using System.Net;
using System.Net.Sockets;
using System.Security.Cryptography.X509Certificates;
using Opc.Ua;
using Opc.Ua.Client;
using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Commons.Browsing;
using ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser;

namespace ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.IntegrationTests;

/// <summary>
///     Gitea #806 — real NAT / port-publish browse. The fixture is an opc-plc container whose hostname is private and
///     whose internal port differs from the published one, so its GetEndpoints advertise an address this machine
///     cannot reach:
///     <code>
///     # shared docker host (#813): compose in Driver.OpcUaClient.IntegrationTests/Docker/nat/
///     ssh dohertj2@10.100.0.35 'cd /opt/otopcua-opcuaclient-nat &amp;&amp; docker compose up -d'
///     OPCUA_NAT_ENDPOINT=opc.tcp://10.100.0.35:50010 dotnet test --filter Fixture=opc-plc-nat
///     # or locally / in CI (scripts/ci/integration-fixtures.sh starts the same shape as otopcua-ci-opcplc-nat):
///     docker run -d --rm --name otopcua-806-nat --hostname otopcua-806-nat-parity -p 32781:50000 \
///         mcr.microsoft.com/iotedge/opc-plc:2.14.10 --pn=50000 --ph=otopcua-806-nat-parity.invalid --autoaccept --ut
///     docker exec otopcua-806-nat bash -c 'cat /app/pki/own/certs/*.der' &gt; /tmp/nat.der   # public cert only
///     OPCUA_NAT_ENDPOINT=opc.tcp://127.0.0.1:32781 OPCUA_NAT_SERVER_CERT=/tmp/nat.der dotnet test --filter Fixture=opc-plc-nat
///     </code>
///     Skipped unless <c>OPCUA_NAT_ENDPOINT</c> is set and accepts TCP. Every test first proves the premise (the
///     advertised URL is NOT the configured host:port, and its host does not resolve here), so a fixture that
///     advertises a reachable address cannot make these pass vacuously. Before the fix the positive cases failed with
///     <c>SocketException: nodename nor servname provided, or not known</c>.
///     <para><b>Secure cases (#813/#816/#818).</b> Every browse here runs on a THROWAWAY browse PKI (the browser's
///     internal PKI-root seam), never the operator's <c>adminui-browse-pki</c>. The refusal case trusts nothing. The
///     positive and host-name cases trust the fixture's PUBLIC certificate — from <c>OPCUA_NAT_SERVER_CERT</c> (a DER or
///     PEM file; what CI exports after copying it out of its throwaway container) or else the committed
///     <c>Docker/nat/opc-plc-nat-server.der</c> (the shared-host stack's certificate, stable since #818 put its PKI on a
///     volume) — and SKIP when the committed certificate is not the one the server presents, so they can never pass
///     against a different server.</para>
/// </summary>
[Trait("Category", "Integration"), Trait("Fixture", "opc-plc-nat")]
public sealed class NatPublishedEndpointBrowseTests : IDisposable
{
    private const string EnvVar = "OPCUA_NAT_ENDPOINT";
    private const string CertEnvVar = "OPCUA_NAT_SERVER_CERT";
    private const string CommittedCertFile = "opc-plc-nat-server.der";

    private readonly string _pkiRoot = Path.Combine(Path.GetTempPath(), "otopcua-nat-pki-" + Guid.NewGuid().ToString("N"));

    private static string? Endpoint => Environment.GetEnvironmentVariable(EnvVar) is { Length: > 0 } e ? e : null;

    /// <inheritdoc />
    public void Dispose()
    {
        try { Directory.Delete(_pkiRoot, recursive: true); } catch { /* best-effort temp cleanup */ }
    }

    /// <summary>A browser on this test's throwaway PKI.</summary>
    private OpcUaClientDriverBrowser Browser() => new(_pkiRoot);

    private static string Json(string endpoint, string policy = "None", string mode = "None", bool? validateHostName = null)
    {
        var certValidation = validateHostName is { } v
            ? $$""","CertificateValidation":{"ValidateServerHostName":{{(v ? "true" : "false")}}}"""
            : "";
        return $$"""
            {
                "EndpointUrl":"{{endpoint}}",
                "SecurityPolicy":"{{policy}}","SecurityMode":"{{mode}}","AuthType":"Anonymous",
                "SessionTimeout":"00:01:00","Timeout":"00:00:10","PerEndpointConnectTimeout":"00:00:10"{{certValidation}}
            }
            """;
    }

    private static string RequireFixture()
    {
        var endpoint = Endpoint;
        if (endpoint is null) Assert.Skip($"{EnvVar} not set — no NAT/port-published opc-plc fixture.");
        var uri = new Uri(endpoint);
        try
        {
            using var tcp = new TcpClient();
            if (!tcp.ConnectAsync(uri.Host, uri.Port).Wait(TimeSpan.FromSeconds(2)) || !tcp.Connected)
                Assert.Skip($"{EnvVar}={endpoint} did not accept TCP within 2s.");
        }
        catch (Exception ex) when (ex is not Xunit.Sdk.SkipException)
        {
            Assert.Skip($"{EnvVar}={endpoint} unreachable: {ex.GetBaseException().Message}");
        }
        return endpoint;
    }

