using Grpc.Core;
using Microsoft.Extensions.Logging.Abstractions;
using Microsoft.Extensions.Options;
using ZB.MOM.WW.ScadaBridge.Communication;
using ZB.MOM.WW.ScadaBridge.Communication.Grpc;

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

/// <summary>
/// The site↔central gRPC control plane's inbound gate (ClusterClient→gRPC migration, T0.3).
/// </summary>
/// <remarks>
/// <para>
/// <c>SiteStreamService</c> shipped unauthenticated: plaintext h2c with no interceptor, so
/// anything that could reach a site node's gRPC port could open a live data stream or pull audit
/// rows back with <c>PullAuditEvents</c>/<c>PullSiteCalls</c>. These tests pin the gate that
/// closes it, and — just as importantly — pin that it does NOT gate LocalDb sync, which has its
/// own interceptor and its own key.
/// </para>
/// <para>
/// Sibling of <see cref="LocalDbSyncAuthInterceptorTests"/>; the two interceptors share a shape
/// deliberately, so the cases mirror each other.
/// </para>
/// </remarks>
public class ControlPlaneAuthInterceptorTests
{
    // Real method paths: package `sitestream`, service `SiteStreamService` (sitestream.proto).
    private const string SubscribeMethod = "/sitestream.SiteStreamService/SubscribeInstance";
    private const string PullAuditMethod = "/sitestream.SiteStreamService/PullAuditEvents";
    private const string LocalDbSyncMethod = "/localdb_sync.v1.LocalDbSync/Sync";

    private static ControlPlaneAuthInterceptor CreateInterceptor(string? psk)
        => new(
            Options.Create(new CommunicationOptions { GrpcPsk = psk ?? "" }),
            NullLogger<ControlPlaneAuthInterceptor>.Instance);

    private static ServerCallContext CreateContext(string method, string? authorizationHeader)
    {
        var headers = new Metadata();
        if (authorizationHeader is not null)
            headers.Add("authorization", authorizationHeader);

        return new FakeServerCallContext(method, headers);
    }

    /// <summary>
    /// Minimal <see cref="ServerCallContext"/> carrying just a method name and request headers —
    /// the only two things the interceptor reads. Hand-rolled for the same reason the LocalDb
    /// sibling hand-rolls one: <c>Grpc.Core.Testing.TestServerCallContext</c> lives in the
    /// retired native package and does not exist on the grpc-dotnet stack.
    /// </summary>
    private sealed class FakeServerCallContext(string method, Metadata requestHeaders)
        : ServerCallContext
    {
        protected override string MethodCore => method;
        protected override string HostCore => "localhost";
        protected override string PeerCore => "ipv4:127.0.0.1:12345";
        protected override DateTime DeadlineCore => DateTime.UtcNow.AddMinutes(1);
        protected override Metadata RequestHeadersCore => requestHeaders;
        protected override CancellationToken CancellationTokenCore => CancellationToken.None;
        protected override Metadata ResponseTrailersCore { get; } = [];
        protected override Status StatusCore { get; set; }
        protected override WriteOptions? WriteOptionsCore { get; set; }
        protected override AuthContext AuthContextCore { get; } =
            new(null, new Dictionary<string, List<AuthProperty>>());

        protected override ContextPropagationToken CreatePropagationTokenCore(
            ContextPropagationOptions? options)
            => throw new NotSupportedException();

        protected override Task WriteResponseHeadersAsyncCore(Metadata responseHeaders)
            => Task.CompletedTask;
    }

    /// <summary>Invokes the interceptor's unary path with a trivial continuation.</summary>
    private static Task<string> Invoke(
        ControlPlaneAuthInterceptor interceptor, ServerCallContext context)
        => interceptor.UnaryServerHandler<string, string>(
            "request", context, (_, _) => Task.FromResult("ok"));

    [Fact]
    public async Task LocalDbSyncMethod_PassesThrough_BecauseItHasItsOwnGateAndItsOwnKey()
    {
        // Both interceptors sit on the same site AddGrpc pipeline and see every call. If this
        // one also gated sync, a site would need its central-facing key to equal its pair-replication
        // key — collapsing two distinct trust relationships into one secret.
        var interceptor = CreateInterceptor("the-site-key");
        var context = CreateContext(LocalDbSyncMethod, authorizationHeader: null);

        Assert.Equal("ok", await Invoke(interceptor, context));
    }

    [Fact]
    public async Task GatedMethod_WithNoKeyConfigured_IsDenied_EvenWithABearerToken()
    {
        // Fail-closed, and this is the case that differs in consequence from LocalDb's: an
        // unset key here does not disable an optional feature, it closes the site's entire
        // central-facing surface. Loud refusal beats silent unauthenticated service.
        var interceptor = CreateInterceptor(psk: null);
        var context = CreateContext(SubscribeMethod, "Bearer anything-at-all");

        var ex = await Assert.ThrowsAsync<RpcException>(() => Invoke(interceptor, context));
        Assert.Equal(StatusCode.PermissionDenied, ex.StatusCode);
    }

    [Fact]
    public async Task GatedMethod_WithNoBearerToken_IsDenied()
    {
        var interceptor = CreateInterceptor("the-site-key");
        var context = CreateContext(SubscribeMethod, authorizationHeader: null);

        var ex = await Assert.ThrowsAsync<RpcException>(() => Invoke(interceptor, context));
        Assert.Equal(StatusCode.PermissionDenied, ex.StatusCode);
    }

