using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Logging.Abstractions;

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

/// <summary>
/// M2.16 (#30) idempotency regression — code-review finding on commit d81f747.
/// <para>
/// <see cref="ServiceCollectionExtensions.AddSiteEventLogHealthMetricsBridge"/> uses a
/// factory-lambda overload of <c>AddHostedService</c>, which sets only
/// <c>ImplementationFactory</c> and leaves <c>ImplementationType</c> null.  The original
/// <c>ImplementationType ==</c> guard was therefore a silent no-op: a second call would spin
/// up a second <see cref="SiteEventLogFailureCountReporter"/> (two timers both polling).
/// The fix uses a private marker singleton whose <c>ServiceType</c> is always set.
/// </para>
/// </summary>
public class AddSiteEventLogHealthMetricsBridgeTests
{
    [Fact]
    public void AddSiteEventLogHealthMetricsBridge_IsIdempotent_DoesNotDoubleRegister_HostedService()
    {
        // M2.16 (#30): calling the bridge method twice must register exactly one
        // SiteEventLogFailureCountReporter. Without the marker-type guard the
        // ImplementationType == check was a no-op for factory-lambda registrations,
        // so the second call would have added a second hosted service (two timers).
        var services = new ServiceCollection();
        services.AddSingleton<ILoggerFactory, NullLoggerFactory>();
        services.AddSingleton(typeof(ILogger<>), typeof(NullLogger<>));
        services.AddHealthMonitoring();

        Func<IServiceProvider, Func<long>> factory = _ => () => 0L;

        services.AddSiteEventLogHealthMetricsBridge(factory);
        services.AddSiteEventLogHealthMetricsBridge(factory);

        // Count IHostedService descriptors whose factory produces a
        // SiteEventLogFailureCountReporter. Because it is factory-registered,
        // ImplementationType is null — we count by resolving and checking type.
        using var provider = services.BuildServiceProvider();
        var reporters = provider.GetServices<IHostedService>()
            .OfType<SiteEventLogFailureCountReporter>()
            .ToList();

        Assert.Single(reporters);
    }
}
