using Microsoft.Extensions.Logging.Abstractions;
using Opc.Ua;
using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Commons.OpcUa;
using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
using ZB.MOM.WW.OtOpcUa.Configuration.Enums;
using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
using ZB.MOM.WW.OtOpcUa.Core.Authorization;
using ZB.MOM.WW.OtOpcUa.OpcUaServer.Security;

namespace ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests;

/// <summary>
///     #520 stage 5 — the node-scoped ACL gate. Every test drives the REAL
///     <see cref="DataPlaneAuthorityState"/> → <see cref="PermissionTrieBuilder"/> →
///     <see cref="TriePermissionEvaluator"/> chain rather than a fake evaluator, because the defect class
///     this stage exists to close is precisely "the pieces are individually correct and nothing connects
///     them". A test that stubs the evaluator would pass against a gate wired to an empty trie.
/// </summary>
public sealed class DataPlaneAuthorizerTests
{
    private const string Cluster = "SITE-A";
    private const string Principal = "scadabridge";
    private const string KeyId = "a1b2c3d4e5f60011";

    // ───────────────────────────── the fail-closed edges ─────────────────────────────

    /// <summary>
    ///     A session with no role-carrying identity is denied. There is no "unauthenticated means
    ///     unrestricted" path: an anonymous session that the host admitted still arrives here as a
    ///     principal, so a null identity means something went wrong upstream.
    /// </summary>
    [Fact]
    public void A_session_with_no_identity_is_denied()
    {
        var gate = Gate(ClusterGrant(NodePermissions.WriteOperate));

        Veto(gate.Authorize(null, OpcUaOperation.WriteOperate, RawNode("Plant/Modbus/dev1/Speed"), AddressSpaceRealm.Raw));
    }

    /// <summary>
    ///     An identity carrying no principal is denied even when a grant would otherwise match. This is the
    ///     legacy two-argument <see cref="RoleCarryingUserIdentity"/> constructor, and the safe reading of it
    ///     is "unknown", not "infer one from the display name" — the display name for every key-bearing
    ///     client is the same static username.
    /// </summary>
    [Fact]
    public void An_identity_with_no_principal_is_denied()
    {
        var gate = Gate(ClusterGrant(NodePermissions.WriteOperate));
        var identity = new RoleCarryingUserIdentity(new UserNameIdentityToken { UserName = "apikey" }, []);

        identity.Principal.ShouldBeEmpty();
        Veto(gate.Authorize(identity, OpcUaOperation.WriteOperate, RawNode("Plant/Modbus/dev1/Speed"), AddressSpaceRealm.Raw));
    }

    /// <summary>
    ///     A node that resolved no cluster identity has no trie to evaluate against, so it denies. Inventing
    ///     a placeholder cluster would be the dangerous alternative — it would apply some other cluster's
    ///     grants to a node whose own cluster is unknown.
    /// </summary>
    [Fact]
    public void A_node_with_no_cluster_identity_denies_everything()
    {
        var state = new DataPlaneAuthorityState();
        state.Apply(clusterId: null, "rev", [], [ClusterGrant(NodePermissions.WriteOperate)], Scopes());

        var gate = new DataPlaneAuthorizer(
            state, new TriePermissionEvaluator(state.Tries), enabled: true, NullLogger.Instance);

        Veto(gate.Authorize(Identity(), OpcUaOperation.WriteOperate, RawNode("Plant/Modbus/dev1/Speed"), AddressSpaceRealm.Raw));
    }

    /// <summary>
    ///     A NodeId whose identifier is not a string addresses no ACL scope — every node this server mints
    ///     carries a string path — so it is denied rather than evaluated against an empty segment list,
    ///     which would match a realm-wide grant.
    /// </summary>
    [Fact]
    public void A_node_id_with_no_string_identifier_is_denied()
    {
        var gate = Gate(ClusterGrant(NodePermissions.WriteOperate));

        Veto(gate.Authorize(Identity(), OpcUaOperation.WriteOperate, new NodeId(42u, 2), AddressSpaceRealm.Raw));
    }

