using System;
using System.Buffers;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Diagnostics;
using System.IO;
using System.IO.Compression;
using System.Linq;
using System.Reflection;
using System.Reflection.Metadata;
using System.Reflection.Metadata.Ecma335;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Security.Cryptography;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using JetBrains.Annotations;
using NetSerializer;
using Newtonsoft.Json.Linq;
using Robust.Shared.ContentPack;
using Robust.Shared.Interfaces.Log;
using Robust.Shared.Interfaces.Network;
using Robust.Shared.IoC;
using Robust.Shared.Log;
using Robust.Shared.Utility;
using YamlDotNet.RepresentationModel;

namespace Robust.Shared.Serialization
{

    /// <summary>
    /// Serializer which manages a mapping of pre-loaded strings to constant
    /// values, for message compression. The mapping is shared between the
    /// server and client.
    /// </summary>
    /// <remarks>
    /// Strings are long and expensive to send over the wire, and lots of
    /// strings involved in messages are sent repeatedly between the server
    /// and client - such as filenames, icon states, constant strings, etc.
    ///
    /// To compress these strings, we use a constant string mapping, decided
    /// by the server when it starts up, that associates strings with a
    /// fixed value. The mapping is shared with clients when they connect.
    ///
    /// When sending these strings over the wire, the serializer can then
    /// send the constant value instead - and at the other end, the
    /// serializer can use the same mapping to recover the original string.
    /// </remarks>
    public class RobustMappedStringSerializer : IStaticTypeSerializer, IRobustMappedStringSerializer
    {

        private INetManager? _net;

        private readonly Lazy<ISawmill> _lazyLogSzr = new Lazy<ISawmill>(() => Logger.GetSawmill("szr"));

        private ISawmill LogSzr => _lazyLogSzr.Value;

        private readonly HashSet<INetChannel> _incompleteHandshakes = new HashSet<INetChannel>();

        /// <summary>
        /// Starts the handshake from the server end of the given channel,
        /// sending a <see cref="MsgRobustMappedStringsSerializerServerHandshake"/>.
        /// </summary>
        /// <param name="channel">The network channel to perform the handshake over.</param>
        /// <remarks>
        /// Locks the string mapping if this is the first time the server is
        /// performing the handshake.
        /// </remarks>
        /// <seealso cref="MsgRobustMappedStringsSerializerClientHandshake"/>
        /// <seealso cref="MsgRobustMappedStringsSerializerStrings"/>
        public async Task Handshake(INetChannel channel)
        {
            var net = channel.NetPeer;

            if (net.IsClient)
            {
                return;
            }

            if (!LockMappedStrings)
            {
                LockMappedStrings = true;
                LogSzr.Debug($"Locked in at {_mappedStrings.Count} mapped strings.");
            }

            _incompleteHandshakes.Add(channel);

            var message = net.CreateNetMessage<MsgRobustMappedStringsSerializerServerHandshake>();
            message.Hash = MappedStringsHash;
            net.ServerSendMessage(message, channel);

            while (_incompleteHandshakes.Contains(channel))
            {
                await Task.Delay(1);
            }

            LogSzr.Debug($"Completed handshake with {channel.RemoteEndPoint.Address}.");
        }

        /// <summary>
        /// Performs the setup so that the serializer can perform the string-
        /// exchange protocol.
        /// </summary>
        /// <remarks>
        /// The string-exchange protocol is started by the server when the
        /// client first connects. The server sends the client a hash of the
        /// string mapping; the client checks that hash against any local
        /// caches; and if necessary, the client requests a new copy of the
        /// mapping from the server.
        ///
        /// Uncached flow: <code>
        /// Client      |      Server
        /// | &lt;-------------- Hash |
        /// | Need Strings ------&gt; |
        /// | &lt;----------- Strings |
        /// | Dont Need Strings -&gt; |
        /// </code>
        ///
        /// Cached flow: <code>
        /// Client      |      Server
        /// | &lt;-------------- Hash |
        /// | Dont Need Strings -&gt; |
        /// </code>
        ///
        /// Verification failure flow: <code>
        /// Client      |      Server
        /// | &lt;-------------- Hash |
        /// | Need Strings ------&gt; |
        /// | &lt;----------- Strings |
        /// + Hash Failed          |
        /// | Need Strings ------&gt; |
        /// | &lt;----------- Strings |
        /// | Dont Need Strings -&gt; |
        ///  </code>
        ///
        /// NOTE: Verification failure flow is currently not implemented.
        /// </remarks>
        /// <param name="net">
        /// The <see cref="INetManager"/> to perform the protocol steps over.
        /// </param>
        /// <seealso cref="MsgRobustMappedStringsSerializerServerHandshake"/>
        /// <seealso cref="MsgRobustMappedStringsSerializerClientHandshake"/>
        /// <seealso cref="MsgRobustMappedStringsSerializerStrings"/>
        /// <seealso cref="HandleServerHandshake"/>
        /// <seealso cref="HandleClientHandshake"/>
        /// <seealso cref="HandleStringsMessage"/>
        /// <seealso cref="OnClientCompleteHandshake"/>
        public void NetworkInitialize(INetManager net)
        {
            _net = net;

            net.RegisterNetMessage<MsgRobustMappedStringsSerializerServerHandshake>(
                nameof(MsgRobustMappedStringsSerializerServerHandshake),
                msg => HandleServerHandshake(net, msg));

            net.RegisterNetMessage<MsgRobustMappedStringsSerializerClientHandshake>(
                nameof(MsgRobustMappedStringsSerializerClientHandshake),
                msg => HandleClientHandshake(net, msg));

            net.RegisterNetMessage<MsgRobustMappedStringsSerializerStrings>(
                nameof(MsgRobustMappedStringsSerializerStrings),
                msg => HandleStringsMessage(net, msg));
        }

