ComplexTypeSystem.cs

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 *
 * OPC Foundation MIT License 1.00
 *
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 * obtaining a copy of this software and associated documentation
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using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.Xml;
using Microsoft.Extensions.Logging;
using Opc.Ua.ComplexTypes;

namespace Opc.Ua.Client.ComplexTypes
{
    /// <summary>
    /// Manages the custom types of a server for a client session.
    /// Loads the custom types into the type factory
    /// of a client session, to allow for decoding and encoding
    /// of custom enumeration types and structured types.
    /// </summary>
    /// <remarks>
    /// Support for V1.03 dictionaries and all V1.04 data type definitions
    /// with the following known restrictions:
    /// - Support only for V1.03 structured types which can be mapped to the V1.04
    /// structured type definition. Unsupported V1.03 types are ignored.
    /// - Concrete Structure-backed sub-types of the abstract <c>OptionSet</c>
    /// DataType are supported. UInteger-backed <c>IsOptionSet</c> DataTypes
    /// are left opaque (their wire form is the plain unsigned integer).
    /// </remarks>
    public class ComplexTypeSystem
    {
        /// <summary>
        /// an internal limit to prevent the retry
        /// datatype loader mechanism to loop forever
        /// </summary>
        internal const int MaxLoopCount = 100;

        /// <summary>
        /// The data type systems that were loaded
        /// </summary>
        public NodeIdDictionary<DataDictionary> DataTypeSystem
            => m_complexTypeResolver.DataTypeSystem;

        /// <summary>
        /// Obsolete constructor
        /// </summary>
        [Obsolete("Use ComplexTypeSystem(IComplexTypeResolver, ITelemetryContext) instead.")]
        public ComplexTypeSystem(IComplexTypeResolver complexTypeResolver)
            // Telemetry is required by the modern ctor; this obsolete bridge forwards null!
            // to preserve the resolver-only instantiation pattern.
            : this(complexTypeResolver, (ITelemetryContext)null!)
        {
        }

        /// <summary>
        /// Obsolete constructor
        /// </summary>
        [Obsolete("Use ComplexTypeSystem(IComplexTypeResolver, IComplexTypeFactory, ITelemetryContext) instead.")]
        public ComplexTypeSystem(
            IComplexTypeResolver complexTypeResolver,
            IComplexTypeFactory complexTypeBuilderFactory)
            // Telemetry is required by the modern ctor; this obsolete bridge forwards null!.
            : this(complexTypeResolver, complexTypeBuilderFactory, null!)
        {
        }

        /// <summary>
        /// Initializes the type system with a session to load the custom types.
        /// </summary>
        public ComplexTypeSystem(ISession session)
            : this(session, session.MessageContext.Telemetry)
        {
        }

        /// <summary>
        /// Initializes the type system with a session to load the custom types.
        /// </summary>
        public ComplexTypeSystem(ISession session, ITelemetryContext telemetry)
            : this(session, new DefaultComplexTypeFactory(), telemetry)
        {
        }

        /// <summary>
        /// Initializes the type system with a complex type resolver to load the custom types.
        /// </summary>
        public ComplexTypeSystem(
            IComplexTypeResolver complexTypeResolver,
            ITelemetryContext telemetry)
            : this(complexTypeResolver, new DefaultComplexTypeFactory(), telemetry)
        {
        }

        /// <summary>
        /// Create complex type system with session and custom type builder factory
        /// </summary>
        public ComplexTypeSystem(
            ISession session,
            IComplexTypeFactory complexTypeBuilderFactory)
            : this(session, complexTypeBuilderFactory, session.MessageContext.Telemetry)
        {
        }

        /// <summary>
        /// Initializes the type system with a session to load the custom types
        /// and a customized type builder factory
        /// </summary>
        public ComplexTypeSystem(
            ISession session,
            IComplexTypeFactory complexTypeBuilderFactory,
            ITelemetryContext telemetry)
            : this(new NodeCacheResolver(session, telemetry), complexTypeBuilderFactory, telemetry)
        {
        }

        /// <summary>
        /// Initializes the type system with a complex type resolver to load the custom types.
        /// </summary>
        public ComplexTypeSystem(
            IComplexTypeResolver complexTypeResolver,
            IComplexTypeFactory complexTypeBuilderFactory,
            ITelemetryContext telemetry)
        {
            m_complexTypeResolver = complexTypeResolver;
            m_complexTypeBuilderFactory = complexTypeBuilderFactory;
            m_logger = telemetry.CreateLogger<ComplexTypeSystem>();
        }

        /// <summary>
        /// Load a single custom type with subtypes.
        /// </summary>
        /// <remarks>
        /// Uses inverse references on the server to find the super type(s).
        /// If the new structure contains a type dependency to a yet
        /// unknown type, it loads also the dependent type(s).
        /// For servers without DataTypeDefinition support, all
        /// custom types are loaded.
        /// </remarks>
        public async Task<IType?> LoadTypeAsync(
            ExpandedNodeId nodeId,
            bool subTypes = false,
            bool throwOnError = false,
            CancellationToken ct = default)
        {
            try
            {
                // add fast path, if no subTypes are requested
                if (!subTypes)
                {
                    IType? systemType = GetSystemType(nodeId);
                    if (systemType != null)
                    {
                        return systemType;
                    }
                }

                // cache the server type system
                _ = await m_complexTypeResolver
                    .LoadDataTypesAsync(DataTypeIds.BaseDataType, true, ct: ct)
                    .ConfigureAwait(false);
                IList<INode> subTypeNodes = (await m_complexTypeResolver
                    .LoadDataTypesAsync(nodeId, subTypes, true, ct: ct)
                    .ConfigureAwait(false))
                    .ToList();
                List<INode> subTypeNodesWithoutKnownTypes = RemoveKnownTypes(subTypeNodes);

                if (subTypeNodesWithoutKnownTypes.Count > 0)
                {
                    IList<INode> serverEnumTypes = [];
                    IList<INode> serverStructTypes = [];
                    foreach (INode node in subTypeNodesWithoutKnownTypes)
                    {
                        await AddEnumerationOrStructureTypeAsync(
                            node,
                            serverEnumTypes,
                            serverStructTypes,
                            ct)
                            .ConfigureAwait(false);
                    }

                    // load server types
                    if (DisableDataTypeDefinition ||
                        !await LoadBaseDataTypesAsync(serverEnumTypes, serverStructTypes, ct)
                            .ConfigureAwait(false))
                    {
                        if (!DisableDataTypeDictionary)
                        {
                            _ = await LoadDictionaryDataTypesAsync(serverEnumTypes, false, ct)
                                .ConfigureAwait(false);
                        }
                    }
                }
                // Commit the changes to the factory
                m_complexTypeResolver.FactoryBuilder.Commit();
                return GetSystemType(nodeId);
            }
            catch (Exception ex)
            {
                m_logger.LogError(ex, "Failed to load the custom type {NodeId}.", nodeId);
                if (throwOnError)
                {
                    throw;
                }
                return null;
            }
        }