    // ───────────────────────────── the grant actually decides ─────────────────────────────

    /// <summary>A cluster-wide WriteOperate grant authorizes a write anywhere in that cluster.</summary>
    [Fact]
    public void A_cluster_grant_authorizes_a_write()
    {
        var gate = Gate(ClusterGrant(NodePermissions.WriteOperate));

        gate.Authorize(Identity(), OpcUaOperation.WriteOperate, RawNode("Plant/Modbus/dev1/Speed"), AddressSpaceRealm.Raw)
            .ShouldBeNull();
    }

    /// <summary>
    ///     The permission bit is honoured, not merely the presence of a grant: a read-only principal is
    ///     refused a write on the very node it may read.
    /// </summary>
    [Fact]
    public void A_read_grant_does_not_authorize_a_write()
    {
        var gate = Gate(ClusterGrant(NodePermissions.Read));

        Veto(gate.Authorize(Identity(), OpcUaOperation.WriteOperate, RawNode("Plant/Modbus/dev1/Speed"), AddressSpaceRealm.Raw));
    }

    /// <summary>
    ///     <b>The heart of the stage.</b> A grant scoped to one device authorizes a tag beneath it and
    ///     refuses a tag under a sibling device. Before this, a narrow grant conferred nothing at all — it
    ///     was inert — so both of these would have been denied, and a test asserting only the denial would
    ///     have passed against the broken build.
    /// </summary>
    [Fact]
    public void A_raw_device_scoped_grant_covers_its_own_tags_and_not_a_siblings()
    {
        var grant = new NodeAcl
        {
            NodeAclId = "acl-dev1",
            ClusterId = Cluster,
            Principal = Principal,
            ScopeKind = NodeAclScopeKind.RawDevice,
            ScopeId = "dev-1",
            PermissionFlags = NodePermissions.WriteOperate,
        };

        var gate = Gate(grant, Scopes(("dev-1", NodeAclScopeKind.RawDevice, ["raw", "Plant", "Modbus", "dev1"])));

        gate.Authorize(Identity(), OpcUaOperation.WriteOperate, RawNode("Plant/Modbus/dev1/Speed"), AddressSpaceRealm.Raw)
            .ShouldBeNull();
        Veto(gate.Authorize(Identity(), OpcUaOperation.WriteOperate, RawNode("Plant/Modbus/dev2/Speed"), AddressSpaceRealm.Raw));
    }

    /// <summary>
    ///     Segment matching is case-SENSITIVE. Raw sibling names are ordinal-unique, so <c>Speed</c> and
    ///     <c>speed</c> can both exist under one device; folding case would let a grant on either silently
    ///     cover both.
    /// </summary>
    [Fact]
    public void Scope_segments_are_matched_case_sensitively()
    {
        var grant = new NodeAcl
        {
            NodeAclId = "acl-tag",
            ClusterId = Cluster,
            Principal = Principal,
            ScopeKind = NodeAclScopeKind.Tag,
            ScopeId = "tag-1",
            PermissionFlags = NodePermissions.WriteOperate,
        };

        var gate = Gate(grant, Scopes(("tag-1", NodeAclScopeKind.Tag, ["raw", "Plant", "Modbus", "dev1", "Speed"])));

        gate.Authorize(Identity(), OpcUaOperation.WriteOperate, RawNode("Plant/Modbus/dev1/Speed"), AddressSpaceRealm.Raw)
            .ShouldBeNull();
        Veto(gate.Authorize(Identity(), OpcUaOperation.WriteOperate, RawNode("Plant/Modbus/dev1/speed"), AddressSpaceRealm.Raw));
    }