        /// <summary>
        /// Handles the reception, verification of a strings package
        /// and subsequent mapping of strings and initiator of
        /// receipt response.
        ///
        /// Uncached flow: <code>
        /// Client      |      Server
        /// | &lt;-------------- Hash |
        /// | Need Strings ------&gt; |
        /// | &lt;----------- Strings |
        /// | Dont Need Strings -&gt; | &lt;- you are here on client
        ///
        /// Verification failure flow: <code>
        /// Client      |      Server
        /// | &lt;-------------- Hash |
        /// | Need Strings ------&gt; |
        /// | &lt;----------- Strings |
        /// + Hash Failed          | &lt;- you are here on client
        /// | Need Strings ------&gt; |
        /// | &lt;----------- Strings |
        /// | Dont Need Strings -&gt; | &lt;- you are here on client
        ///  </code>
        ///
        /// NOTE: Verification failure flow is currently not implemented.
        /// </code>
        /// </summary>
        /// <exception cref="InvalidOperationException">Unable to verify strings package by hash.</exception>
        /// <seealso cref="NetworkInitialize"/>
        private void HandleStringsMessage(INetManager net, MsgRobustMappedStringsSerializerStrings msgRobustMappedStringsSerializer)
        {
            if (net.IsServer)
            {
                LogSzr.Error("Received strings from client.");
                return;
            }

            LockMappedStrings = false;
            ClearStrings();
            DebugTools.Assert(msgRobustMappedStringsSerializer.Package != null, "msg.Package != null");
            LoadStrings(new MemoryStream(msgRobustMappedStringsSerializer.Package!, false));
            var checkHash = CalculateHash(msgRobustMappedStringsSerializer.Package!);
            if (!checkHash.SequenceEqual(ServerHash))
            {
                // TODO: retry sending MsgClientHandshake with NeedsStrings = false
                throw new InvalidOperationException("Unable to verify strings package by hash." + $"\n{ConvertToBase64Url(checkHash)} vs. {ConvertToBase64Url(ServerHash)}");
            }

            _stringMapHash = ServerHash;
            LockMappedStrings = true;

            LogSzr.Debug($"Locked in at {_mappedStrings.Count} mapped strings.");

            WriteStringCache();

            // ok we're good now
            var channel = msgRobustMappedStringsSerializer.MsgChannel;
            OnClientCompleteHandshake(net, channel);
        }

        /// <summary>
        /// Interpret a client's handshake, either sending a package
        /// of strings or completing the handshake.
        ///
        /// Uncached flow: <code>
        /// Client      |      Server
        /// | &lt;-------------- Hash |
        /// | Need Strings ------&gt; | &lt;- you are here on server
        /// | &lt;----------- Strings |
        /// | Dont Need Strings -&gt; | &lt;- you are here on server
        /// </code>
        ///
        /// Cached flow: <code>
        /// Client      |      Server
        /// | &lt;-------------- Hash |
        /// | Dont Need Strings -&gt; | &lt;- you are here on server
        /// </code>
        ///
        /// Verification failure flow: <code>
        /// Client      |      Server
        /// | &lt;-------------- Hash |
        /// | Need Strings ------&gt; | &lt;- you are here on server
        /// | &lt;----------- Strings |
        /// + Hash Failed          |
        /// | Need Strings ------&gt; | &lt;- you are here on server
        /// | &lt;----------- Strings |
        /// | Dont Need Strings -&gt; |
        ///  </code>
        ///
        /// NOTE: Verification failure flow is currently not implemented.
        /// </summary>
        /// <seealso cref="NetworkInitialize"/>
        private void HandleClientHandshake(INetManager net, MsgRobustMappedStringsSerializerClientHandshake msgRobustMappedStringsSerializer)
        {
            if (net.IsClient)
            {
                LogSzr.Error("Received client handshake on client.");
                return;
            }

            LogSzr.Debug($"Received handshake from {msgRobustMappedStringsSerializer.MsgChannel.RemoteEndPoint.Address}.");

            if (!msgRobustMappedStringsSerializer.NeedsStrings)
            {
                LogSzr.Debug($"Completing handshake with {msgRobustMappedStringsSerializer.MsgChannel.RemoteEndPoint.Address}.");
                _incompleteHandshakes.Remove(msgRobustMappedStringsSerializer.MsgChannel);
                return;
            }

