// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Globalization;
using System.Reflection;
using System.Runtime.CompilerServices;
using System.Threading;
using System.Xml;
using System.Xml.Schema;
using System.Xml.Serialization;
 
namespace System.Xml.Serialization
{
    ///<internalonly/>
    /// <devdoc>
    ///    <para>[To be supplied.]</para>
    /// </devdoc>
    public class XmlReflectionImporter
    {
        private readonly TypeScope _typeScope;
        private readonly XmlAttributeOverrides _attributeOverrides;
        private readonly XmlAttributes _defaultAttributes = new XmlAttributes();
        private readonly NameTable _types = new NameTable();      // xmltypename + xmlns -> Mapping
        private readonly NameTable _nullables = new NameTable();  // xmltypename + xmlns -> NullableMapping
        private readonly NameTable _elements = new NameTable();   // xmlelementname + xmlns -> ElementAccessor
        private NameTable? _xsdAttributes;   // xmlattributetname + xmlns -> AttributeAccessor
        private Hashtable? _specials;   // type -> SpecialMapping
        private readonly Hashtable _anonymous = new Hashtable();   // type -> AnonymousMapping
        private NameTable? _serializables;  // type name --> new SerializableMapping
        private StructMapping? _root;
        private readonly string _defaultNs;
        private readonly ModelScope _modelScope;
        private int _arrayNestingLevel;
        private XmlArrayItemAttributes? _savedArrayItemAttributes;
        private string? _savedArrayNamespace;
        private int _choiceNum = 1;
 
        private enum ImportContext
        {
            Text,
            Attribute,
            Element
        }
 
        /// <devdoc>
        ///    <para>[To be supplied.]</para>
        /// </devdoc>
        public XmlReflectionImporter() : this(null, null)
        {
        }
 
        /// <devdoc>
        ///    <para>[To be supplied.]</para>
        /// </devdoc>
        public XmlReflectionImporter(string? defaultNamespace) : this(null, defaultNamespace)
        {
        }
 
        /// <devdoc>
        ///    <para>[To be supplied.]</para>
        /// </devdoc>
        public XmlReflectionImporter(XmlAttributeOverrides? attributeOverrides) : this(attributeOverrides, null)
        {
        }
 
        /// <devdoc>
        ///    <para>[To be supplied.]</para>
        /// </devdoc>
        public XmlReflectionImporter(XmlAttributeOverrides? attributeOverrides, string? defaultNamespace)
        {
            _defaultNs = defaultNamespace ?? string.Empty;
            _attributeOverrides = attributeOverrides ?? new XmlAttributeOverrides();
            _typeScope = new TypeScope();
            _modelScope = new ModelScope(_typeScope);
        }
 
        /// <devdoc>
        ///    <para>[To be supplied.]</para>
        /// </devdoc>
        [RequiresUnreferencedCode(XmlSerializer.TrimSerializationWarning)]
        public void IncludeTypes(ICustomAttributeProvider provider)
        {
            IncludeTypes(provider, new RecursionLimiter());
        }
 
        [RequiresUnreferencedCode("calls IncludeType")]
        private void IncludeTypes(ICustomAttributeProvider provider, RecursionLimiter limiter)
        {
            object[] attrs = provider.GetCustomAttributes(typeof(XmlIncludeAttribute), false);
            for (int i = 0; i < attrs.Length; i++)
            {
                Type type = ((XmlIncludeAttribute)attrs[i]).Type!;
                IncludeType(type, limiter);
            }
        }
 
        /// <devdoc>
        ///    <para>[To be supplied.]</para>
        /// </devdoc>
        [RequiresUnreferencedCode(XmlSerializer.TrimSerializationWarning)]
        public void IncludeType(Type type)
        {
            IncludeType(type, new RecursionLimiter());
        }
 
        [RequiresUnreferencedCode("calls ImportTypeMapping")]
        private void IncludeType(Type type, RecursionLimiter limiter)
        {
            int previousNestingLevel = _arrayNestingLevel;
            XmlArrayItemAttributes? previousArrayItemAttributes = _savedArrayItemAttributes;
            string? previousArrayNamespace = _savedArrayNamespace;
            _arrayNestingLevel = 0;
            _savedArrayItemAttributes = null;
            _savedArrayNamespace = null;
 
            TypeMapping mapping = ImportTypeMapping(_modelScope.GetTypeModel(type), _defaultNs, ImportContext.Element, string.Empty, null, limiter);
            if (mapping.IsAnonymousType && !mapping.TypeDesc!.IsSpecial)
            {
                //XmlAnonymousInclude=Cannot include anonymous type '{0}'.
                throw new InvalidOperationException(SR.Format(SR.XmlAnonymousInclude, type.FullName));
            }
            _arrayNestingLevel = previousNestingLevel;
            _savedArrayItemAttributes = previousArrayItemAttributes;
            _savedArrayNamespace = previousArrayNamespace;
        }
 
        /// <devdoc>
        ///    <para>[To be supplied.]</para>
        /// </devdoc>
        [RequiresUnreferencedCode(XmlSerializer.TrimSerializationWarning)]
        public XmlTypeMapping ImportTypeMapping(Type type)
        {
            return ImportTypeMapping(type, null, null);
        }
 
        /// <devdoc>
        ///    <para>[To be supplied.]</para>
        /// </devdoc>
        [RequiresUnreferencedCode(XmlSerializer.TrimSerializationWarning)]
        public XmlTypeMapping ImportTypeMapping(Type type, string? defaultNamespace)
        {
            return ImportTypeMapping(type, null, defaultNamespace);
        }
 
        /// <devdoc>
        ///    <para>[To be supplied.]</para>
        /// </devdoc>
        [RequiresUnreferencedCode(XmlSerializer.TrimSerializationWarning)]
        public XmlTypeMapping ImportTypeMapping(Type type, XmlRootAttribute? root)
        {
            return ImportTypeMapping(type, root, null);
        }
 
        /// <devdoc>
        ///    <para>[To be supplied.]</para>
        /// </devdoc>
        [RequiresUnreferencedCode(XmlSerializer.TrimSerializationWarning)]
        public XmlTypeMapping ImportTypeMapping(Type type, XmlRootAttribute? root, string? defaultNamespace)
        {
            ArgumentNullException.ThrowIfNull(type);
 
            XmlTypeMapping xmlMapping = new XmlTypeMapping(_typeScope, ImportElement(_modelScope.GetTypeModel(type), root, defaultNamespace, new RecursionLimiter()));
            xmlMapping.SetKeyInternal(XmlMapping.GenerateKey(type, root, defaultNamespace));
            xmlMapping.GenerateSerializer = true;
            return xmlMapping;
        }
 
        /// <devdoc>
        ///    <para>[To be supplied.]</para>
        /// </devdoc>
        [RequiresUnreferencedCode(XmlSerializer.TrimSerializationWarning)]
        public XmlMembersMapping ImportMembersMapping(string? elementName, string? ns, XmlReflectionMember[] members, bool hasWrapperElement)
        {
            return ImportMembersMapping(elementName, ns, members, hasWrapperElement, false);
        }
 
        /// <devdoc>
        ///    <para>[To be supplied.]</para>
        /// </devdoc>
        [RequiresUnreferencedCode(XmlSerializer.TrimSerializationWarning)]
        public XmlMembersMapping ImportMembersMapping(string? elementName, string? ns, XmlReflectionMember[] members, bool hasWrapperElement, bool rpc)
        {
            return ImportMembersMapping(elementName, ns, members, hasWrapperElement, rpc, false);
        }
 
        /// <devdoc>
        ///    <para>[To be supplied.]</para>
        /// </devdoc>
        ///
        [RequiresUnreferencedCode(XmlSerializer.TrimSerializationWarning)]
        public XmlMembersMapping ImportMembersMapping(string? elementName, string? ns, XmlReflectionMember[] members, bool hasWrapperElement, bool rpc, bool openModel)
        {
            return ImportMembersMapping(elementName, ns, members, hasWrapperElement, rpc, openModel, XmlMappingAccess.Read | XmlMappingAccess.Write);
        }
 
        /// <devdoc>
        ///    <para>[To be supplied.]</para>
        /// </devdoc>
        ///
        [RequiresUnreferencedCode(XmlSerializer.TrimSerializationWarning)]
        public XmlMembersMapping ImportMembersMapping(string? elementName, string? ns, XmlReflectionMember[] members, bool hasWrapperElement, bool rpc, bool openModel, XmlMappingAccess access)
        {
            ElementAccessor element = new ElementAccessor();
            element.Name = string.IsNullOrEmpty(elementName) ? elementName : XmlConvert.EncodeLocalName(elementName);
            element.Namespace = ns;
 
            MembersMapping membersMapping = ImportMembersMapping(members, ns, hasWrapperElement, rpc, openModel, new RecursionLimiter());
            element.Mapping = membersMapping;
            element.Form = XmlSchemaForm.Qualified;   // elements within soap:body are always qualified
            if (!rpc)
            {
                if (hasWrapperElement)
                    element = (ElementAccessor)ReconcileAccessor(element, _elements);
                else
                {
                    foreach (MemberMapping mapping in membersMapping.Members!)
                    {
                        if (mapping.Elements != null && mapping.Elements.Length > 0)
                        {
                            mapping.Elements[0] = (ElementAccessor)ReconcileAccessor(mapping.Elements[0], _elements);
                        }
                    }
                }
            }
            XmlMembersMapping xmlMapping = new XmlMembersMapping(_typeScope, element, access);
            xmlMapping.GenerateSerializer = true;
            return xmlMapping;
        }
 
        private XmlAttributes GetAttributes(Type type, bool canBeSimpleType)
        {
            XmlAttributes? attrs = _attributeOverrides[type];
            if (attrs != null) return attrs;
            if (canBeSimpleType && TypeScope.IsKnownType(type))
            {
                return _defaultAttributes;
            }
            return new XmlAttributes(type);
        }
 
        private XmlAttributes GetAttributes(MemberInfo memberInfo)
        {
            XmlAttributes? attrs = _attributeOverrides[memberInfo.DeclaringType!, memberInfo.Name];
            if (attrs != null) return attrs;
            return new XmlAttributes(memberInfo);
        }
 
        [RequiresUnreferencedCode("calls ImportTypeMapping")]
        private ElementAccessor ImportElement(TypeModel model, XmlRootAttribute? root, string? defaultNamespace, RecursionLimiter limiter)
        {
            XmlAttributes a = GetAttributes(model.Type, true);
 
            root ??= a.XmlRoot;
            string ns = root?.Namespace ?? defaultNamespace ?? _defaultNs;
 
            _arrayNestingLevel = -1;
            _savedArrayItemAttributes = null;
            _savedArrayNamespace = null;
            ElementAccessor element = CreateElementAccessor(ImportTypeMapping(model, ns, ImportContext.Element, string.Empty, a, limiter), ns);
 
            if (root != null)
            {
                if (root.ElementName.Length > 0)
                    element.Name = XmlConvert.EncodeLocalName(root.ElementName);
                if (root.GetIsNullableSpecified() && !root.IsNullable && model.TypeDesc.IsOptionalValue)
                    //XmlInvalidNotNullable=IsNullable may not be set to 'false' for a Nullable<{0}> type. Consider using '{0}' type or removing the IsNullable property from the XmlElement attribute.
                    throw new InvalidOperationException(SR.Format(SR.XmlInvalidNotNullable, model.TypeDesc.BaseTypeDesc!.FullName, "XmlRoot"));
                element.IsNullable = root.GetIsNullableSpecified() ? root.IsNullable : model.TypeDesc.IsNullable || model.TypeDesc.IsOptionalValue;
                CheckNullable(element.IsNullable, model.TypeDesc, element.Mapping!);
            }
            else
                element.IsNullable = model.TypeDesc.IsNullable || model.TypeDesc.IsOptionalValue;
            element.Form = XmlSchemaForm.Qualified;
            return (ElementAccessor)ReconcileAccessor(element, _elements);
        }
 
        private static string GetMappingName(Mapping mapping)
        {
            if (mapping is MembersMapping)
                return "(method)";
            else if (mapping is TypeMapping)
                return ((TypeMapping)mapping).TypeDesc!.FullName;
            else
                throw new ArgumentException(SR.XmlInternalError, nameof(mapping));
        }
 
        private ElementAccessor ReconcileLocalAccessor(ElementAccessor accessor, string? ns)
        {
            if (accessor.Namespace == ns) return accessor;
            return (ElementAccessor)ReconcileAccessor(accessor, _elements);
        }
 
        private Accessor ReconcileAccessor(Accessor accessor, NameTable accessors)
        {
            if (accessor.Any && accessor.Name.Length == 0)
                return accessor;
 