    /// <summary>
    ///     The realm is a hard gate at level 1 of the walk: a grant on the raw tree does not reach a UNS
    ///     node that happens to share a path. Blocker #1 is that raw nodes were unrepresentable at all, so
    ///     this pins that both realms now evaluate — and that they stay distinct.
    /// </summary>
    [Fact]
    public void A_raw_grant_does_not_reach_a_uns_node_with_the_same_path()
    {
        var grant = new NodeAcl
        {
            NodeAclId = "acl-raw-realm",
            ClusterId = Cluster,
            Principal = Principal,
            ScopeKind = NodeAclScopeKind.Namespace,
            ScopeId = NodeAclRealms.Raw,
            PermissionFlags = NodePermissions.WriteOperate,
        };

        var gate = Gate(grant, Scopes((NodeAclRealms.Raw, NodeAclScopeKind.Namespace, ["raw"])));

        gate.Authorize(Identity(), OpcUaOperation.WriteOperate, RawNode("Area/Line/Eq/Speed"), AddressSpaceRealm.Raw)
            .ShouldBeNull();
        Veto(gate.Authorize(Identity(), OpcUaOperation.WriteOperate, RawNode("Area/Line/Eq/Speed"), AddressSpaceRealm.Uns));
    }

    /// <summary>
    ///     The Part 9 methods map onto distinct permissions, which the single <c>AlarmAck</c> role they
    ///     replace could not express: a principal granted acknowledge alone cannot shelve.
    /// </summary>
    [Fact]
    public void Alarm_acknowledge_and_shelve_are_separately_grantable()
    {
        var gate = Gate(ClusterGrant(NodePermissions.AlarmAcknowledge));
        var node = RawNode("Plant/Modbus/dev1/Speed");

        gate.Authorize(Identity(), OpcUaOperation.AlarmAcknowledge, node, AddressSpaceRealm.Raw).ShouldBeNull();
        Veto(gate.Authorize(Identity(), OpcUaOperation.AlarmShelve, node, AddressSpaceRealm.Raw));
    }

    /// <summary>
    ///     HistoryRead has its own bit — a Read grant is not sufficient. This is the OPC UA Part 11
    ///     separation, and it is the first time HistoryRead has been gated at all.
    /// </summary>
    [Fact]
    public void History_read_needs_its_own_permission_not_merely_read()
    {
        var node = RawNode("Plant/Modbus/dev1/Speed");

        Veto(Gate(ClusterGrant(NodePermissions.Read))
            .Authorize(Identity(), OpcUaOperation.HistoryRead, node, AddressSpaceRealm.Raw));
        Gate(ClusterGrant(NodePermissions.HistoryRead))
            .Authorize(Identity(), OpcUaOperation.HistoryRead, node, AddressSpaceRealm.Raw)
            .ShouldBeNull();
    }

    // ───────────────────────────── revocation reaches an OPEN session ─────────────────────────────

    /// <summary>
    ///     A deployment that disables a key stops that key's ALREADY-OPEN session, not just future ones.
    ///     Without the per-call re-check a revoked credential keeps its authority until the client happens
    ///     to reconnect, which for a machine-to-machine consumer can be indefinitely — and on a driver-only
    ///     node the artifact is the only revocation channel there is.
    /// </summary>
    [Fact]
    public void Revoking_a_key_denies_its_open_session_on_the_next_deployment()
    {
        var state = new DataPlaneAuthorityState();
        var grant = ClusterGrant(NodePermissions.WriteOperate);
        var node = RawNode("Plant/Modbus/dev1/Speed");
        var gate = new DataPlaneAuthorizer(
            state, new TriePermissionEvaluator(state.Tries), enabled: true, NullLogger.Instance);

        state.Apply(Cluster, "rev-1", [Key(enabled: true)], [grant], Scopes());
        gate.Authorize(Identity(), OpcUaOperation.WriteOperate, node, AddressSpaceRealm.Raw).ShouldBeNull();

        state.Apply(Cluster, "rev-2", [Key(enabled: false)], [grant], Scopes());
        Veto(gate.Authorize(Identity(), OpcUaOperation.WriteOperate, node, AddressSpaceRealm.Raw));
    }

