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using System;
using System.Collections.Generic;
using System.IO;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Logging;
using Opc.Ua;
using Opc.Ua.OpenUsd;
using Opc.Ua.OpenUsd.Server;

namespace Robotics
{
    /// <summary>
    /// Wires the draft OPC UA — OpenUSD Bindings companion model onto the Robotics
    /// server: the well-known OpenUSD facility (stage + representation registries),
    /// a RobotCellStage descriptor, and the generic representation/binding helpers
    /// used by RobotCell.cs.
    /// </summary>
    public sealed partial class RobotCell
    {
        private OpenUsdRootState? m_openUsdRoot;
        private OpenUsdStageState? m_cellStage;

        private const string CellRootLayerIdentifier = "asset-repo/Cell.usd";

        private async ValueTask MaterialiseOpenUsdFacilityAsync(
            CancellationToken cancellationToken)
        {
            try
            {
                ushort ns = (ushort)Server.NamespaceUris.GetIndex(Opc.Ua.OpenUsd.Namespaces.OpenUSD);

                OpenUsdRootState root = SystemContext.CreateInstanceOfOpenUsdRootType(
                    null!, new QualifiedName("OpenUSD", ns));
                root.NodeId = new NodeId("OpenUSD", ns);

                FolderState stages = root.Stages
                    ?? root.CreateOrReplaceStages(SystemContext, null!);
                _ = root.Representations
                    ?? root.CreateOrReplaceRepresentations(SystemContext, null!);

                m_cellStage = SystemContext.CreateInstanceOfOpenUsdStageType(
                    stages, new QualifiedName("RobotCellStage", ns));
                stages.AddChild(m_cellStage);
                m_cellStage.CreateOrReplaceRootLayerIdentifier(SystemContext, null!)
                    .Value = CellRootLayerIdentifier;

                // §5.2 Twin-BOM content integrity: the digest is computed over the
                // *resolved root-layer content*, never over the identifier string, so a
                // connector can detect tampering of the bytes it actually composes.
                List<ServedAsset> servedAssets = LoadServedAssets();
                byte[] rootLayerBytes = servedAssets
                    .Find(a => a.Kind == OpenUsdAssetKindEnum.RootLayer)!.Bytes;
                byte[] digest;
#pragma warning disable CA1850 // Prefer static HashData (net48/netstandard2.0 compatibility)
                using (var sha = System.Security.Cryptography.SHA256.Create())
                {
                    digest = sha.ComputeHash(rootLayerBytes);
                }
#pragma warning restore CA1850
                m_cellStage.CreateOrReplaceRootLayerDigest(
                    SystemContext,
                    SystemContext.CreateOpenUsdStageType_RootLayerDigest(m_cellStage, forInstance: true))
                    .Value = (ByteString)digest;
                m_cellStage.CreateOrReplaceRootLayerDigestAlgorithm(
                    SystemContext,
                    SystemContext.CreateOpenUsdStageType_RootLayerDigestAlgorithm(m_cellStage, forInstance: true))
                    .Value = OpenUsdDigestAlgorithmEnum.Sha256;

                // Per the companion spec §4.2 the OpenUSD facility SHALL be a component
                // of the Server Object (i=2253) so any conformant connector can Browse
                // Server -> OpenUSD -> Representations. Record the inverse reference
                // here; the matching forward reference from the Server Object is added
                // via the externalReferences dictionary in LinkOpenUsdRootToServer.
                root.AddReference(ReferenceTypeIds.HasComponent, true, Opc.Ua.ObjectIds.Server);

                // §5.15 asset content delivery (OU-AssetDelivery): serve this stage's
                // artist-authored USD layer closure so a connector can render the twin
                // with no external asset resolver.
                UsdAssetDelivery.AttachStageAssets(SystemContext, m_cellStage, ns, servedAssets);

                SystemContext.AssignInstanceChildNodeIds(root);
                await Manager.AddPredefinedNodeAsync(root, cancellationToken)
                    .ConfigureAwait(false);

                m_openUsdRoot = root;
                await LinkOpenUsdRootToServerAsync(cancellationToken).ConfigureAwait(false);
                m_logger.MaterialisedOpenUsdFacility(root.NodeId, m_cellStage.NodeId);
            }
            catch (Exception ex)
            {
                m_cellStage = null;
                m_openUsdRoot = null;
                m_logger.OpenUsdFacilityFailed(ex);
            }
        }