            Accessor? existing = (Accessor?)accessors[accessor.Name, accessor.Namespace];
            if (existing == null)
            {
                accessor.IsTopLevelInSchema = true;
                accessors.Add(accessor.Name, accessor.Namespace, accessor);
                return accessor;
            }
 
            if (existing.Mapping == accessor.Mapping)
                return existing;
 
            if (!(accessor.Mapping is MembersMapping) && !(existing.Mapping is MembersMapping))
            {
                if (accessor.Mapping!.TypeDesc == existing.Mapping!.TypeDesc
                    || (existing.Mapping is NullableMapping && accessor.Mapping.TypeDesc == ((NullableMapping)existing.Mapping).BaseMapping!.TypeDesc)
                    || (accessor.Mapping is NullableMapping && ((NullableMapping)accessor.Mapping).BaseMapping!.TypeDesc == existing.Mapping.TypeDesc))
                {
                    // need to compare default values
                    string? value1 = Convert.ToString(accessor.Default, CultureInfo.InvariantCulture);
                    string? value2 = Convert.ToString(existing.Default, CultureInfo.InvariantCulture);
                    if (value1 == value2)
                    {
                        return existing;
                    }
                    throw new InvalidOperationException(SR.Format(SR.XmlCannotReconcileAccessorDefault, accessor.Name, accessor.Namespace, value1, value2));
                }
            }
 
            if (accessor.Mapping is MembersMapping || existing.Mapping is MembersMapping)
                throw new InvalidOperationException(SR.Format(SR.XmlMethodTypeNameConflict, accessor.Name, accessor.Namespace));
 
            if (accessor.Mapping is ArrayMapping)
            {
                if (!(existing.Mapping is ArrayMapping))
                {
                    throw new InvalidOperationException(SR.Format(SR.XmlCannotReconcileAccessor, accessor.Name, accessor.Namespace, GetMappingName(existing.Mapping!), GetMappingName(accessor.Mapping)));
                }
                ArrayMapping mapping = (ArrayMapping)accessor.Mapping;
                ArrayMapping? existingMapping = mapping.IsAnonymousType ? null : (ArrayMapping?)_types[existing.Mapping.TypeName!, existing.Mapping.Namespace];
                ArrayMapping? first = existingMapping;
                while (existingMapping != null)
                {
                    if (existingMapping == accessor.Mapping)
                        return existing;
                    existingMapping = existingMapping.Next;
                }
                mapping.Next = first;
                if (!mapping.IsAnonymousType)
                    _types[existing.Mapping.TypeName!, existing.Mapping.Namespace] = mapping;
                return existing;
            }
            if (accessor is AttributeAccessor)
                throw new InvalidOperationException(SR.Format(SR.XmlCannotReconcileAttributeAccessor, accessor.Name, accessor.Namespace, GetMappingName(existing.Mapping!), GetMappingName(accessor.Mapping!)));
            else
                throw new InvalidOperationException(SR.Format(SR.XmlCannotReconcileAccessor, accessor.Name, accessor.Namespace, GetMappingName(existing.Mapping!), GetMappingName(accessor.Mapping!)));
        }
 
        private static InvalidOperationException CreateReflectionException(string context, Exception e)
        {
            return new InvalidOperationException(SR.Format(SR.XmlReflectionError, context), e);
        }
 
        private static InvalidOperationException CreateTypeReflectionException(string context, Exception e)
        {
            return new InvalidOperationException(SR.Format(SR.XmlTypeReflectionError, context), e);
        }
 
        private static InvalidOperationException CreateMemberReflectionException(FieldModel model, Exception e)
        {
            return new InvalidOperationException(SR.Format(model.IsProperty ? SR.XmlPropertyReflectionError : SR.XmlFieldReflectionError, model.Name), e);
        }
 
        [RequiresUnreferencedCode("calls ImportTypeMapping")]
        private TypeMapping ImportTypeMapping(TypeModel model, string? ns, ImportContext context, string dataType, XmlAttributes? a, RecursionLimiter limiter)
        {
            return ImportTypeMapping(model, ns, context, dataType, a, false, false, limiter);
        }
 
        [RequiresUnreferencedCode("calls ImportEnumMapping")]
        private TypeMapping ImportTypeMapping(TypeModel model, string? ns, ImportContext context, string dataType, XmlAttributes? a, bool repeats, bool openModel, RecursionLimiter limiter)
        {
            try
            {
                if (dataType.Length > 0)
                {
                    TypeDesc modelTypeDesc = TypeScope.IsOptionalValue(model.Type) ? model.TypeDesc.BaseTypeDesc! : model.TypeDesc;
                    if (!modelTypeDesc.IsPrimitive)
                    {
                        throw new InvalidOperationException(SR.Format(SR.XmlInvalidDataTypeUsage, dataType, "XmlElementAttribute.DataType"));
                    }
                    TypeDesc? td = TypeScope.GetTypeDesc(dataType, XmlSchema.Namespace);
                    if (td == null)
                    {
                        throw new InvalidOperationException(SR.Format(SR.XmlInvalidXsdDataType, dataType, "XmlElementAttribute.DataType", new XmlQualifiedName(dataType, XmlSchema.Namespace).ToString()));
                    }
                    if (modelTypeDesc.FullName != td.FullName)
                    {
                        throw new InvalidOperationException(SR.Format(SR.XmlDataTypeMismatch, dataType, "XmlElementAttribute.DataType", modelTypeDesc.FullName));
                    }
                }
 
                a ??= GetAttributes(model.Type, false);
 
                if ((a.XmlFlags & ~(XmlAttributeFlags.Type | XmlAttributeFlags.Root)) != 0)
                    throw new InvalidOperationException(SR.Format(SR.XmlInvalidTypeAttributes, model.Type.FullName));
 
                switch (model.TypeDesc.Kind)
                {
                    case TypeKind.Enum:
                        return ImportEnumMapping((EnumModel)model, ns, repeats);
                    case TypeKind.Primitive:
                        if (a.XmlFlags != 0) throw InvalidAttributeUseException(model.Type);
                        return ImportPrimitiveMapping((PrimitiveModel)model, context, dataType, repeats);
                    case TypeKind.Array:
                    case TypeKind.Collection:
                    case TypeKind.Enumerable:
                        //if (a.XmlFlags != 0) throw InvalidAttributeUseException(model.Type);
                        if (context != ImportContext.Element) throw UnsupportedException(model.TypeDesc, context);
                        _arrayNestingLevel++;
                        ArrayMapping arrayMapping = ImportArrayLikeMapping((ArrayModel)model, ns, limiter);
                        _arrayNestingLevel--;
                        return arrayMapping;
                    case TypeKind.Root:
                    case TypeKind.Class:
                    case TypeKind.Struct:
                        if (context != ImportContext.Element) throw UnsupportedException(model.TypeDesc, context);
                        if (model.TypeDesc.IsOptionalValue)
                        {
                            TypeDesc valueTypeDesc = string.IsNullOrEmpty(dataType) ? model.TypeDesc.BaseTypeDesc! : TypeScope.GetTypeDesc(dataType, XmlSchema.Namespace)!;
                            string? xsdTypeName = valueTypeDesc.DataType == null ? valueTypeDesc.Name : valueTypeDesc.DataType.Name;
                            TypeMapping baseMapping =
                                GetTypeMapping(xsdTypeName, ns, valueTypeDesc, _types, null) ??
                                ImportTypeMapping(_modelScope.GetTypeModel(model.TypeDesc.BaseTypeDesc!.Type!), ns, context, dataType, null, repeats, openModel, limiter);
                            return CreateNullableMapping(baseMapping, model.TypeDesc.Type!);
                        }
                        else
                        {
                            return ImportStructLikeMapping((StructModel)model, ns, openModel, a, limiter);
                        }
                    default:
                        if (model.TypeDesc.Kind == TypeKind.Serializable)
                        {
                            // We allow XmlRoot attribute on IXmlSerializable, but not others
                            if ((a.XmlFlags & ~XmlAttributeFlags.Root) != 0)
                            {
                                throw new InvalidOperationException(SR.Format(SR.XmlSerializableAttributes, model.TypeDesc.FullName, nameof(XmlSchemaProviderAttribute)));
                            }
                        }
                        else
                        {
                            if (a.XmlFlags != 0) throw InvalidAttributeUseException(model.Type);
                        }
                        if (model.TypeDesc.IsSpecial)
                            return ImportSpecialMapping(model.Type, model.TypeDesc, ns, context);
                        throw UnsupportedException(model.TypeDesc, context);
                }
            }
            catch (Exception e)
            {
                if (e is OutOfMemoryException)
                {
                    throw;
                }
                throw CreateTypeReflectionException(model.TypeDesc.FullName, e);
            }
        }
 
        internal static MethodInfo? GetMethodFromSchemaProvider(XmlSchemaProviderAttribute provider,
            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods)] Type type)
        {
            if (provider.IsAny)
            {
                // do not validate the schema provider method for wildcard types.
                return null;
            }
            ArgumentNullException.ThrowIfNull(provider.MethodName, nameof(provider.MethodName));
            if (!CSharpHelpers.IsValidLanguageIndependentIdentifier(provider.MethodName))
                throw new ArgumentException(SR.Format(SR.XmlGetSchemaMethodName, provider.MethodName), nameof(provider.MethodName));
 
            MethodInfo? getMethod = getMethod = type.GetMethod(provider.MethodName, /* BindingFlags.DeclaredOnly | */ BindingFlags.Static | BindingFlags.Public, new Type[] { typeof(XmlSchemaSet) });
            if (getMethod == null)
                throw new InvalidOperationException(SR.Format(SR.XmlGetSchemaMethodMissing, provider.MethodName, nameof(XmlSchemaSet), type.FullName));
 
            if (!(typeof(XmlQualifiedName).IsAssignableFrom(getMethod.ReturnType)) && !(typeof(XmlSchemaType).IsAssignableFrom(getMethod.ReturnType)))
                throw new InvalidOperationException(SR.Format(SR.XmlGetSchemaMethodReturnType, type.Name, provider.MethodName, nameof(XmlSchemaProviderAttribute), typeof(XmlQualifiedName).FullName, typeof(XmlSchemaType).FullName));
 
            return getMethod;
        }
 
        [RequiresUnreferencedCode("calls IncludeTypes")]
        private SpecialMapping ImportSpecialMapping(Type type, TypeDesc typeDesc, string? ns, ImportContext context)
        {
            _specials ??= new Hashtable();
            SpecialMapping? mapping = (SpecialMapping?)_specials[type];
            if (mapping != null)
            {
                CheckContext(mapping.TypeDesc!, context);
                return mapping;
            }
            if (typeDesc.Kind == TypeKind.Serializable)
            {
                SerializableMapping? serializableMapping;
 
                // get the schema method info
                object[] attrs = type.GetCustomAttributes(typeof(XmlSchemaProviderAttribute), false);
 
                if (attrs.Length > 0)
                {
                    // new IXmlSerializable
                    XmlSchemaProviderAttribute provider = (XmlSchemaProviderAttribute)attrs[0];
                    MethodInfo method = GetMethodFromSchemaProvider(provider, type)!;
                    serializableMapping = new SerializableMapping(method, provider.IsAny, ns);
                    XmlQualifiedName? qname = serializableMapping.XsiType;
                    if (qname != null && !qname.IsEmpty)
                    {
                        _serializables ??= new NameTable();
                        SerializableMapping? existingMapping = (SerializableMapping?)_serializables[qname];
                        if (existingMapping != null)
                        {
                            if (existingMapping.Type == null)
                            {
                                serializableMapping = existingMapping;
                            }
                            else if (existingMapping.Type != type)
                            {
                                SerializableMapping? next = existingMapping.Next;
                                existingMapping.Next = serializableMapping;
                                serializableMapping.Next = next;
                            }
                        }
                        else
                        {
                            XmlSchemaType? xsdType = serializableMapping.XsdType;
                            if (xsdType != null)
                                SetBase(serializableMapping, xsdType.DerivedFrom);
                            _serializables[qname] = serializableMapping;
                        }
 
                        serializableMapping.TypeName = qname.Name;
                        serializableMapping.Namespace = qname.Namespace;
                    }
                    serializableMapping.TypeDesc = typeDesc;
                    serializableMapping.Type = type;
                    IncludeTypes(type);
                }
                else
                {
                    // old IXmlSerializable
                    serializableMapping = new SerializableMapping();
                    serializableMapping.TypeDesc = typeDesc;
                    serializableMapping.Type = type;
                }
                mapping = serializableMapping;
            }
            else
            {
                mapping = new SpecialMapping();
                mapping.TypeDesc = typeDesc;
            }
            CheckContext(typeDesc, context);
            _specials.Add(type, mapping);
            _typeScope.AddTypeMapping(mapping);
            return mapping;
        }
 
        internal void SetBase(SerializableMapping mapping, XmlQualifiedName baseQname)
        {
            if (baseQname.IsEmpty) return;
            if (baseQname.Namespace == XmlSchema.Namespace) return;
            XmlSchemaSet schemas = mapping.Schemas!;
            ArrayList srcSchemas = (ArrayList)schemas.Schemas(baseQname.Namespace);
 
            if (srcSchemas.Count == 0)
            {
                throw new InvalidOperationException(SR.Format(SR.XmlMissingSchema, baseQname.Namespace));
            }
            if (srcSchemas.Count > 1)
            {
                throw new InvalidOperationException(SR.Format(SR.XmlGetSchemaInclude, baseQname.Namespace, nameof(IXmlSerializable), "GetSchema"));
            }
            XmlSchema s = (XmlSchema)srcSchemas[0]!;
 
