using Akka.Actor;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Logging.Abstractions;
using Microsoft.Extensions.Options;
using ZB.MOM.WW.ScadaBridge.ClusterInfrastructure;
using ZB.MOM.WW.ScadaBridge.Communication;
using ZB.MOM.WW.ScadaBridge.Host;
using ZB.MOM.WW.ScadaBridge.Host.Actors;

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

/// <summary>
/// Verifies the DI bridge that exposes the Akka <see cref="ActorSystem"/> — owned by
/// <see cref="AkkaHostedService"/>, not registered as a DI singleton — to consumers that
/// resolve <c>ActorSystem</c> from the container (notably the shared ZB.MOM.WW.Health Akka
/// checks). The bridge is registered TRANSIENT so each resolve re-reads the current value:
/// null while the hosted service is warming up (checks treat that as Degraded), the live
/// system afterwards. A SINGLETON would cache the startup-time null forever.
/// </summary>
public sealed class ActorSystemBridgeTests
{
    [Fact]
    public void ActorSystem_ResolvesNull_BeforeHostedServiceStarts()
    {
        var services = new ServiceCollection();

        // Register AkkaHostedService the same way Program.cs does, supplying the minimal
        // constructor dependencies so the container can build it. Its ActorSystem property
        // is null until StartAsync runs — which it never does here.
        services.AddSingleton(Options.Create(new NodeOptions()));
        services.AddSingleton(Options.Create(new ClusterOptions()));
        services.AddSingleton(Options.Create(new CommunicationOptions()));
        services.AddSingleton<ILogger<AkkaHostedService>>(NullLogger<AkkaHostedService>.Instance);
        services.AddSingleton<AkkaHostedService>();

        // The bridge under test: TRANSIENT factory that re-reads the owned ActorSystem.
        services.AddTransient<ActorSystem>(sp =>
            sp.GetRequiredService<AkkaHostedService>().ActorSystem!);

        using var provider = services.BuildServiceProvider();

        // The hosted service has not started, so the bridge must yield null (not throw).
        Assert.Null(provider.GetService<ActorSystem>());
    }
}