UA-.NETStandard/tools/Opc.Ua.SourceGeneration.Core/Dependency/ModelDependencyV1.cs

/* ========================================================================
 * Copyright (c) 2005-2026 The OPC Foundation, Inc. All rights reserved.
 *
 * OPC Foundation MIT License 1.00
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use,
 * copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 *
 * The complete license agreement can be found here:
 * http://opcfoundation.org/License/MIT/1.00/
 * ======================================================================*/

using System;
using System.Collections.Generic;
using System.IO;
using System.IO.Compression;
using System.Text;
using System.Xml;

namespace Opc.Ua.SourceGeneration.Dependency
{
    /// <summary>
    /// Kind of node carried in a <see cref="ModelDependencyV1"/>.
    /// </summary>
    public enum DependencyNodeKind : byte
    {
        /// <summary>
        /// Unknown — invalid in a well-formed dependency payload.
        /// </summary>
        Unknown = 0,

        /// <summary>
        /// ObjectType.
        /// </summary>
        ObjectType = 1,

        /// <summary>
        /// VariableType.
        /// </summary>
        VariableType = 2,

        /// <summary>
        /// ReferenceType.
        /// </summary>
        ReferenceType = 3,

        /// <summary>
        /// DataType.
        /// </summary>
        DataType = 4,

        /// <summary>
        /// Method (when carried as standalone declaration).
        /// </summary>
        Method = 5
    }

    /// <summary>
    /// Reduced view of a <c>DataTypeDesign</c> field carried in a dependency payload.
    /// </summary>
    public readonly record struct DependencyDataField
    {
        /// <summary>
        /// Field name.
        /// </summary>
        public string Name { get; }

        /// <summary>
        /// DataType name (qualified).
        /// </summary>
        public string DataTypeName { get; }

        /// <summary>
        /// DataType namespace URI.
        /// </summary>
        public string DataTypeNamespace { get; }

        /// <summary>Value rank (<see cref="ValueRanks"/>).</summary>
        public int ValueRank { get; }

        /// <summary>
        /// True if the structure field is optional (encoding mask bit).
        /// Carried in the structure field trailer.
        /// </summary>
        public bool IsOptional { get; init; }

        /// <summary>
        /// True if the structure field allows subtypes of its data type
        /// (encoded as ExtensionObject). Carried in the structure field
        /// trailer.
        /// </summary>
        public bool AllowSubTypes { get; init; }

        /// <summary>
        /// The declared array dimensions ("0,0,0"), or <c>null</c>.
        /// Carried in the structure field trailer.
        /// </summary>
        public string? ArrayDimensions { get; init; }

        /// <summary>
        /// Constructor.
        /// </summary>
        public DependencyDataField(string name, string dataTypeName, string dataTypeNamespace, int valueRank)
        {
            Name = name ?? string.Empty;
            DataTypeName = dataTypeName ?? string.Empty;
            DataTypeNamespace = dataTypeNamespace ?? string.Empty;
            ValueRank = valueRank;
        }
    }

    /// <summary>
    /// A method input or output argument carried in a dependency payload.
    /// </summary>
    public readonly record struct DependencyMethodArg
    {
        /// <summary>
        /// Argument name.
        /// </summary>
        public string Name { get; }

        /// <summary>
        /// DataType name (qualified).
        /// </summary>
        public string DataTypeName { get; }

        /// <summary>
        /// DataType namespace URI.
        /// </summary>
        public string DataTypeNamespace { get; }

        /// <summary>
        /// Value rank.
        /// </summary>
        public int ValueRank { get; }

        /// <summary>
        /// Constructor.
        /// </summary>
        public DependencyMethodArg(string name, string dataTypeName, string dataTypeNamespace, int valueRank)
        {
            Name = name ?? string.Empty;
            DataTypeName = dataTypeName ?? string.Empty;
            DataTypeNamespace = dataTypeNamespace ?? string.Empty;
            ValueRank = valueRank;
        }
    }

    /// <summary>
    /// Reduced view of an <c>InstanceDesign</c> child carried in a
    /// dependency payload type. Carries enough metadata for downstream
    /// generators to set <c>OveriddenNode</c> + <c>TypeDefinitionNode</c>
    /// / <c>DataTypeNode</c> on consumer's re-declared inherited
    /// members.
    /// </summary>
    public sealed class DependencyChild
    {
        /// <summary>
        /// Browse name of the child.
        /// </summary>
        public string BrowseName { get; set; } = string.Empty;

        /// <summary>
        /// Namespace URI qualifying <see cref="BrowseName"/>. Empty when the
        /// declaring type's own namespace qualifies it. A child re-declared
        /// from a base type in another namespace keeps the namespace of its
        /// original declaration here, so a consumer that instantiates the
        /// derived type on its own still emits <c>0:EngineeringUnits</c>
        /// rather than re-qualifying it into the declaring model.
        /// </summary>
        public string BrowseNameNamespace { get; set; } = string.Empty;

        /// <summary>
        /// Symbolic name (often equal to BrowseName).
        /// </summary>
        public string SymbolicName { get; set; } = string.Empty;

        /// <summary>
        /// TypeDefinition name (for all kinds). Empty when not declared.
        /// </summary>
        public string TypeDefinitionName { get; set; } = string.Empty;

        /// <summary>
        /// TypeDefinition namespace URI.
        /// </summary>
        public string TypeDefinitionNamespace { get; set; } = string.Empty;

        /// <summary>
        /// DataType name (variables only). Empty when not applicable.
        /// </summary>
        public string DataTypeName { get; set; } = string.Empty;

        /// <summary>
        /// DataType namespace URI (variables only).
        /// </summary>
        public string DataTypeNamespace { get; set; } = string.Empty;

        /// <summary>Value rank (variables only; <c>Scalar = 0</c> per <c>Opc.Ua.ValueRanks</c>).</summary>
        public int ValueRank { get; set; }

        /// <summary>
        /// Modelling rule (0=None, 1=Mandatory, 2=Optional, 3=OptionalPlaceholder, 4=MandatoryPlaceholder, 5=ExposesItsArray).
        /// </summary>
        public byte ModellingRule { get; set; }

        /// <summary>
        /// Instance kind: 1=Object 2=Variable 3=Property 4=Method.
        /// </summary>
        public byte InstanceKind { get; set; }