            XmlSchemaType t = (XmlSchemaType)s.SchemaTypes[baseQname]!;
            t = t.Redefined ?? t;
 
            if (_serializables![baseQname] == null)
            {
                SerializableMapping baseMapping = new SerializableMapping(baseQname, schemas);
                SetBase(baseMapping, t.DerivedFrom);
                _serializables.Add(baseQname, baseMapping);
            }
            mapping.SetBaseMapping((SerializableMapping?)_serializables[baseQname]);
        }
 
        private static string GetContextName(ImportContext context) =>
            context switch
            {
                ImportContext.Element => "element",
                ImportContext.Attribute => "attribute",
                ImportContext.Text => "text",
                _ => throw new ArgumentException(SR.XmlInternalError, nameof(context)),
            };
 
        private static InvalidOperationException InvalidAttributeUseException(Type type)
        {
            return new InvalidOperationException(SR.Format(SR.XmlInvalidAttributeUse, type.FullName));
        }
 
        private static InvalidOperationException UnsupportedException(TypeDesc typeDesc, ImportContext context)
        {
            return new InvalidOperationException(SR.Format(SR.XmlIllegalTypeContext, typeDesc.FullName, GetContextName(context)));
        }
 
        [RequiresUnreferencedCode("calls GetTypeDesc")]
        private StructMapping CreateRootMapping()
        {
            TypeDesc typeDesc = _typeScope.GetTypeDesc(typeof(object));
            StructMapping mapping = new StructMapping();
            mapping.TypeDesc = typeDesc;
            mapping.TypeName = Soap.UrType;
            mapping.Namespace = XmlSchema.Namespace;
            mapping.Members = Array.Empty<MemberMapping>();
            mapping.IncludeInSchema = false;
            return mapping;
        }
 
        private NullableMapping CreateNullableMapping(TypeMapping baseMapping,
           [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)] Type type)
        {
            TypeDesc typeDesc = baseMapping.TypeDesc!.GetNullableTypeDesc(type);
            TypeMapping? existingMapping;
            if (!baseMapping.IsAnonymousType)
            {
                existingMapping = (TypeMapping?)_nullables[baseMapping.TypeName!, baseMapping.Namespace];
            }
            else
            {
                existingMapping = (TypeMapping?)_anonymous[type];
            }
 
            NullableMapping mapping;
            if (existingMapping != null)
            {
                if (existingMapping is NullableMapping)
                {
                    mapping = (NullableMapping)existingMapping;
                    if (mapping.BaseMapping is PrimitiveMapping && baseMapping is PrimitiveMapping)
                        return mapping;
                    else if (mapping.BaseMapping == baseMapping)
                    {
                        return mapping;
                    }
                    else
                    {
                        throw new InvalidOperationException(SR.Format(SR.XmlTypesDuplicate, typeDesc.FullName, existingMapping.TypeDesc!.FullName, typeDesc.Name, existingMapping.Namespace));
                    }
                }
                else
                {
                    throw new InvalidOperationException(SR.Format(SR.XmlTypesDuplicate, typeDesc.FullName, existingMapping.TypeDesc!.FullName, typeDesc.Name, existingMapping.Namespace));
                }
            }
            mapping = new NullableMapping();
            mapping.BaseMapping = baseMapping;
            mapping.TypeDesc = typeDesc;
            mapping.TypeName = baseMapping.TypeName;
            mapping.Namespace = baseMapping.Namespace;
            mapping.IncludeInSchema = baseMapping.IncludeInSchema;
            if (!baseMapping.IsAnonymousType)
            {
                _nullables.Add(baseMapping.TypeName, baseMapping.Namespace, mapping);
            }
            else
            {
                _anonymous[type] = mapping;
            }
 
            _typeScope.AddTypeMapping(mapping);
            return mapping;
        }
 
        [RequiresUnreferencedCode("calls CreateRootMapping")]
        private StructMapping GetRootMapping()
        {
            if (_root == null)
            {
                _root = CreateRootMapping();
                _typeScope.AddTypeMapping(_root);
            }
            return _root;
        }
 
        private TypeMapping? GetTypeMapping(string? typeName, string? ns, TypeDesc typeDesc, NameTable typeLib, Type? type)
        {
            TypeMapping? mapping;
            if (string.IsNullOrEmpty(typeName))
                mapping = type == null ? null : (TypeMapping?)_anonymous[type];
            else
                mapping = (TypeMapping?)typeLib[typeName, ns];
 
            if (mapping == null) return null;
            if (!mapping.IsAnonymousType && mapping.TypeDesc != typeDesc)
                throw new InvalidOperationException(SR.Format(SR.XmlTypesDuplicate, typeDesc.FullName, mapping.TypeDesc!.FullName, typeName, ns));
            return mapping;
        }
 
        [RequiresUnreferencedCode("calls GetRootMapping")]
        private StructMapping ImportStructLikeMapping(StructModel model, string? ns, bool openModel, XmlAttributes? a, RecursionLimiter limiter)
        {
            if (model.TypeDesc.Kind == TypeKind.Root) return GetRootMapping();
            a ??= GetAttributes(model.Type, false);
 
            string? typeNs = ns;
            if (a.XmlType != null && a.XmlType.Namespace != null)
                typeNs = a.XmlType.Namespace;
            else if (a.XmlRoot != null && a.XmlRoot.Namespace != null)
                typeNs = a.XmlRoot.Namespace;
 
            string? typeName = IsAnonymousType(a, ns) ? null : XsdTypeName(model.Type, a, model.TypeDesc.Name);
            typeName = XmlConvert.EncodeLocalName(typeName);
 
            StructMapping? mapping = (StructMapping?)GetTypeMapping(typeName, typeNs, model.TypeDesc, _types, model.Type);
            if (mapping == null)
            {
                mapping = new StructMapping();
                mapping.TypeDesc = model.TypeDesc;
                mapping.Namespace = typeNs;
                mapping.TypeName = typeName;
                if (!mapping.IsAnonymousType)
                    _types.Add(typeName, typeNs, mapping);
                else
                    _anonymous[model.Type] = mapping;
                if (a.XmlType != null)
                {
                    mapping.IncludeInSchema = a.XmlType.IncludeInSchema;
                }
 
                if (limiter.IsExceededLimit)
                {
                    limiter.DeferredWorkItems.Add(new ImportStructWorkItem(model, mapping));
                    return mapping;
                }
 
                limiter.Depth++;
 
                InitializeStructMembers(mapping, model, openModel, typeName, limiter);
                while (limiter.DeferredWorkItems.Count > 0)
                {
                    int index = limiter.DeferredWorkItems.Count - 1;
                    ImportStructWorkItem item = limiter.DeferredWorkItems[index];
                    if (InitializeStructMembers(item.Mapping, item.Model, openModel, typeName, limiter))
                    {
                        //
                        // if InitializeStructMembers returns true, then there were *no* changes to the DeferredWorkItems
                        //
#if DEBUG
                        // use exception in the place of Debug.Assert to avoid throwing asserts from a server process such as aspnet_ewp.exe
                        if (index != limiter.DeferredWorkItems.Count - 1)
                            throw new InvalidOperationException(SR.Format(SR.XmlInternalErrorDetails, "DeferredWorkItems.Count have changed"));
                        if (item != limiter.DeferredWorkItems[index])
                            throw new InvalidOperationException(SR.Format(SR.XmlInternalErrorDetails, "DeferredWorkItems.Top have changed"));
#endif
                        // Remove the last work item
                        limiter.DeferredWorkItems.RemoveAt(index);
                    }
                }
                limiter.Depth--;
            }
            return mapping;
        }
 
        [RequiresUnreferencedCode("calls GetTypeModel")]
        private bool InitializeStructMembers(StructMapping mapping, StructModel model, bool openModel, string? typeName, RecursionLimiter limiter)
        {
            if (mapping.IsFullyInitialized)
                return true;
 
            if (model.TypeDesc.BaseTypeDesc != null)
            {
                TypeModel baseModel = _modelScope.GetTypeModel(model.Type.BaseType!, false);
                if (!(baseModel is StructModel))
                {
                    //XmlUnsupportedInheritance=Using '{0}' as a base type for a class is not supported by XmlSerializer.
                    throw new NotSupportedException(SR.Format(SR.XmlUnsupportedInheritance, model.Type.BaseType!.FullName));
                }
                StructMapping baseMapping = ImportStructLikeMapping((StructModel)baseModel, mapping.Namespace, openModel, null, limiter);
                // check to see if the import of the baseMapping was deferred
                int baseIndex = limiter.DeferredWorkItems.IndexOf(baseMapping);
                if (baseIndex < 0)
                {
                    mapping.BaseMapping = baseMapping;
 
                    ICollection values = mapping.BaseMapping.LocalAttributes.Values;
                    foreach (AttributeAccessor attribute in values)
                    {
                        AddUniqueAccessor(mapping.LocalAttributes, attribute);
                    }
                    if (!mapping.BaseMapping.HasExplicitSequence())
                    {
                        values = mapping.BaseMapping.LocalElements.Values;
                        foreach (ElementAccessor e in values)
                        {
                            AddUniqueAccessor(mapping.LocalElements, e);
                        }
                    }
                }
                else
                {
                    // the import of the baseMapping was deferred, make sure that the derived mappings is deferred as well
                    if (!limiter.DeferredWorkItems.Contains(mapping))
                    {
                        limiter.DeferredWorkItems.Add(new ImportStructWorkItem(model, mapping));
                    }
                    // make sure that baseMapping get processed before the derived
                    int top = limiter.DeferredWorkItems.Count - 1;
                    if (baseIndex < top)
                    {
                        ImportStructWorkItem baseMappingWorkItem = limiter.DeferredWorkItems[baseIndex];
                        limiter.DeferredWorkItems[baseIndex] = limiter.DeferredWorkItems[top];
                        limiter.DeferredWorkItems[top] = baseMappingWorkItem;
                    }
                    return false;
                }
            }
            var members = new List<MemberMapping>();
            TextAccessor? textAccessor = null;
            bool hasElements = false;
            bool isSequence = false;
 
            foreach (MemberInfo memberInfo in model.GetMemberInfos())
            {
                if (!(memberInfo is FieldInfo || memberInfo is PropertyInfo))
                    continue;
                XmlAttributes memberAttrs = GetAttributes(memberInfo);
                if (memberAttrs.XmlIgnore) continue;
                FieldModel? fieldModel = model.GetFieldModel(memberInfo);
                if (fieldModel == null) continue;
                try
                {
                    MemberMapping? member = ImportFieldMapping(model, fieldModel, memberAttrs, mapping.Namespace, limiter);
                    if (member == null) continue;
                    if (mapping.BaseMapping != null)
                    {
                        if (mapping.BaseMapping.Declares(member, mapping.TypeName)) continue;
                    }
                    isSequence |= member.IsSequence;
                    // add All member accessors to the scope accessors
                    AddUniqueAccessor(member, mapping.LocalElements, mapping.LocalAttributes, isSequence);
 
                    if (member.Text != null)
                    {
                        if (!member.Text.Mapping!.TypeDesc!.CanBeTextValue && member.Text.Mapping.IsList)
                            throw new InvalidOperationException(SR.Format(SR.XmlIllegalTypedTextAttribute, typeName, member.Text.Name, member.Text.Mapping.TypeDesc.FullName));
                        if (textAccessor != null)
                        {
                            throw new InvalidOperationException(SR.Format(SR.XmlIllegalMultipleText, model.Type.FullName));
                        }
                        textAccessor = member.Text;
                    }
                    if (member.Xmlns != null)
                    {
                        if (mapping.XmlnsMember != null)
                            throw new InvalidOperationException(SR.Format(SR.XmlMultipleXmlns, model.Type.FullName));
                        mapping.XmlnsMember = member;
                    }
                    if (member.Elements != null && member.Elements.Length != 0)
                    {
                        hasElements = true;
                    }
                    members.Add(member);
                }
                catch (Exception e)
                {
                    if (e is OutOfMemoryException)
                    {
                        throw;
                    }
                    throw CreateMemberReflectionException(fieldModel, e);
                }
            }
            mapping.SetContentModel(textAccessor, hasElements);
            if (isSequence)
            {
                Hashtable ids = new Hashtable();
                for (int i = 0; i < members.Count; i++)
                {
                    MemberMapping member = members[i]!;
                    if (!member.IsParticle)
                        continue;
                    if (member.IsSequence)
                    {
                        if (ids[member.SequenceId] != null)
                        {
                            throw new InvalidOperationException(SR.Format(SR.XmlSequenceUnique, member.SequenceId.ToString(CultureInfo.InvariantCulture), "Order", member.Name));
                        }
                        ids[member.SequenceId] = member;
                    }
                    else
                    {
                        throw new InvalidOperationException(SR.Format(SR.XmlSequenceInconsistent, "Order", member.Name));
                    }
                }
                members.Sort(new MemberMappingComparer());
            }
            mapping.Members = members.ToArray();
 
            mapping.BaseMapping ??= GetRootMapping();
 
            if (mapping.XmlnsMember != null && mapping.BaseMapping.HasXmlnsMember)
                throw new InvalidOperationException(SR.Format(SR.XmlMultipleXmlns, model.Type.FullName));
 
            IncludeTypes(model.Type, limiter);
            _typeScope.AddTypeMapping(mapping);
            if (openModel)
                mapping.IsOpenModel = true;
            return true;
        }
 
        private static bool IsAnonymousType(XmlAttributes a, string? contextNs)
        {
            if (a.XmlType != null && a.XmlType.AnonymousType)
            {
                //
                // check to see if the anonymous type is used in the original context
                // only treat it as Anonymous, if the referencing element's namespace
                // matches the original referencing element, otherwise revert to
                // non-Anonymous handling for backward compatibility.
                //
                string? originalNs = a.XmlType.Namespace;
                return string.IsNullOrEmpty(originalNs) || originalNs == contextNs;
            }
            return false;
        }
 