    /// <summary>
    ///     The premise: the server advertises a host:port other than the configured one, and that host is unresolvable.
    ///     Returns the DER certificate the server presents on its secure endpoint.
    /// </summary>
    private static async Task<byte[]> AssertAdvertisesUnreachableAddressAsync(string endpoint, CancellationToken ct)
    {
        var appConfig = new ApplicationConfiguration(DefaultTelemetry.Create(_ => { }))
        {
            ApplicationName = "OtOpcUa #806 premise",
            ApplicationType = ApplicationType.Client,
            SecurityConfiguration = new SecurityConfiguration(),
            TransportQuotas = new TransportQuotas(),
            ClientConfiguration = new ClientConfiguration(),
            DisableHiResClock = true,
        };
        using var discovery = await DiscoveryClient.CreateAsync(appConfig, new Uri(endpoint), DiagnosticsMasks.None, ct);
        var endpoints = (await discovery.GetEndpointsAsync(default, ct)).ToList();
        endpoints.ShouldNotBeEmpty();

        var configured = new Uri(endpoint);
        foreach (var advertised in endpoints.Select(e => new Uri(e.EndpointUrl!)))
        {
            (advertised.Host, advertised.Port).ShouldNotBe((configured.Host, configured.Port),
                "fixture must advertise a different host:port, or this test proves nothing");
            await Should.ThrowAsync<SocketException>(() => Dns.GetHostAddressesAsync(advertised.Host, ct),
                $"advertised host '{advertised.Host}' must be unresolvable from here, or this test proves nothing");
        }

        return endpoints.First(e => e.SecurityPolicyUri == SecurityPolicies.Basic256Sha256).ServerCertificate.ToArray();
    }

    /// <summary>
    ///     Trust the fixture's public certificate in this test's throwaway PKI, or SKIP when no certificate for THIS
    ///     server is available (see the class remarks). An explicit <c>OPCUA_NAT_SERVER_CERT</c> that does not match
    ///     FAILS: it names the certificate the operator meant, so a mismatch is a fixture problem worth seeing.
    /// </summary>
    /// <param name="presentedDer">The certificate the server presents (from its GetEndpoints answer).</param>
    private void TrustFixtureCertificate(byte[] presentedDer)
    {
        using var presented = X509CertificateLoader.LoadCertificate(presentedDer);
        X509Certificate2 trusted;
        if (Environment.GetEnvironmentVariable(CertEnvVar) is { Length: > 0 } path)
        {
            trusted = LoadPublicCertificate(path);
            trusted.Thumbprint.ShouldBe(presented.Thumbprint,
                $"{CertEnvVar}={path} is not the certificate the NAT fixture presents");
        }
        else
        {
            var committed = Path.Combine(AppContext.BaseDirectory, CommittedCertFile);
            if (!File.Exists(committed))
                Assert.Skip($"{CommittedCertFile} is not deployed next to the tests and {CertEnvVar} is unset.");
            trusted = LoadPublicCertificate(committed);
            if (trusted.Thumbprint != presented.Thumbprint)
                Assert.Skip($"the committed {CommittedCertFile} ({trusted.Thumbprint}) is not this fixture's certificate " +
                            $"({presented.Thumbprint}, expires {presented.NotAfter:yyyy-MM-dd}); set {CertEnvVar} or " +
                            "refresh the committed copy (see Docker/nat/docker-compose.yml).");
        }

        using (trusted)
        {
            trusted.HasPrivateKey.ShouldBeFalse("only a PUBLIC certificate is ever trusted from a file");
            var certs = Path.Combine(_pkiRoot, "trusted", "certs");
            Directory.CreateDirectory(certs);
            File.WriteAllBytes(Path.Combine(certs, "opc-plc-nat.der"), trusted.RawData);
        }
    }

    private static X509Certificate2 LoadPublicCertificate(string path)
    {
        var bytes = File.ReadAllBytes(path);
        var text = System.Text.Encoding.ASCII.GetString(bytes);
        return text.Contains("-----BEGIN CERTIFICATE-----", StringComparison.Ordinal)
            ? X509Certificate2.CreateFromPem(text)
            : X509CertificateLoader.LoadCertificate(bytes);
    }

    private static StatusCode? FindStatus(Exception? ex)
    {
        for (; ex is not null; ex = ex.InnerException)
            if (ex is ServiceResultException sre) return sre.StatusCode;
        return null;
    }

    [Fact]
    public async Task Browse_through_a_published_port_succeeds_and_namespaced_ids_round_trip()
    {
        var endpoint = RequireFixture();
        var ct = TestContext.Current.CancellationToken;
        await AssertAdvertisesUnreachableAddressAsync(endpoint, ct);

        await using var session = await Browser().OpenAsync(Json(endpoint), ct);
        var roots = await session.RootAsync(ct);
        roots.Count.ShouldBeGreaterThan(0);