        /// <summary>
        /// Name of the reference type binding the child to its parent. Empty
        /// when the kind default applies (<c>HasProperty</c> for a property,
        /// <c>HasComponent</c> otherwise).
        /// </summary>
        public string ReferenceTypeName { get; set; } = string.Empty;

        /// <summary>
        /// Namespace URI of <see cref="ReferenceTypeName"/>.
        /// </summary>
        public string ReferenceTypeNamespace { get; set; } = string.Empty;

        /// <summary>
        /// ModelDesign access level value (variables only).
        /// </summary>
        public byte AccessLevel { get; set; }

        /// <summary>
        /// Whether <see cref="AccessLevel"/> was explicitly specified.
        /// </summary>
        public bool AccessLevelSpecified { get; set; }

        /// <summary>
        /// Exact OPC UA AccessLevel bitmask imported from NodeSet2.
        /// </summary>
        public uint? RawAccessLevel { get; set; }

        /// <summary>
        /// Exact OPC UA UserAccessLevel bitmask imported from NodeSet2.
        /// </summary>
        public uint? RawUserAccessLevel { get; set; }

        /// <summary>
        /// Minimum sampling interval (variables only).
        /// </summary>
        public int MinimumSamplingInterval { get; set; }

        /// <summary>
        /// Whether <see cref="MinimumSamplingInterval"/> was explicitly specified.
        /// </summary>
        public bool MinimumSamplingIntervalSpecified { get; set; }

        /// <summary>
        /// Whether historical data is collected (variables only).
        /// </summary>
        public bool Historizing { get; set; }

        /// <summary>
        /// Whether <see cref="Historizing"/> was explicitly specified.
        /// </summary>
        public bool HistorizingSpecified { get; set; }

        /// <summary>
        /// Serialized ModelDesign default value XML (variables only).
        /// </summary>
        public string? DefaultValueXml { get; set; }

        /// <summary>
        /// The namespace table the namespace indexes in
        /// <see cref="DefaultValueXml"/> refer to in the producing model
        /// (index 0 is the OPC UA namespace): the producer's design
        /// namespaces, or the table of the NodeSet or dependency the value
        /// was decoded from. Null when the payload does not carry it (older
        /// producers); the consumer then resolves the indexes as before.
        /// Carried in the value namespace trailer.
        /// </summary>
        public IReadOnlyList<string>? DefaultValueNamespaceUris { get; set; }

        /// <summary>
        /// Input arguments (methods only).
        /// </summary>
        public IReadOnlyList<DependencyMethodArg> InputArguments { get; set; } = [];

        /// <summary>
        /// Output arguments (methods only).
        /// </summary>
        public IReadOnlyList<DependencyMethodArg> OutputArguments { get; set; } = [];

        /// <summary>
        /// Qualified method state identity used by the producing assembly.
        /// Empty for payloads without method identity and non-method children.
        /// </summary>
        public string MethodStateName { get; set; } = string.Empty;

        /// <summary>
        /// Namespace URI for <see cref="MethodStateName"/>.
        /// </summary>
        public string MethodStateNamespace { get; set; } = string.Empty;

        /// <summary>
        /// Qualified method declaration identity used on the wire.
        /// Empty for payloads without method identity and non-method children.
        /// </summary>
        public string MethodDeclarationName { get; set; } = string.Empty;

        /// <summary>
        /// Namespace URI for <see cref="MethodDeclarationName"/>.
        /// </summary>
        public string MethodDeclarationNamespace { get; set; } = string.Empty;

        /// <summary>
        /// Numeric NodeId identifier for the effective method declaration.
        /// </summary>
        public uint MethodDeclarationNumericId { get; set; }

        /// <summary>
        /// String NodeId identifier for the effective method declaration.
        /// </summary>
        public string? MethodDeclarationStringId { get; set; }
    }

    /// <summary>
    /// Reduced view of a node entry carried in a dependency payload. One entry per
    /// node the producing assembly emits as a public type definition
    /// (objects/instances are not carried; consumers re-derive
    /// inheritance via <see cref="BaseTypeName"/>).
    /// </summary>
    public sealed class DependencyNode
    {
        /// <summary>
        /// Symbolic name.
        /// </summary>
        public string SymbolicName { get; set; } = string.Empty;

        /// <summary>
        /// Symbolic namespace URI.
        /// </summary>
        public string SymbolicNamespace { get; set; } = string.Empty;

        /// <summary>
        /// Emitted C# class name (post-Type-suffix-stripping).
        /// </summary>
        public string ClassName { get; set; } = string.Empty;

        /// <summary>
        /// Node kind.
        /// </summary>
        public DependencyNodeKind Kind { get; set; }

        /// <summary>
        /// Base type name (null for root types).
        /// </summary>
        public string? BaseTypeName { get; set; }

        /// <summary>
        /// Base type namespace URI (null for root types).
        /// </summary>
        public string? BaseTypeNamespace { get; set; }

        /// <summary>
        /// Numeric NodeId (0 when not assigned).
        /// </summary>
        public uint NumericId { get; set; }

        /// <summary>
        /// Optional string NodeId.
        /// </summary>
        public string? StringId { get; set; }

        /// <summary>
        /// Optional Guid NodeId in the "D" format (null when not assigned).
        /// </summary>
        public string? GuidId { get; set; }

        /// <summary>
        /// Optional opaque NodeId as base64 (null when not assigned).
        /// </summary>
        public string? OpaqueId { get; set; }

        /// <summary>
        /// True when the type is abstract.
        /// </summary>
        public bool IsAbstract { get; set; }

        /// <summary>
        /// True when the entry represents an enumeration DataType.
        /// </summary>
        public bool IsEnumeration { get; set; }

        /// <summary>
        /// DataType restriction of a VariableType (null for every other kind).
        /// A consumer needs it to decide whether a variable typed by this
        /// VariableType requires a template parameter on its generated state
        /// class; without it the consumer cannot tell State&lt;T&gt; from the
        /// non-generic state and dereferences a null DataTypeNode.
        /// </summary>
        public string? DataTypeName { get; set; }

        /// <summary>
        /// Namespace URI of <see cref="DataTypeName"/>.
        /// </summary>
        public string? DataTypeNamespace { get; set; }

        /// <summary>
        /// ValueRank of a VariableType, or null when the VariableType does not
        /// specify one (ValueRankSpecified = false upstream).
        /// </summary>
        public int? ValueRank { get; set; }

