#region Copyright notice and license
// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file or at
// https://developers.google.com/open-source/licenses/bsd
#endregion

#if DEBUG
    #define WITH_BENCHMARKING
#endif

using Google.Protobuf.Collections;
using Google.Protobuf.WellKnownTypes;
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.IO;
using System.Linq;
using System.Threading;
using static Google.Protobuf.Reflection.SourceCodeInfo.Types;

namespace Google.Protobuf.Reflection
{
    /// <summary>
    /// The syntax of a .proto file
    /// </summary>
    [Obsolete("Use features instead")]
    public enum Syntax
    {
        /// <summary>
        /// Proto2 syntax
        /// </summary>
        Proto2,
        /// <summary>
        /// Proto3 syntax
        /// </summary>
        Proto3,
        /// <summary>
        /// Editions syntax
        /// </summary>
        Editions,
        /// <summary>
        /// An unknown declared syntax
        /// </summary>
        Unknown
    }

    /// <summary>
    /// Describes a .proto file, including everything defined within.
    /// IDescriptor is implemented such that the File property returns this descriptor,
    /// and the FullName is the same as the Name.
    /// </summary>
    public sealed class FileDescriptor : IDescriptor
    {
        // Prevent linker failures when using IL2CPP with the well-known types.
        static FileDescriptor()
        {
#pragma warning disable CS0618 // Type or member is obsolete
            ForceReflectionInitialization<Syntax>();
#pragma warning restore CS0618 // Type or member is obsolete
            ForceReflectionInitialization<NullValue>();
            ForceReflectionInitialization<Field.Types.Cardinality>();
            ForceReflectionInitialization<Field.Types.Kind>();
            ForceReflectionInitialization<Value.KindOneofCase>();
        }

        private readonly Lazy<Dictionary<IDescriptor, DescriptorDeclaration>> declarations;

        private static readonly Dictionary<string, List<Extension>> allDependedExtensionsCache = new();
        private static bool extensionCachingEnabled = true;

        /// <summary>
        /// Disables caching of discovered extensions. Greatly reduces performance in highly nested protos but lowers the memory usage.
        /// </summary>
        public static void DisableExtensionCaching()
        {
            extensionCachingEnabled = false;
        }

#if WITH_BENCHMARKING

        /// <summary>
        /// Resets the benchmarking counters.
        /// </summary>
        public static void ResetCounters()
        {
            GetAllExtensionsCount = 0;
            TotalReturnedExtensionsCount = 0;
            GetAllGeneratedExtensionsCount = 0;
            GetAllDependedExtensionsCount = 0;
            GetAllDependedExtensionsFromMessageCount = 0;
        }

        internal static long GetAllExtensionsCount { get; private set; }
        internal static long TotalReturnedExtensionsCount { get; private set;}
        internal static long GetAllGeneratedExtensionsCount { get; private set; }
        internal static long GetAllDependedExtensionsCount { get; private set; }
        internal static long GetAllDependedExtensionsFromMessageCount { get; private set; }

        internal static TextWriter WriteBenchmark(TextWriter writer)
        {
            if (writer == null)
            {
                return writer;
            }

            writer.WriteLine($"GetAllExtensionsCount: {GetAllExtensionsCount}");
            writer.WriteLine($"GetAllGeneratedExtensionsCount: {GetAllGeneratedExtensionsCount}");
            writer.WriteLine($"GetAllDependedExtensionsCount: {GetAllDependedExtensionsCount}");
            writer.WriteLine($"GetAllDependedExtensionsFromMessageCount: {GetAllDependedExtensionsFromMessageCount}");
            writer.WriteLine($"TotalReturnedExtensionsCount: {TotalReturnedExtensionsCount}");

            return writer;
        }
#else
        internal static TextWriter WriteBenchmark(TextWriter writer)
        {
            writer?.WriteLine("Benchmarking is disabled");

            return writer;
        }
#endif


        private FileDescriptor(ByteString descriptorData, FileDescriptorProto proto, IList<FileDescriptor> dependencies, DescriptorPool pool, bool allowUnknownDependencies, GeneratedClrTypeInfo generatedCodeInfo)
        {
            SerializedData = descriptorData;
            DescriptorPool = pool;
            Proto = proto;
            // Note: the Edition property relies on the proto being set first, so this line
            // has to come after Proto = proto.
            Features = FeatureSetDescriptor.GetEditionDefaults(Edition).MergedWith(proto.Options?.Features);
            Dependencies = new ReadOnlyCollection<FileDescriptor>(dependencies.ToList());