        [RequiresUnreferencedCode("calls GetTypeDesc")]
        internal string XsdTypeName(Type type)
        {
            if (type == typeof(object)) return Soap.UrType;
            TypeDesc typeDesc = _typeScope.GetTypeDesc(type);
            if (typeDesc.IsPrimitive && typeDesc.DataType != null && typeDesc.DataType.Name != null && typeDesc.DataType.Name.Length > 0)
                return typeDesc.DataType.Name;
            return XsdTypeName(type, GetAttributes(type, false), typeDesc.Name);
        }
 
        [RequiresUnreferencedCode("Calls XsdTypeName")]
        internal string XsdTypeName(Type type, XmlAttributes a, string name)
        {
            string typeName = name;
            if (a.XmlType != null && a.XmlType.TypeName.Length > 0)
                typeName = a.XmlType.TypeName;
 
            if (type.IsGenericType && typeName.Contains('{'))
            {
                Type genType = type.GetGenericTypeDefinition();
                Type[] names = genType.GetGenericArguments();
                Type[] types = type.GetGenericArguments();
 
                for (int i = 0; i < names.Length; i++)
                {
                    string argument = $"{{{names[i]}}}";
                    if (typeName.Contains(argument))
                    {
                        typeName = typeName.Replace(argument, XsdTypeName(types[i]));
                        if (!typeName.Contains('{'))
                        {
                            break;
                        }
                    }
                }
            }
            return typeName;
        }
 
        private static int CountAtLevel(XmlArrayItemAttributes attributes, int level)
        {
            int sum = 0;
            for (int i = 0; i < attributes.Count; i++)
                if (attributes[i]!.NestingLevel == level) sum++;
            return sum;
        }
 
        [RequiresUnreferencedCode("calls XsdTypeName")]
        private void SetArrayMappingType(ArrayMapping mapping, string? defaultNs, Type type)
        {
            XmlAttributes a = GetAttributes(type, false);
            bool isAnonymous = IsAnonymousType(a, defaultNs);
            if (isAnonymous)
            {
                mapping.TypeName = null;
                mapping.Namespace = defaultNs;
                return;
            }
            string? name;
            string? ns;
            TypeMapping? itemTypeMapping;
            ElementAccessor? element = null;
 
            if (mapping.Elements!.Length == 1)
            {
                element = mapping.Elements[0];
                itemTypeMapping = element.Mapping;
            }
            else
            {
                itemTypeMapping = null;
            }
 
            bool generateTypeName = true;
            if (a.XmlType != null)
            {
                ns = a.XmlType.Namespace;
                name = XsdTypeName(type, a, a.XmlType.TypeName);
                name = XmlConvert.EncodeLocalName(name);
                generateTypeName = name == null;
            }
            else if (itemTypeMapping is EnumMapping)
            {
                ns = itemTypeMapping.Namespace;
                name = itemTypeMapping.DefaultElementName;
            }
            else if (itemTypeMapping is PrimitiveMapping)
            {
                ns = defaultNs;
                name = itemTypeMapping.TypeDesc!.DataType!.Name;
            }
            else if (itemTypeMapping is StructMapping && itemTypeMapping.TypeDesc!.IsRoot)
            {
                ns = defaultNs;
                name = Soap.UrType;
            }
            else if (itemTypeMapping != null)
            {
                ns = itemTypeMapping.Namespace == XmlSchema.Namespace ? defaultNs : itemTypeMapping.Namespace;
                name = itemTypeMapping.DefaultElementName;
            }
            else
            {
                ns = defaultNs;
                name = $"Choice{(_choiceNum++)}";
            }
 
            name ??= "Any";
 
            if (element != null)
                ns = element.Namespace;
 
            ns ??= defaultNs;
 
            string uniqueName = name = generateTypeName ? $"ArrayOf{CodeIdentifier.MakePascal(name)}" : name;
            int i = 1;
            TypeMapping? existingMapping = (TypeMapping?)_types[uniqueName, ns];
            while (existingMapping != null)
            {
                if (existingMapping is ArrayMapping arrayMapping)
                {
                    if (AccessorMapping.ElementsMatch(arrayMapping.Elements, mapping.Elements))
                    {
                        break;
                    }
                }
                // need to re-name the mapping
                uniqueName = name + i.ToString(CultureInfo.InvariantCulture);
                existingMapping = (TypeMapping?)_types[uniqueName, ns];
                i++;
            }
            mapping.TypeName = uniqueName;
            mapping.Namespace = ns;
        }
 
        [RequiresUnreferencedCode("calls SetArrayMappingType")]
        private ArrayMapping ImportArrayLikeMapping(ArrayModel model, string? ns, RecursionLimiter limiter)
        {
            ArrayMapping mapping = new ArrayMapping();
            mapping.TypeDesc = model.TypeDesc;
 
            _savedArrayItemAttributes ??= new XmlArrayItemAttributes();
            if (CountAtLevel(_savedArrayItemAttributes, _arrayNestingLevel) == 0)
                _savedArrayItemAttributes.Add(CreateArrayItemAttribute(_arrayNestingLevel));
            CreateArrayElementsFromAttributes(mapping, _savedArrayItemAttributes, model.Element.Type, _savedArrayNamespace ?? ns, limiter);
            SetArrayMappingType(mapping, ns, model.Type);
 
            // reconcile accessors now that we have the ArrayMapping namespace
            for (int i = 0; i < mapping.Elements!.Length; i++)
            {
                mapping.Elements[i] = ReconcileLocalAccessor(mapping.Elements[i], mapping.Namespace);
            }
 
            IncludeTypes(model.Type);
 
            // in the case of an ArrayMapping we can have more that one mapping correspond to a type
            // examples of that are ArrayList and object[] both will map tp ArrayOfur-type
            // so we create a link list for all mappings of the same XSD type
            ArrayMapping? existingMapping = (ArrayMapping?)_types[mapping.TypeName, mapping.Namespace];
            if (existingMapping != null)
            {
                ArrayMapping? first = existingMapping;
                while (existingMapping != null)
                {
                    if (existingMapping.TypeDesc == model.TypeDesc)
                        return existingMapping;
                    existingMapping = existingMapping.Next;
                }
                mapping.Next = first;
                if (!mapping.IsAnonymousType)
                    _types[mapping.TypeName, mapping.Namespace] = mapping;
                else
                    _anonymous[model.Type] = mapping;
                return mapping;
            }
            _typeScope.AddTypeMapping(mapping);
            if (!mapping.IsAnonymousType)
                _types.Add(mapping.TypeName, mapping.Namespace, mapping);
            else
                _anonymous[model.Type] = mapping;
            return mapping;
        }
 
        private static void CheckContext(TypeDesc typeDesc, ImportContext context)
        {
            switch (context)
            {
                case ImportContext.Element:
                    if (typeDesc.CanBeElementValue) return;
                    break;
                case ImportContext.Attribute:
                    if (typeDesc.CanBeAttributeValue) return;
                    break;
                case ImportContext.Text:
                    if (typeDesc.CanBeTextValue || typeDesc.IsEnum || typeDesc.IsPrimitive)
                        return;
                    break;
                default:
                    throw new ArgumentException(SR.XmlInternalError, nameof(context));
            }
            throw UnsupportedException(typeDesc, context);
        }
 
        private static PrimitiveMapping ImportPrimitiveMapping(PrimitiveModel model, ImportContext context, string dataType, bool repeats)
        {
            PrimitiveMapping mapping = new PrimitiveMapping();
            if (dataType.Length > 0)
            {
                mapping.TypeDesc = TypeScope.GetTypeDesc(dataType, XmlSchema.Namespace);
                if (mapping.TypeDesc == null)
                {
                    // try it as a non-Xsd type
                    mapping.TypeDesc = TypeScope.GetTypeDesc(dataType, UrtTypes.Namespace);
                    if (mapping.TypeDesc == null)
                    {
                        throw new InvalidOperationException(SR.Format(SR.XmlUdeclaredXsdType, dataType));
                    }
                }
            }
            else
            {
                mapping.TypeDesc = model.TypeDesc;
            }
            mapping.TypeName = mapping.TypeDesc.DataType!.Name;
            mapping.Namespace = mapping.TypeDesc.IsXsdType ? XmlSchema.Namespace : UrtTypes.Namespace;
            mapping.IsList = repeats;
            CheckContext(mapping.TypeDesc, context);
            return mapping;
        }
 
        [RequiresUnreferencedCode("calls XsdTypeName")]
        private EnumMapping ImportEnumMapping(EnumModel model, string? ns, bool repeats)
        {
            XmlAttributes a = GetAttributes(model.Type, false);
            string? typeNs = ns;
            if (a.XmlType != null && a.XmlType.Namespace != null)
                typeNs = a.XmlType.Namespace;
 
            string? typeName = IsAnonymousType(a, ns) ? null : XsdTypeName(model.Type, a, model.TypeDesc.Name);
            typeName = XmlConvert.EncodeLocalName(typeName);
 
            EnumMapping? mapping = (EnumMapping?)GetTypeMapping(typeName, typeNs, model.TypeDesc, _types, model.Type);
            if (mapping == null)
            {
                mapping = new EnumMapping();
                mapping.TypeDesc = model.TypeDesc;
                mapping.TypeName = typeName;
                mapping.Namespace = typeNs;
                mapping.IsFlags = model.Type.IsDefined(typeof(FlagsAttribute), false);
                if (mapping.IsFlags && repeats)
                    throw new InvalidOperationException(SR.Format(SR.XmlIllegalAttributeFlagsArray, model.TypeDesc.FullName));
                mapping.IsList = repeats;
                mapping.IncludeInSchema = a.XmlType == null ? true : a.XmlType.IncludeInSchema;
                if (!mapping.IsAnonymousType)
                    _types.Add(typeName, typeNs, mapping);
                else
                    _anonymous[model.Type] = mapping;
                var constants = new List<ConstantMapping>();
                for (int i = 0; i < model.Constants.Length; i++)
                {
                    ConstantMapping? constant = ImportConstantMapping(model.Constants[i]);
                    if (constant != null) constants.Add(constant);
                }
                if (constants.Count == 0)
                {
                    throw new InvalidOperationException(SR.Format(SR.XmlNoSerializableMembers, model.TypeDesc.FullName));
                }
                mapping.Constants = constants.ToArray();
                _typeScope.AddTypeMapping(mapping);
            }
            return mapping;
        }
 
        private ConstantMapping? ImportConstantMapping(ConstantModel model)
        {
            XmlAttributes a = GetAttributes(model.FieldInfo);
            if (a.XmlIgnore) return null;
            if ((a.XmlFlags & ~XmlAttributeFlags.Enum) != 0)
                throw new InvalidOperationException(SR.XmlInvalidConstantAttribute);
            a.XmlEnum ??= new XmlEnumAttribute();
 
            ConstantMapping constant = new ConstantMapping();
            constant.XmlName = a.XmlEnum.Name ?? model.Name;
            constant.Name = model.Name;
            constant.Value = model.Value;
            return constant;
        }
 
        [RequiresUnreferencedCode("calls GetTypeDesc")]
        private MembersMapping ImportMembersMapping(XmlReflectionMember[] xmlReflectionMembers, string? ns, bool hasWrapperElement, bool rpc, bool openModel, RecursionLimiter limiter)
        {
            MembersMapping members = new MembersMapping();
            members.TypeDesc = _typeScope.GetTypeDesc(typeof(object[]));
            MemberMapping[] mappings = new MemberMapping[xmlReflectionMembers.Length];
            NameTable elements = new NameTable();
            NameTable attributes = new NameTable();
            TextAccessor? textAccessor = null;
            bool isSequence = false;
 
            for (int i = 0; i < mappings.Length; i++)
            {
                try
                {
                    MemberMapping mapping = ImportMemberMapping(xmlReflectionMembers[i], ns, xmlReflectionMembers, rpc, openModel, limiter);
                    if (!hasWrapperElement)
                    {
                        if (mapping.Attribute != null)
                        {
                            if (rpc)
                            {
                                throw new InvalidOperationException(SR.XmlRpcLitAttributeAttributes);
                            }
                            else
                            {
                                throw new InvalidOperationException(SR.Format(SR.XmlInvalidAttributeType, "XmlAttribute"));
                            }
                        }
                    }
                    if (rpc && xmlReflectionMembers[i].IsReturnValue)
                    {
                        if (i > 0) throw new InvalidOperationException(SR.XmlInvalidReturnPosition);
                        mapping.IsReturnValue = true;
                    }
                    mappings[i] = mapping;
                    isSequence |= mapping.IsSequence;
                    if (!xmlReflectionMembers[i].XmlAttributes.XmlIgnore)
                    {
                        // add All member accessors to the scope accessors
                        AddUniqueAccessor(mapping, elements, attributes, isSequence);
                    }
 
                    mappings[i] = mapping;
                    if (mapping.Text != null)
                    {
                        if (textAccessor != null)
                        {
                            throw new InvalidOperationException(SR.XmlIllegalMultipleTextMembers);
                        }
                        textAccessor = mapping.Text;
                    }
 
                    if (mapping.Xmlns != null)
                    {
                        if (members.XmlnsMember != null)
                            throw new InvalidOperationException(SR.XmlMultipleXmlnsMembers);
                        members.XmlnsMember = mapping;
                    }
                }
                catch (Exception e)
                {
                    if (e is OutOfMemoryException)
                    {
                        throw;
                    }
                    throw CreateReflectionException(xmlReflectionMembers[i].MemberName, e);
                }
            }
            if (isSequence)
            {
                throw new InvalidOperationException(SR.Format(SR.XmlSequenceMembers, "Order"));
            }
            members.Members = mappings;
            members.HasWrapperElement = hasWrapperElement;
            return members;
        }
 