        /// <summary>
        /// DataType fields (empty for non-DataType kinds).
        /// </summary>
        public IReadOnlyList<DependencyDataField> Fields { get; set; } = [];

        /// <summary>
        /// Declared instance children (empty for DataType / no-child types).
        /// </summary>
        public IReadOnlyList<DependencyChild> Children { get; set; } = [];
    }

    /// <summary>
    /// In-memory representation of a <c>ModelDependencyV1</c> payload.
    /// </summary>
    public sealed class ModelDependencyV1
    {
        /// <summary>
        /// The magic byte sequence.
        /// </summary>
        public static readonly byte[] Magic = [0xAA, 0xC7];

        /// <summary>
        /// The version byte for V1.
        /// </summary>
        public const byte Version = 1;

        /// <summary>
        /// Compression scheme: 1 = Deflate.
        /// </summary>
        public const byte CompressionDeflate = 1;

        private const byte kFluentAccessorsEmitted = 0x01;
        private const byte kFluentAccessorsKnown = 0x40;
        private const byte kMethodIdentityTrailer = 0x80;
        private const byte kMethodIdentityTrailerVersion = 1;
        private const byte kNodeIsAbstract = 0x01;
        private const byte kNodeIsEnumeration = 0x02;
        // The declaration trailer carries the DataType restriction of each
        // VariableType and the BrowseName namespace and ReferenceType of each
        // child, with a flag byte per node and per child.
        private const byte kDeclarationTrailer = 0x04;
        private const byte kDeclarationTrailerVersion = 1;
        private const byte kDeclarationDataType = 0x01;
        private const byte kDeclarationBrowseNameNamespace = 0x01;
        private const byte kDeclarationReferenceType = 0x02;
        private const byte kExtendedIdentifierTrailer = 0x20;
        private const byte kExtendedIdentifierTrailerVersion = 1;
        private const byte kStructureFieldTrailer = 0x10;
        private const byte kStructureFieldTrailerVersion = 1;
        private const byte kValueNamespaceTrailer = 0x08;
        private const byte kValueNamespaceTrailerVersion = 1;
        private const byte kFieldIsOptional = 0x01;
        private const byte kFieldAllowSubTypes = 0x02;
        private const byte kAccessLevelSpecified = 0x01;
        private const byte kRawAccessLevel = 0x02;
        private const byte kRawUserAccessLevel = 0x04;
        private const byte kMinimumSamplingIntervalSpecified = 0x08;
        private const byte kHistorizingSpecified = 0x10;

        /// <summary>
        /// Namespace URI that qualifies the standard reference types.
        /// </summary>
        public const string OpcUaNamespaceUri = "http://opcfoundation.org/UA/";

        /// <summary>
        /// Reference type a child of the given instance kind is bound with when
        /// the declaring model does not name one. Mirrors the defaulting the
        /// validator applies to a locally declared instance, so a child
        /// materialised from a dependency payload is bound the same way as the
        /// identical child declared in the consuming model.
        /// </summary>
        /// <param name="instanceKind">
        /// Instance kind: 1=Object 2=Variable 3=Property 4=Method.
        /// </param>
        public static string GetDefaultReferenceTypeName(byte instanceKind)
        {
            return instanceKind == 3 ? "HasProperty" : "HasComponent";
        }

        /// <summary>
        /// The model URI this dependency payload describes.
        /// </summary>
        public string ModelUri { get; set; } = string.Empty;

        /// <summary>
        /// Whether the producing assembly emitted the per-ObjectType typed
        /// fluent accessor extension classes. <c>null</c> means the payload
        /// does not declare whether accessors exist.
        /// </summary>
        public bool? FluentAccessorsEmitted { get; set; }

        /// <summary>
        /// Nodes in the dependency payload.
        /// </summary>
        public List<DependencyNode> Nodes { get; } = [];

        /// <summary>
        /// Serialises the dependency payload to a base64-encoded
        /// Deflate-compressed payload suitable for embedding in
        /// <c>ModelDependencyAttribute</c>.
        /// </summary>
        public string ToBase64Payload()
        {
            using var raw = new MemoryStream();
            WriteUncompressed(raw);
            raw.Position = 0;

            using var output = new MemoryStream();
            // Header is uncompressed; payload below is Deflate-compressed.
            output.WriteByte(Magic[0]);
            output.WriteByte(Magic[1]);
            output.WriteByte(Version);
            output.WriteByte(CompressionDeflate);

            using (var deflate = new DeflateStream(output, CompressionLevel.Optimal, leaveOpen: true))
            {
                raw.CopyTo(deflate);
            }
            return Convert.ToBase64String(output.ToArray());
        }

        /// <summary>
        /// Reads a dependency payload from a base64-encoded payload.
        /// </summary>
        /// <returns>Null when the payload version is unrecognised or the
        /// magic does not match.</returns>
        public static ModelDependencyV1? FromBase64Payload(string base64)
        {
            if (string.IsNullOrEmpty(base64))
            {
                return null;
            }
            byte[] bytes;
            try
            {
                bytes = Convert.FromBase64String(base64);
            }
            catch (FormatException)
            {
                return null;
            }
            if (bytes.Length < 4)
            {
                return null;
            }
            if (bytes[0] != Magic[0] || bytes[1] != Magic[1])
            {
                return null;
            }
            if (bytes[2] != Version)
            {
                return null;
            }
            if (bytes[3] != CompressionDeflate)
            {
                return null;
            }
            using var input = new MemoryStream(bytes, index: 4, count: bytes.Length - 4, writable: false);
            using var deflate = new DeflateStream(input, CompressionMode.Decompress, leaveOpen: false);
            using var inflated = new MemoryStream();
            deflate.CopyTo(inflated);
            inflated.Position = 0;

            var result = new ModelDependencyV1();
            result.ReadUncompressed(inflated);
            return result;
        }

