may only be mutated on the
/// renderer's synchronization context — and that write was NOT covered by the
/// request-generation guard at all, so even a correctly-marshaled version of it
/// could still reset the operator's page out from under a newer navigation. The fix
/// resolves the target page into a local at fetch start and applies it only behind
/// the same generation check as every other piece of state
/// (<c>LoadDataAsync(resetToFirstPage:)</c>), so a stale filter-debounce flight is
/// discarded exactly like a stale flight on any other initiator.
/// </para>
///
/// <para>
/// Both races are driven deterministically with <see cref="TaskCompletionSource{T}"/>
/// -backed repository stubs — never sleep-then-assert timing. Both tests reference
/// methods/fields the fix introduces (<c>_requestGeneration</c>,
/// <c>DispatchFilterReloadAsync</c>), so they fail — by compile error or reflection
/// NRE — against the unfixed source, in addition to failing behaviourally once a
/// same-shaped unfixed build is exercised; verified via a saved pre-fix copy of
/// <c>Deployments.razor</c>, not <c>git stash</c> (repo-wide, unsafe to use in this
/// worktree wave).
/// </para>
/// </summary>
public class DeploymentsRequestGenerationTests : BunitContext
{
    private IDeploymentManagerRepository _deployRepo = null!;
    private DeploymentStatusNotifier _notifier = null!;

    /// <summary>
    /// One controllable response per call to <c>QueryDeploymentListPageAsync</c>, in
    /// call order. A queued <see cref="TaskCompletionSource{T}"/> lets the test choose
    /// exactly when each flight's fetch resolves, regardless of when it started.
    /// </summary>
    private readonly List<TaskCompletionSource<DeploymentListPage>> _pageResponses = new();
    private int _pageCallIndex;

    private void RegisterServices()
    {
        _deployRepo = Substitute.For<IDeploymentManagerRepository>();
        _notifier = new DeploymentStatusNotifier(NullLogger<DeploymentStatusNotifier>.Instance);

        _deployRepo.QueryDeploymentListPageAsync(
                Arg.Any<DeploymentListFilter>(), Arg.Any<int>(), Arg.Any<int>(), Arg.Any<CancellationToken>())
            .Returns(_ =>
            {
                var index = Interlocked.Increment(ref _pageCallIndex) - 1;
                return index < _pageResponses.Count
                    ? _pageResponses[index].Task
                    : Task.FromResult(DeploymentListPage.Empty);
            });

        _deployRepo.GetDeploymentStatusCountsAsync(
                Arg.Any<DeploymentListFilter>(), Arg.Any<CancellationToken>())
            .Returns(DeploymentStatusCounts.Empty);

        Services.AddSingleton(_deployRepo);
        Services.AddSingleton<IDeploymentStatusNotifier>(_notifier);

        var identity = new ClaimsIdentity(
            new[] { new Claim(ClaimTypes.Name, "deployer") }, "TestCookie");
        var stubAuth = new StubAuthStateProvider(
            new AuthenticationState(new ClaimsPrincipal(identity)));
        Services.AddSingleton<AuthenticationStateProvider>(stubAuth);
        Services.AddScoped(_ => new SiteScopeService(stubAuth));
    }

    private sealed class StubAuthStateProvider : AuthenticationStateProvider
    {
        private readonly AuthenticationState _state;
        public StubAuthStateProvider(AuthenticationState state) => _state = state;
        public override Task<AuthenticationState> GetAuthenticationStateAsync()
            => Task.FromResult(_state);
    }

    private static TaskCompletionSource<DeploymentListPage> Gate() =>
        new(TaskCreationOptions.RunContinuationsAsynchronously);

    private static TaskCompletionSource<DeploymentListPage> CompletedGate(DeploymentListPage page)
    {
        var tcs = Gate();
        tcs.SetResult(page);
        return tcs;
    }

    private static DeploymentListRow Row(int id, string instance) =>
        new(
            Id: id,
            DeploymentId: $"dep-{id:D4}",
            InstanceId: id,
            InstanceUniqueName: instance,
            SiteId: 1,
            Status: DeploymentStatus.Success,
            RevisionHash: $"rev{id:D4}hash",
            DeployedBy: "deployer",
            DeployedAt: DateTimeOffset.UtcNow.AddMinutes(-id),
            CompletedAt: DateTimeOffset.UtcNow,
            ErrorMessage: null);