        /// <summary>
        /// Load all custom types of a namespace.
        /// </summary>
        /// <remarks>
        /// If a new type in the namespace contains a type dependency to an
        /// unknown type in another namespace, it loads also the dependent type(s).
        /// For servers without DataTypeDefinition support all
        /// custom types are loaded.
        /// </remarks>
        /// <exception cref="ServiceResultException"></exception>
        public async Task<bool> LoadNamespaceAsync(
            string ns,
            bool throwOnError = false,
            CancellationToken ct = default)
        {
            try
            {
                int index = m_complexTypeResolver.NamespaceUris.GetIndex(ns);
                if (index < 0)
                {
                    throw new ServiceResultException(
                        $"Bad argument {ns}. Namespace not found.");
                }
                ushort nameSpaceIndex = (ushort)index;
                _ = await m_complexTypeResolver
                    .LoadDataTypesAsync(DataTypeIds.BaseDataType, true, ct: ct)
                    .ConfigureAwait(false);
                IList<INode> serverEnumTypes = (await m_complexTypeResolver
                    .LoadDataTypesAsync(DataTypeIds.Enumeration, ct: ct)
                    .ConfigureAwait(false)).ToList();
                IList<INode> serverStructTypes = (await m_complexTypeResolver
                    .LoadDataTypesAsync(DataTypeIds.Structure, true, ct: ct)
                    .ConfigureAwait(false)).ToList();
                // filter for namespace
                serverEnumTypes = [.. serverEnumTypes.Where(
                    rd => rd.NodeId.NamespaceIndex == nameSpaceIndex)];
                serverStructTypes = [.. serverStructTypes.Where(
                    rd => rd.NodeId.NamespaceIndex == nameSpaceIndex)];
                // load types
                bool allTypesLoaded;
                if (DisableDataTypeDefinition ||
                    !await LoadBaseDataTypesAsync(serverEnumTypes, serverStructTypes, ct)
                        .ConfigureAwait(false))
                {
                    if (DisableDataTypeDictionary)
                    {
                        return false;
                    }
                    allTypesLoaded = await LoadDictionaryDataTypesAsync(serverEnumTypes, false, ct)
                        .ConfigureAwait(false);
                }
                else
                {
                    allTypesLoaded = true;
                }
                // Commit the changes to the factory
                m_complexTypeResolver.FactoryBuilder.Commit();
                return allTypesLoaded;
            }
            catch (Exception ex)
            {
                m_logger.LogError(ex, "Failed to load the custom type namespace {Namespace}.", ns);
                if (throwOnError)
                {
                    throw;
                }
                return false;
            }
        }

        /// <summary>
        /// <see cref="LoadAsync(bool, bool, CancellationToken)"/>
        /// </summary>
        [Obsolete("Use LoadAsync instead.")]
        public Task<bool> Load(
            bool onlyEnumTypes = false,
            bool throwOnError = false,
            CancellationToken ct = default)
        {
            return LoadAsync(onlyEnumTypes, throwOnError, ct).AsTask();
        }

        /// <summary>
        /// Load all custom types from a server into the session system type factory.
        /// </summary>
        /// <remarks>
        /// The loader follows the following strategy:
        /// - Load all DataType nodes of the Enumeration subtypes.
        /// - Load all DataType nodes of the Structure subtypes.
        /// - Create all enumerated custom types using the DataTypeDefinion attribute, if available.
        /// - Create all remaining enumerated custom types using the EnumValues or EnumStrings property, if available.
        /// - Create all structured types using the DataTypeDefinion attribute, if available.
        /// if there are type definitions remaining
        /// - Load the binary schema dictionaries with type definitions.
        /// - Create all remaining enumerated custom types using the dictionaries.
        /// - Convert all structured types in the dictionaries to the DataTypeDefinion attribute, if possible.
        /// - Create all structured types from the dictionaries using the converted DataTypeDefinion attribute.
        /// </remarks>
        /// <returns>true if all DataTypes were loaded.</returns>
        public async ValueTask<bool> LoadAsync(
            bool onlyEnumTypes = false,
            bool throwOnError = false,
            CancellationToken ct = default)
        {
            try
            {
                // load server types in cache
                _ = await m_complexTypeResolver
                    .LoadDataTypesAsync(DataTypeIds.BaseDataType, true, ct: ct)
                    .ConfigureAwait(false);
                IList<INode> serverEnumTypes = (await m_complexTypeResolver
                    .LoadDataTypesAsync(DataTypeIds.Enumeration, ct: ct)
                    .ConfigureAwait(false)).ToList();
                IList<INode> serverStructTypes = onlyEnumTypes
                    ? []
                    : (await m_complexTypeResolver
                        .LoadDataTypesAsync(DataTypeIds.Structure, true, ct: ct)
                        .ConfigureAwait(false)).ToList();
                bool allTypesLoaded;
                if (DisableDataTypeDefinition ||
                    !await LoadBaseDataTypesAsync(serverEnumTypes, serverStructTypes, ct)
                        .ConfigureAwait(false))
                {
                    if (DisableDataTypeDictionary)
                    {
                        return false;
                    }
                    allTypesLoaded = await LoadDictionaryDataTypesAsync(serverEnumTypes, true, ct)
                        .ConfigureAwait(false);
                }
                else
                {
                    allTypesLoaded = true;
                }
                // Commit the changes to the factory
                m_complexTypeResolver.FactoryBuilder.Commit();
                return allTypesLoaded;
            }
            catch (Exception ex)
            {
                m_logger.LogError(ex, "Failed to load the custom types.");
                if (throwOnError)
                {
                    throw;
                }
                return false;
            }
        }

        /// <summary>
        /// Get the types defined in this type system.
        /// </summary>
        public IReadOnlyList<XmlQualifiedName> GetDefinedTypes()
        {
            return [.. m_complexTypeBuilderFactory.GetTypes().Select(c => c.XmlName)];
        }

        /// <summary>
        /// Returns data types node ids for everything that was defined.
        /// </summary>
        public IEnumerable<ExpandedNodeId> GetDefinedDataTypeIds()
        {
            return m_dataTypeDefinitionCache.Keys.Select(nodeId =>
                NodeId.ToExpandedNodeId(nodeId, m_complexTypeResolver.NamespaceUris));
        }

        /// <summary>
        /// Get the data type definition and dependent definitions for a data type node id.
        /// Recursive through the cache to find all dependent types for structures fields
        /// contained in the cache.
        /// </summary>
        public NodeIdDictionary<DataTypeDefinition> GetDataTypeDefinitionsForDataType(
            ExpandedNodeId dataTypeId)
        {
            var dataTypeDefinitions = new NodeIdDictionary<DataTypeDefinition>();

            var dataTypeNodeId = ExpandedNodeId.ToNodeId(
                dataTypeId,
                m_complexTypeResolver.NamespaceUris);
            if (!dataTypeNodeId.IsNull)
            {
                CollectAllDataTypeDefinitions(dataTypeNodeId, dataTypeDefinitions);
            }

            return dataTypeDefinitions;

            void CollectAllDataTypeDefinitions(
                NodeId nodeId,
                NodeIdDictionary<DataTypeDefinition> collect)
            {
                if (nodeId.IsNull)
                {
                    return;
                }

                if (m_dataTypeDefinitionCache.TryGetValue(
                    nodeId,
                    out DataTypeDefinition? dataTypeDefinition))
                {
                    collect[nodeId] = dataTypeDefinition;

                    if (dataTypeDefinition is StructureDefinition structureDefinition)
                    {
                        foreach (StructureField field in structureDefinition.Fields)
                        {
                            if (!IsRecursiveDataType(nodeId, field.DataType) &&
                                !collect.ContainsKey(field.DataType))
                            {
                                CollectAllDataTypeDefinitions(field.DataType, collect);
                            }
                        }
                    }
                }
            }
        }

