ScadaBridge/tests/ZB.MOM.WW.ScadaBridge.CentralUI.Tests/Deployment/DebugViewRenderCoalescingTests.cs

using System.Collections;
using System.Reflection;
using System.Security.Claims;
using Bunit;
using Microsoft.AspNetCore.Components.Authorization;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging.Abstractions;
using Microsoft.Extensions.Options;
using NSubstitute;
using ZB.MOM.WW.ScadaBridge.CentralUI.Auth;
using ZB.MOM.WW.ScadaBridge.Commons.Entities.Sites;
using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Repositories;
using ZB.MOM.WW.ScadaBridge.Commons.Messages.Streaming;
using ZB.MOM.WW.ScadaBridge.Communication;
using ZB.MOM.WW.ScadaBridge.Communication.Grpc;
using DebugViewPage = ZB.MOM.WW.ScadaBridge.CentralUI.Components.Pages.Deployment.DebugView;

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

/// <summary>
/// Regression tests for the Debug View render coalescing (arch-review WP2.4). Every streamed
/// event used to marshal onto the circuit dispatcher and call <c>StateHasChanged</c> on its
/// own, so a chatty instance drove one full render — and two full composition-tree rebuilds —
/// per value change. Events are now buffered and applied once per ~250 ms window: a burst
/// costs a handful of renders instead of one per event, and no event is dropped.
/// </summary>
public class DebugViewRenderCoalescingTests : BunitContext
{
    private IRenderedComponent<DebugViewPage> RenderPage()
    {
        JSInterop.Mode = JSRuntimeMode.Loose;

        var repo = Substitute.For<ITemplateEngineRepository>();
        var siteRepo = Substitute.For<ISiteRepository>();
        siteRepo.GetAllSitesAsync().Returns(new List<Site>());
        Services.AddSingleton(repo);
        Services.AddSingleton(siteRepo);

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

        var grpcFactory = new SiteStreamGrpcClientFactory(NullLoggerFactory.Instance);
        var debugStream = new DebugStreamService(
            comms, new ServiceCollection().BuildServiceProvider(), grpcFactory,
            NullLogger<DebugStreamService>.Instance);
        Services.AddSingleton(debugStream);

        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));

        return Render<DebugViewPage>();
    }

    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 MethodInfo HandleStreamEvent => typeof(DebugViewPage).GetMethod(
        "HandleStreamEvent", BindingFlags.Instance | BindingFlags.NonPublic)!;

    private static IDictionary AttributeValues(DebugViewPage c) => (IDictionary)
        typeof(DebugViewPage).GetField("_attributeValues",
            BindingFlags.Instance | BindingFlags.NonPublic)!.GetValue(c)!;

    private static void Send(DebugViewPage page, string name, object value) =>
        HandleStreamEvent.Invoke(page, new object[]
        {
            new AttributeValueChanged("Inst-1", name, name, value, "Good", DateTimeOffset.UtcNow),
        });

    [Fact]
    public void BurstOfEvents_RendersOnce_ButAppliesEveryEvent()
    {
        var cut = RenderPage();
        var dict = AttributeValues(cut.Instance);
        var rendersBefore = cut.RenderCount;

        const int burst = 300;
        for (var i = 0; i < burst; i++)
        {
            Send(cut.Instance, $"Tag.{i}", i);
        }

        cut.WaitForState(() => dict.Count == burst, TimeSpan.FromSeconds(5));

        // Pre-fix this was one render per event. The window may close mid-burst, so allow a
        // few flushes — the point is that it is a small constant, not O(events).
        var renders = cut.RenderCount - rendersBefore;
        Assert.InRange(renders, 1, 5);
    }

    [Fact]
    public void RepeatedUpdatesToOneTag_CollapseToTheLatestValue()
    {
        var cut = RenderPage();
        var dict = AttributeValues(cut.Instance);

        for (var i = 0; i < 50; i++)
        {
            Send(cut.Instance, "Pump.Speed", i);
        }

        cut.WaitForState(() => dict.Count == 1, TimeSpan.FromSeconds(5));
        var applied = (AttributeValueChanged)dict["Pump.Speed"]!;
        Assert.Equal(49, applied.Value);
    }

    [Fact]
    public void EventArrivingAfterAFlush_StillArmsANewWindow()
    {
        var cut = RenderPage();
        var dict = AttributeValues(cut.Instance);

        Send(cut.Instance, "First", 1);
        cut.WaitForState(() => dict.Count == 1, TimeSpan.FromSeconds(5));

        // The window disarms on drain; a later event must arm a fresh one rather than
        // sitting in the pending map until some unrelated event happens to arrive.
        Send(cut.Instance, "Second", 2);
        cut.WaitForState(() => dict.Count == 2, TimeSpan.FromSeconds(5));
    }

    [Fact]
    public void EventsAfterDispose_AreDroppedWithoutThrowing()
    {
        var cut = RenderPage();
        cut.Instance.Dispose();

        var ex = Record.Exception(() => Send(cut.Instance, "Late", 1));

        Assert.Null(ex);
        Assert.Empty(AttributeValues(cut.Instance));
    }
}