    /// <summary>
    /// Invokes a private async method on the component via the renderer's dispatcher
    /// (mirroring the pattern in <c>DebugViewConnectDisposeRaceTests</c>) and hands
    /// back the resulting <see cref="Task"/> without awaiting it, so the caller can
    /// act while the flight is still in progress.
    /// </summary>
    private static async Task<Task> InvokePrivateAsync(
        IRenderedComponent<DeploymentsPage> cut, string methodName, params object?[] args)
    {
        var method = typeof(DeploymentsPage).GetMethod(methodName, BindingFlags.Instance | BindingFlags.NonPublic)!;
        Task? task = null;
        await cut.InvokeAsync(() => { task = (Task)method.Invoke(cut.Instance, args)!; });
        return task!;
    }

    private static IReadOnlyList<DeploymentListRow> GetRows(DeploymentsPage page) =>
        (IReadOnlyList<DeploymentListRow>)typeof(DeploymentsPage)
            .GetField("_rows", BindingFlags.Instance | BindingFlags.NonPublic)!
            .GetValue(page)!;

    private static int GetCurrentPage(DeploymentsPage page) =>
        (int)typeof(DeploymentsPage)
            .GetField("_currentPage", BindingFlags.Instance | BindingFlags.NonPublic)!
            .GetValue(page)!;

    [Fact]
    public async Task StaleFlightArrivingAfterANewerOne_DoesNotOverwriteTheGrid()
    {
        RegisterServices();

        var initialRows = Enumerable.Range(1, 25).Select(i => Row(i, $"Init-{i}")).ToList();
        _pageResponses.Add(CompletedGate(new DeploymentListPage(initialRows, TotalCount: 100))); // call #1: initial render

        var stale = Gate(); // call #2: page-2 flight — held open, the SLOW, STALE flight
        _pageResponses.Add(stale);

        // call #3: status-filter flight — resolves immediately, the FAST, NEWER flight
        _pageResponses.Add(CompletedGate(
            new DeploymentListPage(new[] { Row(999, "TileFilteredFreshRow") }, TotalCount: 1)));

        var cut = Render<DeploymentsPage>();
        cut.WaitForAssertion(() => Assert.Contains(GetRows(cut.Instance), r => r.InstanceUniqueName == "Init-1"));

        // Flight A starts FIRST (a page click) and blocks awaiting `stale`.
        var flightA = await InvokePrivateAsync(cut, "GoToPageAsync", 2);
        Assert.False(flightA.IsCompleted);

        // Flight B starts SECOND (a status-tile click) while A is still in flight, and
        // resolves immediately — it is the newer, correct result.
        var flightB = await InvokePrivateAsync(cut, "SetStatusFilterAsync", DeploymentStatus.Failed);
        await flightB.WaitAsync(TimeSpan.FromSeconds(5));

        Assert.Contains(GetRows(cut.Instance), r => r.InstanceUniqueName == "TileFilteredFreshRow");

        // Now let the STALE flight (page 2) resolve, arriving AFTER the newer one has
        // already applied. Awaiting flightA guarantees its continuation — including
        // the apply-time generation check under test — has fully run before we
        // assert, rather than racing bUnit's render pump.
        stale.SetResult(new DeploymentListPage(new[] { Row(2, "PageTwoStaleRow") }, TotalCount: 100));
        await flightA.WaitAsync(TimeSpan.FromSeconds(5));