    /// <summary>
    ///     An expired key is refused on the same path, and expiry is read against the injected clock rather
    ///     than wall time so the test pins the comparison rather than waiting for it.
    /// </summary>
    [Fact]
    public void An_expired_key_denies_its_open_session()
    {
        var clock = new FakeTimeProvider(new DateTime(2026, 8, 1, 12, 0, 0, DateTimeKind.Utc));
        var state = new DataPlaneAuthorityState();
        var key = Key(enabled: true);
        key.ExpiresUtc = new DateTime(2026, 8, 1, 13, 0, 0, DateTimeKind.Utc);
        state.Apply(Cluster, "rev-1", [key], [ClusterGrant(NodePermissions.WriteOperate)], Scopes());

        var gate = new DataPlaneAuthorizer(
            state, new TriePermissionEvaluator(state.Tries), enabled: true, NullLogger.Instance, clock);
        var node = RawNode("Plant/Modbus/dev1/Speed");

        gate.Authorize(Identity(), OpcUaOperation.WriteOperate, node, AddressSpaceRealm.Raw).ShouldBeNull();

        clock.Advance(TimeSpan.FromHours(2));
        Veto(gate.Authorize(Identity(), OpcUaOperation.WriteOperate, node, AddressSpaceRealm.Raw));
    }

    /// <summary>
    ///     Anonymous carries no key id, so the revocation probe must not fire for it — otherwise every
    ///     anonymous request would be denied by a lookup for a key that was never presented.
    /// </summary>
    [Fact]
    public void An_anonymous_session_is_not_denied_by_the_key_revocation_check()
    {
        var grant = ClusterGrant(NodePermissions.Read);
        grant.Principal = OpcUaPrincipals.Anonymous;
        var gate = Gate(grant);
        var anonymous = new RoleCarryingUserIdentity(
            new AnonymousIdentityToken(), [], OpcUaPrincipals.Anonymous, apiKeyId: null);

        gate.Authorize(anonymous, OpcUaOperation.Read, RawNode("Plant/Modbus/dev1/Speed"), AddressSpaceRealm.Raw)
            .ShouldBeNull();
    }

    // ───────────────────────────── the generation stamp ─────────────────────────────

    /// <summary>
    ///     A deployment that adds a grant takes effect on an open session immediately — the session is
    ///     stamped with the current generation on every call, so it never pins itself to the generation it
    ///     activated under and then has to be bounced to pick an ACL change up.
    /// </summary>
    [Fact]
    public void A_grant_added_by_a_later_deployment_reaches_an_open_session()
    {
        var state = new DataPlaneAuthorityState();
        var node = RawNode("Plant/Modbus/dev1/Speed");
        var gate = new DataPlaneAuthorizer(
            state, new TriePermissionEvaluator(state.Tries), enabled: true, NullLogger.Instance);

        state.Apply(Cluster, "rev-1", [Key(enabled: true)], [], Scopes());
        Veto(gate.Authorize(Identity(), OpcUaOperation.WriteOperate, node, AddressSpaceRealm.Raw));

        state.Apply(Cluster, "rev-2", [Key(enabled: true)], [ClusterGrant(NodePermissions.WriteOperate)], Scopes());
        gate.Authorize(Identity(), OpcUaOperation.WriteOperate, node, AddressSpaceRealm.Raw).ShouldBeNull();
    }

    /// <summary>
    ///     And the reverse: revoking a GRANT (rather than the key) also lands on the open session. Both
    ///     directions matter — an ACL edit that only widens would be the easy half.
    /// </summary>
    [Fact]
    public void A_grant_removed_by_a_later_deployment_stops_an_open_session()
    {
        var state = new DataPlaneAuthorityState();
        var node = RawNode("Plant/Modbus/dev1/Speed");
        var gate = new DataPlaneAuthorizer(
            state, new TriePermissionEvaluator(state.Tries), enabled: true, NullLogger.Instance);

        state.Apply(Cluster, "rev-1", [Key(enabled: true)], [ClusterGrant(NodePermissions.WriteOperate)], Scopes());
        gate.Authorize(Identity(), OpcUaOperation.WriteOperate, node, AddressSpaceRealm.Raw).ShouldBeNull();

        state.Apply(Cluster, "rev-2", [Key(enabled: true)], [], Scopes());
        Veto(gate.Authorize(Identity(), OpcUaOperation.WriteOperate, node, AddressSpaceRealm.Raw));
    }