        /// <summary>
        /// Clear references in datatype cache.
        /// </summary>
        public void ClearDataTypeCache()
        {
            m_dataTypeDefinitionCache.Clear();
        }

        /// <summary>
        /// Disable the use of DataTypeDefinition to create the complex type definition.
        /// </summary>
        public bool DisableDataTypeDefinition { get; set; }

        /// <summary>
        /// Disable the use of DataType Dictionaries to create the complex type definition.
        /// </summary>
        public bool DisableDataTypeDictionary { get; set; }

        /// <summary>
        /// Load listed custom types from dictionaries
        /// into the sessions system type factory.
        /// </summary>
        /// <remarks>
        /// Loads all custom types at this time to avoid
        /// complexity when resolving type dependencies.
        /// </remarks>
        private async Task<bool> LoadDictionaryDataTypesAsync(
            IList<INode> serverEnumTypes,
            bool fullTypeList,
            CancellationToken ct = default)
        {
            // build a type dictionary with all known new types
            IList<INode> allEnumTypes = fullTypeList
                ? serverEnumTypes
                : (await m_complexTypeResolver.LoadDataTypesAsync(DataTypeIds.Enumeration, ct: ct)
                    .ConfigureAwait(false)).ToList();
            var typeDictionary = new Dictionary<XmlQualifiedName, NodeId>();

            // strip known types from list
            serverEnumTypes = RemoveKnownTypes(allEnumTypes);

            // load the binary schema dictionaries from the server
            IReadOnlyDictionary<NodeId, DataDictionary> typeSystem = await m_complexTypeResolver
                .LoadDataTypeSystem(ct: ct)
                .ConfigureAwait(false);

            // sort dictionaries with import dependencies to the end of the list
            var sortedTypeSystem = typeSystem.OrderBy(t => t.Value.TypeDictionary?.Import?.Length)
                .ToList();

            bool allTypesLoaded = true;

            // create custom types for all dictionaries
            foreach (KeyValuePair<NodeId, DataDictionary> dictionaryId in sortedTypeSystem)
            {
                try
                {
                    DataDictionary dictionary = dictionaryId.Value;
                    if (dictionary.TypeDictionary == null ||
                        dictionary.TypeDictionary.Items == null)
                    {
                        continue;
                    }
                    string? targetDictionaryNamespace = dictionary.TypeDictionary.TargetNamespace;
                    // TargetNamespace is nullable on the imported XSD type; an OPC UA type
                    // dictionary always carries one when it reaches this code path.
                    int targetNamespaceIndex = m_complexTypeResolver.NamespaceUris
                        .GetIndex(targetDictionaryNamespace!);
                    var structureList = new List<Schema.Binary.TypeDescription>();
                    var enumList = new List<Schema.Binary.TypeDescription>();

                    // split into enumeration and structure types and sort
                    // types with dependencies to the end of the list.
                    SplitAndSortDictionary(dictionary, structureList, enumList);

                    // create assembly for all types in the same module
                    // See note above: targetDictionaryNamespace is required here.
                    IComplexTypeBuilder complexTypeBuilder = m_complexTypeBuilderFactory.Create(
                        targetDictionaryNamespace!,
                        targetNamespaceIndex,
                        dictionary.Name);

                    // Add all unknown enumeration types in dictionary
                    await AddEnumTypesAsync(
                            complexTypeBuilder,
                            typeDictionary,
                            enumList,
                            allEnumTypes,
                            serverEnumTypes,
                            ct)
                        .ConfigureAwait(false);

                    // handle structures
                    int loopCounter = 0;
                    int lastStructureCount = 0;
                    while (
                        structureList.Count > 0 &&
                        structureList.Count != lastStructureCount &&
                        loopCounter < MaxLoopCount)
                    {
                        loopCounter++;
                        lastStructureCount = structureList.Count;
                        var retryStructureList = new List<Schema.Binary.TypeDescription>();
                        // build structured types
                        foreach (Schema.Binary.TypeDescription item in structureList)
                        {
                            if (item is Schema.Binary.StructuredType structuredObject)
                            {
                                NodeId nodeId = dictionary.DataTypes
                                    .FirstOrDefault(d => d.Value.Name == item.Name)
                                    .Key;
                                if (nodeId.IsNull)
                                {
                                    m_logger.LogError(
                                        Utils.TraceMasks.Error,
                                        "Skip the type definition of {DataType} because the data type node was not found.",
                                        item.Name);
                                    continue;
                                }

                                // find the data type node and the binary encoding id
                                (ExpandedNodeId typeId, ExpandedNodeId binaryEncodingId, DataTypeNode? dataTypeNode) =
                                    await m_complexTypeResolver
                                        .BrowseTypeIdsForDictionaryComponentAsync(nodeId, ct)
                                        .ConfigureAwait(false);

                                if (dataTypeNode == null)
                                {
                                    m_logger.LogError(
                                        Utils.TraceMasks.Error,
                                        "Skip the type definition of {DataType} because the data type node was not found.",
                                        item.Name);
                                    continue;
                                }

                                if (GetSystemType(typeId) != null)
                                {
                                    XmlQualifiedName qName =
                                        structuredObject.QName
                                        ?? new XmlQualifiedName(
                                            structuredObject.Name,
                                            targetDictionaryNamespace);
                                    typeDictionary[qName] = ExpandedNodeId.ToNodeId(
                                        typeId,
                                        m_complexTypeResolver.NamespaceUris);
                                    m_logger.LogInformation(
                                        "Skip the type definition of {DataType} because the type already exists.",
                                        item.Name);
                                    continue;
                                }

                                // Use DataTypeDefinition attribute, if available (>=V1.04)
                                StructureDefinition? structureDefinition = null;
                                if (!DisableDataTypeDefinition)
                                {
                                    structureDefinition = GetStructureDefinition(dataTypeNode);
                                }
                                if (structureDefinition == null)
                                {
                                    try
                                    {
                                        // convert the binary schema description to a StructureDefinition
                                        structureDefinition = structuredObject
                                            .ToStructureDefinition(
                                                binaryEncodingId,
                                                typeDictionary,
                                                m_complexTypeResolver.NamespaceUris,
                                                dataTypeNode.NodeId);
                                    }
                                    catch (DataTypeNotSupportedException)
                                    {
                                        m_logger.LogError(
                                            "Skipped the type definition of {DataType} because it is not supported.",
                                            item.Name);
                                        continue;
                                    }
                                    catch (ServiceResultException sre)
                                    {
                                        m_logger.LogError(
                                            sre,
                                            "Skip the type definition of {DataType}.",
                                            item.Name);
                                        continue;
                                    }
                                }

                                List<ExpandedNodeId>? missingTypeIds = null;
                                IEncodeableType? complexType = null;
                                if (structureDefinition != null)
                                {
                                    ArrayOf<NodeId> encodingIds;
                                    ExpandedNodeId xmlEncodingId;
                                    (encodingIds, binaryEncodingId, xmlEncodingId)
                                        = await m_complexTypeResolver
                                        .BrowseForEncodingsAsync(typeId, s_supportedEncodings, ct)
                                        .ConfigureAwait(false);
                                    try
                                    {
                                        // build the actual .NET structured type in assembly
                                        (complexType, missingTypeIds)
                                            = await AddStructuredTypeAsync(
                                                complexTypeBuilder,
                                                structureDefinition,
                                                dataTypeNode.BrowseName,
                                                typeId,
                                                binaryEncodingId,
                                                xmlEncodingId,
                                                ct)
                                            .ConfigureAwait(false);
                                    }
                                    catch (DataTypeNotSupportedException typeNotSupportedException)
                                    {
                                        m_logger.LogInformation(
                                            typeNotSupportedException,
                                            "Skipped the type definition of {DataType} because it is not supported.",
                                            item.Name);
                                        continue;
                                    }