            // TODO: count and limit number of requests to send strings during handshake

            var strings = msgRobustMappedStringsSerializer.MsgChannel.NetPeer.CreateNetMessage<MsgRobustMappedStringsSerializerStrings>();
            using (var ms = new MemoryStream())
            {
                WriteStringPackage(ms);
                ms.Position = 0;
                strings.Package = ms.ToArray();
                LogSzr.Debug($"Sending {ms.Length} bytes sized mapped strings package to {msgRobustMappedStringsSerializer.MsgChannel.RemoteEndPoint.Address}.");
            }

            msgRobustMappedStringsSerializer.MsgChannel.SendMessage(strings);
        }

        /// <summary>
        /// Interpret a server's handshake, either requesting a package
        /// of strings or completing the handshake.
        ///
        /// Uncached flow: <code>
        /// Client      |      Server
        /// | &lt;-------------- Hash | &lt;- you are here on client
        /// | Need Strings ------&gt; |
        /// | &lt;----------- Strings |
        /// | Dont Need Strings -&gt; |
        /// </code>
        ///
        /// Cached flow: <code>
        /// Client      |      Server
        /// | &lt;-------------- Hash | &lt;- you are here on client
        /// | Dont Need Strings -&gt; |
        /// </code>
        ///
        /// Verification failure flow: <code>
        /// Client      |      Server
        /// | &lt;-------------- Hash | &lt;- you are here on client
        /// | Need Strings ------&gt; |
        /// | &lt;----------- Strings |
        /// + Hash Failed          |
        /// | Need Strings ------&gt; |
        /// | &lt;----------- Strings |
        /// | Dont Need Strings -&gt; |
        ///  </code>
        ///
        /// NOTE: Verification failure flow is currently not implemented.
        /// </summary>
        /// <exception cref="InvalidOperationException">Mapped strings are locked.</exception>
        /// <seealso cref="NetworkInitialize"/>
        private void HandleServerHandshake(INetManager net, MsgRobustMappedStringsSerializerServerHandshake msgRobustMappedStringsSerializer)
        {
            if (net.IsServer)
            {
                LogSzr.Error("Received server handshake on server.");
                return;
            }

            ServerHash = msgRobustMappedStringsSerializer.Hash;
            LockMappedStrings = false;

            if (LockMappedStrings)
            {
                throw new InvalidOperationException("Mapped strings are locked.");
            }

            ClearStrings();

            var hashStr = ConvertToBase64Url(Convert.ToBase64String(msgRobustMappedStringsSerializer.Hash!));

            LogSzr.Debug($"Received server handshake with hash {hashStr}.");

            var fileName = CacheForHash(hashStr);
            if (!File.Exists(fileName))
            {
                LogSzr.Debug($"No string cache for {hashStr}.");
                var handshake = net.CreateNetMessage<MsgRobustMappedStringsSerializerClientHandshake>();
                LogSzr.Debug("Asking server to send mapped strings.");
                handshake.NeedsStrings = true;
                msgRobustMappedStringsSerializer.MsgChannel.SendMessage(handshake);
            }
            else
            {
                LogSzr.Debug($"We had a cached string map that matches {hashStr}.");
                using var file = File.OpenRead(fileName);
                var added = LoadStrings(file);

                _stringMapHash = msgRobustMappedStringsSerializer.Hash!;
                LogSzr.Debug($"Read {added} strings from cache {hashStr}.");
                LockMappedStrings = true;
                LogSzr.Debug($"Locked in at {_mappedStrings.Count} mapped strings.");
                // ok we're good now
                var channel = msgRobustMappedStringsSerializer.MsgChannel;
                OnClientCompleteHandshake(net, channel);
            }
        }

        /// <summary>
        /// Inform the server that the client has a complete copy of the
        /// mapping, and alert other code that the handshake is over.
        /// </summary>
        /// <seealso cref="ClientHandshakeComplete"/>
        /// <seealso cref="NetworkInitialize"/>
        private void OnClientCompleteHandshake(INetManager net, INetChannel channel)
        {
            LogSzr.Debug("Letting server know we're good to go.");
            var handshake = net.CreateNetMessage<MsgRobustMappedStringsSerializerClientHandshake>();
            handshake.NeedsStrings = false;
            channel.SendMessage(handshake);

            if (ClientHandshakeComplete == null)
            {
                LogSzr.Warning("There's no handler attached to ClientHandshakeComplete.");
            }

            ClientHandshakeComplete?.Invoke();
        }

        /// <summary>
        /// Gets the cache file associated with the given hash.
        /// </summary>
        /// <param name="hashStr">The hash to look up the cache for.</param>
        /// <returns>
        /// The filename where the cache for the given hash would be. The
        /// file itself may or may not exist. If it does not exist, no cache
        /// was made for the given hash.
        /// </returns>
        private string CacheForHash(string hashStr)
            => PathHelpers.ExecutableRelativeFile($"strings-{hashStr}");

        /// <summary>
        ///  Saves the string cache to a file based on it's hash.
        /// </summary>
        private void WriteStringCache()
        {
            var hashStr = Convert.ToBase64String(MappedStringsHash);
            hashStr = ConvertToBase64Url(hashStr);

            var fileName = CacheForHash(hashStr);
            using var file = File.OpenWrite(fileName);
            WriteStringPackage(file);

            LogSzr.Debug($"Wrote string cache {hashStr}.");
        }

        private byte[]? _mappedStringsPackage;

        private byte[] MappedStringsPackage => LockMappedStrings
            ? _mappedStringsPackage ??= WriteStringPackage()
            : throw new InvalidOperationException("Mapped strings must be locked.");

        /// <summary>
        /// Writes strings to a package and converts to an array of bytes.
        /// </summary>
        /// <remarks>
        /// This is invoked by accessing <see cref="MappedStringsPackage"/> for the first time.
        /// </remarks>
        private byte[] WriteStringPackage()
        {
            using var ms = new MemoryStream();
            WriteStringPackage(ms);
            return ms.ToArray();
        }