        [RequiresUnreferencedCode("Calls TypeScope.GetTypeDesc(Type) and XmlReflectionImporter.ImportAccessorMapping both of which RequireUnreferencedCode")]
        private MemberMapping ImportMemberMapping(XmlReflectionMember xmlReflectionMember, string? ns, XmlReflectionMember[] xmlReflectionMembers, bool rpc, bool openModel, RecursionLimiter limiter)
        {
            XmlSchemaForm form = rpc ? XmlSchemaForm.Unqualified : XmlSchemaForm.Qualified;
            XmlAttributes a = xmlReflectionMember.XmlAttributes;
            TypeDesc typeDesc = _typeScope.GetTypeDesc(xmlReflectionMember.MemberType!);
 
            if (a.XmlFlags == 0)
            {
                if (typeDesc.IsArrayLike)
                {
                    XmlArrayAttribute xmlArray = CreateArrayAttribute();
                    xmlArray.ElementName = xmlReflectionMember.MemberName;
                    xmlArray.Namespace = rpc ? null : ns;
                    xmlArray.Form = form;
                    a.XmlArray = xmlArray;
                }
                else
                {
                    XmlElementAttribute xmlElement = CreateElementAttribute(typeDesc);
                    // If there is no metadata specified on a parameter, then see if someone used
                    // an XmlRoot attribute on the struct or class.
                    if (typeDesc.IsStructLike)
                    {
                        XmlAttributes structAttrs = new XmlAttributes(xmlReflectionMember.MemberType!);
                        if (structAttrs.XmlRoot != null)
                        {
                            if (structAttrs.XmlRoot.ElementName.Length > 0)
                                xmlElement.ElementName = structAttrs.XmlRoot.ElementName;
                            if (rpc)
                            {
                                xmlElement.Namespace = null;
                                if (structAttrs.XmlRoot.GetIsNullableSpecified())
                                    xmlElement.IsNullable = structAttrs.XmlRoot.IsNullable;
                            }
                            else
                            {
                                xmlElement.Namespace = structAttrs.XmlRoot.Namespace;
                                xmlElement.IsNullable = structAttrs.XmlRoot.IsNullable;
                            }
                        }
                    }
                    if (xmlElement.ElementName.Length == 0)
                        xmlElement.ElementName = xmlReflectionMember.MemberName;
                    if (xmlElement.Namespace == null && !rpc)
                        xmlElement.Namespace = ns;
                    xmlElement.Form = form;
                    a.XmlElements.Add(xmlElement);
                }
            }
            else if (a.XmlRoot != null)
            {
                CheckNullable(a.XmlRoot.IsNullable, typeDesc, null);
            }
            MemberMapping member = new MemberMapping();
            member.Name = xmlReflectionMember.MemberName;
            bool checkSpecified = FindSpecifiedMember(xmlReflectionMember.MemberName, xmlReflectionMembers) != null;
            FieldModel model = new FieldModel(xmlReflectionMember.MemberName, xmlReflectionMember.MemberType!, _typeScope.GetTypeDesc(xmlReflectionMember.MemberType!), checkSpecified, false);
            member.CheckShouldPersist = model.CheckShouldPersist;
            member.CheckSpecified = model.CheckSpecified;
            member.ReadOnly = model.ReadOnly; // || !model.FieldTypeDesc.HasDefaultConstructor;
 
            Type? choiceIdentifierType = null;
            if (a.XmlChoiceIdentifier != null)
            {
                choiceIdentifierType = GetChoiceIdentifierType(a.XmlChoiceIdentifier, xmlReflectionMembers, typeDesc.IsArrayLike, model.Name);
            }
            ImportAccessorMapping(member, model, a, ns, choiceIdentifierType, rpc, openModel, limiter);
            if (xmlReflectionMember.OverrideIsNullable && member.Elements!.Length > 0)
                member.Elements[0].IsNullable = false;
            return member;
        }
 
        internal static XmlReflectionMember? FindSpecifiedMember(string memberName, XmlReflectionMember[] reflectionMembers)
        {
            for (int i = 0; i < reflectionMembers.Length; i++)
                if (string.Equals(reflectionMembers[i].MemberName, $"{memberName}Specified", StringComparison.Ordinal))
                    return reflectionMembers[i];
            return null;
        }
 
        [RequiresUnreferencedCode("calls ImportAccessorMapping")]
        private MemberMapping ImportFieldMapping(StructModel parent, FieldModel model, XmlAttributes a, string? ns, RecursionLimiter limiter)
        {
            MemberMapping member = new MemberMapping();
            member.Name = model.Name;
            member.CheckShouldPersist = model.CheckShouldPersist;
            member.CheckSpecified = model.CheckSpecified;
            member.MemberInfo = model.MemberInfo;
            member.CheckSpecifiedMemberInfo = model.CheckSpecifiedMemberInfo;
            member.CheckShouldPersistMethodInfo = model.CheckShouldPersistMethodInfo;
            member.ReadOnly = model.ReadOnly; // || !model.FieldTypeDesc.HasDefaultConstructor;
            Type? choiceIdentifierType = null;
            if (a.XmlChoiceIdentifier != null)
            {
                choiceIdentifierType = GetChoiceIdentifierType(a.XmlChoiceIdentifier, parent, model.FieldTypeDesc.IsArrayLike, model.Name);
            }
            ImportAccessorMapping(member, model, a, ns, choiceIdentifierType, false, false, limiter);
            return member;
        }
 
        private static Type CheckChoiceIdentifierType(Type type, bool isArrayLike, string identifierName, string memberName)
        {
            if (type.IsArray)
            {
                if (!isArrayLike)
                {
                    // Inconsistent type of the choice identifier '{0}'.  Please use {1}.
                    throw new InvalidOperationException(SR.Format(SR.XmlChoiceIdentifierType, identifierName, memberName, type.GetElementType()!.FullName));
                }
                type = type.GetElementType()!;
            }
            else if (isArrayLike)
            {
                // Inconsistent type of the choice identifier '{0}'.  Please use {1}.
                throw new InvalidOperationException(SR.Format(SR.XmlChoiceIdentifierArrayType, identifierName, memberName, type.FullName));
            }
 
            if (!type!.IsEnum)
            {
                // Choice identifier '{0}' must be an enum.
                throw new InvalidOperationException(SR.Format(SR.XmlChoiceIdentifierTypeEnum, identifierName));
            }
            return type;
        }
 
        private static Type GetChoiceIdentifierType(XmlChoiceIdentifierAttribute choice, XmlReflectionMember[] xmlReflectionMembers, bool isArrayLike, string accessorName)
        {
            for (int i = 0; i < xmlReflectionMembers.Length; i++)
            {
                if (choice.MemberName == xmlReflectionMembers[i].MemberName)
                {
                    return CheckChoiceIdentifierType(xmlReflectionMembers[i].MemberType!, isArrayLike, choice.MemberName, accessorName);
                }
            }
            // Missing '{0}' needed for serialization of choice '{1}'.
            throw new InvalidOperationException(SR.Format(SR.XmlChoiceIdentifierMemberMissing, choice.MemberName, accessorName));
        }
 
        [RequiresUnreferencedCode("calls GetFieldModel")]
        private static Type GetChoiceIdentifierType(XmlChoiceIdentifierAttribute choice, StructModel structModel, bool isArrayLike, string accessorName)
        {
            // check that the choice field exists
 
            MemberInfo[] infos = structModel.Type.GetMember(choice.MemberName, BindingFlags.DeclaredOnly | BindingFlags.Public | BindingFlags.Instance | BindingFlags.Static);
            if (infos == null || infos.Length == 0)
            {
                // if we can not find the choice identifier between fields, check properties
                PropertyInfo? info = structModel.Type.GetProperty(choice.MemberName, BindingFlags.DeclaredOnly | BindingFlags.Public | BindingFlags.Instance | BindingFlags.Static);
 
                if (info == null)
                {
                    // Missing '{0}' needed for serialization of choice '{1}'.
                    throw new InvalidOperationException(SR.Format(SR.XmlChoiceIdentifierMemberMissing, choice.MemberName, accessorName));
                }
                infos = new MemberInfo[] { info };
            }
            else if (infos.Length > 1)
            {
                // Ambiguous choice identifier: there are several members named '{0}'.
                throw new InvalidOperationException(SR.Format(SR.XmlChoiceIdentifierAmbiguous, choice.MemberName));
            }
 
            FieldModel? member = structModel.GetFieldModel(infos[0]);
            if (member == null)
            {
                // Missing '{0}' needed for serialization of choice '{1}'.
                throw new InvalidOperationException(SR.Format(SR.XmlChoiceIdentifierMemberMissing, choice.MemberName, accessorName));
            }
            choice.SetMemberInfo(member.MemberInfo);
            Type enumType = member.FieldType;
            enumType = CheckChoiceIdentifierType(enumType, isArrayLike, choice.MemberName, accessorName);
            return enumType;
        }
 
        [RequiresUnreferencedCode("calls ImportTypeMapping")]
        private void CreateArrayElementsFromAttributes(ArrayMapping arrayMapping, XmlArrayItemAttributes attributes, Type arrayElementType, string? arrayElementNs, RecursionLimiter limiter)
        {
            NameTable arrayItemElements = new NameTable();   // xmlelementname + xmlns -> ElementAccessor
 
            for (int i = 0; attributes != null && i < attributes.Count; i++)
            {
                XmlArrayItemAttribute xmlArrayItem = attributes[i]!;
                if (xmlArrayItem.NestingLevel != _arrayNestingLevel)
                    continue;
                Type targetType = xmlArrayItem.Type ?? arrayElementType;
                TypeDesc targetTypeDesc = _typeScope.GetTypeDesc(targetType);
                ElementAccessor arrayItemElement = new ElementAccessor();
                arrayItemElement.Namespace = xmlArrayItem.Namespace ?? arrayElementNs;
                arrayItemElement.Mapping = ImportTypeMapping(_modelScope.GetTypeModel(targetType), arrayItemElement.Namespace, ImportContext.Element, xmlArrayItem.DataType, null, limiter);
                arrayItemElement.Name = xmlArrayItem.ElementName.Length == 0 ? arrayItemElement.Mapping.DefaultElementName : XmlConvert.EncodeLocalName(xmlArrayItem.ElementName);
                arrayItemElement.IsNullable = xmlArrayItem.GetIsNullableSpecified() ? xmlArrayItem.IsNullable : targetTypeDesc.IsNullable || targetTypeDesc.IsOptionalValue;
                arrayItemElement.Form = xmlArrayItem.Form == XmlSchemaForm.None ? XmlSchemaForm.Qualified : xmlArrayItem.Form;
                CheckForm(arrayItemElement.Form, arrayElementNs != arrayItemElement.Namespace);
                CheckNullable(arrayItemElement.IsNullable, targetTypeDesc, arrayItemElement.Mapping);
                AddUniqueAccessor(arrayItemElements, arrayItemElement);
            }
            arrayMapping.Elements = (ElementAccessor[])arrayItemElements.ToArray(typeof(ElementAccessor));
        }
 
        [RequiresUnreferencedCode("calls GetArrayElementType")]
        private void ImportAccessorMapping(MemberMapping accessor, FieldModel model, XmlAttributes a, string? ns, Type? choiceIdentifierType, bool rpc, bool openModel, RecursionLimiter limiter)
        {
            XmlSchemaForm elementFormDefault = XmlSchemaForm.Qualified;
            int previousNestingLevel = _arrayNestingLevel;
            int sequenceId = -1;
            XmlArrayItemAttributes? previousArrayItemAttributes = _savedArrayItemAttributes;
            string? previousArrayNamespace = _savedArrayNamespace;
            _arrayNestingLevel = 0;
            _savedArrayItemAttributes = null;
            _savedArrayNamespace = null;
            Type accessorType = model.FieldType;
            string accessorName = model.Name;
            ArrayList elementList = new ArrayList();
            NameTable elements = new NameTable();
            accessor.TypeDesc = _typeScope.GetTypeDesc(accessorType);
            XmlAttributeFlags flags = a.XmlFlags;
            accessor.Ignore = a.XmlIgnore;
            if (rpc)
                CheckTopLevelAttributes(a);
            else
                CheckAmbiguousChoice(a, accessorType, accessorName);
 
            XmlAttributeFlags elemFlags = XmlAttributeFlags.Elements | XmlAttributeFlags.Text | XmlAttributeFlags.AnyElements | XmlAttributeFlags.ChoiceIdentifier;
            XmlAttributeFlags attrFlags = XmlAttributeFlags.Attribute | XmlAttributeFlags.AnyAttribute;
            XmlAttributeFlags arrayFlags = XmlAttributeFlags.Array | XmlAttributeFlags.ArrayItems;
 