            PublicDependencies = DeterminePublicDependencies(this, proto, dependencies, allowUnknownDependencies);

            pool.AddPackage(Package, this);

            MessageTypes = DescriptorUtil.ConvertAndMakeReadOnly(proto.MessageType,
                                                                 (message, index) =>
                                                                 new MessageDescriptor(message, this, null, index, generatedCodeInfo?.NestedTypes[index]));

            EnumTypes = DescriptorUtil.ConvertAndMakeReadOnly(proto.EnumType,
                                                              (enumType, index) =>
                                                              new EnumDescriptor(enumType, this, null, index, generatedCodeInfo?.NestedEnums[index]));

            Services = DescriptorUtil.ConvertAndMakeReadOnly(proto.Service,
                                                             (service, index) =>
                                                             new ServiceDescriptor(service, this, index));

            Extensions = new ExtensionCollection(this, generatedCodeInfo?.Extensions);

            declarations = new Lazy<Dictionary<IDescriptor, DescriptorDeclaration>>(CreateDeclarationMap, LazyThreadSafetyMode.ExecutionAndPublication);
        }

        private Dictionary<IDescriptor, DescriptorDeclaration> CreateDeclarationMap()
        {
            var dictionary = new Dictionary<IDescriptor, DescriptorDeclaration>();
            foreach (var location in Proto.SourceCodeInfo?.Location ?? Enumerable.Empty<Location>())
            {
                var descriptor = FindDescriptorForPath(location.Path);
                if (descriptor != null)
                {
                    dictionary[descriptor] = DescriptorDeclaration.FromProto(descriptor, location);
                }
            }
            return dictionary;
        }

        private IDescriptor FindDescriptorForPath(IList<int> path)
        {
            // All complete declarations have an even, non-empty path length
            // (There can be an empty path for a descriptor declaration, but that can't have any comments,
            // so we currently ignore it.)
            if (path.Count == 0 || (path.Count & 1) != 0)
            {
                return null;
            }
            IReadOnlyList<DescriptorBase> topLevelList = GetNestedDescriptorListForField(path[0]);
            DescriptorBase current = GetDescriptorFromList(topLevelList, path[1]);

            for (int i = 2; current != null && i < path.Count; i += 2)
            {
                var list = current.GetNestedDescriptorListForField(path[i]);
                current = GetDescriptorFromList(list, path[i + 1]);
            }
            return current;
        }

        private static DescriptorBase GetDescriptorFromList(IReadOnlyList<DescriptorBase> list, int index)
        {
            // This is fine: it may be a newer version of protobuf than we understand, with a new descriptor
            // field.
            if (list == null)
            {
                return null;
            }
            // We *could* return null to silently continue, but this is basically data corruption.
            if (index < 0 || index >= list.Count)
            {
                // We don't have much extra information to give at this point unfortunately. If this becomes a problem,
                // we can pass in the complete path and report that and the file name.
                throw new InvalidProtocolBufferException($"Invalid descriptor location path: index out of range");
            }
            return list[index];
        }

        private IReadOnlyList<DescriptorBase> GetNestedDescriptorListForField(int fieldNumber) =>
            fieldNumber switch
            {
                FileDescriptorProto.ServiceFieldNumber => (IReadOnlyList<DescriptorBase>)Services,
                FileDescriptorProto.MessageTypeFieldNumber => (IReadOnlyList<DescriptorBase>)MessageTypes,
                FileDescriptorProto.EnumTypeFieldNumber => (IReadOnlyList<DescriptorBase>)EnumTypes,
                _ => null,
            };

        internal DescriptorDeclaration GetDeclaration(IDescriptor descriptor)
        {
            declarations.Value.TryGetValue(descriptor, out DescriptorDeclaration declaration);
            return declaration;
        }

        /// <summary>
        /// Computes the full name of a descriptor within this file, with an optional parent message.
        /// </summary>
        internal string ComputeFullName(MessageDescriptor parent, string name)
        {
            if (parent != null)
            {
                return parent.FullName + "." + name;
            }
            if (Package.Length > 0)
            {
                return Package + "." + name;
            }
            return name;
        }