        /// <summary>
        /// Writes a strings package to a stream.
        /// </summary>
        /// <param name="stream">A writable stream.</param>
        /// <exception cref="NotImplementedException">Overly long string in strings package.</exception>
        public void WriteStringPackage(Stream stream)
        {
            // ReSharper disable once SuggestVarOrType_Elsewhere
            Span<byte> buf = stackalloc byte[MaxMappedStringSize];
            var sw = Stopwatch.StartNew();
            var enc = Encoding.UTF8.GetEncoder();

            using (var zs = new DeflateStream(stream, CompressionLevel.Optimal, true))
            {
                var bytesWritten = WriteCompressedUnsignedInt(zs, (uint) MappedStrings.Count);
                foreach (var str in MappedStrings)
                {
                    if (str.Length >= MaxMappedStringSize)
                    {
                        throw new NotImplementedException("Overly long string in strings package.");
                    }

                    var l = enc.GetBytes(str, buf, true);

                    if (l >= MaxMappedStringSize)
                    {
                        throw new NotImplementedException("Overly long string in strings package.");
                    }

                    bytesWritten += WriteCompressedUnsignedInt(zs, (uint) l);

                    zs.Write(buf.Slice(0,l));

                    bytesWritten += l;

                    enc.Reset();
                }

                zs.Write(BitConverter.GetBytes(bytesWritten));
                zs.Flush();
            }

            LogSzr.Debug($"Wrote {MappedStrings.Count} strings to package in {sw.ElapsedMilliseconds}ms.");
        }

        /// <summary>
        /// Loads a strings package from a stream.
        /// </summary>
        /// <remarks>
        /// Uses <see cref="ReadStringPackage"/> to extract strings and adds them to the mapping.
        /// </remarks>
        /// <param name="stream">A readable stream.</param>
        /// <returns>The number of strings loaded.</returns>
        /// <exception cref="InvalidOperationException">Mapped strings are locked, will not load.</exception>
        /// <exception cref="InvalidDataException">Did not read all bytes in package!</exception>
        private int LoadStrings(Stream stream)
        {
            if (LockMappedStrings)
            {
                throw new InvalidOperationException("Mapped strings are locked, will not load.");
            }

            var started = MappedStrings.Count;
            foreach (var str in ReadStringPackage(stream))
            {
                _stringMapping[str] = _mappedStrings.Count;
                _mappedStrings.Add(str);
            }

            if (stream.CanSeek && stream.CanRead)
            {
                if (stream.Position != stream.Length)
                {
                    throw new InvalidDataException("Did not read all bytes in package!");
                }
            }

            var added = MappedStrings.Count - started;
            return added;
        }

        /// <summary>
        /// Reads the contents of a strings package.
        /// </summary>
        /// <remarks>
        /// Does not add strings to the current mapping.
        /// </remarks>
        /// <param name="stream">A readable stream.</param>
        /// <returns>Strings from within the package.</returns>
        /// <exception cref="InvalidDataException">Could not read the full length of string #N.</exception>
        private IEnumerable<string> ReadStringPackage(Stream stream)
        {
            var buf = ArrayPool<byte>.Shared.Rent(65536);
            var sw = Stopwatch.StartNew();
            using var zs = new DeflateStream(stream, CompressionMode.Decompress);

            var c = ReadCompressedUnsignedInt(zs, out var x);
            var bytesRead = x;
            for (var i = 0; i < c; ++i)
            {
                var l = (int) ReadCompressedUnsignedInt(zs, out x);
                bytesRead += x;
                var y = zs.Read(buf, 0, l);
                if (y != l)
                {
                    throw new InvalidDataException($"Could not read the full length of string #{i}.");
                }

                bytesRead += y;
                var str = Encoding.UTF8.GetString(buf, 0, l);
                yield return str;
            }

            zs.Read(buf, 0, 4);
            var checkBytesRead = BitConverter.ToInt32(buf, 0);
            if (checkBytesRead != bytesRead)
            {
                throw new InvalidDataException("Could not verify package was read correctly.");
            }

            LogSzr.Debug($"Read package of {c} strings in {sw.ElapsedMilliseconds}ms.");
        }

        /// <summary>
        /// Converts a byte array such as a hash to a Base64 representation that is URL safe.
        /// </summary>
        /// <param name="data"></param>
        /// <returns>A base64url string form of the byte array.</returns>
        private string ConvertToBase64Url(byte[]? data)
            => data == null ? "" : ConvertToBase64Url(Convert.ToBase64String(data));

        /// <summary>
        /// Converts a a Base64 string to one that is URL safe.
        /// </summary>
        /// <returns>A base64url formed string.</returns>
        private string ConvertToBase64Url(string b64Str)
        {
            if (b64Str is null)
            {
                throw new ArgumentNullException(nameof(b64Str));
            }

            var cut = b64Str[^1] == '=' ? b64Str[^2] == '=' ? 2 : 1 : 0;
            b64Str = new StringBuilder(b64Str).Replace('+', '-').Replace('/', '_').ToString(0, b64Str.Length - cut);
            return b64Str;
        }

        /// <summary>
        /// Converts a URL-safe Base64 string into a byte array.
        /// </summary>
        /// <param name="s">A base64url formed string.</param>
        /// <returns>The represented byte array.</returns>
        public byte[] ConvertFromBase64Url(string s)
        {
            var l = s.Length % 3;
            var sb = new StringBuilder(s);
            sb.Replace('-', '+').Replace('_', '/');
            for (var i = 0; i < l; ++i)
            {
                sb.Append('=');
            }

            s = sb.ToString();
            return Convert.FromBase64String(s);
        }

        public byte[]? ServerHash;

        private readonly List<string> _mappedStrings = new List<string>();

        private readonly Dictionary<string, int> _stringMapping = new Dictionary<string, int>();

        public IReadOnlyList<String> MappedStrings => new ReadOnlyCollection<string>(_mappedStrings);