        private void WriteUncompressed(Stream destination)
        {
            using var writer = new BinaryWriter(destination, Encoding.UTF8, leaveOpen: true);
            WriteString(writer, ModelUri);
            writer.Write(Nodes.Count);
            foreach (DependencyNode node in Nodes)
            {
                WriteString(writer, node.SymbolicName);
                WriteString(writer, node.SymbolicNamespace);
                WriteString(writer, node.ClassName);
                writer.Write((byte)node.Kind);
                WriteNullableString(writer, node.BaseTypeName);
                WriteNullableString(writer, node.BaseTypeNamespace);
                writer.Write(node.NumericId);
                WriteNullableString(writer, node.StringId);
                byte flags = 0;
                if (node.IsAbstract)
                {
                    flags |= kNodeIsAbstract;
                }
                if (node.IsEnumeration)
                {
                    flags |= kNodeIsEnumeration;
                }
                writer.Write(flags);
                writer.Write(node.Fields.Count);
                foreach (DependencyDataField field in node.Fields)
                {
                    WriteString(writer, field.Name);
                    WriteString(writer, field.DataTypeName);
                    WriteString(writer, field.DataTypeNamespace);
                    writer.Write(field.ValueRank);
                }
                writer.Write(node.Children.Count);
                foreach (DependencyChild child in node.Children)
                {
                    WriteString(writer, child.BrowseName);
                    WriteString(writer, child.SymbolicName);
                    WriteString(writer, child.TypeDefinitionName);
                    WriteString(writer, child.TypeDefinitionNamespace);
                    WriteString(writer, child.DataTypeName);
                    WriteString(writer, child.DataTypeNamespace);
                    writer.Write(child.ValueRank);
                    writer.Write(child.ModellingRule);
                    writer.Write(child.InstanceKind);
                    byte variableFlags = 0;
                    if (child.AccessLevelSpecified)
                    {
                        variableFlags |= kAccessLevelSpecified;
                    }
                    if (child.RawAccessLevel.HasValue)
                    {
                        variableFlags |= kRawAccessLevel;
                    }
                    if (child.RawUserAccessLevel.HasValue)
                    {
                        variableFlags |= kRawUserAccessLevel;
                    }
                    if (child.MinimumSamplingIntervalSpecified)
                    {
                        variableFlags |= kMinimumSamplingIntervalSpecified;
                    }
                    if (child.HistorizingSpecified)
                    {
                        variableFlags |= kHistorizingSpecified;
                    }
                    writer.Write(variableFlags);
                    writer.Write(child.AccessLevel);
                    writer.Write(child.RawAccessLevel.GetValueOrDefault());
                    writer.Write(child.RawUserAccessLevel.GetValueOrDefault());
                    writer.Write(child.MinimumSamplingInterval);
                    writer.Write(child.Historizing);
                    WriteNullableString(writer, child.DefaultValueXml);
                    writer.Write(child.InputArguments.Count);
                    foreach (DependencyMethodArg a in child.InputArguments)
                    {
                        WriteString(writer, a.Name);
                        WriteString(writer, a.DataTypeName);
                        WriteString(writer, a.DataTypeNamespace);
                        writer.Write(a.ValueRank);
                    }
                    writer.Write(child.OutputArguments.Count);
                    foreach (DependencyMethodArg a in child.OutputArguments)
                    {
                        WriteString(writer, a.Name);
                        WriteString(writer, a.DataTypeName);
                        WriteString(writer, a.DataTypeNamespace);
                        writer.Write(a.ValueRank);
                    }
                }
            }
            bool hasMethodIdentityTrailer = HasMethodIdentityTrailer();
            bool hasStructureFieldTrailer = HasStructureFieldTrailer();
            bool hasValueNamespaceTrailer = HasValueNamespaceTrailer();
            bool hasDeclarationTrailer = HasDeclarationTrailer();
            // The structure field, value namespace and declaration trailers
            // are written after the extended identifier trailer, which is
            // always written with them: a reader that predates them only reads
            // the capabilities as "trailers present" (honouring the
            // FluentAccessorsKnown bit) when the method identity or the
            // extended identifier bit is set, and it stops reading after the
            // trailers it knows - so it never sees the new ones.
            bool hasExtendedIdentifierTrailer =
                hasStructureFieldTrailer ||
                hasValueNamespaceTrailer ||
                hasDeclarationTrailer ||
                HasExtendedIdentifierTrailer();
            if (FluentAccessorsEmitted.HasValue ||
                hasMethodIdentityTrailer ||
                hasExtendedIdentifierTrailer)
            {
                byte capabilities = 0;
                if (FluentAccessorsEmitted.HasValue)
                {
                    capabilities |= kFluentAccessorsKnown;
                    if (FluentAccessorsEmitted.Value)
                    {
                        capabilities |= kFluentAccessorsEmitted;
                    }
                }
                if (hasMethodIdentityTrailer)
                {
                    capabilities |= kMethodIdentityTrailer;
                }
                if (hasExtendedIdentifierTrailer)
                {
                    capabilities |= kExtendedIdentifierTrailer;
                }
                if (hasStructureFieldTrailer)
                {
                    capabilities |= kStructureFieldTrailer;
                }
                if (hasValueNamespaceTrailer)
                {
                    capabilities |= kValueNamespaceTrailer;
                }
                if (hasDeclarationTrailer)
                {
                    capabilities |= kDeclarationTrailer;
                }
                writer.Write(capabilities);
                if (hasMethodIdentityTrailer)
                {
                    WriteMethodIdentityTrailer(writer);
                }
                if (hasExtendedIdentifierTrailer)
                {
                    WriteExtendedIdentifierTrailer(writer);
                }
                if (hasStructureFieldTrailer)
                {
                    WriteStructureFieldTrailer(writer);
                }
                if (hasValueNamespaceTrailer)
                {
                    WriteValueNamespaceTrailer(writer);
                }
                if (hasDeclarationTrailer)
                {
                    WriteDeclarationTrailer(writer);
                }
            }
        }