        /// <summary>
        /// Extracts public dependencies from direct dependencies. This is a static method despite its
        /// first parameter, as the value we're in the middle of constructing is only used for exceptions.
        /// </summary>
        private static IList<FileDescriptor> DeterminePublicDependencies(FileDescriptor @this, FileDescriptorProto proto, IEnumerable<FileDescriptor> dependencies, bool allowUnknownDependencies)
        {
            var nameToFileMap = dependencies.ToDictionary(file => file.Name);
            var publicDependencies = new List<FileDescriptor>();
            for (int i = 0; i < proto.PublicDependency.Count; i++)
            {
                int index = proto.PublicDependency[i];
                if (index < 0 || index >= proto.Dependency.Count)
                {
                    throw new DescriptorValidationException(@this, "Invalid public dependency index.");
                }
                string name = proto.Dependency[index];
                if (!nameToFileMap.TryGetValue(name, out FileDescriptor file))
                {
                    if (!allowUnknownDependencies)
                    {
                        throw new DescriptorValidationException(@this, "Invalid public dependency: " + name);
                    }
                    // Ignore unknown dependencies.
                }
                else
                {
                    publicDependencies.Add(file);
                }
            }
            return new ReadOnlyCollection<FileDescriptor>(publicDependencies);
        }

        /// <value>
        /// The descriptor in its protocol message representation.
        /// </value>
        internal FileDescriptorProto Proto { get; }

        /// <summary>
        /// Returns a clone of the underlying <see cref="FileDescriptorProto"/> describing this file.
        /// Note that a copy is taken every time this method is called, so clients using it frequently
        /// (and not modifying it) may want to cache the returned value.
        /// </summary>
        /// <returns>A protobuf representation of this file descriptor.</returns>
        public FileDescriptorProto ToProto() => Proto.Clone();

        /// <summary>
        /// The feature set for this file, including inherited features.
        /// </summary>
        internal FeatureSetDescriptor Features { get; }

        /// <summary>
        /// Returns the edition of the file descriptor.
        /// </summary>
        internal Edition Edition => Proto.Syntax switch
        {
            "editions" => Proto.Edition,
            "proto3" => Edition.Proto3,
            _ => Edition.Proto2
        };

        /// <summary>
        /// The syntax of the file.
        /// </summary>
        [Obsolete("Use features instead of proto syntax.")]
        public Syntax Syntax => Proto.HasEdition ?  Syntax.Editions
            : Proto.Syntax switch
            {
                "proto3" => Syntax.Proto3,
                "proto2" => Syntax.Proto2,
                "" => Syntax.Proto2,
                _ => throw new InvalidOperationException("No edition or known syntax present")
            };

        /// <value>
        /// The file name.
        /// </value>
        public string Name => Proto.Name;

        /// <summary>
        /// The package as declared in the .proto file. This may or may not
        /// be equivalent to the .NET namespace of the generated classes.
        /// </summary>
        public string Package => Proto.Package;

        /// <value>
        /// Unmodifiable list of top-level message types declared in this file.
        /// </value>
        public IList<MessageDescriptor> MessageTypes { get; }

        /// <value>
        /// Unmodifiable list of top-level enum types declared in this file.
        /// </value>
        public IList<EnumDescriptor> EnumTypes { get; }

        /// <value>
        /// Unmodifiable list of top-level services declared in this file.
        /// </value>
        public IList<ServiceDescriptor> Services { get; }

        /// <summary>
        /// Unmodifiable list of top-level extensions declared in this file.
        /// Note that some extensions may be incomplete (FieldDescriptor.Extension may be null)
        /// if this descriptor was generated using a version of protoc that did not fully
        /// support extensions in C#.
        /// </summary>
        public ExtensionCollection Extensions { get; }

        /// <value>
        /// Unmodifiable list of this file's dependencies (imports).
        /// </value>
        public IList<FileDescriptor> Dependencies { get; }

        /// <value>
        /// Unmodifiable list of this file's public dependencies (public imports).
        /// </value>
        public IList<FileDescriptor> PublicDependencies { get; }

        /// <value>
        /// The original serialized binary form of this descriptor.
        /// </value>
        public ByteString SerializedData { get; }

        /// <value>
        /// Implementation of IDescriptor.FullName - just returns the same as Name.
        /// </value>
        string IDescriptor.FullName => Name;

        /// <value>
        /// Implementation of IDescriptor.File - just returns this descriptor.
        /// </value>
        FileDescriptor IDescriptor.File => this;

        /// <value>
        /// Pool containing symbol descriptors.
        /// </value>
        internal DescriptorPool DescriptorPool { get; }