        /// <summary>
        /// Whether the string mapping is decided, and cannot be changed.
        /// </summary>
        /// <value>
        /// <para>
        /// While <c>false</c>, strings can be added to the mapping, but
        /// it cannot be saved to a cache.
        /// </para>
        /// <para>
        /// While <c>true</c>, the mapping cannot be modified, but can be
        /// shared between the server and client and saved to a cache.
        /// </para>
        /// </value>
        public bool LockMappedStrings { get; set; }

        private readonly Regex _rxSymbolSplitter
            = new Regex(
                @"(?<=[^\s\W])(?=[A-Z]) # Match for split at start of new capital letter
                            |(?<=[^0-9\s\W])(?=[0-9]) # Match for split before spans of numbers
                            |(?<=[A-Za-z0-9])(?=_) # Match for a split before an underscore
                            |(?=[.\\\/,#$?!@|&*()^`""'`~[\]{}:;\-]) # Match for a split after symbols
                            |(?<=[.\\\/,#$?!@|&*()^`""'`~[\]{}:;\-]) # Match for a split before symbols too",
                RegexOptions.CultureInvariant
                | RegexOptions.Compiled
                | RegexOptions.IgnorePatternWhitespace
            );

        /// <summary>
        /// Add a string to the constant mapping.
        /// </summary>
        /// <remarks>
        /// If the string has multiple detectable subcomponents, such as a
        /// filepath, it may result in more than one string being added to
        /// the mapping. As string parts are commonly sent as subsets or
        /// scoped names, this increases the likelyhood of a successful
        /// string mapping.
        /// </remarks>
        /// <returns>
        /// <c>true</c> if the string was added to the mapping for the first
        /// time, <c>false</c> otherwise.
        /// </returns>
        /// <exception cref="InvalidOperationException">
        /// Thrown if the string is not normalized (<see cref="String.IsNormalized()"/>).
        /// </exception>
        public bool AddString(string str)
        {
            if (LockMappedStrings)
            {
                if (_net!.IsClient)
                {
                    //LogSzr.Debug("On client and mapped strings are locked, will not add.");
                    return false;
                }

                //throw new InvalidOperationException("Mapped strings are locked, will not add.");
                LogSzr.Debug("On server and mapped strings are locked, will not add.");
                return false;
            }

            if (String.IsNullOrEmpty(str))
            {
                return false;
            }

            if (!str.IsNormalized())
            {
                throw new InvalidOperationException("Only normalized strings may be added.");
            }

            if (_stringMapping.ContainsKey(str))
            {
                return false;
            }

            if (str.Length >= MaxMappedStringSize) return false;

            if (str.Length <= MinMappedStringSize) return false;

            str = str.Trim();

            if (str.Length <= MinMappedStringSize) return false;

            str = str.Replace(Environment.NewLine, "\n");

            if (str.Length <= MinMappedStringSize) return false;

            var symTrimmedStr = str.Trim(TrimmableSymbolChars);
            if (symTrimmedStr != str)
            {
                AddString(symTrimmedStr);
            }

            if (str.Contains('/'))
            {
                var parts = str.Split('/', StringSplitOptions.RemoveEmptyEntries);
                for (var i = 0; i < parts.Length; ++i)
                {
                    for (var l = 1; l <= parts.Length - i; ++l)
                    {
                        var subStr = String.Join('/', parts.Skip(i).Take(l));
                        if (_stringMapping.TryAdd(subStr, _mappedStrings.Count))
                        {
                            _mappedStrings.Add(subStr);
                        }

                        if (!subStr.Contains('.'))
                        {
                            continue;
                        }

                        var subParts = subStr.Split('.', StringSplitOptions.RemoveEmptyEntries);
                        for (var si = 0; si < subParts.Length; ++si)
                        {
                            for (var sl = 1; sl <= subParts.Length - si; ++sl)
                            {
                                var subSubStr = String.Join('.', subParts.Skip(si).Take(sl));
                                // ReSharper disable once InvertIf
                                if (_stringMapping.TryAdd(subSubStr, _mappedStrings.Count))
                                {
                                    _mappedStrings.Add(subSubStr);
                                }
                            }
                        }
                    }
                }
            }
            else if (str.Contains("_"))
            {
                foreach (var substr in str.Split("_"))
                {
                    AddString(substr);
                }
            }
            else if (str.Contains(" "))
            {
                foreach (var substr in str.Split(" "))
                {
                    if (substr == str) continue;

                    AddString(substr);
                }
            }
            else
            {
                var parts = _rxSymbolSplitter.Split(str);
                foreach (var substr in parts)
                {
                    if (substr == str) continue;

                    AddString(substr);
                }

                for (var si = 0; si < parts.Length; ++si)
                {
                    for (var sl = 1; sl <= parts.Length - si; ++sl)
                    {
                        var subSubStr = String.Concat(parts.Skip(si).Take(sl));
                        if (_stringMapping.TryAdd(subSubStr, _mappedStrings.Count))
                        {
                            _mappedStrings.Add(subSubStr);
                        }
                    }
                }
            }

            if (_stringMapping.TryAdd(str, _mappedStrings.Count))
            {
                _mappedStrings.Add(str);
            }

            _stringMapHash = null;
            _mappedStringsPackage = null;
            return true;
        }