        private void ReadUncompressed(Stream source)
        {
            using var reader = new BinaryReader(source, Encoding.UTF8, leaveOpen: true);
            ModelUri = ReadString(reader);
            int typeCount = reader.ReadInt32();
            if (typeCount is < 0 or > 1_000_000)
            {
                throw new InvalidDataException(
                    "ModelDependencyV1: invalid type count " + typeCount);
            }
            Nodes.Capacity = typeCount;
            for (int i = 0; i < typeCount; i++)
            {
                var node = new DependencyNode
                {
                    SymbolicName = ReadString(reader),
                    SymbolicNamespace = ReadString(reader),
                    ClassName = ReadString(reader),
                    Kind = (DependencyNodeKind)reader.ReadByte(),
                    BaseTypeName = ReadNullableString(reader),
                    BaseTypeNamespace = ReadNullableString(reader),
                    NumericId = reader.ReadUInt32(),
                    StringId = ReadNullableString(reader)
                };
                byte flags = reader.ReadByte();
                node.IsAbstract = (flags & kNodeIsAbstract) != 0;
                node.IsEnumeration = (flags & kNodeIsEnumeration) != 0;
                int fieldCount = reader.ReadInt32();
                if (fieldCount is < 0 or > 100_000)
                {
                    throw new InvalidDataException(
                        "ModelDependencyV1: invalid field count " + fieldCount);
                }
                if (fieldCount > 0)
                {
                    var fields = new DependencyDataField[fieldCount];
                    for (int j = 0; j < fieldCount; j++)
                    {
                        fields[j] = new DependencyDataField(
                            ReadString(reader),
                            ReadString(reader),
                            ReadString(reader),
                            reader.ReadInt32());
                    }
                    node.Fields = fields;
                }
                int childCount = reader.ReadInt32();
                if (childCount is < 0 or > 100_000)
                {
                    throw new InvalidDataException(
                        "ModelDependencyV1: invalid child count " + childCount);
                }
                if (childCount > 0)
                {
                    var children = new DependencyChild[childCount];
                    for (int j = 0; j < childCount; j++)
                    {
                        var c = new DependencyChild
                        {
                            BrowseName = ReadString(reader),
                            SymbolicName = ReadString(reader),
                            TypeDefinitionName = ReadString(reader),
                            TypeDefinitionNamespace = ReadString(reader),
                            DataTypeName = ReadString(reader),
                            DataTypeNamespace = ReadString(reader),
                            ValueRank = reader.ReadInt32(),
                            ModellingRule = reader.ReadByte(),
                            InstanceKind = reader.ReadByte()
                        };
                        byte variableFlags = reader.ReadByte();
                        c.AccessLevelSpecified =
                            (variableFlags & kAccessLevelSpecified) != 0;
                        c.AccessLevel = reader.ReadByte();
                        uint rawAccessLevel = reader.ReadUInt32();
                        if ((variableFlags & kRawAccessLevel) != 0)
                        {
                            c.RawAccessLevel = rawAccessLevel;
                        }
                        uint rawUserAccessLevel = reader.ReadUInt32();
                        if ((variableFlags & kRawUserAccessLevel) != 0)
                        {
                            c.RawUserAccessLevel = rawUserAccessLevel;
                        }
                        c.MinimumSamplingInterval = reader.ReadInt32();
                        c.MinimumSamplingIntervalSpecified =
                            (variableFlags & kMinimumSamplingIntervalSpecified) != 0;
                        c.Historizing = reader.ReadBoolean();
                        c.HistorizingSpecified =
                            (variableFlags & kHistorizingSpecified) != 0;
                        c.DefaultValueXml = ReadNullableString(reader);
                        if (c.DefaultValueXml != null)
                        {
                            ValidateDefaultValueXml(c.DefaultValueXml);
                        }
                        int inCount = reader.ReadInt32();
                        if (inCount is < 0 or > 100)
                        {
                            throw new InvalidDataException(
                                "ModelDependencyV1: invalid input arg count " + inCount);
                        }
                        if (inCount > 0)
                        {
                            var args = new DependencyMethodArg[inCount];
                            for (int k = 0; k < inCount; k++)
                            {
                                args[k] = new DependencyMethodArg(
                                    ReadString(reader),
                                    ReadString(reader),
                                    ReadString(reader),
                                    reader.ReadInt32());
                            }
                            c.InputArguments = args;
                        }
                        int outCount = reader.ReadInt32();
                        if (outCount is < 0 or > 100)
                        {
                            throw new InvalidDataException(
                                "ModelDependencyV1: invalid output arg count " + outCount);
                        }
                        if (outCount > 0)
                        {
                            var args = new DependencyMethodArg[outCount];
                            for (int k = 0; k < outCount; k++)
                            {
                                args[k] = new DependencyMethodArg(
                                    ReadString(reader),
                                    ReadString(reader),
                                    ReadString(reader),
                                    reader.ReadInt32());
                            }
                            c.OutputArguments = args;
                        }
                        children[j] = c;
                    }
                    node.Children = children;
                }
                Nodes.Add(node);
            }
            if (reader.BaseStream.Position < reader.BaseStream.Length)
            {
                byte capabilities = reader.ReadByte();
                bool hasMethodIdentityTrailer =
                    (capabilities & kMethodIdentityTrailer) != 0;
                bool hasExtendedIdentifierTrailer =
                    (capabilities & kExtendedIdentifierTrailer) != 0;
                if (hasMethodIdentityTrailer || hasExtendedIdentifierTrailer)
                {
                    FluentAccessorsEmitted =
                        (capabilities & kFluentAccessorsKnown) != 0
                            ? (capabilities & kFluentAccessorsEmitted) != 0
                            : null;
                }
                else
                {
                    FluentAccessorsEmitted =
                        (capabilities & kFluentAccessorsEmitted) != 0;
                }
                // Trailers carry no length prefix, so a trailer of a version
                // this reader does not know cannot be skipped: its body is left
                // unread and whatever follows it cannot be located. Stop there
                // rather than parse the next trailer out of the middle of the
                // unknown one - which either assigned garbage identifiers or
                // threw and dropped the whole payload.
                bool trailersReadable = true;
                if (hasMethodIdentityTrailer &&
                    reader.BaseStream.Position < reader.BaseStream.Length)
                {
                    trailersReadable = ReadMethodIdentityTrailer(reader);
                }
                if (trailersReadable &&
                    hasExtendedIdentifierTrailer &&
                    reader.BaseStream.Position < reader.BaseStream.Length)
                {
                    trailersReadable = ReadExtendedIdentifierTrailer(reader);
                }
                // The later trailers are length prefixed: an unknown version
                // is skipped and the ones after it stay readable.
                if (trailersReadable &&
                    (capabilities & kStructureFieldTrailer) != 0 &&
                    reader.BaseStream.Position < reader.BaseStream.Length)
                {
                    ReadStructureFieldTrailer(reader);
                }
                if (trailersReadable &&
                    (capabilities & kValueNamespaceTrailer) != 0 &&
                    reader.BaseStream.Position < reader.BaseStream.Length)
                {
                    ReadValueNamespaceTrailer(reader);
                }
                if (trailersReadable &&
                    (capabilities & kDeclarationTrailer) != 0 &&
                    reader.BaseStream.Position < reader.BaseStream.Length)
                {
                    ReadDeclarationTrailer(reader);
                }
            }
        }

        private bool HasDeclarationTrailer()
        {
            foreach (DependencyNode node in Nodes)
            {
                if (node.DataTypeName != null)
                {
                    return true;
                }
                foreach (DependencyChild child in node.Children)
                {
                    if (!string.IsNullOrEmpty(child.BrowseNameNamespace) ||
                        !string.IsNullOrEmpty(child.ReferenceTypeName))
                    {
                        return true;
                    }
                }
            }
            return false;
        }