        /// <summary>
        /// Finds a type (message, enum, service or extension) in the file by name. Does not find nested types.
        /// </summary>
        /// <param name="name">The unqualified type name to look for.</param>
        /// <typeparam name="T">The type of descriptor to look for</typeparam>
        /// <returns>The type's descriptor, or null if not found.</returns>
        public T FindTypeByName<T>(string name)
            where T : class, IDescriptor
        {
            // Don't allow looking up nested types.  This will make optimization
            // easier later.
            if (name.IndexOf('.') != -1)
            {
                return null;
            }
            if (Package.Length > 0)
            {
                name = Package + "." + name;
            }
            T result = DescriptorPool.FindSymbol<T>(name);
            if (result != null && result.File == this)
            {
                return result;
            }
            return null;
        }

        /// <summary>
        /// Builds a FileDescriptor from its protocol buffer representation.
        /// </summary>
        /// <param name="descriptorData">The original serialized descriptor data.
        /// We have only limited proto2 support, so serializing FileDescriptorProto
        /// would not necessarily give us this.</param>
        /// <param name="proto">The protocol message form of the FileDescriptor.</param>
        /// <param name="dependencies">FileDescriptors corresponding to all of the
        /// file's dependencies, in the exact order listed in the .proto file. May be null,
        /// in which case it is treated as an empty array.</param>
        /// <param name="allowUnknownDependencies">Whether unknown dependencies are ignored (true) or cause an exception to be thrown (false).</param>
        /// <param name="generatedCodeInfo">Details about generated code, for the purposes of reflection.</param>
        /// <exception cref="DescriptorValidationException">If <paramref name="proto"/> is not
        /// a valid descriptor. This can occur for a number of reasons, such as a field
        /// having an undefined type or because two messages were defined with the same name.</exception>
        private static FileDescriptor BuildFrom(ByteString descriptorData, FileDescriptorProto proto, FileDescriptor[] dependencies, bool allowUnknownDependencies, GeneratedClrTypeInfo generatedCodeInfo)
        {
            // Building descriptors involves two steps: translating and linking.
            // In the translation step (implemented by FileDescriptor's
            // constructor), we build an object tree mirroring the
            // FileDescriptorProto's tree and put all of the descriptors into the
            // DescriptorPool's lookup tables.  In the linking step, we look up all
            // type references in the DescriptorPool, so that, for example, a
            // FieldDescriptor for an embedded message contains a pointer directly
            // to the Descriptor for that message's type.  We also detect undefined
            // types in the linking step.
            if (dependencies == null)
            {
                dependencies = new FileDescriptor[0];
            }

            DescriptorPool pool = new DescriptorPool(dependencies);
            FileDescriptor result = new FileDescriptor(descriptorData, proto, dependencies, pool, allowUnknownDependencies, generatedCodeInfo);

            // Validate that the dependencies we've been passed (as FileDescriptors) are actually the ones we
            // need.
            if (dependencies.Length != proto.Dependency.Count)
            {
                throw new DescriptorValidationException(
                    result,
                    "Dependencies passed to FileDescriptor.BuildFrom() don't match " +
                    "those listed in the FileDescriptorProto.");
            }

            result.CrossLink();
            return result;
        }

        private void CrossLink()
        {
            foreach (MessageDescriptor message in MessageTypes)
            {
                message.CrossLink();
            }

            foreach (ServiceDescriptor service in Services)
            {
                service.CrossLink();
            }

            Extensions.CrossLink();
        }

        /// <summary>
        /// Creates a descriptor for generated code.
        /// </summary>
        /// <remarks>
        /// This method is only designed to be used by the results of generating code with protoc,
        /// which creates the appropriate dependencies etc. It has to be public because the generated
        /// code is "external", but should not be called directly by end users.
        /// </remarks>
        public static FileDescriptor FromGeneratedCode(
            byte[] descriptorData,
            FileDescriptor[] dependencies,
            GeneratedClrTypeInfo generatedCodeInfo)
        {
            ExtensionRegistry registry = new();
            registry.AddRange(GetAllExtensions(dependencies, generatedCodeInfo));

            FileDescriptorProto proto;
            try
            {
                proto = FileDescriptorProto.Parser.WithExtensionRegistry(registry).ParseFrom(descriptorData);
            }
            catch (InvalidProtocolBufferException e)
            {
                throw new ArgumentException("Failed to parse protocol buffer descriptor for generated code.", e);
            }

            try
            {
                // When building descriptors for generated code, we allow unknown
                // dependencies by default.
                return BuildFrom(ByteString.CopyFrom(descriptorData), proto, dependencies, true, generatedCodeInfo);
            }
            catch (DescriptorValidationException e)
            {
                throw new ArgumentException($"Invalid embedded descriptor for \"{proto.Name}\".", e);
            }
        }

        private static IEnumerable<Extension> GetAllExtensions(FileDescriptor[] dependencies, GeneratedClrTypeInfo generatedInfo)
        {
#if WITH_BENCHMARKING
            GetAllExtensionsCount++;
#endif

            var allExtensions = dependencies.SelectMany(GetAllDependedExtensions).Distinct(ExtensionRegistry.ExtensionComparer.Instance).Concat(GetAllGeneratedExtensions(generatedInfo)).ToList();