        /// <summary>
        /// Add the constant strings from an <see cref="Assembly"/> to the
        /// mapping.
        /// </summary>
        /// <param name="asm">The assembly from which to collect constant strings.</param>
        [MethodImpl(MethodImplOptions.Synchronized)]
        public unsafe void AddStrings(Assembly asm)
        {
            if (LockMappedStrings)
            {
                if (_net!.IsClient)
                {
                    //LogSzr.Debug("On client and mapped strings are locked, will not add.");
                    return;
                }

                //throw new InvalidOperationException("Mapped strings are locked, will not add .");
                LogSzr.Debug("On server and mapped strings are locked, will not add.");
                return;
            }

            var started = MappedStrings.Count;
            var sw = Stopwatch.StartNew();
            if (asm.TryGetRawMetadata(out var blob, out var len))
            {
                var reader = new MetadataReader(blob, len);
                var usrStrHandle = default(UserStringHandle);
                do
                {
                    var userStr = reader.GetUserString(usrStrHandle);
                    if (userStr != "")
                    {
                        AddString(String.Intern(userStr.Normalize()));
                    }

                    usrStrHandle = reader.GetNextHandle(usrStrHandle);
                } while (usrStrHandle != default);

                var strHandle = default(StringHandle);
                do
                {
                    var str = reader.GetString(strHandle);
                    if (str != "")
                    {
                        AddString(String.Intern(str.Normalize()));
                    }

                    strHandle = reader.GetNextHandle(strHandle);
                } while (strHandle != default);
            }

            var added = MappedStrings.Count - started;
            LogSzr.Debug($"Mapping {added} strings from {asm.GetName().Name} took {sw.ElapsedMilliseconds}ms.");
        }

        /// <summary>
        /// Add strings from the given <see cref="YamlStream"/> to the mapping.
        /// </summary>
        /// <remarks>
        /// Strings are taken from YAML anchors, tags, and leaf nodes.
        /// </remarks>
        /// <param name="yaml">The YAML to collect strings from.</param>
        /// <param name="name">The stream name. Only used for logging.</param>
        [MethodImpl(MethodImplOptions.Synchronized)]
        public void AddStrings(YamlStream yaml, string name)
        {
            if (LockMappedStrings)
            {
                if (_net!.IsClient)
                {
                    //LogSzr.Debug("On client and mapped strings are locked, will not add.");
                    return;
                }

                //throw new InvalidOperationException("Mapped strings are locked, will not add.");
                LogSzr.Debug("On server and mapped strings are locked, will not add.");
                return;
            }

            var started = MappedStrings.Count;
            var sw = Stopwatch.StartNew();
            foreach (var doc in yaml)
            {
                foreach (var node in doc.AllNodes)
                {
                    var a = node.Anchor;
                    if (!String.IsNullOrEmpty(a))
                    {
                        AddString(a);
                    }

                    var t = node.Tag;
                    if (!String.IsNullOrEmpty(t))
                    {
                        AddString(t);
                    }

                    switch (node)
                    {
                        case YamlScalarNode scalar:
                        {
                            var v = scalar.Value;
                            if (String.IsNullOrEmpty(v))
                            {
                                continue;
                            }

                            AddString(v);
                            break;
                        }
                    }
                }
            }

            var added = MappedStrings.Count - started;
            LogSzr.Debug($"Mapping {added} strings from {name} took {sw.ElapsedMilliseconds}ms.");
        }

        /// <summary>
        /// Add strings from the given <see cref="JObject"/> to the mapping.
        /// </summary>
        /// <remarks>
        /// Strings are taken from JSON property names and string nodes.
        /// </remarks>
        /// <param name="obj">The JSON to collect strings from.</param>
        /// <param name="name">The stream name. Only used for logging.</param>
        public void AddStrings(JObject obj, string name)
        {
            if (LockMappedStrings)
            {
                if (_net!.IsClient)
                {
                    //LogSzr.Debug("On client and mapped strings are locked, will not add.");
                    return;
                }

                //throw new InvalidOperationException("Mapped strings are locked, will not add.");
                LogSzr.Debug("On server and mapped strings are locked, will not add.");
                return;
            }

            var started = MappedStrings.Count;
            var sw = Stopwatch.StartNew();
            foreach (var node in obj.DescendantsAndSelf())
            {
                switch (node)
                {
                    case JValue value:
                    {
                        if (value.Type != JTokenType.String)
                        {
                            continue;
                        }

                        var v = value.Value?.ToString();
                        if (String.IsNullOrEmpty(v))
                        {
                            continue;
                        }

                        AddString(v);
                        break;
                    }
                    case JProperty prop:
                    {
                        var propName = prop.Name;
                        if (String.IsNullOrEmpty(propName))
                        {
                            continue;
                        }

                        AddString(propName);
                        break;
                    }
                }
            }

            var added = MappedStrings.Count - started;
            LogSzr.Debug($"Mapping {added} strings from {name} took {sw.ElapsedMilliseconds}ms.");
        }

        /// <summary>
        /// Remove all strings from the mapping, completely resetting it.
        /// </summary>
        /// <exception cref="InvalidOperationException">
        /// Thrown if the mapping is locked.
        /// </exception>
        public void ClearStrings()
        {
            if (LockMappedStrings)
            {
                throw new InvalidOperationException("Mapped strings are locked, will not clear.");
            }

            _mappedStrings.Clear();
            _stringMapping.Clear();
            _stringMapHash = null;
        }