                                    // Add new type to factory
                                    if (complexType != null)
                                    {
                                        // match namespace and add new type to type factory
                                        foreach (NodeId encodingId in encodingIds)
                                        {
                                            AddEncodeableType(encodingId, complexType);
                                        }
                                        AddEncodeableType(typeId, complexType);
                                        XmlQualifiedName qName =
                                            structuredObject.QName
                                            ?? new XmlQualifiedName(
                                                structuredObject.Name,
                                                targetDictionaryNamespace);
                                        typeDictionary[qName] = ExpandedNodeId.ToNodeId(
                                            typeId,
                                            m_complexTypeResolver.NamespaceUris);
                                    }
                                }

                                if (complexType == null)
                                {
                                    retryStructureList.Add(item);
                                    m_logger.LogTrace(
                                        "Skipped the type definition of {DataType}, missing {MissingTypeIds}. Retry in next round.",
                                        item.Name,
                                        missingTypeIds == null ?
                                            string.Empty :
                                            string.Join(",", [.. missingTypeIds.Select(id => id.ToString())]));
                                }
                            }
                        }
                        structureList = retryStructureList;
                    }
                    allTypesLoaded = allTypesLoaded && structureList.Count == 0;
                }
                catch (ServiceResultException sre)
                {
                    m_logger.LogError(
                        sre,
                        "Unexpected error processing ditionary {DictionaryName}.",
                        dictionaryId.Value.Name);
                }
            }
            return allTypesLoaded;
        }

        /// <summary>
        /// Load all custom types with DataTypeDefinition into the type factory.
        /// </summary>
        /// <returns>true if all types were loaded, false otherwise</returns>
        private async Task<bool> LoadBaseDataTypesAsync(
            IList<INode> serverEnumTypes,
            IList<INode> serverStructTypes,
            CancellationToken ct = default)
        {
            IList<INode> enumTypesToDoList = [];
            IList<INode> structTypesToDoList = [];

            bool repeatDataTypeLoad;
            do
            {
                // strip known types
                serverEnumTypes = RemoveKnownTypes(serverEnumTypes);
                serverStructTypes = RemoveKnownTypes(serverStructTypes);

                repeatDataTypeLoad = false;
                try
                {
                    enumTypesToDoList = await LoadBaseEnumDataTypesAsync(serverEnumTypes, ct)
                        .ConfigureAwait(false);
                    structTypesToDoList = await LoadBaseStructureDataTypesAsync(
                        serverStructTypes,
                        ct)
                        .ConfigureAwait(false);
                }
                catch (DataTypeNotFoundException dtnfex)
                {
                    m_logger.LogWarning("Data type not found: {Message}", dtnfex.Message);
                    foreach (ExpandedNodeId nodeId in dtnfex.NodeIds.ToList())
                    {
                        // add missing types to list
                        INode? dataTypeNode = await m_complexTypeResolver.FindAsync(nodeId, ct)
                            .ConfigureAwait(false);
                        if (dataTypeNode != null)
                        {
                            await AddEnumerationOrStructureTypeAsync(
                                    dataTypeNode,
                                    serverEnumTypes,
                                    serverStructTypes,
                                    ct)
                                .ConfigureAwait(false);
                            repeatDataTypeLoad = true;
                        }
                        else
                        {
                            m_logger.LogWarning("Datatype {NodeId} was not found.", nodeId);
                        }
                    }
                }
            } while (repeatDataTypeLoad);

            // all types loaded
            if (enumTypesToDoList.Count == 0 && structTypesToDoList.Count == 0)
            {
                return true;
            }

            // Provide some diagnostics so users understand why types could not be serialized.
            if (enumTypesToDoList.Count > 0)
            {
                m_logger.LogWarning(
                    "{TodoCount} enum types could not be loaded from the server.",
                    enumTypesToDoList.Count);
                if (enumTypesToDoList.Count < 10)
                {
                    m_logger.LogInformation(
                        "Missing enum types: {MissingEnumTypes}",
                        string.Join(", ", enumTypesToDoList.Select(e => e.BrowseName)));
                }
            }
            if (structTypesToDoList.Count > 0)
            {
                m_logger.LogWarning(
                    "{TodoCount} structure types could not be loaded from the server.",
                    structTypesToDoList.Count);
                if (structTypesToDoList.Count < 10)
                {
                    m_logger.LogInformation(
                        "Missing structure types: {MissingStructureTypes}",
                        string.Join(", ", structTypesToDoList.Select(e => e.BrowseName)));
                }
            }
            return false;
        }

        /// <summary>
        /// Load all custom types with DataTypeDefinition into the type factory.
        /// </summary>
        /// <returns>true if all types were loaded, false otherwise</returns>
        private async Task<IList<INode>> LoadBaseEnumDataTypesAsync(
            IList<INode> serverEnumTypes,
            CancellationToken ct = default)
        {
            // strip known types
            serverEnumTypes = RemoveKnownTypes(serverEnumTypes);

            // add new enum Types for all namespaces
            var enumTypesToDoList = new List<INode>();
            int namespaceCount = m_complexTypeResolver.NamespaceUris.Count;

            // create enumeration types for all namespaces
            for (uint i = 0; i < namespaceCount; i++)
            {
                IComplexTypeBuilder? complexTypeBuilder = null;
                var enumTypes = serverEnumTypes.Where(node => node.NodeId.NamespaceIndex == i)
                    .ToList();
                if (enumTypes.Count != 0)
                {
                    if (complexTypeBuilder == null)
                    {
                        string? targetNamespace = m_complexTypeResolver.NamespaceUris.GetString(i);
                        // GetString returns null only for unknown indexes; namespace index i
                        // is iterated over the live NamespaceUris collection so a registered
                        // namespace always exists at this index.
                        complexTypeBuilder = m_complexTypeBuilderFactory.Create(
                            targetNamespace!,
                            (int)i);
                    }
                    foreach (INode enumType in enumTypes)
                    {
                        IEnumeratedType? newType = await AddEnumTypeAsync(
                            complexTypeBuilder,
                            enumType as DataTypeNode,
                            ct)
                            .ConfigureAwait(false);
                        if (newType != null)
                        {
                            // match namespace and add to type factory
                            AddEncodeableType(enumType.NodeId, newType);
                        }
                        else
                        {
                            enumTypesToDoList.Add(enumType);
                        }
                    }
                }
            }

            // all types loaded, return remaining
            return enumTypesToDoList;
        }

        /// <summary>
        /// Load all structure custom types with DataTypeDefinition into the type factory.
        /// </summary>
        /// <returns>true if all types were loaded, false otherwise</returns>
        private async Task<IList<INode>> LoadBaseStructureDataTypesAsync(
            IList<INode> serverStructTypes,
            CancellationToken ct = default)
        {
            // strip known types
            serverStructTypes = RemoveKnownTypes(serverStructTypes);