    // ───────────────────────────── the cached hot path ─────────────────────────────

    /// <summary>
    ///     A second identical question is answered from the decision cache without re-walking the grants —
    ///     which on the reordered hot path also means without rebuilding the <see cref="NodeScope"/> the
    ///     walk would need, because the lookup happens before the scope is built at all.
    /// </summary>
    /// <remarks>
    ///     The evaluator count is the observable half: a hit that still built a scope would have nothing to
    ///     do with it, so the only way to see the short-circuit from outside is that the walk never ran. The
    ///     cache size pins that the second call was a hit rather than a second miss that happened to
    ///     overwrite the first entry.
    /// </remarks>
    [Fact]
    public void A_cache_hit_does_not_rebuild_the_scope()
    {
        var gate = CountingGate(ClusterGrant(NodePermissions.Read), out var evaluator);
        var node = RawNode("Plant/Modbus/dev1/Speed");

        gate.AuthorizeCached(Identity(), OpcUaOperation.Read, node, AddressSpaceRealm.Raw).ShouldBeNull();
        gate.AuthorizeCached(Identity(), OpcUaOperation.Read, node, AddressSpaceRealm.Raw).ShouldBeNull();

        evaluator.Calls.ShouldBe(1);
        gate.Decisions.Count.ShouldBe(1);
    }

    /// <summary>
    ///     <b>Pins the ordering the hot path must keep:</b> the key's usability is re-checked BEFORE the
    ///     decision cache is consulted, so a cached allow cannot outlive the key that earned it.
    /// </summary>
    /// <remarks>
    ///     Expiry rather than a disabling redeploy is the falsifiable form of this. A redeploy advances the
    ///     generation, which drops the cache wholesale — so a gate that consulted the cache first would
    ///     still deny, and the test would pass against the broken ordering. Expiry moves with the CLOCK and
    ///     leaves the generation (and therefore the memoized allow) exactly where it was, so the denial can
    ///     only have come from the key check running ahead of the lookup.
    /// </remarks>
    [Fact]
    public void Key_revocation_is_rechecked_on_a_cache_hit()
    {
        var clock = new FakeTimeProvider(new DateTime(2026, 8, 1, 12, 0, 0, DateTimeKind.Utc));
        var state = new DataPlaneAuthorityState();
        var key = Key(enabled: true);
        key.ExpiresUtc = new DateTime(2026, 8, 1, 13, 0, 0, DateTimeKind.Utc);
        state.Apply(Cluster, "rev-1", [key], [ClusterGrant(NodePermissions.Read)], Scopes());

        var gate = new DataPlaneAuthorizer(
            state, new TriePermissionEvaluator(state.Tries), enabled: true, NullLogger.Instance, clock);
        var node = RawNode("Plant/Modbus/dev1/Speed");

        gate.AuthorizeCached(Identity(), OpcUaOperation.Read, node, AddressSpaceRealm.Raw).ShouldBeNull();
        gate.Decisions.Count.ShouldBe(1, "the allow was memoized, so the next call takes the hit path");

        clock.Advance(TimeSpan.FromHours(2));

        Veto(gate.AuthorizeCached(Identity(), OpcUaOperation.Read, node, AddressSpaceRealm.Raw));
        gate.Decisions.Generation.ShouldBe(state.Current.GenerationId);
        gate.Decisions.Count.ShouldBe(1, "the memoized allow is untouched — the denial came from the key check");
    }

    /// <summary>The flag is carried faithfully; the seams read it to decide whether to consult the gate at all.</summary>
    [Theory]
    [InlineData(true)]
    [InlineData(false)]
    public void The_enabled_flag_is_reported_as_configured(bool enabled)
    {
        var state = new DataPlaneAuthorityState();
        new DataPlaneAuthorizer(state, new TriePermissionEvaluator(state.Tries), enabled, NullLogger.Instance)
            .Enabled.ShouldBe(enabled);
    }