        /// <summary>
        /// Add strings from the given enumeration to the mapping.
        /// </summary>
        /// <param name="strings">The strings to add.</param>
        /// <param name="providerName">The source provider of the strings to be logged.</param>
        [MethodImpl(MethodImplOptions.Synchronized)]
        public void AddStrings(IEnumerable<string> strings, string providerName)
        {
            if (LockMappedStrings)
            {
                if (_net!.IsClient)
                {
                    //LogSzr.Debug("On client and mapped strings are locked, will not add.");
                    return;
                }

                //throw new InvalidOperationException("Mapped strings are locked, will not add.");
                LogSzr.Debug("On server and mapped strings are locked, will not add.");
                return;
            }

            var started = MappedStrings.Count;
            foreach (var str in strings)
            {
                AddString(str);
            }

            var added = MappedStrings.Count - started;
            LogSzr.Debug($"Mapping {added} strings from {providerName}.");
        }

        private byte[]? _stringMapHash;

        /// <value>
        /// The hash of the string mapping.
        /// </value>
        /// <exception cref="InvalidOperationException">
        /// Thrown if the mapping is not locked.
        /// </exception>
        public byte[] MappedStringsHash => _stringMapHash ??= CalculateMappedStringsHash();

        private byte[] CalculateMappedStringsHash()
        {
            if (!LockMappedStrings)
            {
                throw new InvalidOperationException("String table should be locked before attempting to retrieve hash.");
            }

            var sw = Stopwatch.StartNew();

            var hash = CalculateHash(MappedStringsPackage);

            LogSzr.Debug($"Hashing {MappedStrings.Count} strings took {sw.ElapsedMilliseconds}ms.");
            LogSzr.Debug($"Size: {MappedStringsPackage.Length} bytes, Hash: {ConvertToBase64Url(hash)}");
            return hash;
        }

        /// <summary>
        /// Creates a SHA512 hash of the given array of bytes.
        /// </summary>
        /// <param name="data">An array of bytes to be hashed.</param>
        /// <returns>A 512-bit (64-byte) hash result as an array of bytes.</returns>
        /// <exception cref="ArgumentNullException"></exception>
        private byte[] CalculateHash(byte[] data)
        {
            if (data is null)
            {
                throw new ArgumentNullException(nameof(data));
            }

            using var hasher = SHA512.Create();
            var hash = hasher.ComputeHash(data);
            return hash;
        }

        /// <summary>
        /// Implements <see cref="ITypeSerializer.Handles"/>.
        /// Specifies that this implementation handles strings.
        /// </summary>
        public bool Handles(Type type) => type == typeof(string);

        /// <summary>
        /// Implements <see cref="ITypeSerializer.GetSubtypes"/>.
        /// </summary>
        public IEnumerable<Type> GetSubtypes(Type type) => Type.EmptyTypes;

        /// <summary>
        /// Implements <see cref="IStaticTypeSerializer.GetStaticWriter"/>.
        /// </summary>
        /// <seealso cref="WriteMappedString"/>
        public MethodInfo GetStaticWriter(Type type) => WriteMappedStringMethodInfo;

        /// <summary>
        /// Implements <see cref="IStaticTypeSerializer.GetStaticReader"/>.
        /// </summary>
        /// <seealso cref="ReadMappedString"/>
        public MethodInfo GetStaticReader(Type type) => ReadMappedStringMethodInfo;

        private delegate void WriteStringDelegate(Stream stream, string? value);

        private delegate void ReadStringDelegate(Stream stream, out string? value);

        private static readonly MethodInfo WriteMappedStringMethodInfo
            = ((WriteStringDelegate) StaticWriteMappedString).Method;

        private static readonly MethodInfo ReadMappedStringMethodInfo
            = ((ReadStringDelegate) StaticReadMappedString).Method;

        private static readonly char[] TrimmableSymbolChars =
        {
            '.', '\\', '/', ',', '#', '$', '?', '!', '@', '|', '&',
            '*', '(', ')', '^', '`', '"', '\'', '`', '~', '[', ']',
            '{', '}', ':', ';', '-'
        };

        /// <summary>
        /// The shortest a string can be in order to be inserted in the mapping.
        /// </summary>
        /// <remarks>
        /// Strings below a certain length aren't worth compressing.
        /// </remarks>
        private const int MinMappedStringSize = 3;

        /// <summary>
        /// The longest a string can be in order to be inserted in the mapping.
        /// </summary>
        private const int MaxMappedStringSize = 420;

        /// <summary>
        /// The special value corresponding to a <c>null</c> string in the
        /// encoding.
        /// </summary>
        private const int MappedNull = 0;

        /// <summary>
        /// The special value corresponding to a string which was not mapped.
        /// This is followed by the bytes of the unmapped string.
        /// </summary>
        private const int UnmappedString = 1;

        /// <summary>
        /// The first non-special value, used for encoding mapped strings.
        /// </summary>
        /// <remarks>
        /// Since previous values are taken by <see cref="MappedNull"/> and
        /// <see cref="UnmappedString"/>, this value is used to encode
        /// mapped strings at an offset - in the encoding, a value
        /// <c>>= FirstMappedIndexStart</c> represents the string with
        /// mapping of that value <c> - FirstMappedIndexStart</c>.
        /// </remarks>
        private const int FirstMappedIndexStart = 2;