            // add new enum Types for all namespaces
            int namespaceCount = m_complexTypeResolver.NamespaceUris.Count;

            bool retryAddStructType;
            var structTypesToDoList = new List<INode>();
            IList<INode> structTypesWorkList = serverStructTypes;

            // allow the loader to cache the encodings
            ArrayOf<ExpandedNodeId> nodeIds = [.. serverStructTypes.Select(n => n.NodeId)];
            _ = await m_complexTypeResolver
                .BrowseForEncodingsAsync(nodeIds, s_supportedEncodings, ct)
                .ConfigureAwait(false);

            // create structured types for all namespaces
            int loopCounter = 0;
            do
            {
                loopCounter++;
                retryAddStructType = false;
                for (uint i = 0; i < namespaceCount; i++)
                {
                    IComplexTypeBuilder? complexTypeBuilder = null;
                    var structTypes = structTypesWorkList.Where(
                        node => node.NodeId.NamespaceIndex == i).ToList();
                    if (structTypes.Count != 0)
                    {
                        if (complexTypeBuilder == null)
                        {
                            string? targetNamespace = m_complexTypeResolver.NamespaceUris
                                .GetString(i);
                            // GetString returns null only for unknown indexes; namespace index i
                            // iterates over the live NamespaceUris collection so a registered
                            // namespace always exists at this index.
                            complexTypeBuilder = m_complexTypeBuilderFactory.Create(
                                targetNamespace!,
                                (int)i);
                        }
                        foreach (INode? structType in structTypes)
                        {
                            IType? newType = null;
                            if (structType is not DataTypeNode dataTypeNode ||
                                dataTypeNode.IsAbstract)
                            {
                                continue;
                            }

                            StructureDefinition? structureDefinition = GetStructureDefinition(
                                dataTypeNode);
                            if (structureDefinition != null)
                            {
                                (
                                    ArrayOf<NodeId> encodingIds,
                                    ExpandedNodeId binaryEncodingId,
                                    ExpandedNodeId xmlEncodingId
                                ) = await m_complexTypeResolver
                                    .BrowseForEncodingsAsync(
                                        structType.NodeId,
                                        s_supportedEncodings,
                                        ct)
                                    .ConfigureAwait(false);
                                try
                                {
                                    ExpandedNodeId typeId = NormalizeExpandedNodeId(
                                        structType.NodeId);
                                    List<ExpandedNodeId>? missingTypeIds;
                                    (newType, missingTypeIds) = await AddStructuredTypeAsync(
                                            complexTypeBuilder,
                                            structureDefinition,
                                            dataTypeNode.BrowseName,
                                            typeId,
                                            binaryEncodingId,
                                            xmlEncodingId,
                                            ct)
                                        .ConfigureAwait(false);

                                    if (missingTypeIds?.Count > 0)
                                    {
                                        var missingTypeIdsFromWorkList
                                            = new List<ExpandedNodeId>();
                                        foreach (ExpandedNodeId missingTypeId in missingTypeIds)
                                        {
                                            INode? typeMatch = structTypesWorkList
                                                .FirstOrDefault(n =>
                                                    n.NodeId == missingTypeId);
                                            if (typeMatch == null)
                                            {
                                                missingTypeIdsFromWorkList.Add(missingTypeId);
                                            }
                                        }
                                        foreach (ExpandedNodeId id in missingTypeIdsFromWorkList)
                                        {
                                            if (!structTypesToDoList.Any(n => n.NodeId == id))
                                            {
                                                INode? todo = await m_complexTypeResolver.FindAsync(id, ct)
                                                        .ConfigureAwait(false);
                                                if (todo != null)
                                                {
                                                    structTypesToDoList.Add(todo);
                                                    retryAddStructType = true;
                                                }
                                            }
                                            else
                                            {
                                                retryAddStructType = true;
                                            }
                                        }
                                    }
                                }
                                catch (DataTypeNotSupportedException)
                                {
                                    m_logger.LogError(
                                        "Skipped the type definition of {DataType} because it is not supported.",
                                        dataTypeNode.BrowseName.Name);
                                }
                                catch
                                {
                                    // creating the new type failed, likely a missing dependency, retry later
                                    retryAddStructType = true;
                                }

                                if (newType != null)
                                {
                                    foreach (NodeId encodingId in encodingIds)
                                    {
                                        AddEncodeableType(encodingId, newType);
                                    }
                                    AddEncodeableType(structType.NodeId, newType);
                                }
                            }

                            if (newType == null)
                            {
                                if (structureDefinition != null)
                                {
                                    structTypesToDoList.Add(structType);
                                    retryAddStructType = true;
                                }
                                else if (await IsOptionSetSubtypeAsync(structType.NodeId, ct)
                                    .ConfigureAwait(false))
                                {
                                    // Concrete Structure-backed sub-type of the
                                    // abstract OptionSet DataType. The wire
                                    // format is the inherited Value/ValidBits
                                    // ByteStrings; field semantics come from an
                                    // EnumDefinition or the OptionSetValues
                                    // property.
                                    (
                                        ArrayOf<NodeId> encodingIds,
                                        ExpandedNodeId binaryEncodingId,
                                        ExpandedNodeId xmlEncodingId
                                    ) = await m_complexTypeResolver
                                        .BrowseForEncodingsAsync(
                                            structType.NodeId,
                                            s_supportedEncodings,
                                            ct)
                                        .ConfigureAwait(false);
                                    ExpandedNodeId typeId = NormalizeExpandedNodeId(
                                        structType.NodeId);
                                    newType = await AddOptionSetTypeAsync(
                                            complexTypeBuilder,
                                            dataTypeNode,
                                            typeId,
                                            binaryEncodingId,
                                            xmlEncodingId,
                                            ct)
                                        .ConfigureAwait(false);
                                    if (newType != null)
                                    {
                                        foreach (NodeId encodingId in encodingIds)
                                        {
                                            AddEncodeableType(encodingId, newType);
                                        }
                                        AddEncodeableType(structType.NodeId, newType);
                                    }
                                    else
                                    {
                                        m_logger.LogInformation(
                                            "Skipped OptionSet sub-type {DataType} because no EnumDefinition or OptionSetValues property was found.",
                                            dataTypeNode.BrowseName.Name);
                                    }
                                }
                                else
                                {
                                    // A non-abstract Structure subtype without a valid
                                    // DataTypeDefinition cannot be materialized by this path.
                                    // Skip silently so the overall load is not marked as failed
                                    // when the server exposes such unresolvable types.
                                    m_logger.LogInformation(
                                        "Skipped the type definition of {DataType} because no DataTypeDefinition is available.",
                                        dataTypeNode.BrowseName.Name);
                                }
                            }
                        }
                    }
                }
                // due to type dependencies, retry missing types until there is no more progress
                if (retryAddStructType &&
                    structTypesWorkList.Count != structTypesToDoList.Count &&
                    loopCounter < MaxLoopCount)
                {
                    structTypesWorkList = structTypesToDoList;
                    structTypesToDoList = [];
                }
                else
                {
                    break;
                }
            } while (retryAddStructType);