    // ───────────────────────────── the shared root folder ─────────────────────────────

    /// <summary>
    ///     <b>The load-bearing allow.</b> Both realm trees hang under one anchor folder
    ///     (<c>s=OtOpcUa</c>, raw namespace), and the node manager's Browse gate refuses the WHOLE browse
    ///     when its source node is denied — so a session whose only grant is a narrow Browse deep in the raw
    ///     tree could not get past the front door at all. The anchor's identifier is a display name rather
    ///     than a path, so the ordinary split produced a one-segment scope (<c>["OtOpcUa"]</c>) that no
    ///     grant path can ever contain.
    /// </summary>
    [Fact]
    public void The_shared_root_folder_is_browsable_on_a_narrow_raw_browse_grant()
    {
        var gate = Gate(
            ScopedGrant(NodePermissions.Browse, NodeAclScopeKind.Tag, "tag-1"),
            Scopes(("tag-1", NodeAclScopeKind.Tag, ["raw", "Plant", "Modbus", "dev1", "Speed"])));

        gate.AuthorizeCached(Identity(), OpcUaOperation.Browse, Anchor(), AddressSpaceRealm.Raw)
            .ShouldBeNull();
    }

    /// <summary>
    ///     The anchor fronts BOTH trees, so a principal whose only Browse grant lives in the UNS tree still
    ///     enters through this raw-namespace node — the gate must consider transit in either realm.
    /// </summary>
    /// <remarks>
    ///     This is the test that falsifies the second walk: delete the UNS OR-leg from
    ///     <c>DataPlaneAuthorizer.Evaluate</c> and only this fact goes red, because the first walk asks the
    ///     raw realm root, which a purely-UNS grant never marks.
    /// </remarks>
    [Fact]
    public void The_shared_root_folder_is_browsable_on_a_uns_only_browse_grant()
    {
        var gate = Gate(
            ScopedGrant(NodePermissions.Browse, NodeAclScopeKind.Equipment, "eq-1"),
            Scopes(("eq-1", NodeAclScopeKind.Equipment, ["uns", "Area", "Line", "Eq"])));

        gate.AuthorizeCached(Identity(), OpcUaOperation.Browse, Anchor(), AddressSpaceRealm.Raw)
            .ShouldBeNull();
    }

    /// <summary>
    ///     The anchor is not a bypass: a principal holding no grant at all still cannot browse it, so the
    ///     mapping opens the front door only for a session that has somewhere to go.
    /// </summary>
    [Fact]
    public void The_shared_root_folder_is_denied_without_any_grant()
    {
        var state = new DataPlaneAuthorityState();
        state.Apply(Cluster, "rev-1", [Key(enabled: true)], [], Scopes());
        var gate = new DataPlaneAuthorizer(
            state, new TriePermissionEvaluator(state.Tries), enabled: true, NullLogger.Instance);

        Veto(gate.AuthorizeCached(Identity(), OpcUaOperation.Browse, Anchor(), AddressSpaceRealm.Raw));
    }

    /// <summary>
    ///     Transit is marked only by grants that actually carry <c>Browse</c>. A deep Read-only grant leaves
    ///     the anchor closed — the node is readable by NodeId, not discoverable by navigating.
    /// </summary>
    [Fact]
    public void The_shared_root_folder_is_denied_when_the_deep_grant_lacks_browse()
    {
        var gate = Gate(
            ScopedGrant(NodePermissions.Read, NodeAclScopeKind.Tag, "tag-1"),
            Scopes(("tag-1", NodeAclScopeKind.Tag, ["raw", "Plant", "Modbus", "dev1", "Speed"])));

        Veto(gate.AuthorizeCached(Identity(), OpcUaOperation.Browse, Anchor(), AddressSpaceRealm.Raw));
    }