        /// <summary>
        /// Loads the embedded artist-authored USD layers this server serves (spec §5.15).
        /// </summary>
        /// <returns></returns>
        private static List<ServedAsset> LoadServedAssets()
        {
            return
            [
                new("Cell.usda", OpenUsdAssetKindEnum.RootLayer, ReadEmbeddedAsset("Cell.usda")),
                new("robot.usda", OpenUsdAssetKindEnum.Reference, ReadEmbeddedAsset("robot.usda")),
                new("tool.usda", OpenUsdAssetKindEnum.Reference, ReadEmbeddedAsset("tool.usda"))
            ];
        }

        private static byte[] ReadEmbeddedAsset(string resourceName)
        {
            using Stream? s = typeof(RobotCell).Assembly.GetManifestResourceStream(resourceName);
            if (s == null)
            {
                return [];
            }
            using var ms = new MemoryStream();
            s.CopyTo(ms);
            return ms.ToArray();
        }

        private async ValueTask LinkOpenUsdRootToServerAsync(
            CancellationToken cancellationToken)
        {
            if (m_openUsdRoot == null)
            {
                return;
            }

            var references = new IReference[]
            {
                new NodeStateReference(
                    ReferenceTypeIds.HasComponent,
                    false,
                    m_openUsdRoot.NodeId)
            };
            await Server.NodeManager.AddReferencesAsync(
                Opc.Ua.ObjectIds.Server,
                references,
                cancellationToken).ConfigureAwait(false);
            m_logger.LinkedOpenUsdFacility();
        }

        /// <summary>
        /// Attaches an OpenUsdRepresentation AddIn to an Object and registers it in the
        /// discovery registry (Server/OpenUSD/Representations, Organizes). Returns the
        /// representation so the caller can add live/component bindings to it.
        /// </summary>
        /// <param name="owner"></param>
        /// <param name="primPath"></param>
        /// <param name="ns"></param>
        /// <returns></returns>
        private OpenUsdRepresentationState AttachRepresentation(
            NodeState owner, string primPath, ushort ns)
        {
            OpenUsdRepresentationState rep = SystemContext.CreateRepresentation(
                owner, m_cellStage!.NodeId, primPath, ns);
            return rep;
        }

        /// <summary>
        /// Adds the Organizes reference pair between the discovery registry and a
        /// representation, so a generic connector discovers it without domain knowledge.
        /// </summary>
        /// <param name="rep"></param>
        private void OrganiseRepresentation(OpenUsdRepresentationState rep)
        {
            FolderState? registry = m_openUsdRoot?.Representations;
            if (registry == null)
            {
                return;
            }
            registry.AddReference(ReferenceTypeIds.Organizes, false, rep.NodeId);
            rep.AddReference(ReferenceTypeIds.Organizes, true, registry.NodeId);
        }