            // all types loaded
            return structTypesToDoList;
        }

        /// <summary>
        /// Return the structure definition from a DataTypeDefinition
        /// </summary>
        private static StructureDefinition? GetStructureDefinition(DataTypeNode dataTypeNode)
        {
            if (dataTypeNode.DataTypeDefinition.TryGetValue(
                out StructureDefinition? structureDefinition))
            {
                // Validate the DataTypeDefinition structure,
                // but not if the type is supported
                // TryGetValue<T> returning true implies structureDefinition is non-null
                // but its signature lacks [NotNullWhen(true)].
                if (structureDefinition!.Fields.IsNull ||
                    structureDefinition.BaseDataType.IsNull ||
                    structureDefinition.BinaryEncodingId.IsNull)
                {
                    return null;
                }
                // Validate the structure according to Part3, Table 36
                foreach (StructureField field in structureDefinition.Fields)
                {
                    // validate if the DataTypeDefinition is correctly
                    // filled out, some servers don't do it yet...
                    if (field.BinaryEncodingId.IsNull ||
                        field.DataType.IsNull ||
                        field.TypeId.IsNull ||
                        field.Name == null)
                    {
                        return null;
                    }
                    if (field.ValueRank is not (ValueRanks.Scalar or >= ValueRanks.OneDimension))
                    {
                        return null;
                    }
                }
                return structureDefinition;
            }
            return null;
        }

        /// <summary>
        /// Helper to ensure the expanded nodeId contains a valid namespaceUri.
        /// </summary>
        /// <param name="expandedNodeId">The expanded nodeId.</param>
        /// <returns>The normalized expanded nodeId.</returns>
        private ExpandedNodeId NormalizeExpandedNodeId(ExpandedNodeId expandedNodeId)
        {
            var nodeId = ExpandedNodeId.ToNodeId(
                expandedNodeId,
                m_complexTypeResolver.NamespaceUris);
            return NodeId.ToExpandedNodeId(nodeId, m_complexTypeResolver.NamespaceUris);
        }

        /// <summary>
        /// Add data type to enumeration or structure base type list depending on supertype.
        /// </summary>
        /// <exception cref="ServiceResultException"></exception>
        private async Task AddEnumerationOrStructureTypeAsync(
            INode dataTypeNode,
            IList<INode> serverEnumTypes,
            IList<INode> serverStructTypes,
            CancellationToken ct = default)
        {
            var superType = ExpandedNodeId.ToNodeId(
                dataTypeNode.NodeId,
                m_complexTypeResolver.NamespaceUris);
            while (true)
            {
                superType = await m_complexTypeResolver.FindSuperTypeAsync(superType, ct)
                    .ConfigureAwait(false);
                if (superType.IsNull)
                {
                    throw new ServiceResultException(
                        StatusCodes.BadNodeIdInvalid,
                        $"SuperType for {dataTypeNode.NodeId} not found.");
                }
                if (superType == DataTypeIds.Enumeration)
                {
                    serverEnumTypes.Insert(0, dataTypeNode);
                    break;
                }
                else if (superType == DataTypeIds.Structure)
                {
                    serverStructTypes.Insert(0, dataTypeNode);
                    break;
                }
                else if (TypeInfo.GetBuiltInType(superType) != BuiltInType.Null)
                {
                    break;
                }
            }
        }

        /// <summary>
        /// Remove all known types in the type factory from a list of DataType nodes.
        /// </summary>
        private List<INode> RemoveKnownTypes(IList<INode> nodeList)
        {
            return [.. nodeList.Where(node => GetSystemType(node.NodeId) == null).Distinct()];
        }

        /// <summary>
        /// Get the factory system type for an expanded node id.
        /// </summary>
        private IType? GetSystemType(ExpandedNodeId nodeId)
        {
            if (!nodeId.IsAbsolute)
            {
                nodeId = NormalizeExpandedNodeId(nodeId);
            }

            // TODO: get everything including system types.
            // return TypeInfo.GetSystemType(nodeId, m_complexTypeResolver.FactoryBuilder);

            if (m_complexTypeResolver.FactoryBuilder.TryGetType(nodeId, out IType? type))
            {
                return type;
            }
            return null;
        }

        /// <summary>
        /// Add an enum type defined in a binary schema dictionary.
        /// </summary>
        private async Task AddEnumTypesAsync(
            IComplexTypeBuilder complexTypeBuilder,
            Dictionary<XmlQualifiedName, NodeId> typeDictionary,
            IList<Schema.Binary.TypeDescription> enumList,
            IList<INode> allEnumerationTypes,
            IList<INode> enumerationTypes,
            CancellationToken ct = default)
        {
            foreach (Schema.Binary.TypeDescription item in enumList)
            {
                IType? newType = null;
                DataTypeNode? enumDescription = null;
                var enumType =
                    enumerationTypes.FirstOrDefault(node =>
                        node.BrowseName.Name == item.Name &&
                        (
                            node.BrowseName.NamespaceIndex == complexTypeBuilder
                                .TargetNamespaceIndex ||
                            complexTypeBuilder.TargetNamespaceIndex == -1)
                    ) as DataTypeNode;
                if (enumType != null)
                {
                    enumDescription = enumType;

                    // try dictionary enum definition
                    if (item is Schema.Binary.EnumeratedType enumeratedObject)
                    {
                        // 1. use Dictionary entry
                        // EnumeratedType.Name is nullable on the imported schema; valid OPC UA
                        // enumerated types always carry a name.
                        var enumDefinition = enumeratedObject.ToEnumDefinition(
                            enumeratedObject.Name!);

                        if (enumDefinition != null)
                        {
                            // Add EnumDefinition to cache
                            m_dataTypeDefinitionCache[enumType.NodeId] = enumDefinition;

                            newType = complexTypeBuilder.AddEnumType(
                                QualifiedName.From(enumeratedObject.Name!),
                                enumDefinition);
                        }
                    }
                    if (newType == null)
                    {
                        // 2. use node cache
                        var dataTypeNode =
                            await m_complexTypeResolver.FindAsync(enumType.NodeId, ct)
                                .ConfigureAwait(false) as
                            DataTypeNode;
                        newType = await AddEnumTypeAsync(complexTypeBuilder, dataTypeNode, ct)
                            .ConfigureAwait(false);
                    }
                }
                else
                {
                    enumDescription =
                        allEnumerationTypes.FirstOrDefault(node =>
                            node.BrowseName.Name == item.Name &&
                            (
                                node.BrowseName.NamespaceIndex == complexTypeBuilder
                                    .TargetNamespaceIndex ||
                                complexTypeBuilder.TargetNamespaceIndex == -1)
                        ) as DataTypeNode;
                }
                if (enumDescription != null)
                {
                    var qName = new XmlQualifiedName(item.Name, complexTypeBuilder.TargetNamespace);
                    typeDictionary[qName] = enumDescription.NodeId;
                }
                if (newType != null)
                {
                    // match namespace and add to type factory
                    AddEncodeableType(enumType?.NodeId ?? default, newType);
                }
            }
        }

        /// <summary>
        /// Helper to add new type with absolute ExpandedNodeId.
        /// </summary>
        private void AddEncodeableType(ExpandedNodeId nodeId, IType type)
        {
            if (nodeId.IsNull || type == null)
            {
                return;
            }

            ExpandedNodeId internalNodeId = NormalizeExpandedNodeId(nodeId);
            m_logger.LogDebug("Adding Type {DataType} as: {NodeId}", type.XmlName, internalNodeId);

            switch (type)
            {
                case IEncodeableType encodeableType:
                    m_complexTypeResolver.FactoryBuilder.AddEncodeableType(
                        internalNodeId,
                        encodeableType);
                    break;
                case IEnumeratedType enumeratedType:
                    m_complexTypeResolver.FactoryBuilder.AddEnumeratedType(
                        internalNodeId,
                        enumeratedType);
                    break;
            }
        }