    /// <summary>
    ///     Transit confers navigation and nothing else, at the anchor exactly as at every other ancestor: a
    ///     deep Browse grant does not make the root folder readable.
    /// </summary>
    [Fact]
    public void The_shared_root_folder_is_not_readable_on_transit_alone()
    {
        var gate = Gate(
            ScopedGrant(NodePermissions.Browse, NodeAclScopeKind.Tag, "tag-1"),
            Scopes(("tag-1", NodeAclScopeKind.Tag, ["raw", "Plant", "Modbus", "dev1", "Speed"])));

        gate.AuthorizeCached(Identity(), OpcUaOperation.Browse, Anchor(), AddressSpaceRealm.Raw).ShouldBeNull();
        Veto(gate.AuthorizeCached(Identity(), OpcUaOperation.Read, Anchor(), AddressSpaceRealm.Raw));
    }

    /// <summary>
    ///     Guard order is unchanged by the anchor branch: the key's usability is re-checked before any walk
    ///     runs, so a revoked key is refused the anchor even though its grant would confer transit.
    /// </summary>
    [Fact]
    public void A_revoked_key_is_denied_the_shared_root_folder()
    {
        var state = new DataPlaneAuthorityState();
        var grant = ScopedGrant(NodePermissions.Browse, NodeAclScopeKind.Tag, "tag-1");
        var scopes = Scopes(("tag-1", NodeAclScopeKind.Tag, ["raw", "Plant", "Modbus", "dev1", "Speed"]));
        var gate = new DataPlaneAuthorizer(
            state, new TriePermissionEvaluator(state.Tries), enabled: true, NullLogger.Instance);

        state.Apply(Cluster, "rev-1", [Key(enabled: true)], [grant], scopes);
        gate.AuthorizeCached(Identity(), OpcUaOperation.Browse, Anchor(), AddressSpaceRealm.Raw).ShouldBeNull();

        state.Apply(Cluster, "rev-2", [Key(enabled: false)], [grant], scopes);
        Veto(gate.AuthorizeCached(Identity(), OpcUaOperation.Browse, Anchor(), AddressSpaceRealm.Raw));
    }

    /// <summary>
    ///     Anchor semantics are realm-qualified. In the UNS namespace <c>s=OtOpcUa</c> is an ordinary Area
    ///     that an operator happened to name after the root folder, and it must be evaluated as the path it
    ///     is — a Browse grant in an unrelated UNS subtree must not open it.
    /// </summary>
    /// <remarks>
    ///     The discriminating grant is a <b>UNS</b> one deliberately. Un-qualifying
    ///     <c>IsSharedRootFolder</c> maps this node onto the zero-segment UNS scope, which the unrelated
    ///     grant's own transit marks — so the Area silently becomes browsable for a principal granted
    ///     nothing anywhere near it. A raw-only grant would have been refused either way and would have
    ///     proven nothing.
    /// </remarks>
    [Fact]
    public void A_uns_area_named_like_the_anchor_gets_no_anchor_semantics()
    {
        var unsArea = new NodeId(V3NodeIds.SharedRootFolderId, 3);
        var gate = Gate(
            ScopedGrant(NodePermissions.Browse, NodeAclScopeKind.Equipment, "eq-1"),
            Scopes(("eq-1", NodeAclScopeKind.Equipment, ["uns", "Area", "Line", "Eq"])));

        Veto(gate.AuthorizeCached(Identity(), OpcUaOperation.Browse, unsArea, AddressSpaceRealm.Uns));

        // Non-vacuity, twice over: the grant's OWN ancestor Area is browsable on transit, and the same
        // identifier in the RAW namespace — the real anchor — is browsable on the same grant.
        gate.AuthorizeCached(Identity(), OpcUaOperation.Browse, new NodeId("Area", 3), AddressSpaceRealm.Uns)
            .ShouldBeNull();
        gate.AuthorizeCached(Identity(), OpcUaOperation.Browse, Anchor(), AddressSpaceRealm.Raw)
            .ShouldBeNull();
    }