            // special case for byte[]. It can be a primitive (base64Binary or hexBinary), or it can
            // be an array of bytes. Our default is primitive; specify [XmlArray] to get array behavior.
            if ((flags & arrayFlags) != 0 && accessorType == typeof(byte[]))
                accessor.TypeDesc = _typeScope.GetArrayTypeDesc(accessorType);
 
            if (a.XmlChoiceIdentifier != null)
            {
                accessor.ChoiceIdentifier = new ChoiceIdentifierAccessor();
                accessor.ChoiceIdentifier.MemberName = a.XmlChoiceIdentifier.MemberName;
                accessor.ChoiceIdentifier.MemberInfo = a.XmlChoiceIdentifier.GetMemberInfo();
                accessor.ChoiceIdentifier.Mapping = ImportTypeMapping(_modelScope.GetTypeModel(choiceIdentifierType!), ns, ImportContext.Element, string.Empty, null, limiter);
                CheckChoiceIdentifierMapping((EnumMapping)accessor.ChoiceIdentifier.Mapping);
            }
 
            if (accessor.TypeDesc.IsArrayLike)
            {
                Type arrayElementType = TypeScope.GetArrayElementType(accessorType, $"{model.FieldTypeDesc.FullName}.{model.Name}")!;
 
                if ((flags & attrFlags) != 0)
                {
                    if ((flags & attrFlags) != flags)
                        throw new InvalidOperationException(SR.XmlIllegalAttributesArrayAttribute);
 
                    if (a.XmlAttribute != null && !accessor.TypeDesc.ArrayElementTypeDesc!.IsPrimitive && !accessor.TypeDesc.ArrayElementTypeDesc.IsEnum)
                    {
                        if (accessor.TypeDesc.ArrayElementTypeDesc.Kind == TypeKind.Serializable)
                        {
                            throw new InvalidOperationException(SR.Format(SR.XmlIllegalAttrOrTextInterface, accessorName, accessor.TypeDesc.ArrayElementTypeDesc.FullName, nameof(IXmlSerializable)));
                        }
                        else
                        {
                            throw new InvalidOperationException(SR.Format(SR.XmlIllegalAttrOrText, accessorName, accessor.TypeDesc.ArrayElementTypeDesc.FullName));
                        }
                    }
 
                    bool isList = a.XmlAttribute != null && (accessor.TypeDesc.ArrayElementTypeDesc!.IsPrimitive || accessor.TypeDesc.ArrayElementTypeDesc.IsEnum);
 
                    if (a.XmlAnyAttribute != null)
                    {
                        a.XmlAttribute = new XmlAttributeAttribute();
                    }
 
                    AttributeAccessor attribute = new AttributeAccessor();
                    Type targetType = a.XmlAttribute!.Type == null ? arrayElementType : a.XmlAttribute.Type!;
                    TypeDesc targetTypeDesc = _typeScope.GetTypeDesc(targetType);
                    attribute.Name = Accessor.EscapeQName(a.XmlAttribute.AttributeName.Length == 0 ? accessorName : a.XmlAttribute.AttributeName);
                    attribute.Namespace = a.XmlAttribute.Namespace ?? ns;
                    attribute.Form = a.XmlAttribute.Form;
                    if (attribute.Form == XmlSchemaForm.None && ns != attribute.Namespace)
                    {
                        attribute.Form = XmlSchemaForm.Qualified;
                    }
                    attribute.CheckSpecial();
                    CheckForm(attribute.Form, ns != attribute.Namespace);
                    attribute.Mapping = ImportTypeMapping(_modelScope.GetTypeModel(targetType), ns, ImportContext.Attribute, a.XmlAttribute.DataType, null, isList, false, limiter);
                    attribute.IsList = isList;
                    attribute.Default = GetDefaultValue(model.FieldTypeDesc, model.FieldType, a);
                    attribute.Any = (a.XmlAnyAttribute != null);
                    if (attribute.Form == XmlSchemaForm.Qualified && attribute.Namespace != ns)
                    {
                        _xsdAttributes ??= new NameTable();
                        attribute = (AttributeAccessor)ReconcileAccessor(attribute, _xsdAttributes);
                    }
                    accessor.Attribute = attribute;
                }
                else if ((flags & elemFlags) != 0)
                {
                    if ((flags & elemFlags) != flags)
                        throw new InvalidOperationException(SR.XmlIllegalElementsArrayAttribute);
 
                    if (a.XmlText != null)
                    {
                        TextAccessor text = new TextAccessor();
                        Type targetType = a.XmlText.Type ?? arrayElementType;
                        TypeDesc targetTypeDesc = _typeScope.GetTypeDesc(targetType);
                        text.Name = accessorName; // unused except to make more helpful error messages
                        text.Mapping = ImportTypeMapping(_modelScope.GetTypeModel(targetType), ns, ImportContext.Text, a.XmlText.DataType, null, true, false, limiter);
                        if (!(text.Mapping is SpecialMapping) && targetTypeDesc != _typeScope.GetTypeDesc(typeof(string)))
                            throw new InvalidOperationException(SR.Format(SR.XmlIllegalArrayTextAttribute, accessorName));
 
                        accessor.Text = text;
                    }
                    if (a.XmlText == null && a.XmlElements.Count == 0 && a.XmlAnyElements.Count == 0)
                        a.XmlElements.Add(CreateElementAttribute(accessor.TypeDesc));
 
                    for (int i = 0; i < a.XmlElements.Count; i++)
                    {
                        XmlElementAttribute xmlElement = a.XmlElements[i]!;
                        Type targetType = xmlElement.Type ?? arrayElementType;
                        TypeDesc targetTypeDesc = _typeScope.GetTypeDesc(targetType);
                        TypeModel typeModel = _modelScope.GetTypeModel(targetType);
                        ElementAccessor element = new ElementAccessor();
                        element.Namespace = rpc ? null : xmlElement.Namespace ?? ns;
                        element.Mapping = ImportTypeMapping(typeModel, rpc ? ns : element.Namespace, ImportContext.Element, xmlElement.DataType, null, limiter);
                        if (a.XmlElements.Count == 1)
                        {
                            element.Name = XmlConvert.EncodeLocalName(xmlElement.ElementName.Length == 0 ? accessorName : xmlElement.ElementName);
                            //element.IsUnbounded = element.Mapping is ArrayMapping;
                        }
                        else
                        {
                            element.Name = xmlElement.ElementName.Length == 0 ? element.Mapping.DefaultElementName : XmlConvert.EncodeLocalName(xmlElement.ElementName);
                        }
                        element.Default = GetDefaultValue(model.FieldTypeDesc, model.FieldType, a);
                        if (xmlElement.GetIsNullableSpecified() && !xmlElement.IsNullable && typeModel.TypeDesc.IsOptionalValue)
                            //XmlInvalidNotNullable=IsNullable may not be set to 'false' for a Nullable<{0}> type. Consider using '{0}' type or removing the IsNullable property from the XmlElement attribute.
                            throw new InvalidOperationException(SR.Format(SR.XmlInvalidNotNullable, typeModel.TypeDesc.BaseTypeDesc!.FullName, "XmlElement"));
                        element.IsNullable = xmlElement.GetIsNullableSpecified() ? xmlElement.IsNullable : typeModel.TypeDesc.IsOptionalValue;
                        element.Form = rpc ? XmlSchemaForm.Unqualified : xmlElement.Form == XmlSchemaForm.None ? elementFormDefault : xmlElement.Form;
 
                        CheckNullable(element.IsNullable, targetTypeDesc, element.Mapping);
                        if (!rpc)
                        {
                            CheckForm(element.Form, ns != element.Namespace);
                            element = ReconcileLocalAccessor(element, ns);
                        }
                        if (xmlElement.Order != -1)
                        {
                            if (xmlElement.Order != sequenceId && sequenceId != -1)
                                throw new InvalidOperationException(SR.Format(SR.XmlSequenceMatch, "Order"));
                            sequenceId = xmlElement.Order;
                        }
                        AddUniqueAccessor(elements, element);
                        elementList.Add(element);
                    }
                    NameTable anys = new NameTable();
                    for (int i = 0; i < a.XmlAnyElements.Count; i++)
                    {
                        XmlAnyElementAttribute xmlAnyElement = a.XmlAnyElements[i]!;
                        Type targetType = typeof(IXmlSerializable).IsAssignableFrom(arrayElementType) ? arrayElementType : typeof(XmlNode).IsAssignableFrom(arrayElementType) ? arrayElementType : typeof(XmlElement);
                        if (!arrayElementType.IsAssignableFrom(targetType))
                            throw new InvalidOperationException(SR.Format(SR.XmlIllegalAnyElement, arrayElementType.FullName));
                        string anyName = xmlAnyElement.Name.Length == 0 ? xmlAnyElement.Name : XmlConvert.EncodeLocalName(xmlAnyElement.Name);
                        string? anyNs = xmlAnyElement.GetNamespaceSpecified() ? xmlAnyElement.Namespace : null;
                        if (anys[anyName, anyNs] != null)
                        {
                            // ignore duplicate anys
                            continue;
                        }
                        anys[anyName, anyNs] = xmlAnyElement;
                        if (elements[anyName, anyNs ?? ns] != null)
                        {
                            throw new InvalidOperationException(SR.Format(SR.XmlAnyElementDuplicate, accessorName, xmlAnyElement.Name, xmlAnyElement.Namespace ?? "null"));
                        }
                        ElementAccessor element = new ElementAccessor();
                        element.Name = anyName;
                        element.Namespace = anyNs ?? ns;
                        element.Any = true;
                        element.AnyNamespaces = anyNs;
                        TypeDesc targetTypeDesc = _typeScope.GetTypeDesc(targetType);
                        TypeModel typeModel = _modelScope.GetTypeModel(targetType);
                        if (element.Name.Length > 0)
                            typeModel.TypeDesc.IsMixed = true;
                        element.Mapping = ImportTypeMapping(typeModel, element.Namespace, ImportContext.Element, string.Empty, null, limiter);
                        element.Default = GetDefaultValue(model.FieldTypeDesc, model.FieldType, a);
                        element.IsNullable = false;
                        element.Form = elementFormDefault;
 
                        CheckNullable(element.IsNullable, targetTypeDesc, element.Mapping);
                        if (!rpc)
                        {
                            CheckForm(element.Form, ns != element.Namespace);
                            element = ReconcileLocalAccessor(element, ns);
                        }
                        elements.Add(element.Name, element.Namespace, element);
                        elementList.Add(element);
                        if (xmlAnyElement.Order != -1)
                        {
                            if (xmlAnyElement.Order != sequenceId && sequenceId != -1)
                                throw new InvalidOperationException(SR.Format(SR.XmlSequenceMatch, "Order"));
                            sequenceId = xmlAnyElement.Order;
                        }
                    }
                }
                else
                {
                    if ((flags & arrayFlags) != 0)
                    {
                        if ((flags & arrayFlags) != flags)
                            throw new InvalidOperationException(SR.XmlIllegalArrayArrayAttribute);
                    }
 
                    TypeDesc arrayElementTypeDesc = _typeScope.GetTypeDesc(arrayElementType);
                    a.XmlArray ??= CreateArrayAttribute();
                    if (CountAtLevel(a.XmlArrayItems, _arrayNestingLevel) == 0)
                        a.XmlArrayItems.Add(CreateArrayItemAttribute(_arrayNestingLevel));
                    ElementAccessor arrayElement = new ElementAccessor();
                    arrayElement.Name = XmlConvert.EncodeLocalName(a.XmlArray.ElementName.Length == 0 ? accessorName : a.XmlArray.ElementName);
                    arrayElement.Namespace = rpc ? null : a.XmlArray.Namespace ?? ns;
                    _savedArrayItemAttributes = a.XmlArrayItems;
                    _savedArrayNamespace = arrayElement.Namespace;
                    ArrayMapping arrayMapping = ImportArrayLikeMapping(_modelScope.GetArrayModel(accessorType), ns, limiter);
                    arrayElement.Mapping = arrayMapping;
                    arrayElement.IsNullable = a.XmlArray.IsNullable;
                    arrayElement.Form = rpc ? XmlSchemaForm.Unqualified : a.XmlArray.Form == XmlSchemaForm.None ? elementFormDefault : a.XmlArray.Form;
                    sequenceId = a.XmlArray.Order;
                    CheckNullable(arrayElement.IsNullable, accessor.TypeDesc, arrayElement.Mapping);
                    if (!rpc)
                    {
                        CheckForm(arrayElement.Form, ns != arrayElement.Namespace);
                        arrayElement = ReconcileLocalAccessor(arrayElement, ns);
                    }
                    _savedArrayItemAttributes = null;
                    _savedArrayNamespace = null;
 