#if WITH_BENCHMARKING
            TotalReturnedExtensionsCount += allExtensions.Count;
#endif

            return allExtensions;
        }

        private static IEnumerable<Extension> GetAllGeneratedExtensions(GeneratedClrTypeInfo generated)
        {
#if WITH_BENCHMARKING
            GetAllGeneratedExtensionsCount++;
#endif
            return generated.Extensions.Concat(generated.NestedTypes.Where(t => t != null).SelectMany(GetAllGeneratedExtensions)).ToList();
        }

        private static IEnumerable<Extension> GetAllDependedExtensions(FileDescriptor descriptor)
        {
            if (extensionCachingEnabled && allDependedExtensionsCache.TryGetValue(descriptor.Name, out List<Extension> cachedExtensions))
            {
                return cachedExtensions;
            }

#if WITH_BENCHMARKING
            GetAllDependedExtensionsCount++;
#endif
            var extensions = descriptor.Extensions.UnorderedExtensions
                .Select(s => s.Extension)
                .Where(e => e != null)
                .Concat(descriptor.Dependencies.Concat(descriptor.PublicDependencies).SelectMany(GetAllDependedExtensions))
                .Concat(descriptor.MessageTypes.SelectMany(GetAllDependedExtensionsFromMessage)).ToList();

            if (extensionCachingEnabled)
            {
                allDependedExtensionsCache[descriptor.Name] = extensions;
            }

            return extensions;
        }

        private static IEnumerable<Extension> GetAllDependedExtensionsFromMessage(MessageDescriptor descriptor)
        {
#if WITH_BENCHMARKING
            GetAllDependedExtensionsFromMessageCount++;
#endif
            return descriptor.Extensions.UnorderedExtensions
                .Select(s => s.Extension)
                .Where(e => e != null)
                .Concat(descriptor.NestedTypes.SelectMany(GetAllDependedExtensionsFromMessage)).ToList();
        }

        /// <summary>
        /// Converts the given descriptor binary data into FileDescriptor objects.
        /// Note: reflection using the returned FileDescriptors is not currently supported.
        /// </summary>
        /// <param name="descriptorData">The binary file descriptor proto data. Must not be null, and any
        /// dependencies must come before the descriptor which depends on them. (If A depends on B, and B
        /// depends on C, then the descriptors must be presented in the order C, B, A.) This is compatible
        /// with the order in which protoc provides descriptors to plugins.</param>
        /// <param name="registry">The extension registry to use when parsing, or null if no extensions are required.</param>
        /// <returns>The file descriptors corresponding to <paramref name="descriptorData"/>.</returns>
        public static IReadOnlyList<FileDescriptor> BuildFromByteStrings(IEnumerable<ByteString> descriptorData, ExtensionRegistry registry)
        {
            ProtoPreconditions.CheckNotNull(descriptorData, nameof(descriptorData));

            var parser = FileDescriptorProto.Parser.WithExtensionRegistry(registry);

            // TODO: See if we can build a single DescriptorPool instead of building lots of them.
            // This will all behave correctly, but it's less efficient than we'd like.
            var descriptors = new List<FileDescriptor>();
            var descriptorsByName = new Dictionary<string, FileDescriptor>();
            foreach (var data in descriptorData)
            {
                var proto = parser.ParseFrom(data);
                var dependencies = new List<FileDescriptor>();
                foreach (var dependencyName in proto.Dependency)
                {
                    if (!descriptorsByName.TryGetValue(dependencyName, out FileDescriptor dependency))
                    {
                        throw new ArgumentException($"Dependency missing: {dependencyName}");
                    }
                    dependencies.Add(dependency);
                }
                var pool = new DescriptorPool(dependencies);
                FileDescriptor descriptor = new FileDescriptor(
                    data, proto, dependencies, pool,
                    allowUnknownDependencies: false, generatedCodeInfo: null);
                descriptor.CrossLink();
                descriptors.Add(descriptor);
                if (descriptorsByName.ContainsKey(descriptor.Name))
                {
                    throw new ArgumentException($"Duplicate descriptor name: {descriptor.Name}");
                }
                descriptorsByName.Add(descriptor.Name, descriptor);
            }
            return new ReadOnlyCollection<FileDescriptor>(descriptors);
        }