    // ───────────────────────────── helpers ─────────────────────────────

    /// <summary>The single shared root folder both realm trees hang under, in the raw namespace.</summary>
    private static NodeId Anchor() => new(V3NodeIds.SharedRootFolderId, 2);

    private static NodeAcl ScopedGrant(NodePermissions flags, NodeAclScopeKind kind, string scopeId) => new()
    {
        NodeAclId = $"acl-{scopeId}",
        ClusterId = Cluster,
        Principal = Principal,
        ScopeKind = kind,
        ScopeId = scopeId,
        PermissionFlags = flags,
    };

    private static void Veto(ServiceResult? result)
    {
        result.ShouldNotBeNull();
        result!.StatusCode.Code.ShouldBe(StatusCodes.BadUserAccessDenied);
    }

    private static DataPlaneAuthorizer Gate(
        NodeAcl grant,
        IReadOnlyDictionary<AclScopeRef, IReadOnlyList<NodeAclPath>>? scopePaths = null)
    {
        var state = new DataPlaneAuthorityState();
        state.Apply(Cluster, "rev-1", [Key(enabled: true)], [grant], scopePaths ?? Scopes());
        return new DataPlaneAuthorizer(
            state, new TriePermissionEvaluator(state.Tries), enabled: true, NullLogger.Instance);
    }

    /// <summary>
    ///     The same gate <see cref="Gate"/> builds, with the REAL evaluator wrapped in a call counter — the
    ///     chain under test stays end-to-end, and only the number of walks becomes observable.
    /// </summary>
    private static DataPlaneAuthorizer CountingGate(NodeAcl grant, out CountingEvaluator evaluator)
    {
        var state = new DataPlaneAuthorityState();
        state.Apply(Cluster, "rev-1", [Key(enabled: true)], [grant], Scopes());
        evaluator = new CountingEvaluator(new TriePermissionEvaluator(state.Tries));
        return new DataPlaneAuthorizer(state, evaluator, enabled: true, NullLogger.Instance);
    }

    private static RoleCarryingUserIdentity Identity() =>
        new(new UserNameIdentityToken { UserName = "apikey" }, [], Principal, KeyId);

    private static NodeId RawNode(string path) => new(path, 2);

    private static NodeAcl ClusterGrant(NodePermissions flags) => new()
    {
        NodeAclId = "acl-cluster",
        ClusterId = Cluster,
        Principal = Principal,
        ScopeKind = NodeAclScopeKind.Cluster,
        PermissionFlags = flags,
    };

    private static ApiKey Key(bool enabled) => new()
    {
        ApiKeyId = KeyId,
        Name = "stage5",
        SecretHash = "hash",
        Principal = Principal,
        Enabled = enabled,
    };

    private static IReadOnlyDictionary<AclScopeRef, IReadOnlyList<NodeAclPath>> Scopes(
        params (string ScopeId, NodeAclScopeKind Kind, string[] Segments)[] scopes)
    {
        var map = new Dictionary<AclScopeRef, IReadOnlyList<NodeAclPath>>();
        foreach (var (scopeId, kind, segments) in scopes)
            map[new AclScopeRef(kind, scopeId)] = [new NodeAclPath(segments)];
        return map;
    }

    /// <summary>Counts grant walks without changing any of their answers.</summary>
    private sealed class CountingEvaluator(IPermissionEvaluator inner) : IPermissionEvaluator
    {
        public int Calls { get; private set; }

        public AuthorizationDecision Authorize(
            UserAuthorizationState session, OpcUaOperation operation, NodeScope scope)
        {
            Calls++;
            return inner.Authorize(session, operation, scope);
        }
    }

    /// <summary>Minimal controllable clock — the suite needs only "now" and "advance".</summary>
    private sealed class FakeTimeProvider(DateTime utcNow) : TimeProvider
    {
        private DateTimeOffset _now = new(utcNow, TimeSpan.Zero);

        public override DateTimeOffset GetUtcNow() => _now;

        public void Advance(TimeSpan by) => _now = _now.Add(by);
    }
}