                    AddUniqueAccessor(elements, arrayElement);
                    elementList.Add(arrayElement);
                }
            }
            else if (!accessor.TypeDesc.IsVoid)
            {
                XmlAttributeFlags allFlags = XmlAttributeFlags.Elements | XmlAttributeFlags.Text | XmlAttributeFlags.Attribute | XmlAttributeFlags.AnyElements | XmlAttributeFlags.ChoiceIdentifier | XmlAttributeFlags.XmlnsDeclarations;
                if ((flags & allFlags) != flags)
                    throw new InvalidOperationException(SR.XmlIllegalAttribute);
 
                if (accessor.TypeDesc.IsPrimitive || accessor.TypeDesc.IsEnum)
                {
                    if (a.XmlAnyElements.Count > 0) throw new InvalidOperationException(SR.Format(SR.XmlIllegalAnyElement, accessor.TypeDesc.FullName));
 
                    if (a.XmlAttribute != null)
                    {
                        if (a.XmlElements.Count > 0) throw new InvalidOperationException(SR.XmlIllegalAttribute);
                        if (a.XmlAttribute.Type != null) throw new InvalidOperationException(SR.Format(SR.XmlIllegalType, "XmlAttribute"));
                        AttributeAccessor attribute = new AttributeAccessor();
                        attribute.Name = Accessor.EscapeQName(a.XmlAttribute.AttributeName.Length == 0 ? accessorName : a.XmlAttribute.AttributeName);
                        attribute.Namespace = a.XmlAttribute.Namespace ?? ns;
                        attribute.Form = a.XmlAttribute.Form;
                        if (attribute.Form == XmlSchemaForm.None && ns != attribute.Namespace)
                        {
                            attribute.Form = XmlSchemaForm.Qualified;
                        }
                        attribute.CheckSpecial();
                        CheckForm(attribute.Form, ns != attribute.Namespace);
                        attribute.Mapping = ImportTypeMapping(_modelScope.GetTypeModel(accessorType), ns, ImportContext.Attribute, a.XmlAttribute.DataType, null, limiter);
                        attribute.Default = GetDefaultValue(model.FieldTypeDesc, model.FieldType, a);
                        attribute.Any = a.XmlAnyAttribute != null;
                        if (attribute.Form == XmlSchemaForm.Qualified && attribute.Namespace != ns)
                        {
                            _xsdAttributes ??= new NameTable();
                            attribute = (AttributeAccessor)ReconcileAccessor(attribute, _xsdAttributes);
                        }
                        accessor.Attribute = attribute;
                    }
                    else
                    {
                        if (a.XmlText != null)
                        {
                            if (a.XmlText.Type != null && a.XmlText.Type != accessorType)
                                throw new InvalidOperationException(SR.Format(SR.XmlIllegalType, "XmlText"));
                            TextAccessor text = new TextAccessor();
                            text.Name = accessorName; // unused except to make more helpful error messages
                            text.Mapping = ImportTypeMapping(_modelScope.GetTypeModel(accessorType), ns, ImportContext.Text, a.XmlText.DataType, null, limiter);
                            accessor.Text = text;
                        }
                        else if (a.XmlElements.Count == 0)
                        {
                            a.XmlElements.Add(CreateElementAttribute(accessor.TypeDesc));
                        }
 
                        for (int i = 0; i < a.XmlElements.Count; i++)
                        {
                            XmlElementAttribute xmlElement = a.XmlElements[i]!;
                            if (xmlElement!.Type != null)
                            {
                                if (_typeScope.GetTypeDesc(xmlElement.Type) != accessor.TypeDesc)
                                    throw new InvalidOperationException(SR.Format(SR.XmlIllegalType, "XmlElement"));
                            }
                            ElementAccessor element = new ElementAccessor();
                            element.Name = XmlConvert.EncodeLocalName(xmlElement.ElementName.Length == 0 ? accessorName : xmlElement.ElementName);
                            element.Namespace = rpc ? null : xmlElement.Namespace ?? ns;
                            TypeModel typeModel = _modelScope.GetTypeModel(accessorType);
                            element.Mapping = ImportTypeMapping(typeModel, rpc ? ns : element.Namespace, ImportContext.Element, xmlElement.DataType, null, limiter);
                            if (element.Mapping.TypeDesc!.Kind == TypeKind.Node)
                            {
                                element.Any = true;
                            }
                            element.Default = GetDefaultValue(model.FieldTypeDesc, model.FieldType, a);
                            if (xmlElement.GetIsNullableSpecified() && !xmlElement.IsNullable && typeModel.TypeDesc.IsOptionalValue)
                                //XmlInvalidNotNullable=IsNullable may not be set to 'false' for a Nullable<{0}> type. Consider using '{0}' type or removing the IsNullable property from the XmlElement attribute.
                                throw new InvalidOperationException(SR.Format(SR.XmlInvalidNotNullable, typeModel.TypeDesc.BaseTypeDesc!.FullName, "XmlElement"));
                            element.IsNullable = xmlElement.GetIsNullableSpecified() ? xmlElement.IsNullable : typeModel.TypeDesc.IsOptionalValue;
                            element.Form = rpc ? XmlSchemaForm.Unqualified : xmlElement.Form == XmlSchemaForm.None ? elementFormDefault : xmlElement.Form;
 
                            CheckNullable(element.IsNullable, accessor.TypeDesc, element.Mapping);
                            if (!rpc)
                            {
                                CheckForm(element.Form, ns != element.Namespace);
                                element = ReconcileLocalAccessor(element, ns);
                            }
                            if (xmlElement.Order != -1)
                            {
                                if (xmlElement.Order != sequenceId && sequenceId != -1)
                                    throw new InvalidOperationException(SR.Format(SR.XmlSequenceMatch, "Order"));
                                sequenceId = xmlElement.Order;
                            }
                            AddUniqueAccessor(elements, element);
                            elementList.Add(element);
                        }
                    }
                }
                else if (a.Xmlns)
                {
                    if (flags != XmlAttributeFlags.XmlnsDeclarations)
                        throw new InvalidOperationException(SR.XmlSoleXmlnsAttribute);
 
                    if (accessorType != typeof(System.Xml.Serialization.XmlSerializerNamespaces))
                    {
                        throw new InvalidOperationException(SR.Format(SR.XmlXmlnsInvalidType, accessorName, accessorType.FullName, typeof(System.Xml.Serialization.XmlSerializerNamespaces).FullName));
                    }
                    accessor.Xmlns = new XmlnsAccessor();
                    accessor.Ignore = true;
                }
                else
                {
                    if (a.XmlAttribute != null || a.XmlText != null)
                    {
                        if (accessor.TypeDesc.Kind == TypeKind.Serializable)
                        {
                            throw new InvalidOperationException(SR.Format(SR.XmlIllegalAttrOrTextInterface, accessorName, accessor.TypeDesc.FullName, nameof(IXmlSerializable)));
                        }
                        else
                        {
                            throw new InvalidOperationException(SR.Format(SR.XmlIllegalAttrOrText, accessorName, accessor.TypeDesc));
                        }
                    }
                    if (a.XmlElements.Count == 0 && a.XmlAnyElements.Count == 0)
                        a.XmlElements.Add(CreateElementAttribute(accessor.TypeDesc));
                    for (int i = 0; i < a.XmlElements.Count; i++)
                    {
                        XmlElementAttribute xmlElement = a.XmlElements[i]!;
                        Type targetType = xmlElement.Type ?? accessorType;
                        TypeDesc targetTypeDesc = _typeScope.GetTypeDesc(targetType);
                        ElementAccessor element = new ElementAccessor();
                        TypeModel typeModel = _modelScope.GetTypeModel(targetType);
                        element.Namespace = rpc ? null : xmlElement.Namespace ?? ns;
                        element.Mapping = ImportTypeMapping(typeModel, rpc ? ns : element.Namespace, ImportContext.Element, xmlElement.DataType, null, false, openModel, limiter);
                        if (a.XmlElements.Count == 1)
                        {
                            element.Name = XmlConvert.EncodeLocalName(xmlElement.ElementName.Length == 0 ? accessorName : xmlElement.ElementName);
                        }
                        else
                        {
                            element.Name = xmlElement.ElementName.Length == 0 ? element.Mapping.DefaultElementName : XmlConvert.EncodeLocalName(xmlElement.ElementName);
                        }
                        element.Default = GetDefaultValue(model.FieldTypeDesc, model.FieldType, a);
                        if (xmlElement.GetIsNullableSpecified() && !xmlElement.IsNullable && typeModel.TypeDesc.IsOptionalValue)
                            //XmlInvalidNotNullable=IsNullable may not be set to 'false' for a Nullable<{0}> type. Consider using '{0}' type or removing the IsNullable property from the XmlElement attribute.
                            throw new InvalidOperationException(SR.Format(SR.XmlInvalidNotNullable, typeModel.TypeDesc.BaseTypeDesc!.FullName, "XmlElement"));
                        element.IsNullable = xmlElement.GetIsNullableSpecified() ? xmlElement.IsNullable : typeModel.TypeDesc.IsOptionalValue;
                        element.Form = rpc ? XmlSchemaForm.Unqualified : xmlElement.Form == XmlSchemaForm.None ? elementFormDefault : xmlElement.Form;
                        CheckNullable(element.IsNullable, targetTypeDesc, element.Mapping);
 
                        if (!rpc)
                        {
                            CheckForm(element.Form, ns != element.Namespace);
                            element = ReconcileLocalAccessor(element, ns);
                        }
                        if (xmlElement.Order != -1)
                        {
                            if (xmlElement.Order != sequenceId && sequenceId != -1)
                                throw new InvalidOperationException(SR.Format(SR.XmlSequenceMatch, "Order"));
                            sequenceId = xmlElement.Order;
                        }
                        AddUniqueAccessor(elements, element);
                        elementList.Add(element);
                    }
                    NameTable anys = new NameTable();
                    for (int i = 0; i < a.XmlAnyElements.Count; i++)
                    {
                        XmlAnyElementAttribute xmlAnyElement = a.XmlAnyElements[i]!;
                        Type targetType = typeof(IXmlSerializable).IsAssignableFrom(accessorType) ? accessorType : typeof(XmlNode).IsAssignableFrom(accessorType) ? accessorType : typeof(XmlElement);
                        if (!accessorType.IsAssignableFrom(targetType))
                            throw new InvalidOperationException(SR.Format(SR.XmlIllegalAnyElement, accessorType.FullName));
 
                        string anyName = xmlAnyElement.Name.Length == 0 ? xmlAnyElement.Name : XmlConvert.EncodeLocalName(xmlAnyElement.Name);
                        string? anyNs = xmlAnyElement.GetNamespaceSpecified() ? xmlAnyElement.Namespace : null;
                        if (anys[anyName, anyNs] != null)
                        {
                            // ignore duplicate anys
                            continue;
                        }
                        anys[anyName, anyNs] = xmlAnyElement;
                        if (elements[anyName, anyNs ?? ns] != null)
                        {
                            throw new InvalidOperationException(SR.Format(SR.XmlAnyElementDuplicate, accessorName, xmlAnyElement.Name, xmlAnyElement.Namespace ?? "null"));
                        }
                        ElementAccessor element = new ElementAccessor();
                        element.Name = anyName;
                        element.Namespace = anyNs ?? ns;
                        element.Any = true;
                        element.AnyNamespaces = anyNs;
                        TypeDesc targetTypeDesc = _typeScope.GetTypeDesc(targetType);
                        TypeModel typeModel = _modelScope.GetTypeModel(targetType);
 
                        if (element.Name.Length > 0)
                            typeModel.TypeDesc.IsMixed = true;
                        element.Mapping = ImportTypeMapping(typeModel, element.Namespace, ImportContext.Element, string.Empty, null, false, openModel, limiter);
                        element.Default = GetDefaultValue(model.FieldTypeDesc, model.FieldType, a);
                        element.IsNullable = false;
                        element.Form = elementFormDefault;
                        CheckNullable(element.IsNullable, targetTypeDesc, element.Mapping);
                        if (!rpc)
                        {
                            CheckForm(element.Form, ns != element.Namespace);
                            element = ReconcileLocalAccessor(element, ns);
                        }
                        if (xmlAnyElement.Order != -1)
                        {
                            if (xmlAnyElement.Order != sequenceId && sequenceId != -1)
                                throw new InvalidOperationException(SR.Format(SR.XmlSequenceMatch, "Order"));
                            sequenceId = xmlAnyElement.Order;
                        }
                        elements.Add(element.Name, element.Namespace, element);
                        elementList.Add(element);
                    }
                }
            }
            accessor.Elements = (ElementAccessor[])elementList.ToArray(typeof(ElementAccessor));
            accessor.SequenceId = sequenceId;
 
            if (rpc)
            {
                if (accessor.TypeDesc.IsArrayLike && accessor.Elements.Length > 0 && !(accessor.Elements[0].Mapping is ArrayMapping))
                    throw new InvalidOperationException(SR.Format(SR.XmlRpcLitArrayElement, accessor.Elements[0].Name));
 
                if (accessor.Xmlns != null)
                    throw new InvalidOperationException(SR.Format(SR.XmlRpcLitXmlns, accessor.Name));
            }
 
            if (accessor.ChoiceIdentifier != null)
            {
                // find the enum value corresponding to each element
                accessor.ChoiceIdentifier.MemberIds = new string[accessor.Elements.Length];
                for (int i = 0; i < accessor.Elements.Length; i++)
                {
                    bool found = false;
                    ElementAccessor element = accessor.Elements[i];
                    EnumMapping choiceMapping = (EnumMapping)accessor.ChoiceIdentifier.Mapping!;
                    for (int j = 0; j < choiceMapping.Constants!.Length; j++)
                    {
                        string xmlName = choiceMapping.Constants[j].XmlName;
 
                        if (element.Any && element.Name.Length == 0)
                        {
                            string anyNs = element.AnyNamespaces ?? "##any";
                            if (xmlName.Substring(0, xmlName.Length - 1) == anyNs)
                            {
                                accessor.ChoiceIdentifier.MemberIds[i] = choiceMapping.Constants[j].Name;
                                found = true;
                                break;
                            }
                            continue;
                        }
                        int colon = xmlName.LastIndexOf(':');
                        string? choiceNs = colon < 0 ? choiceMapping.Namespace : xmlName.Substring(0, colon);
                        string choiceName = colon < 0 ? xmlName : xmlName.Substring(colon + 1);
 