        /// <summary>
        /// Writes the declaration trailer: per node the DataType and ValueRank
        /// of a VariableType, and per child of that node the namespace of its
        /// BrowseName and the ReferenceType that binds it, each behind a flag
        /// byte. The body is length prefixed so that a reader can skip a
        /// later version.
        /// </summary>
        private void WriteDeclarationTrailer(BinaryWriter writer)
        {
            using var body = new MemoryStream();
            using (var bodyWriter = new BinaryWriter(body, Encoding.UTF8, leaveOpen: true))
            {
                bodyWriter.Write(Nodes.Count);
                foreach (DependencyNode node in Nodes)
                {
                    bool hasDataType = node.DataTypeName != null;
                    bodyWriter.Write(hasDataType ? kDeclarationDataType : (byte)0);
                    if (hasDataType)
                    {
                        WriteString(bodyWriter, node.DataTypeName ?? string.Empty);
                        WriteString(bodyWriter, node.DataTypeNamespace ?? string.Empty);
                        bodyWriter.Write(node.ValueRank.HasValue);
                        bodyWriter.Write(node.ValueRank ?? 0);
                    }
                    bodyWriter.Write(node.Children.Count);
                    foreach (DependencyChild child in node.Children)
                    {
                        bool hasBrowseNameNamespace =
                            !string.IsNullOrEmpty(child.BrowseNameNamespace);
                        bool hasReferenceType =
                            !string.IsNullOrEmpty(child.ReferenceTypeName);
                        byte childFlags = 0;
                        if (hasBrowseNameNamespace)
                        {
                            childFlags |= kDeclarationBrowseNameNamespace;
                        }
                        if (hasReferenceType)
                        {
                            childFlags |= kDeclarationReferenceType;
                        }
                        bodyWriter.Write(childFlags);
                        if (hasBrowseNameNamespace)
                        {
                            WriteString(bodyWriter, child.BrowseNameNamespace);
                        }
                        if (hasReferenceType)
                        {
                            WriteString(bodyWriter, child.ReferenceTypeName);
                            WriteString(bodyWriter, child.ReferenceTypeNamespace);
                        }
                    }
                }
            }
            writer.Write(kDeclarationTrailerVersion);
            writer.Write((int)body.Length);
            writer.Write(body.GetBuffer(), 0, (int)body.Length);
        }

        private void ReadDeclarationTrailer(BinaryReader reader)
        {
            byte trailerVersion = reader.ReadByte();
            int length = reader.ReadInt32();
            if (length < 0 || length > reader.BaseStream.Length - reader.BaseStream.Position)
            {
                throw new InvalidDataException(
                    "ModelDependencyV1: invalid declaration trailer length " + length);
            }
            if (trailerVersion != kDeclarationTrailerVersion)
            {
                // Length prefixed: a later version is skipped as a whole.
                reader.BaseStream.Seek(length, SeekOrigin.Current);
                return;
            }

            int nodeCount = reader.ReadInt32();
            if (nodeCount != Nodes.Count)
            {
                throw new InvalidDataException(
                    "ModelDependencyV1: invalid declaration node count " + nodeCount);
            }
            for (int i = 0; i < nodeCount; i++)
            {
                DependencyNode node = Nodes[i];
                byte nodeFlags = reader.ReadByte();
                if ((nodeFlags & kDeclarationDataType) != 0)
                {
                    node.DataTypeName = ReadString(reader);
                    node.DataTypeNamespace = ReadString(reader);
                    bool valueRankSpecified = reader.ReadBoolean();
                    int valueRank = reader.ReadInt32();
                    node.ValueRank = valueRankSpecified ? valueRank : null;
                }
                int childCount = reader.ReadInt32();
                if (childCount != node.Children.Count)
                {
                    throw new InvalidDataException(
                        "ModelDependencyV1: invalid declaration child count " + childCount);
                }
                for (int j = 0; j < childCount; j++)
                {
                    DependencyChild child = node.Children[j];
                    byte childFlags = reader.ReadByte();
                    if ((childFlags & kDeclarationBrowseNameNamespace) != 0)
                    {
                        child.BrowseNameNamespace = ReadString(reader);
                    }
                    if ((childFlags & kDeclarationReferenceType) != 0)
                    {
                        child.ReferenceTypeName = ReadString(reader);
                        child.ReferenceTypeNamespace = ReadString(reader);
                    }
                }
            }
        }

        private bool HasValueNamespaceTrailer()
        {
            foreach (DependencyNode node in Nodes)
            {
                foreach (DependencyChild child in node.Children)
                {
                    if (child.DefaultValueNamespaceUris != null)
                    {
                        return true;
                    }
                }
            }
            return false;
        }

        /// <summary>
        /// Writes the value namespace trailer: the distinct namespace tables
        /// the default values of the children refer to, then per node and
        /// child (in order) the index of the child's table, -1 for none. The
        /// body is length prefixed so that a reader can skip a later version.
        /// </summary>
        private void WriteValueNamespaceTrailer(BinaryWriter writer)
        {
            var tables = new List<IReadOnlyList<string>>();
            var tableIndexes = new Dictionary<string, int>(StringComparer.Ordinal);
            using var body = new MemoryStream();
            using (var bodyWriter = new BinaryWriter(body, Encoding.UTF8, leaveOpen: true))
            {
                var childTables = new List<int>();
                foreach (DependencyNode node in Nodes)
                {
                    foreach (DependencyChild child in node.Children)
                    {
                        IReadOnlyList<string>? uris = child.DefaultValueNamespaceUris;
                        if (uris == null)
                        {
                            childTables.Add(-1);
                            continue;
                        }
                        string key = GetTableKey(uris);
                        if (!tableIndexes.TryGetValue(key, out int index))
                        {
                            index = tables.Count;
                            tables.Add(uris);
                            tableIndexes.Add(key, index);
                        }
                        childTables.Add(index);
                    }
                }

                bodyWriter.Write(tables.Count);
                foreach (IReadOnlyList<string> table in tables)
                {
                    bodyWriter.Write(table.Count);
                    foreach (string uri in table)
                    {
                        WriteString(bodyWriter, uri);
                    }
                }
                int next = 0;
                bodyWriter.Write(Nodes.Count);
                foreach (DependencyNode node in Nodes)
                {
                    bodyWriter.Write(node.Children.Count);
                    for (int j = 0; j < node.Children.Count; j++)
                    {
                        bodyWriter.Write(childTables[next++]);
                    }
                }
            }
            writer.Write(kValueNamespaceTrailerVersion);
            writer.Write((int)body.Length);
            writer.Write(body.GetBuffer(), 0, (int)body.Length);
        }