        // opc-plc's own nodes live in a non-zero namespace; the browse encodes them namespace-URI-stable (nsu=).
        var folder = roots.FirstOrDefault(n => n.Kind == BrowseNodeKind.Folder && n.NodeId.StartsWith("nsu="));
        folder.ShouldNotBeNull("expected an opc-plc folder in its own (nsu=) namespace under Objects");
        var children = await session.ExpandAsync(folder.NodeId, ct);
        children.Count.ShouldBeGreaterThan(0);
    }

    /// <summary>
    ///     Review of #816: with the host-name check ON, an unsecured browse still opens although the NAT certificate (sent
    ///     in the GetEndpoints reply even for the None endpoint) names another host — the check never runs on None.
    /// </summary>
    [Fact]
    public async Task Host_name_validation_does_not_apply_to_a_None_browse()
    {
        var endpoint = RequireFixture();
        var ct = TestContext.Current.CancellationToken;
        await AssertAdvertisesUnreachableAddressAsync(endpoint, ct);

        await using var session = await Browser().OpenAsync(Json(endpoint, validateHostName: true), ct);
        (await session.RootAsync(ct)).Count.ShouldBeGreaterThan(0);
    }

    [Fact]
    public async Task Unreachable_configured_endpoint_still_fails_cleanly()
    {
        RequireFixture();
        var ct = TestContext.Current.CancellationToken;
        // A closed loopback port: the rewrite must not invent a reachable address; the open fails promptly.
        var sw = System.Diagnostics.Stopwatch.StartNew();
        await Should.ThrowAsync<Exception>(() => Browser().OpenAsync(Json("opc.tcp://127.0.0.1:1"), ct));
        sw.Elapsed.ShouldBeLessThan(TimeSpan.FromSeconds(30));
    }

    [Fact]
    public async Task Secure_browse_reaches_the_server_and_keeps_strict_certificate_validation()
    {
        var endpoint = RequireFixture();
        var ct = TestContext.Current.CancellationToken;
        await AssertAdvertisesUnreachableAddressAsync(endpoint, ct);

        // Basic256Sha256/SignAndEncrypt through the published port, on a browse PKI that trusts NOTHING (the browse
        // never auto-accepts): the open must be refused on the certificate — which proves the session reached the
        // SERVER (no DNS failure on the advertised host) and that the rewrite did not relax trust.
        var ex = await Should.ThrowAsync<Exception>(async () =>
        {
            await using var session = await Browser().OpenAsync(Json(endpoint, "Basic256Sha256", "SignAndEncrypt"), ct);
        });
        TestContext.Current.TestOutputHelper?.WriteLine($"secure open refused: {ex.GetType().Name}: {ex.Message}");
        ex.ShouldNotBeOfType<SocketException>($"must not fail on DNS for the advertised host: {ex}");
        var status = FindStatus(ex);
        status.ShouldNotBeNull($"expected a certificate refusal, got {ex.GetType().Name}: {ex.Message}");
        status.Value.ShouldBeOneOf(
            StatusCodes.BadCertificateUntrusted, StatusCodes.BadSecurityChecksFailed,
            StatusCodes.BadCertificateChainIncomplete);
    }

    /// <summary>
    ///     #818 — the positive secure case, runnable in CI. #816 — with the host-name check unset (the default) or
    ///     explicitly off, a trusted certificate is accepted although it names <c>*-nat-private.invalid</c> and the
    ///     browse dialled the published address: the NAT opt-out.
    /// </summary>
    [Theory]
    [InlineData(null)]
    [InlineData(false)]
    public async Task Secure_browse_with_the_fixture_certificate_trusted_succeeds_without_a_host_name_check(bool? validate)
    {
        var endpoint = RequireFixture();
        var ct = TestContext.Current.CancellationToken;
        TrustFixtureCertificate(await AssertAdvertisesUnreachableAddressAsync(endpoint, ct));

        await using var session = await Browser().OpenAsync(
            Json(endpoint, "Basic256Sha256", "SignAndEncrypt", validate), ct);
        (await session.RootAsync(ct)).Count.ShouldBeGreaterThan(0);
    }

    /// <summary>
    ///     #816 — with the host-name check on, the SAME trusted certificate is refused, and the host checked is the one
    ///     the operator configured (the published address), not the server-advertised private name the certificate lists.
    /// </summary>
    [Fact]
    public async Task Host_name_validation_checks_the_configured_host_and_refuses_the_NAT_certificate()
    {
        var endpoint = RequireFixture();
        var ct = TestContext.Current.CancellationToken;
        TrustFixtureCertificate(await AssertAdvertisesUnreachableAddressAsync(endpoint, ct));

        var ex = await Should.ThrowAsync<Exception>(async () =>
        {
            await using var session = await Browser().OpenAsync(
                Json(endpoint, "Basic256Sha256", "SignAndEncrypt", validateHostName: true), ct);
        });
        TestContext.Current.TestOutputHelper?.WriteLine($"secure open refused: {ex.GetType().Name}: {ex.Message}");
        FindStatus(ex).ShouldBe(StatusCodes.BadCertificateHostNameInvalid, $"expected a host-name refusal, got {ex}");
        ex.ToString().ShouldContain($"'{new Uri(endpoint).IdnHost}'");
    }
}