        /// <summary>
        /// Converts the given descriptor binary data into FileDescriptor objects.
        /// Note: reflection using the returned FileDescriptors is not currently supported.
        /// </summary>
        /// <param name="descriptorData">The binary file descriptor proto data. Must not be null, and any
        /// dependencies must come before the descriptor which depends on them. (If A depends on B, and B
        /// depends on C, then the descriptors must be presented in the order C, B, A.) This is compatible
        /// with the order in which protoc provides descriptors to plugins.</param>
        /// <returns>The file descriptors corresponding to <paramref name="descriptorData"/>.</returns>
        public static IReadOnlyList<FileDescriptor> BuildFromByteStrings(IEnumerable<ByteString> descriptorData) =>
            BuildFromByteStrings(descriptorData, null);

        /// <summary>
        /// Returns a <see cref="System.String" /> that represents this instance.
        /// </summary>
        /// <returns>
        /// A <see cref="System.String" /> that represents this instance.
        /// </returns>
        public override string ToString()
        {
            return $"FileDescriptor for {Name}";
        }

        /// <summary>
        /// Returns the file descriptor for descriptor.proto.
        /// </summary>
        /// <remarks>
        /// This is used for protos which take a direct dependency on <c>descriptor.proto</c>, typically for
        /// annotations. While <c>descriptor.proto</c> is a proto2 file, it is built into the Google.Protobuf
        /// runtime for reflection purposes. The messages are internal to the runtime as they would require
        /// proto2 semantics for full support, but the file descriptor is available via this property. The
        /// C# codegen in protoc automatically uses this property when it detects a dependency on <c>descriptor.proto</c>.
        /// </remarks>
        /// <value>
        /// The file descriptor for <c>descriptor.proto</c>.
        /// </value>
        public static FileDescriptor DescriptorProtoFileDescriptor => DescriptorReflection.Descriptor;

        /// <summary>
        /// The (possibly empty) set of custom options for this file.
        /// </summary>
        [Obsolete("CustomOptions are obsolete. Use the GetOptions() method.")]
        public CustomOptions CustomOptions => new CustomOptions(Proto.Options?._extensions?.ValuesByNumber);

        /// <summary>
        /// The <c>FileOptions</c>, defined in <c>descriptor.proto</c>.
        /// If the options message is not present (i.e. there are no options), <c>null</c> is returned.
        /// Custom options can be retrieved as extensions of the returned message.
        /// NOTE: A defensive copy is created each time this property is retrieved.
        /// </summary>
        public FileOptions GetOptions()
        {
            var clone = Proto.Options?.Clone();
            if (clone is null)
            {
                return null;
            }
            // Clients should be using feature accessor methods, not accessing features on the
            // options proto.
            clone.Features = null;
            return clone;
        }

        /// <summary>
        /// Gets a single value file option for this descriptor
        /// </summary>
        [Obsolete("GetOption is obsolete. Use the GetOptions() method.")]
        public T GetOption<T>(Extension<FileOptions, T> extension)
        {
            var value = Proto.Options.GetExtension(extension);
            return value is IDeepCloneable<T> ? (value as IDeepCloneable<T>).Clone() : value;
        }

        /// <summary>
        /// Gets a repeated value file option for this descriptor
        /// </summary>
        [Obsolete("GetOption is obsolete. Use the GetOptions() method.")]
        public RepeatedField<T> GetOption<T>(RepeatedExtension<FileOptions, T> extension)
        {
            return Proto.Options.GetExtension(extension).Clone();
        }

        /// <summary>
        /// Performs initialization for the given generic type argument.
        /// </summary>
        /// <remarks>
        /// This method is present for the sake of AOT compilers. It allows code (whether handwritten or generated)
        /// to make calls into the reflection machinery of this library to express an intention to use that type
        /// reflectively (e.g. for JSON parsing and formatting). The call itself does almost nothing, but AOT compilers
        /// attempting to determine which generic type arguments need to be handled will spot the code path and act
        /// accordingly.
        /// </remarks>
        /// <typeparam name="T">The type to force initialization for.</typeparam>
        public static void ForceReflectionInitialization<T>() => ReflectionUtil.ForceInitialize<T>();
    }
}