Entkube/tests/EntKube.Clusters.Tests/Features/DiscoverPrometheusHandlerTests.cs

using EntKube.Clusters.Domain;
using EntKube.Clusters.Features.DiscoverPrometheus;
using EntKube.Clusters.Infrastructure;
using EntKube.SharedKernel.Domain;
using FluentAssertions;

namespace EntKube.Clusters.Tests.Features;

public class DiscoverPrometheusHandlerTests
{
    private readonly InMemoryClusterRepository repository;

    public DiscoverPrometheusHandlerTests()
    {
        repository = new InMemoryClusterRepository();
    }

    [Fact]
    public async Task HandleAsync_WithDiscoveredEndpoints_StoresThemOnCluster()
    {
        // Arrange — A registered cluster and a scanner that finds two Prometheus instances.

        KubernetesCluster cluster = KubernetesCluster.Register(
            "production",
            "https://k8s.example.com:6443",
            "kubeconfig-data",
            Guid.NewGuid(),
            "prod-ctx", Guid.NewGuid());

        await repository.AddAsync(cluster);

        List<PrometheusEndpoint> fakeEndpoints = new()
        {
            new PrometheusEndpoint("http://prometheus.monitoring:9090", "monitoring", "prometheus-server"),
            new PrometheusEndpoint("http://prometheus.observability:9090", "observability", "prom-stack")
        };

        FakePrometheusScanner scanner = new(fakeEndpoints);
        DiscoverPrometheusHandler handler = new(repository, scanner);

        // Act — Run discovery on the cluster.

        Result<List<PrometheusEndpoint>> result = await handler.HandleAsync(cluster.Id);

        // Assert — Both endpoints should be stored and returned.

        result.IsSuccess.Should().BeTrue();
        result.Value.Should().HaveCount(2);
        result.Value![0].Namespace.Should().Be("monitoring");
        result.Value[1].Namespace.Should().Be("observability");

        KubernetesCluster? updated = await repository.GetByIdAsync(cluster.Id);
        updated!.PrometheusEndpoints.Should().HaveCount(2);
    }

    [Fact]
    public async Task HandleAsync_WithNoPrometheus_ReturnsEmptyList()
    {
        // Arrange — A cluster with no Prometheus running.

        KubernetesCluster cluster = KubernetesCluster.Register(
            "staging",
            "https://staging.example.com:6443",
            "kubeconfig-data",
            Guid.NewGuid(),
            "staging-ctx", Guid.NewGuid());

        await repository.AddAsync(cluster);

        FakePrometheusScanner scanner = new(new List<PrometheusEndpoint>());
        DiscoverPrometheusHandler handler = new(repository, scanner);

        // Act

        Result<List<PrometheusEndpoint>> result = await handler.HandleAsync(cluster.Id);

        // Assert — Success but empty list. No Prometheus found is not an error.

        result.IsSuccess.Should().BeTrue();
        result.Value.Should().BeEmpty();
    }

    [Fact]
    public async Task HandleAsync_WithNonExistentCluster_ReturnsFailure()
    {
        // Arrange

        FakePrometheusScanner scanner = new(new List<PrometheusEndpoint>());
        DiscoverPrometheusHandler handler = new(repository, scanner);

        // Act

        Result<List<PrometheusEndpoint>> result = await handler.HandleAsync(Guid.NewGuid());

        // Assert

        result.IsFailure.Should().BeTrue();
        result.Error.Should().Contain("not found");
    }

    [Fact]
    public async Task HandleAsync_ReplacesExistingEndpoints_OnRediscovery()
    {
        // Arrange — A cluster that already had endpoints from a previous scan.

        KubernetesCluster cluster = KubernetesCluster.Register(
            "production",
            "https://k8s.example.com:6443",
            "kubeconfig-data",
            Guid.NewGuid(),
            "prod-ctx", Guid.NewGuid());

        cluster.SetPrometheusEndpoints(new List<PrometheusEndpoint>
        {
            new("http://old-prometheus:9090", "legacy", "old-prom")
        });

        await repository.AddAsync(cluster);

        // A new scan finds a different Prometheus.

        List<PrometheusEndpoint> newEndpoints = new()
        {
            new PrometheusEndpoint("http://prometheus.monitoring:9090", "monitoring", "prometheus-server")
        };

        FakePrometheusScanner scanner = new(newEndpoints);
        DiscoverPrometheusHandler handler = new(repository, scanner);

        // Act

        Result<List<PrometheusEndpoint>> result = await handler.HandleAsync(cluster.Id);

        // Assert — The old endpoint is replaced by the new one.

        result.IsSuccess.Should().BeTrue();
        result.Value.Should().HaveCount(1);
        result.Value![0].ServiceName.Should().Be("prometheus-server");

        KubernetesCluster? updated = await repository.GetByIdAsync(cluster.Id);
        updated!.PrometheusEndpoints.Should().HaveCount(1);
    }
}

/// <summary>
/// Test double that returns pre-configured Prometheus endpoints
/// without actually connecting to a Kubernetes cluster.
/// </summary>
public class FakePrometheusScanner : IPrometheusScanner
{
    private readonly List<PrometheusEndpoint> endpoints;

    public FakePrometheusScanner(List<PrometheusEndpoint> endpoints)
    {
        this.endpoints = endpoints;
    }

    public Task<List<PrometheusEndpoint>> ScanAsync(KubernetesCluster cluster, CancellationToken ct = default)
    {
        return Task.FromResult(endpoints);
    }
}