        // Pre-fix, flight A's late arrival clobbers _rows with the stale page-2 data.
        // Post-fix, its generation is no longer current, so it discards its own
        // results and the newer grid survives untouched.
        Assert.DoesNotContain(GetRows(cut.Instance), r => r.InstanceUniqueName == "PageTwoStaleRow");
        Assert.Contains(GetRows(cut.Instance), r => r.InstanceUniqueName == "TileFilteredFreshRow");
    }

    /// <summary>
    /// The "does the timer refresh reset the page mid-search" half of P6-11. The
    /// filter-debounce ("timer") reload fires first, as if 500ms had elapsed after a
    /// keystroke, and is held open. While it is still in flight the operator
    /// navigates to page 2 by other means (a fresh, faster flight). The debounce
    /// flight — which intends to reset to page 1 — must not resolve later and
    /// clobber a page the operator has since, and more recently, navigated to.
    /// <para>
    /// This is driven through <c>DispatchFilterReloadAsync</c> directly (rather than
    /// the outer <c>OnFilterDebounceElapsed</c> timer callback, which is fire-and-
    /// forget and gives no <see cref="Task"/> handle to await) so completion of the
    /// apply step under test — including the generation check — can be awaited
    /// deterministically instead of racing bUnit's render pump.
    /// </para>
    /// </summary>
    [Fact]
    public async Task StaleFilterDebounceFlight_DoesNotResetThePageAfterANewerNavigation()
    {
        RegisterServices();

        var initialRows = Enumerable.Range(1, 25).Select(i => Row(i, $"Init-{i}")).ToList();
        _pageResponses.Add(CompletedGate(new DeploymentListPage(initialRows, TotalCount: 100))); // call #1: initial render

        var staleSearch = Gate(); // call #2: the debounce-triggered ("timer") flight — held open, STALE
        _pageResponses.Add(staleSearch);

        // call #3: page-2 click — resolves immediately, NEWER.
        _pageResponses.Add(CompletedGate(
            new DeploymentListPage(new[] { Row(2, "PageTwoFreshRow") }, TotalCount: 100)));

        var cut = Render<DeploymentsPage>();
        cut.WaitForAssertion(() => Assert.Contains(GetRows(cut.Instance), r => r.InstanceUniqueName == "Init-1"));

        // The filter-debounce ("timer") reload starts FIRST and blocks on `staleSearch`.
        var staleFlight = await InvokePrivateAsync(cut, "DispatchFilterReloadAsync");
        Assert.False(staleFlight.IsCompleted);

        // While it is still in flight, the operator navigates to page 2 — a fresh
        // action that resolves immediately.
        var nav = await InvokePrivateAsync(cut, "GoToPageAsync", 2);
        await nav.WaitAsync(TimeSpan.FromSeconds(5));

        Assert.Equal(2, GetCurrentPage(cut.Instance));
        Assert.Contains(GetRows(cut.Instance), r => r.InstanceUniqueName == "PageTwoFreshRow");

        // Now let the STALE debounce flight resolve, arriving after the navigation
        // already applied. Awaiting staleFlight guarantees its continuation —
        // including the apply-time generation check under test — has fully run
        // before we assert, rather than racing bUnit's render pump.
        staleSearch.SetResult(
            new DeploymentListPage(new[] { Row(1, "SearchPageOneStaleRow") }, TotalCount: 1));
        await staleFlight.WaitAsync(TimeSpan.FromSeconds(5));

        // Pre-fix, the stale flight unconditionally wrote _currentPage = 1 up front
        // and then overwrote the grid with page-1 data once it resolved — resetting
        // the operator's page mid an already-completed navigation. Post-fix, its
        // generation is no longer current, so both the page and the grid are left
        // untouched.
        Assert.Equal(2, GetCurrentPage(cut.Instance));
        Assert.Contains(GetRows(cut.Instance), r => r.InstanceUniqueName == "PageTwoFreshRow");
        Assert.DoesNotContain(GetRows(cut.Instance), r => r.InstanceUniqueName == "SearchPageOneStaleRow");
    }
}