        /// <summary>
        /// Instantiates the OpenUsdLiveBinding <Binding> placeholder as a concrete
        /// browsable child of a representation and sets its members (spec §5.4/§5.10/§5.11).
        /// Thin adapter over the reusable Opc.Ua.OpenUsd.Server authoring API: binds the
        /// cell stage and forwards. The binding-authoring logic lives in the SDK
        /// (OpenUsdRepresentationAuthoring.AddLiveBinding), not in this sample.
        /// </summary>
        /// <param name="rep"></param>
        /// <param name="ns"></param>
        /// <param name="name"></param>
        /// <param name="bindingDefinitionId"></param>
        /// <param name="sourceNodeId"></param>
        /// <param name="targetPrimPath"></param>
        /// <param name="targetPropertyName"></param>
        /// <param name="targetUsdTypeName"></param>
        /// <param name="kind"></param>
        /// <param name="scale"></param>
        /// <param name="bindingTypeId"></param>
        /// <param name="signalRole"></param>
        /// <param name="sourceSemanticId"></param>
        /// <param name="alarmAspect"></param>
        /// <param name="commandTargetNodeId"></param>
        /// <param name="commandTriggerPropertyName"></param>
        /// <returns></returns>
        private OpenUsdLiveBindingState CreateBinding(
            OpenUsdRepresentationState rep, ushort ns, string name,
            Guid bindingDefinitionId, NodeId sourceNodeId, string targetPrimPath,
            string targetPropertyName, string targetUsdTypeName,
            OpenUsdRenderTargetKindEnum? kind, double scale,
            uint bindingTypeId = Opc.Ua.OpenUsd.ObjectTypes.OpenUsdValueChangeBindingType,
            OpenUsdSignalRoleEnum signalRole = OpenUsdSignalRoleEnum.Observable,
            string? sourceSemanticId = null,
            OpenUsdAlarmAspectEnum? alarmAspect = null,
            NodeId commandTargetNodeId = default,
            string? commandTriggerPropertyName = null)
        {
            OpenUsdLiveBindingState binding = rep.AddLiveBinding(
                SystemContext, ns, m_cellStage!.NodeId, name, bindingDefinitionId, sourceNodeId,
                targetPrimPath, targetPropertyName, targetUsdTypeName, kind, scale,
                bindingTypeId, signalRole, sourceSemanticId, alarmAspect,
                commandTargetNodeId, commandTriggerPropertyName);
            AssignInstanceSubtree(binding, rep);
            return binding;
        }

        /// <summary>
        /// Instantiates the OpenUsdComponentBinding <Component> placeholder on a
        /// representation and sets its members (spec §5.12–5.14).
        /// Thin adapter over the reusable Opc.Ua.OpenUsd.Server authoring API: the
        /// component/composition-binding logic lives in the SDK
        /// (OpenUsdRepresentationAuthoring.AddComponentBinding), not in this sample.
        /// </summary>
        /// <param name="rep"></param>
        /// <param name="ns"></param>
        /// <param name="name"></param>
        /// <param name="bindingDefinitionId"></param>
        /// <param name="cardinality"></param>
        /// <param name="arc"></param>
        /// <param name="targetPrimPath"></param>
        /// <param name="componentRepresentation"></param>
        /// <param name="assetReference"></param>
        /// <param name="dynamic"></param>
        /// <param name="changeEventSource"></param>
        /// <param name="componentTypeDefinition"></param>
        private void CreateComponentBinding(
            OpenUsdRepresentationState rep, ushort ns, string name, Guid bindingDefinitionId,
            OpenUsdCardinalityEnum cardinality, OpenUsdCompositionArcEnum arc, string targetPrimPath,
            NodeId componentRepresentation = default, string? assetReference = null,
            bool dynamic = false, NodeId changeEventSource = default,
            NodeId componentTypeDefinition = default)
        {
            OpenUsdComponentBindingState binding = rep.AddComponentBinding(
                SystemContext, ns, name, bindingDefinitionId, cardinality, arc, targetPrimPath,
                componentRepresentation, assetReference, dynamic, changeEventSource,
                componentTypeDefinition: componentTypeDefinition);
            AssignInstanceSubtree(binding, rep);
        }
    }

    internal static partial class OpenUsdRepresentationLog
    {
        [LoggerMessage(EventId = MinimalRobotServerEventIds.OpenUsdRepresentation + 1,
            Level = LogLevel.Information,
            Message = "Materialised OpenUSD facility (root {RootId}, RobotCellStage {StageId}).")]
        public static partial void MaterialisedOpenUsdFacility(
            this ILogger logger, NodeId rootId, NodeId stageId);

        [LoggerMessage(EventId = MinimalRobotServerEventIds.OpenUsdRepresentation + 2,
            Level = LogLevel.Error,
            Message = "Failed to materialise the OpenUSD facility.")]
        public static partial void OpenUsdFacilityFailed(
            this ILogger logger,
            Exception exception);

        [LoggerMessage(EventId = MinimalRobotServerEventIds.OpenUsdRepresentation + 3,
            Level = LogLevel.Information,
            Message = "Linked OpenUSD facility under the Server Object (i=2253).")]
        public static partial void LinkedOpenUsdFacility(this ILogger logger);
    }
}