        /// <summary>
        /// Add an enum type defined in a DataType node.
        /// </summary>
        private async Task<IEnumeratedType?> AddEnumTypeAsync(
            IComplexTypeBuilder complexTypeBuilder,
            DataTypeNode? enumTypeNode,
            CancellationToken ct = default)
        {
            IEnumeratedType? newType = null;
            if (enumTypeNode != null)
            {
                QualifiedName name = enumTypeNode.BrowseName;

                // 1. use DataTypeDefinition
                if (DisableDataTypeDefinition ||
                    !enumTypeNode.DataTypeDefinition.TryGetValue(
                        out EnumDefinition? enumDefinition))
                {
                    // browse for EnumFields or EnumStrings property
                    Variant enumTypeArray = await m_complexTypeResolver
                        .GetEnumTypeArrayAsync(enumTypeNode.NodeId, ct)
                        .ConfigureAwait(false);
                    if (enumTypeArray.TryGetValue(out ArrayOf<ExtensionObject> extensionObject))
                    {
                        // 2. use EnumValues
                        // QualifiedName.Name is nullable but the enum type was resolved by
                        // browse name and always carries a non-null Name here.
                        enumDefinition = extensionObject.ToEnumDefinition(name.Name!);
                    }
                    else if (enumTypeArray.TryGetValue(out ArrayOf<LocalizedText> localizedText))
                    {
                        // 3. use EnumStrings
                        // See note above: name.Name is required.
                        enumDefinition = localizedText.ToEnumDefinition(name.Name!);
                    }
                    else
                    {
                        // 4. Give up
                        enumDefinition = null;
                    }
                }

                if (enumDefinition != null)
                {
                    // Add EnumDefinition to cache
                    m_dataTypeDefinitionCache[enumTypeNode.NodeId] = enumDefinition;

                    newType = complexTypeBuilder.AddEnumType(name, enumDefinition);
                }
            }
            return newType;
        }

        /// <summary>
        /// Add an OptionSet type defined in a DataType node whose wire
        /// format is the inherited <c>Value</c>/<c>ValidBits</c>
        /// ByteStrings of the abstract <c>OptionSet</c> DataType.
        /// </summary>
        private async Task<IEncodeableType?> AddOptionSetTypeAsync(
            IComplexTypeBuilder complexTypeBuilder,
            DataTypeNode dataTypeNode,
            ExpandedNodeId typeId,
            ExpandedNodeId binaryEncodingId,
            ExpandedNodeId xmlEncodingId,
            CancellationToken ct = default)
        {
            QualifiedName name = dataTypeNode.BrowseName;

            // 1. use DataTypeDefinition
            if (DisableDataTypeDefinition ||
                !dataTypeNode.DataTypeDefinition.TryGetValue(
                    out EnumDefinition? enumDefinition))
            {
                // 2. fall back to OptionSetValues property (LocalizedText[])
                Variant enumTypeArray = await m_complexTypeResolver
                    .GetEnumTypeArrayAsync(dataTypeNode.NodeId, ct)
                    .ConfigureAwait(false);
                if (enumTypeArray.TryGetValue(out ArrayOf<LocalizedText> localizedText))
                {
                    // QualifiedName.Name is nullable but the option-set type was resolved by
                    // browse name and always carries a non-null Name here.
                    enumDefinition = localizedText.ToEnumDefinition(name.Name!);
                }
                else
                {
                    enumDefinition = null;
                }
            }

            if (enumDefinition == null)
            {
                return null;
            }

            // Mark as OptionSet (bit positions rather than ordinal values).
            enumDefinition.IsOptionSet = true;

            // Add EnumDefinition to cache
            m_dataTypeDefinitionCache[dataTypeNode.NodeId] = enumDefinition;

            return complexTypeBuilder.AddOptionSetType(
                name,
                typeId,
                binaryEncodingId,
                xmlEncodingId,
                enumDefinition);
        }

        /// <summary>
        /// Returns <c>true</c> if <paramref name="dataTypeId"/> is a
        /// concrete sub-type of the abstract <c>OptionSet</c> DataType.
        /// </summary>
        private async Task<bool> IsOptionSetSubtypeAsync(
            ExpandedNodeId dataTypeId,
            CancellationToken ct)
        {
            var superType = ExpandedNodeId.ToNodeId(
                dataTypeId,
                m_complexTypeResolver.NamespaceUris);
            while (!superType.IsNull)
            {
                superType = await m_complexTypeResolver
                    .FindSuperTypeAsync(superType, ct)
                    .ConfigureAwait(false);
                if (superType == DataTypeIds.OptionSet)
                {
                    return true;
                }
                if (superType == DataTypeIds.Structure ||
                    superType == DataTypeIds.Enumeration ||
                    TypeInfo.GetBuiltInType(superType) != BuiltInType.Null)
                {
                    return false;
                }
            }
            return false;
        }

        /// <summary>
        /// Add structured type to assembly with StructureDefinition.
        /// </summary>
        private async Task<(IEncodeableType? structureType, List<ExpandedNodeId>? missingTypes)> AddStructuredTypeAsync(
            IComplexTypeBuilder complexTypeBuilder,
            StructureDefinition structureDefinition,
            QualifiedName typeName,
            ExpandedNodeId complexTypeId,
            ExpandedNodeId binaryEncodingId,
            ExpandedNodeId xmlEncodingId,
            CancellationToken ct = default)
        {
            // init missing type list
            List<ExpandedNodeId>? missingTypes = null;

            var localDataTypeId = ExpandedNodeId.ToNodeId(
                complexTypeId,
                m_complexTypeResolver.NamespaceUris);
            bool allowSubTypes = IsAllowSubTypes(structureDefinition);

            // check all types
            var typeList = new List<IType?>();
            foreach (StructureField field in structureDefinition.Fields.ToList())
            {
                IType? fieldType = await GetFieldTypeAsync(field, allowSubTypes, ct).ConfigureAwait(false);
                if (fieldType?.Type == null &&
                    !IsRecursiveDataType(localDataTypeId, field.DataType))
                {
                    if (missingTypes == null)
                    {
                        missingTypes = [field.DataType];
                    }
                    else if (!missingTypes.Contains(field.DataType))
                    {
                        missingTypes.Add(field.DataType);
                    }
                }
                else
                {
                    typeList.Add(fieldType);
                }
            }

            if (missingTypes != null)
            {
                return (null, missingTypes);
            }

            // Add StructureDefinition to cache
            m_dataTypeDefinitionCache[localDataTypeId] = structureDefinition;

            IComplexTypeFieldBuilder fieldBuilder = complexTypeBuilder.AddStructuredType(
                typeName,
                structureDefinition);

            fieldBuilder.AddTypeIdAttribute(complexTypeId, binaryEncodingId, xmlEncodingId);

            int order = 1;
            List<IType?>.Enumerator typeListEnumerator = typeList.GetEnumerator();
            foreach (StructureField field in structureDefinition.Fields)
            {
                _ = typeListEnumerator.MoveNext();