    [Fact]
    public async Task GatedMethod_WithWrongBearerToken_IsDenied()
    {
        var interceptor = CreateInterceptor("the-site-key");
        var context = CreateContext(SubscribeMethod, "Bearer some-other-sites-key");

        var ex = await Assert.ThrowsAsync<RpcException>(() => Invoke(interceptor, context));
        Assert.Equal(StatusCode.PermissionDenied, ex.StatusCode);
    }

    [Fact]
    public async Task GatedMethod_WithCorrectBearerToken_PassesThrough()
    {
        var interceptor = CreateInterceptor("the-site-key");
        var context = CreateContext(SubscribeMethod, "Bearer the-site-key");

        Assert.Equal("ok", await Invoke(interceptor, context));
    }

    [Fact]
    public async Task GatedMethod_WithCorrectKey_ButNoBearerScheme_IsDenied()
    {
        // A raw key with no "Bearer " prefix is not what ControlPlaneCredentials sends;
        // accepting it would widen the accepted credential shape for nothing.
        var interceptor = CreateInterceptor("the-site-key");
        var context = CreateContext(SubscribeMethod, "the-site-key");

        var ex = await Assert.ThrowsAsync<RpcException>(() => Invoke(interceptor, context));
        Assert.Equal(StatusCode.PermissionDenied, ex.StatusCode);
    }

    [Fact]
    public async Task GatedMethod_TokenComparison_IsNotAPrefixMatch()
    {
        // A StartsWith comparison would accept a truncated key and make the secret recoverable
        // one character at a time. FixedTimeEquals also rejects on length.
        var interceptor = CreateInterceptor("the-site-key");
        var context = CreateContext(SubscribeMethod, "Bearer the-site-ke");

        var ex = await Assert.ThrowsAsync<RpcException>(() => Invoke(interceptor, context));
        Assert.Equal(StatusCode.PermissionDenied, ex.StatusCode);
    }

    [Fact]
    public async Task ServerStreaming_IsGated_BecauseThatIsHowSubscriptionsActuallyRun()
    {
        // SubscribeInstance/SubscribeSite are server-streaming. Gating only the unary path
        // would leave the live data feed wide open while every unary test still passed.
        var interceptor = CreateInterceptor("the-site-key");
        var context = CreateContext(SubscribeMethod, "Bearer the-wrong-key");

        var ex = await Assert.ThrowsAsync<RpcException>(() =>
            interceptor.ServerStreamingServerHandler<string, string>(
                "request",
                responseStream: null!,
                context,
                (_, _, _) => Task.CompletedTask));

        Assert.Equal(StatusCode.PermissionDenied, ex.StatusCode);
    }

    [Fact]
    public async Task PullRpcs_AreGated_BecauseTheyReturnAuditRows()
    {
        // The strongest reason this gate exists: PullAuditEvents/PullSiteCalls hand back audit
        // content to anyone who asks. Unary, so it would be easy to miss in a streaming-focused
        // reading of the service.
        var interceptor = CreateInterceptor("the-site-key");
        var context = CreateContext(PullAuditMethod, authorizationHeader: null);

        var ex = await Assert.ThrowsAsync<RpcException>(() => Invoke(interceptor, context));
        Assert.Equal(StatusCode.PermissionDenied, ex.StatusCode);
    }

    [Fact]
    public async Task GatedPrefixes_AreConstructorProvided_SoLaterPhasesAddServicesNotInterceptors()
    {
        // Phases 1A/1B add CentralControlService and SiteCommandService to this same gate.
        var interceptor = new ControlPlaneAuthInterceptor(
            Options.Create(new CommunicationOptions { GrpcPsk = "k" }),
            NullLogger<ControlPlaneAuthInterceptor>.Instance,
            new[] { "/scadabridge.sitecommand.v1.SiteCommandService/" });

        var gated = CreateContext("/scadabridge.sitecommand.v1.SiteCommandService/ExecuteQuery", null);
        var ex = await Assert.ThrowsAsync<RpcException>(() => Invoke(interceptor, gated));
        Assert.Equal(StatusCode.PermissionDenied, ex.StatusCode);

        // ...and the default set is no longer implied once an explicit set is supplied.
        var notGated = CreateContext(SubscribeMethod, authorizationHeader: null);
        Assert.Equal("ok", await Invoke(interceptor, notGated));
    }

    [Fact]
    public void TheInterceptorHasExactlyOnePublicConstructor()
    {
        // Grpc.AspNetCore registers this interceptor BY TYPE, and
        // InterceptorRegistration.GetFactory() throws "Multiple constructors accepting all given
        // argument types have been found" the moment a second public constructor is applicable.
        // The throw lands inside the pipeline on every call, so the symptom is not a startup
        // failure but a gate that authorizes nothing and fails everything with
        // Unknown / "Exception was thrown by handler" — a shape that looks like a handler bug,
        // not an auth bug. This shipped once and was caught only on the docker rig; the
        // prefix-set constructor is internal now to keep it from recurring.
        var publicCtors = typeof(ControlPlaneAuthInterceptor).GetConstructors();

        Assert.Single(publicCtors);
    }

    [Fact]
    public void DefaultGatedPrefixes_MatchTheRealSiteStreamServicePath()
    {
        // A typo here disables the whole gate silently: every call would simply pass through.
        // Pin it against a path taken from the generated service, not from the proto text.
        var method = SiteStreamService.Descriptor.FullName;
        Assert.Contains(
            ControlPlaneAuthInterceptor.DefaultGatedPrefixes,
            p => p == $"/{method}/");
    }
}