        /// <summary>
        /// An unambiguous key for a namespace table (length prefixed URIs).
        /// </summary>
        private static string GetTableKey(IReadOnlyList<string> uris)
        {
            var key = new StringBuilder();
            foreach (string uri in uris)
            {
                string value = uri ?? string.Empty;
                key.Append(value.Length.ToString(System.Globalization.CultureInfo.InvariantCulture))
                    .Append(':')
                    .Append(value);
            }
            return key.ToString();
        }

        private void ReadValueNamespaceTrailer(BinaryReader reader)
        {
            byte trailerVersion = reader.ReadByte();
            int length = reader.ReadInt32();
            if (length < 0 || length > reader.BaseStream.Length - reader.BaseStream.Position)
            {
                throw new InvalidDataException(
                    "ModelDependencyV1: invalid value namespace trailer length " + length);
            }
            if (trailerVersion != kValueNamespaceTrailerVersion)
            {
                // Length prefixed: a later version is skipped as a whole.
                reader.BaseStream.Seek(length, SeekOrigin.Current);
                return;
            }

            int tableCount = reader.ReadInt32();
            if (tableCount is < 0 or > 100_000)
            {
                throw new InvalidDataException(
                    "ModelDependencyV1: invalid value namespace table count " + tableCount);
            }
            string[][] tables = new string[tableCount][];
            for (int i = 0; i < tableCount; i++)
            {
                int uriCount = reader.ReadInt32();
                if (uriCount is < 1 or > ushort.MaxValue + 1)
                {
                    throw new InvalidDataException(
                        "ModelDependencyV1: invalid value namespace table size " + uriCount);
                }
                string[] uris = new string[uriCount];
                for (int k = 0; k < uriCount; k++)
                {
                    uris[k] = ReadString(reader);
                }
                tables[i] = uris;
            }

            int nodeCount = reader.ReadInt32();
            if (nodeCount != Nodes.Count)
            {
                throw new InvalidDataException(
                    "ModelDependencyV1: invalid value namespace node count " + nodeCount);
            }
            for (int i = 0; i < nodeCount; i++)
            {
                DependencyNode node = Nodes[i];
                int childCount = reader.ReadInt32();
                if (childCount != node.Children.Count)
                {
                    throw new InvalidDataException(
                        "ModelDependencyV1: invalid value namespace child count " + childCount);
                }
                for (int j = 0; j < childCount; j++)
                {
                    int index = reader.ReadInt32();
                    if (index < -1 || index >= tableCount)
                    {
                        throw new InvalidDataException(
                            "ModelDependencyV1: invalid value namespace table index " + index);
                    }
                    node.Children[j].DefaultValueNamespaceUris =
                        index < 0 ? null : tables[index];
                }
            }
        }

        private bool HasStructureFieldTrailer()
        {
            foreach (DependencyNode node in Nodes)
            {
                foreach (DependencyDataField field in node.Fields)
                {
                    if (field.IsOptional ||
                        field.AllowSubTypes ||
                        !string.IsNullOrEmpty(field.ArrayDimensions))
                    {
                        return true;
                    }
                }
            }
            return false;
        }

        /// <summary>
        /// Writes the structure field trailer: the IsOptional, AllowSubTypes
        /// and ArrayDimensions of every field, in node and field order. The
        /// body is length prefixed so that a reader can skip a later version.
        /// </summary>
        private void WriteStructureFieldTrailer(BinaryWriter writer)
        {
            using var body = new MemoryStream();
            using (var bodyWriter = new BinaryWriter(body, Encoding.UTF8, leaveOpen: true))
            {
                bodyWriter.Write(Nodes.Count);
                foreach (DependencyNode node in Nodes)
                {
                    bodyWriter.Write(node.Fields.Count);
                    foreach (DependencyDataField field in node.Fields)
                    {
                        byte fieldFlags = 0;
                        if (field.IsOptional)
                        {
                            fieldFlags |= kFieldIsOptional;
                        }
                        if (field.AllowSubTypes)
                        {
                            fieldFlags |= kFieldAllowSubTypes;
                        }
                        bodyWriter.Write(fieldFlags);
                        WriteNullableString(
                            bodyWriter,
                            string.IsNullOrEmpty(field.ArrayDimensions) ? null : field.ArrayDimensions);
                    }
                }
            }
            writer.Write(kStructureFieldTrailerVersion);
            writer.Write((int)body.Length);
            writer.Write(body.GetBuffer(), 0, (int)body.Length);
        }

        private void ReadStructureFieldTrailer(BinaryReader reader)
        {
            byte trailerVersion = reader.ReadByte();
            int length = reader.ReadInt32();
            if (length < 0 || length > reader.BaseStream.Length - reader.BaseStream.Position)
            {
                throw new InvalidDataException(
                    "ModelDependencyV1: invalid structure field trailer length " + length);
            }
            if (trailerVersion != kStructureFieldTrailerVersion)
            {
                // Length prefixed: a later version is skipped as a whole.
                reader.BaseStream.Seek(length, SeekOrigin.Current);
                return;
            }