        /// <summary>
        /// Write the encoding of the given string to the stream.
        /// Static form of <see cref="WriteMappedString"/> for use by <see cref="NetSerializer"/>.
        /// </summary>
        /// <param name="stream">The stream to write to.</param>
        /// <param name="value"> The (possibly null) string to write.</param>
        public static void StaticWriteMappedString(Stream stream, string? value)
        {
            var mss = IoCManager.Resolve<IRobustMappedStringSerializer>();
            mss.WriteMappedString(stream, value);
        }

        /// <summary>
        /// Write the encoding of the given string to the stream.
        /// </summary>
        /// <param name="stream">The stream to write to.</param>
        /// <param name="value"> The (possibly null) string to write.</param>
        public void WriteMappedString(Stream stream, string? value)
        {
            if (!LockMappedStrings)
            {
                LogSzr.Warning("Performing unlocked string mapping.");
            }

            if (value == null)
            {
                WriteCompressedUnsignedInt(stream, MappedNull);
                return;
            }

            if (_stringMapping.TryGetValue(value, out var mapping))
            {
#if DEBUG
                if (mapping >= _mappedStrings.Count || mapping < 0)
                {
                    throw new InvalidOperationException("A string mapping outside of the mapped string table was encountered.");
                }
#endif
                WriteCompressedUnsignedInt(stream, (uint) mapping + FirstMappedIndexStart);
                //Logger.DebugS("szr", $"Encoded mapped string: {value}");
                return;
            }

            // indicate not mapped
            WriteCompressedUnsignedInt(stream, UnmappedString);
            var buf = Encoding.UTF8.GetBytes(value);
            //Logger.DebugS("szr", $"Encoded unmapped string: {value}");
            WriteCompressedUnsignedInt(stream, (uint) buf.Length);
            stream.Write(buf);
        }

        /// <summary>
        /// Try to read a string from the given stream.
        /// Static form of <see cref="ReadMappedString"/> for use by <see cref="NetSerializer"/>.
        /// </summary>
        /// <param name="stream">The stream to read from.</param>
        /// <param name="value"> The (possibly null) string read.</param>
        /// <exception cref="InvalidOperationException">
        /// Thrown if the mapping is not locked.
        /// </exception>
        public static void StaticReadMappedString(Stream stream, out string? value)
        {
            var mss = IoCManager.Resolve<IRobustMappedStringSerializer>();
            mss.ReadMappedString(stream, out value);
        }

        /// <summary>
        /// Try to read a string from the given stream.
        /// </summary>
        /// <param name="stream">The stream to read from.</param>
        /// <param name="value"> The (possibly null) string read.</param>
        /// <exception cref="InvalidOperationException">
        /// Thrown if the mapping is not locked.
        /// </exception>
        public void ReadMappedString(Stream stream, out string? value)
        {
            if (!LockMappedStrings)
            {
                throw new InvalidOperationException("Not performing unlocked string mapping.");
            }

            var mapIndex = ReadCompressedUnsignedInt(stream, out _);
            if (mapIndex == MappedNull)
            {
                value = null;
                return;
            }

            if (mapIndex == UnmappedString)
            {
                // not mapped
                var length = checked((int)ReadCompressedUnsignedInt(stream, out _));
                // ReSharper disable once SuggestVarOrType_Elsewhere
                Span<byte> buf = stackalloc byte[length];
                stream.Read(buf);
                value = Encoding.UTF8.GetString(buf);
                //Logger.DebugS("szr", $"Decoded unmapped string: {value}");

                return;
            }

            value = _mappedStrings[(int) mapIndex - FirstMappedIndexStart];
            //Logger.DebugS("szr", $"Decoded mapped string: {value}");
        }

        // TODO: move the below methods to some stream helpers class

#if ROBUST_SERIALIZER_DISABLE_COMPRESSED_UINTS
            public static int WriteCompressedUnsignedInt(Stream stream, uint value)
            {
                WriteUnsignedInt(stream, value);
                return 4;
            }

            public static uint ReadCompressedUnsignedInt(Stream stream, out int byteCount)
            {
                byteCount = 4;
                return ReadUnsignedInt(stream);
            }
#else
        public static int WriteCompressedUnsignedInt(Stream stream, uint value)
        {
            var length = 1;
            while (value >= 0x80)
            {
                stream.WriteByte((byte) (0x80 | value));
                value >>= 7;
                ++length;
            }

            stream.WriteByte((byte) value);
            return length;
        }

        public static uint ReadCompressedUnsignedInt(Stream stream, out int byteCount)
        {
            byteCount = 0;
            var value = 0u;
            var shift = 0;
            while (stream.CanRead)
            {
                var current = stream.ReadByte();
                ++byteCount;
                if (current == -1)
                {
                    throw new EndOfStreamException();
                }

                value |= (0x7Fu & (byte) current) << shift;
                shift += 7;
                if ((0x80 & current) == 0)
                {
                    return value;
                }
            }

            throw new EndOfStreamException();
        }
#endif

        [UsedImplicitly]
        public static unsafe void WriteUnsignedInt(Stream stream, uint value)
        {
            var bytes = MemoryMarshal.AsBytes(new ReadOnlySpan<uint>(&value, 1));
            stream.Write(bytes);
        }

        [UsedImplicitly]
        public static unsafe uint ReadUnsignedInt(Stream stream)
        {
            uint value;
            var bytes = MemoryMarshal.AsBytes(new Span<uint>(&value, 1));
            stream.Read(bytes);
            return value;
        }

        /// <summary>
        /// See <see cref="OnClientCompleteHandshake"/>.
        /// </summary>
        public event Action? ClientHandshakeComplete;

    }

}