                // check for recursive data type:
                //    field has the same data type as the parent structure
                var nodeId = ExpandedNodeId.ToNodeId(
                    complexTypeId,
                    m_complexTypeResolver.NamespaceUris);
                bool isRecursiveDataType = IsRecursiveDataType(nodeId, field.DataType);
                if (isRecursiveDataType)
                {
                    fieldBuilder.AddField(
                        field,
                        fieldBuilder.GetStructureType(),
                        order,
                        allowSubTypes);
                }
                else
                {
                    fieldBuilder.AddField(
                        field,
                        typeListEnumerator.Current,
                        order,
                        allowSubTypes);
                }
                order++;
            }

            return (fieldBuilder.CreateType(), missingTypes);
        }

        private static bool IsAllowSubTypes(StructureDefinition structureDefinition)
        {
            switch (structureDefinition.StructureType)
            {
                case StructureType.UnionWithSubtypedValues:
                case StructureType.StructureWithSubtypedValues:
                    return true;
                case StructureType.Structure:
                case StructureType.StructureWithOptionalFields:
                case StructureType.Union:
                    return false;
                default:
                    Debug.Fail($"Unexpected StructureType {structureDefinition.StructureType}.");
                    return false;
            }
        }

        private async Task<bool> IsAbstractTypeAsync(
            NodeId fieldDataType,
            CancellationToken ct = default)
        {
            var dataTypeNode =
                await m_complexTypeResolver.FindAsync(fieldDataType, ct)
                    .ConfigureAwait(false) as DataTypeNode;
            return dataTypeNode?.IsAbstract == true;
        }

        private static bool IsRecursiveDataType(NodeId structureDataType, NodeId fieldDataType)
        {
            return fieldDataType.Equals(structureDataType);
        }

        /// <summary>
        /// Determine the type of a field in a StructureField definition.
        /// </summary>
        /// <exception cref="DataTypeNotSupportedException"></exception>
        private async Task<IType?> GetFieldTypeAsync(
            StructureField field,
            bool allowSubTypes,
            CancellationToken ct = default)
        {
            if (field.ValueRank is not ValueRanks.Scalar and < ValueRanks.OneDimension)
            {
                throw new DataTypeNotSupportedException(
                    field.DataType,
                    $"The ValueRank {field.ValueRank} is not supported.");
            }

            IType? fieldType =
                field.DataType.NamespaceIndex == 0
                    ? TypeInfo.GetSystemType(field.DataType, m_complexTypeResolver.FactoryBuilder)
                    : GetSystemType(field.DataType);

            if (fieldType == null)
            {
                NodeId superType = await GetBuiltInSuperTypeAsync(
                    field.DataType,
                    allowSubTypes,
                    field.IsOptional,
                    ct)
                    .ConfigureAwait(false);
                if (!superType.IsNull)
                {
                    field.DataType = superType;
                    return await GetFieldTypeAsync(field, allowSubTypes, ct).ConfigureAwait(false);
                }
                return null;
            }
            return fieldType;
        }

        /// <summary>
        /// Find superType for a datatype.
        /// </summary>
        /// <exception cref="DataTypeNotSupportedException"></exception>
        private async Task<NodeId> GetBuiltInSuperTypeAsync(
            NodeId dataType,
            bool allowSubTypes,
            bool isOptional,
            CancellationToken ct = default)
        {
            const int maxSuperTypes = 100;

            int iterations = 0;
            NodeId superType = dataType;
            while (iterations++ < maxSuperTypes)
            {
                superType = await m_complexTypeResolver.FindSuperTypeAsync(superType, ct)
                    .ConfigureAwait(false);
                if (superType.IsNull)
                {
                    return default;
                }
                if (superType.NamespaceIndex == 0)
                {
                    if (superType == DataTypeIds.Enumeration && dataType.NamespaceIndex == 0)
                    {
                        // enumerations of namespace 0 in a structure
                        // which are not in the type system are encoded as UInt32
                        return DataTypeIds.UInt32;
                    }
                    if (superType == DataTypeIds.Enumeration)
                    {
                        return default;
                    }
                    else if (superType == DataTypeIds.Structure)
                    {
                        // throw on invalid combinations of allowSubTypes, isOptional and abstract types
                        // in such case the encoding as ExtensionObject is undetermined and not specified
                        if ((dataType != DataTypeIds.Structure) &&
                            ((allowSubTypes && !isOptional) || !allowSubTypes) &&
                            await IsAbstractTypeAsync(dataType, ct).ConfigureAwait(false))
                        {
                            throw new DataTypeNotSupportedException(
                                "Invalid definition of a abstract subtype of a structure.");
                        }

                        if (allowSubTypes && isOptional)
                        {
                            return superType;
                        }
                        return default;
                    }
                    // end search if a valid BuiltInType is found. Treat type as opaque.
                    else if (superType.TryGetValue(out uint id) &&
                        id >= (uint)BuiltInType.Boolean &&
                        id <= (uint)BuiltInType.DiagnosticInfo)
                    {
                        return superType;
                    }
                    // no valid supertype found
                    else if (superType == DataTypeIds.BaseDataType)
                    {
                        break;
                    }
                }
            }
            return default;
        }

        /// <summary>
        /// Split the dictionary types into a list of structures and enumerations.
        /// Sort the structures by dependencies, with structures with dependent
        /// types at the end of the list, so they can be added to the factory in order.
        /// </summary>
        /// <exception cref="ServiceResultException"></exception>
        /// <exception cref="ArgumentException"></exception>
        private static void SplitAndSortDictionary(
            DataDictionary dictionary,
            List<Schema.Binary.TypeDescription> structureList,
            List<Schema.Binary.TypeDescription> enumList)
        {
            if (dictionary.TypeDictionary == null)
            {
                throw new ArgumentException("Type dictionary in dictionary was not validated");
            }

            // TypeDictionary.Items is nullable on the imported XSD type but the validation
            // at the top of this method (TypeDictionary != null) guarantees we have items
            // to iterate; an empty type dictionary is filtered by the caller.
            foreach (Schema.Binary.TypeDescription item in dictionary.TypeDictionary.Items!)
            {
                if (item is Schema.Binary.StructuredType structuredObject)
                {
                    // StructuredType.Field and FieldType.TypeName are both nullable on the
                    // imported schema; the dictionary loader rejects malformed entries before
                    // they reach this code, so the bangs reflect that lifecycle invariant.
                    IEnumerable<Schema.Binary.FieldType> dependentFields = structuredObject.Field!
                        .Where(f =>
                            f.TypeName!.Namespace == dictionary.TypeDictionary.TargetNamespace);
                    if (!dependentFields.Any())
                    {
                        structureList.Insert(0, structuredObject);
                    }
                    else
                    {
                        structureList.Add(structuredObject);
                    }
                }
                else if (item is Schema.Binary.EnumeratedType)
                {
                    enumList.Add(item);
                }
                else if (item is Schema.Binary.OpaqueType)
                {
                    // no need to handle Opaque types
                }
                else
                {
                    throw ServiceResultException.Unexpected(
                        "Unexpected Type in binary schema: {0}.",
                        item.GetType().Name);
                }
            }
        }

        private readonly ILogger m_logger;
        private readonly IComplexTypeResolver m_complexTypeResolver;
        private readonly IComplexTypeFactory m_complexTypeBuilderFactory;
        private readonly NodeIdDictionary<DataTypeDefinition> m_dataTypeDefinitionCache = [];

        private static readonly string[] s_supportedEncodings =
        [
            BrowseNames.DefaultBinary,
            BrowseNames.DefaultXml
        ];
    }
}