lmxopcua/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Tests/MqttBrowserLayeringTests.cs

using System.Reflection;
using Shouldly;
using Xunit;

namespace ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Tests;

/// <summary>
///     Pins the MQTT project layering that Gitea #512 restored: <c>.Browser</c> depends on the shared
///     <c>.Contracts</c> + <c>.Transport</c> leaves, never on the runtime <c>.Driver</c>.
/// </summary>
/// <remarks>
///     <para>
///     <b>Why this is worth a test.</b> <c>.Browser</c> used to reference the runtime driver, and the
///     AdminUI references <c>.Browser</c> — so the AdminUI's build/deploy graph transitively contained
///     the whole MQTT driver runtime plus Core, Polly.Core and Serilog. Nothing failed; the cost was
///     invisible. A reference re-added out of convenience would be invisible in exactly the same way,
///     which is precisely what a guard is for.
///     </para>
///     <para>
///     <b>What it can and cannot catch.</b> It asserts on emitted assembly references, so it fires when
///     the browser actually <em>uses</em> a driver-runtime type — the case that matters. A
///     <c>ProjectReference</c> re-added but never used would not trip it (the compiler emits no
///     reference), so the csproj comment remains the primary record of the decision.
///     </para>
/// </remarks>
[Trait("Category", "Unit")]
public sealed class MqttBrowserLayeringTests
{
    private const string BrowserAssembly = "ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Browser";
    private const string DriverRuntimeAssembly = "ZB.MOM.WW.OtOpcUa.Driver.Mqtt";
    private const string ContractsAssembly = "ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Contracts";
    private const string TransportAssembly = "ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Transport";

    private static string[] BrowserReferences()
    {
        var browser = Assembly.Load(BrowserAssembly);
        return [.. browser.GetReferencedAssemblies().Select(a => a.Name!)];
    }

    [Fact]
    public void Browser_does_not_reference_the_runtime_driver()
        => BrowserReferences().ShouldNotContain(
            DriverRuntimeAssembly,
            "the MQTT browser is back to referencing the runtime driver — every other bespoke browser " +
            "in this repo (OpcUaClient, Galaxy) depends on its .Contracts leaf only, and this reference " +
            "reaches the AdminUI. If shared connection policy is needed, put it in .Transport; if shared " +
            "protocol/codec is needed, put it in .Contracts. Do NOT copy the TLS/CA-pin logic.");

    [Fact]
    public void Browser_reaches_the_shared_leaves_instead()
    {
        // The positive control. Asserting only the absence above would also pass if the browser stopped
        // referencing anything MQTT at all — e.g. if this test loaded the wrong assembly, or the type
        // names drifted — so pin what it SHOULD depend on in the same breath.
        var references = BrowserReferences();

        references.ShouldContain(ContractsAssembly);
        references.ShouldContain(TransportAssembly);
    }

    [Fact]
    public void Transport_stays_a_leaf_that_does_not_reach_back_into_the_runtime_driver()
    {
        // .Transport holds connection POLICY only. If it ever referenced the runtime driver, routing the
        // browser through it would restore the coupling this whole change removed, one hop further out.
        var references = Assembly.Load(TransportAssembly)
            .GetReferencedAssemblies()
            .Select(a => a.Name!)
            .ToArray();

        references.ShouldNotContain(DriverRuntimeAssembly);
        references.ShouldNotContain(BrowserAssembly);
    }

    [Fact]
    public void Contracts_stays_transport_free()
        => Assembly.Load(ContractsAssembly)
            .GetReferencedAssemblies()
            .Select(a => a.Name!)
            .ShouldNotContain(
                "MQTTnet",
                "Driver.Mqtt.Contracts is deliberately transport-free — it carries the Sparkplug wire " +
                "schema and codec, and is referenced by ControlPlane, which has no business with a " +
                "broker client. MQTTnet-typed connection policy belongs in .Transport.");
}