            int nodeCount = reader.ReadInt32();
            if (nodeCount != Nodes.Count)
            {
                throw new InvalidDataException(
                    "ModelDependencyV1: invalid structure field node count " + nodeCount);
            }
            for (int i = 0; i < nodeCount; i++)
            {
                DependencyNode node = Nodes[i];
                int fieldCount = reader.ReadInt32();
                if (fieldCount != node.Fields.Count)
                {
                    throw new InvalidDataException(
                        "ModelDependencyV1: invalid structure field count " + fieldCount);
                }
                if (fieldCount == 0)
                {
                    continue;
                }
                var fields = new DependencyDataField[fieldCount];
                for (int j = 0; j < fieldCount; j++)
                {
                    byte fieldFlags = reader.ReadByte();
                    fields[j] = node.Fields[j] with
                    {
                        IsOptional = (fieldFlags & kFieldIsOptional) != 0,
                        AllowSubTypes = (fieldFlags & kFieldAllowSubTypes) != 0,
                        ArrayDimensions = ReadNullableString(reader)
                    };
                }
                node.Fields = fields;
            }
        }

        private bool HasExtendedIdentifierTrailer()
        {
            foreach (DependencyNode node in Nodes)
            {
                // Null, not empty, means "not assigned" for both: an empty
                // GuidId has to be written or it reads back as null.
                if (node.GuidId != null ||
                    node.OpaqueId != null)
                {
                    return true;
                }
            }
            return false;
        }

        private void WriteExtendedIdentifierTrailer(BinaryWriter writer)
        {
            writer.Write(kExtendedIdentifierTrailerVersion);
            writer.Write(Nodes.Count);
            foreach (DependencyNode node in Nodes)
            {
                WriteNullableString(writer, node.GuidId);
                WriteNullableString(writer, node.OpaqueId);
            }
        }

        /// <summary>
        /// Reads the extended identifier trailer. Returns false when the
        /// trailer has a version this reader does not know - its body is
        /// then left unread and no later trailer can be located.
        /// </summary>
        private bool ReadExtendedIdentifierTrailer(BinaryReader reader)
        {
            byte trailerVersion = reader.ReadByte();
            if (trailerVersion != kExtendedIdentifierTrailerVersion)
            {
                return false;
            }

            int nodeCount = reader.ReadInt32();
            if (nodeCount != Nodes.Count)
            {
                throw new InvalidDataException(
                    "ModelDependencyV1: invalid extended identifier node count " + nodeCount);
            }
            for (int i = 0; i < nodeCount; i++)
            {
                Nodes[i].GuidId = ReadNullableString(reader);
                Nodes[i].OpaqueId = ReadNullableString(reader);
            }
            return true;
        }

        private bool HasMethodIdentityTrailer()
        {
            foreach (DependencyNode node in Nodes)
            {
                foreach (DependencyChild child in node.Children)
                {
                    // Every field the trailer carries, or a child whose only
                    // method identity is a namespace does not round-trip.
                    if (!string.IsNullOrEmpty(child.MethodStateName) ||
                        !string.IsNullOrEmpty(child.MethodStateNamespace) ||
                        !string.IsNullOrEmpty(child.MethodDeclarationName) ||
                        !string.IsNullOrEmpty(child.MethodDeclarationNamespace) ||
                        child.MethodDeclarationNumericId != 0 ||
                        !string.IsNullOrEmpty(child.MethodDeclarationStringId))
                    {
                        return true;
                    }
                }
            }
            return false;
        }

        private void WriteMethodIdentityTrailer(BinaryWriter writer)
        {
            writer.Write(kMethodIdentityTrailerVersion);
            writer.Write(Nodes.Count);
            foreach (DependencyNode node in Nodes)
            {
                writer.Write(node.Children.Count);
                foreach (DependencyChild child in node.Children)
                {
                    WriteString(writer, child.MethodStateName);
                    WriteString(writer, child.MethodStateNamespace);
                    WriteString(writer, child.MethodDeclarationName);
                    WriteString(writer, child.MethodDeclarationNamespace);
                    writer.Write(child.MethodDeclarationNumericId);
                    WriteNullableString(writer, child.MethodDeclarationStringId);
                }
            }
        }

        /// <summary>
        /// Reads the method identity trailer. Returns false when the trailer
        /// has a version this reader does not know - its body is then left
        /// unread and no later trailer can be located.
        /// </summary>
        private bool ReadMethodIdentityTrailer(BinaryReader reader)
        {
            byte trailerVersion = reader.ReadByte();
            if (trailerVersion != kMethodIdentityTrailerVersion)
            {
                return false;
            }

            int nodeCount = reader.ReadInt32();
            if (nodeCount != Nodes.Count)
            {
                throw new InvalidDataException(
                    "ModelDependencyV1: invalid method identity node count " + nodeCount);
            }
            for (int i = 0; i < nodeCount; i++)
            {
                DependencyNode node = Nodes[i];
                int childCount = reader.ReadInt32();
                if (childCount != node.Children.Count)
                {
                    throw new InvalidDataException(
                        "ModelDependencyV1: invalid method identity child count " + childCount);
                }
                for (int j = 0; j < childCount; j++)
                {
                    DependencyChild child = node.Children[j];
                    child.MethodStateName = ReadString(reader);
                    child.MethodStateNamespace = ReadString(reader);
                    child.MethodDeclarationName = ReadString(reader);
                    child.MethodDeclarationNamespace = ReadString(reader);
                    child.MethodDeclarationNumericId = reader.ReadUInt32();
                    child.MethodDeclarationStringId = ReadNullableString(reader);
                }
            }
            return true;
        }

        private static void WriteString(BinaryWriter writer, string value)
        {
            writer.Write(value ?? string.Empty);
        }

        private static void ValidateDefaultValueXml(string value)
        {
            try
            {
                using var textReader = new StringReader(value);
                using XmlReader reader = XmlReader.Create(
                    textReader,
                    CoreUtils.DefaultXmlReaderSettings());
                var document = new XmlDocument();
                document.Load(reader);
                if (document.DocumentElement == null)
                {
                    throw new XmlException("Default value XML has no document element.");
                }
            }
            catch (XmlException ex)
            {
                throw new InvalidDataException(
                    "ModelDependencyV1: invalid default value XML.",
                    ex);
            }
        }

        private static void WriteNullableString(BinaryWriter writer, string? value)
        {
            if (value == null)
            {
                writer.Write((byte)0);
            }
            else
            {
                writer.Write((byte)1);
                writer.Write(value);
            }
        }

        private static string ReadString(BinaryReader reader)
        {
            return reader.ReadString();
        }

        private static string? ReadNullableString(BinaryReader reader)
        {
            byte marker = reader.ReadByte();
            return marker == 0 ? null : reader.ReadString();
        }
    }
}