                        if (element.Name == choiceName)
                        {
                            if ((element.Form == XmlSchemaForm.Unqualified && string.IsNullOrEmpty(choiceNs)) || element.Namespace == choiceNs)
                            {
                                accessor.ChoiceIdentifier.MemberIds[i] = choiceMapping.Constants[j].Name;
                                found = true;
                                break;
                            }
                        }
                    }
                    if (!found)
                    {
                        if (element.Any && element.Name.Length == 0)
                        {
                            // Type {0} is missing enumeration value '##any' for XmlAnyElementAttribute.
                            throw new InvalidOperationException(SR.Format(SR.XmlChoiceMissingAnyValue, accessor.ChoiceIdentifier.Mapping!.TypeDesc!.FullName));
                        }
                        else
                        {
                            string id = element.Namespace != null && element.Namespace.Length > 0 ? $"{element.Namespace}:{element.Name}" : element.Name;
                            // Type {0} is missing value for '{1}'.
                            throw new InvalidOperationException(SR.Format(SR.XmlChoiceMissingValue, accessor.ChoiceIdentifier.Mapping!.TypeDesc!.FullName, id, element.Name, element.Namespace));
                        }
                    }
                }
            }
            _arrayNestingLevel = previousNestingLevel;
            _savedArrayItemAttributes = previousArrayItemAttributes;
            _savedArrayNamespace = previousArrayNamespace;
        }
 
 
        private static void CheckTopLevelAttributes(XmlAttributes a)
        {
            XmlAttributeFlags flags = a.XmlFlags;
 
            if ((flags & (XmlAttributeFlags.Attribute | XmlAttributeFlags.AnyAttribute)) != 0)
                throw new InvalidOperationException(SR.XmlRpcLitAttributeAttributes);
 
            if ((flags & (XmlAttributeFlags.Text | XmlAttributeFlags.AnyElements | XmlAttributeFlags.ChoiceIdentifier)) != 0)
                throw new InvalidOperationException(SR.XmlRpcLitAttributes);
 
            if (a.XmlElements != null && a.XmlElements.Count > 0)
            {
                if (a.XmlElements.Count > 1)
                {
                    throw new InvalidOperationException(SR.XmlRpcLitElements);
                }
                XmlElementAttribute xmlElement = a.XmlElements[0]!;
                if (xmlElement.Namespace != null)
                {
                    throw new InvalidOperationException(SR.Format(SR.XmlRpcLitElementNamespace, "Namespace", xmlElement.Namespace));
                }
                if (xmlElement.IsNullable)
                {
                    throw new InvalidOperationException(SR.Format(SR.XmlRpcLitElementNullable, "IsNullable", "true"));
                }
            }
            if (a.XmlArray != null && a.XmlArray.Namespace != null)
            {
                throw new InvalidOperationException(SR.Format(SR.XmlRpcLitElementNamespace, "Namespace", a.XmlArray.Namespace));
            }
        }
 
        private void CheckAmbiguousChoice(XmlAttributes a, Type accessorType, string accessorName)
        {
            Hashtable choiceTypes = new Hashtable();
 
            XmlElementAttributes elements = a.XmlElements;
            if (elements != null && elements.Count >= 2 && a.XmlChoiceIdentifier == null)
            {
                for (int i = 0; i < elements.Count; i++)
                {
                    Type type = elements[i]!.Type == null ? accessorType : elements[i]!.Type!;
                    if (choiceTypes.Contains(type))
                    {
                        // You need to add {0} to the '{1}'.
                        throw new InvalidOperationException(SR.Format(SR.XmlChoiceIdentifierMissing, nameof(XmlChoiceIdentifierAttribute), accessorName));
                    }
                    else
                    {
                        choiceTypes.Add(type, false);
                    }
                }
            }
            if (choiceTypes.Contains(typeof(XmlElement)) && a.XmlAnyElements.Count > 0)
            {
                // You need to add {0} to the '{1}'.
                throw new InvalidOperationException(SR.Format(SR.XmlChoiceIdentifierMissing, nameof(XmlChoiceIdentifierAttribute), accessorName));
            }
 
            XmlArrayItemAttributes items = a.XmlArrayItems;
            if (items != null && items.Count >= 2)
            {
                NameTable arrayTypes = new NameTable();
 
                for (int i = 0; i < items.Count; i++)
                {
                    Type type = items[i]!.Type == null ? accessorType : items[i]!.Type!;
                    string ns = items[i]!.NestingLevel.ToString(CultureInfo.InvariantCulture);
                    XmlArrayItemAttribute? item = (XmlArrayItemAttribute?)arrayTypes[type.FullName, ns];
                    if (item != null)
                    {
                        throw new InvalidOperationException(SR.Format(SR.XmlArrayItemAmbiguousTypes, accessorName, item.ElementName, items[i]!.ElementName, nameof(XmlElementAttribute), nameof(XmlChoiceIdentifierAttribute), accessorName));
                    }
                    else
                    {
                        arrayTypes[type.FullName, ns] = items[i];
                    }
                }
            }
        }
 
        private static void CheckChoiceIdentifierMapping(EnumMapping choiceMapping)
        {
            NameTable ids = new NameTable();
            for (int i = 0; i < choiceMapping.Constants!.Length; i++)
            {
                string choiceId = choiceMapping.Constants[i].XmlName;
                int colon = choiceId.LastIndexOf(':');
                string choiceName = colon < 0 ? choiceId : choiceId.Substring(colon + 1);
                string choiceNs = colon < 0 ? "" : choiceId.Substring(0, colon);
 
                if (ids[choiceName, choiceNs] != null)
                {
                    // Enum values in the XmlChoiceIdentifier '{0}' have to be unique.  Value '{1}' already present.
                    throw new InvalidOperationException(SR.Format(SR.XmlChoiceIdDuplicate, choiceMapping.TypeName, choiceId));
                }
                ids.Add(choiceName, choiceNs, choiceMapping.Constants[i]);
            }
        }
 
        private static object? GetDefaultValue(TypeDesc fieldTypeDesc, Type t, XmlAttributes a)
        {
            if (a.XmlDefaultValue == null || a.XmlDefaultValue == DBNull.Value) return null;
            if (!(fieldTypeDesc.Kind == TypeKind.Primitive || fieldTypeDesc.Kind == TypeKind.Enum))
            {
                //throw new InvalidOperationException(SR.XmlIllegalDefault);
                a.XmlDefaultValue = null;
                return a.XmlDefaultValue;
            }
            // for enums validate and return a string representation
            if (fieldTypeDesc.Kind == TypeKind.Enum)
            {
                string strValue = Enum.Format(t, a.XmlDefaultValue, "G").Replace(",", " ");
                string numValue = Enum.Format(t, a.XmlDefaultValue, "D");
                if (strValue == numValue) // means enum value wasn't recognized
                    throw new InvalidOperationException(SR.Format(SR.XmlInvalidDefaultValue, strValue, a.XmlDefaultValue.GetType().FullName));
                return strValue;
            }
            return a.XmlDefaultValue;
        }
 
        private static XmlArrayItemAttribute CreateArrayItemAttribute(int nestingLevel)
        {
            XmlArrayItemAttribute xmlArrayItem = new XmlArrayItemAttribute();
            xmlArrayItem.NestingLevel = nestingLevel;
            return xmlArrayItem;
        }
 
        private static XmlArrayAttribute CreateArrayAttribute()
        {
            XmlArrayAttribute xmlArrayItem = new XmlArrayAttribute();
            return xmlArrayItem;
        }
 
        private static XmlElementAttribute CreateElementAttribute(TypeDesc typeDesc)
        {
            XmlElementAttribute xmlElement = new XmlElementAttribute();
            xmlElement.IsNullable = typeDesc.IsOptionalValue;
            return xmlElement;
        }
 
        private static void AddUniqueAccessor(INameScope scope, Accessor accessor)
        {
            Accessor? existing = (Accessor?)scope[accessor.Name, accessor.Namespace];
            if (existing != null)
            {
                if (accessor is ElementAccessor)
                {
                    throw new InvalidOperationException(SR.Format(SR.XmlDuplicateElementName, existing.Name, existing.Namespace));
                }
                else
                {
#if DEBUG
                    if (!(accessor is AttributeAccessor))
                        throw new InvalidOperationException(SR.Format(SR.XmlInternalErrorDetails, "Bad accessor type " + accessor.GetType().FullName));
#endif
                    throw new InvalidOperationException(SR.Format(SR.XmlDuplicateAttributeName, existing.Name, existing.Namespace));
                }
            }
            else
            {
                scope[accessor.Name, accessor.Namespace] = accessor;
            }
        }
 
        private static void AddUniqueAccessor(MemberMapping member, INameScope elements, INameScope attributes, bool isSequence)
        {
            if (member.Attribute != null)
            {
                AddUniqueAccessor(attributes, member.Attribute);
            }
            else if (!isSequence && member.Elements != null && member.Elements.Length > 0)
            {
                for (int i = 0; i < member.Elements.Length; i++)
                {
                    AddUniqueAccessor(elements, member.Elements[i]);
                }
            }
        }
 
        private static void CheckForm(XmlSchemaForm form, bool isQualified)
        {
            if (isQualified && form == XmlSchemaForm.Unqualified) throw new InvalidOperationException(SR.XmlInvalidFormUnqualified);
        }
 
        private static void CheckNullable(bool isNullable, TypeDesc typeDesc, TypeMapping? mapping)
        {
            if (mapping is NullableMapping) return;
            if (mapping is SerializableMapping) return;
            if (isNullable && !typeDesc.IsNullable) throw new InvalidOperationException(SR.Format(SR.XmlInvalidIsNullable, typeDesc.FullName));
        }
 
        private static ElementAccessor CreateElementAccessor(TypeMapping mapping, string ns)
        {
            ElementAccessor element = new ElementAccessor();
            bool isAny = mapping.TypeDesc!.Kind == TypeKind.Node;
            if (!isAny && mapping is SerializableMapping)
            {
                isAny = ((SerializableMapping)mapping).IsAny;
            }
            if (isAny)
            {
                element.Any = true;
            }
            else
            {
                element.Name = mapping.DefaultElementName;
                element.Namespace = ns;
            }
            element.Mapping = mapping;
            return element;
        }
 
        // will create a shallow type mapping for a top-level type
        [RequiresUnreferencedCode("Calls TypeScope.GetTypeDesc(Type) which has RequiresUnreferencedCode")]
        internal static XmlTypeMapping GetTopLevelMapping(Type type, string? defaultNamespace)
        {
            defaultNamespace ??= string.Empty;
            XmlAttributes a = new XmlAttributes(type);
            TypeDesc typeDesc = new TypeScope().GetTypeDesc(type);
            ElementAccessor element = new ElementAccessor();
 
            if (typeDesc.Kind == TypeKind.Node)
            {
                element.Any = true;
            }
            else
            {
                string? ns = a.XmlRoot == null ? defaultNamespace : a.XmlRoot.Namespace;
                string typeName = string.Empty;
                if (a.XmlType != null)
                    typeName = a.XmlType.TypeName;
                if (typeName.Length == 0)
                    typeName = type.Name;
 
                element.Name = XmlConvert.EncodeLocalName(typeName);
                element.Namespace = ns;
            }
            XmlTypeMapping mapping = new XmlTypeMapping(null, element);
            mapping.SetKeyInternal(XmlMapping.GenerateKey(type, a.XmlRoot, defaultNamespace));
            return mapping;
        }
    }
    internal sealed class ImportStructWorkItem
    {
        private readonly StructModel _model;
        private readonly StructMapping _mapping;
 
        internal ImportStructWorkItem(StructModel model, StructMapping mapping)
        {
            _model = model;
            _mapping = mapping;
        }
 
        internal StructModel Model { get { return _model; } }
        internal StructMapping Mapping { get { return _mapping; } }
    }
 
    internal sealed class WorkItems
    {
        private readonly ArrayList _list = new ArrayList();
 
        internal ImportStructWorkItem this[int index]
        {
            get
            {
                return (ImportStructWorkItem)_list[index]!;
            }
            set
            {
                _list[index] = value;
            }
        }
 
        internal int Count
        {
            get
            {
                return _list.Count;
            }
        }
 
        internal void Add(ImportStructWorkItem item)
        {
            _list.Add(item);
        }
 
        internal bool Contains(StructMapping mapping)
        {
            return IndexOf(mapping) >= 0;
        }
 
        internal int IndexOf(StructMapping mapping)
        {
            for (int i = 0; i < Count; i++)
            {
                if (this[i].Mapping == mapping)
                    return i;
            }
            return -1;
        }
 
        internal void RemoveAt(int index)
        {
            _list.RemoveAt(index);
        }
    }
 
    internal sealed class RecursionLimiter
    {
        private readonly int _maxDepth;
        private int _depth;
        private WorkItems? _deferredWorkItems;
 
        internal RecursionLimiter()
        {
            _depth = 0;
            _maxDepth = DiagnosticsSwitches.NonRecursiveTypeLoading.Enabled ? 1 : int.MaxValue;
        }
 
        internal bool IsExceededLimit { get { return _depth > _maxDepth; } }
        internal int Depth { get { return _depth; } set { _depth = value; } }
 
        internal WorkItems DeferredWorkItems => _deferredWorkItems ??= new WorkItems();
    }
}