using System;
using System.Collections;
using System.Collections.Generic;
using System.Runtime.CompilerServices;
using System.Text;
using Unity.Collections;
using Unity.Collections.LowLevel.Unsafe;
using UnityEngine;

namespace Unity.Netcode
{
    internal class HandlerNotRegisteredException : SystemException
    {
        public HandlerNotRegisteredException()
        {
        }

        public HandlerNotRegisteredException(string issue) : base(issue)
        {
        }
    }

    internal class InvalidMessageStructureException : SystemException
    {
        public InvalidMessageStructureException()
        {
        }

        public InvalidMessageStructureException(string issue) : base(issue)
        {
        }
    }

    internal class NetworkMessageManager : IDisposable
    {
        public bool StopProcessing = false;
        private static Type s_ConnectionApprovedType = typeof(ConnectionApprovedMessage);
        private static Type s_ConnectionRequestType = typeof(ConnectionRequestMessage);
        private static Type s_DisconnectReasonType = typeof(DisconnectReasonMessage);

        private struct ReceiveQueueItem
        {
            public FastBufferReader Reader;
            public NetworkMessageHeader Header;
            public ulong SenderId;
            public float Timestamp;
            public int MessageHeaderSerializedSize;
        }

        private struct SendQueueItem
        {
            public NetworkBatchHeader BatchHeader;
            public FastBufferWriter Writer;
            public readonly NetworkDelivery NetworkDelivery;

            public SendQueueItem(NetworkDelivery delivery, int writerSize, Allocator writerAllocator, int maxWriterSize = -1)
            {
                Writer = new FastBufferWriter(writerSize, writerAllocator, maxWriterSize);
                NetworkDelivery = delivery;
                BatchHeader = new NetworkBatchHeader { Magic = NetworkBatchHeader.MagicValue };
            }
        }

        internal delegate void MessageHandler(FastBufferReader reader, ref NetworkContext context, NetworkMessageManager manager);

        internal delegate int VersionGetter();

        private NativeList<ReceiveQueueItem> m_IncomingMessageQueue = new NativeList<ReceiveQueueItem>(16, Allocator.Persistent);

        // These array will grow as we need more message handlers. 4 is just a starting size.
        private MessageHandler[] m_MessageHandlers = new MessageHandler[4];
        private Type[] m_ReverseTypeMap = new Type[4];

        private Dictionary<Type, uint> m_MessageTypes = new Dictionary<Type, uint>();
        private Dictionary<ulong, NativeList<SendQueueItem>> m_SendQueues = new Dictionary<ulong, NativeList<SendQueueItem>>();

        private HashSet<ulong> m_DisconnectedClients = new HashSet<ulong>();

        // This is m_PerClientMessageVersion[clientId][messageType] = version
        private Dictionary<ulong, Dictionary<Type, int>> m_PerClientMessageVersions = new Dictionary<ulong, Dictionary<Type, int>>();
        private Dictionary<uint, Type> m_MessagesByHash = new Dictionary<uint, Type>();
        private Dictionary<Type, int> m_LocalVersions = new Dictionary<Type, int>();

        private List<INetworkHooks> m_Hooks = new List<INetworkHooks>();

        private uint m_HighMessageType;
        private object m_Owner;
        private INetworkMessageSender m_Sender;
        private bool m_Disposed;

        private ulong m_LocalClientId;

        internal Type[] MessageTypes => m_ReverseTypeMap;
        internal MessageHandler[] MessageHandlers => m_MessageHandlers;

        internal uint MessageHandlerCount => m_HighMessageType;

        internal uint GetMessageType(Type t)
        {
            return m_MessageTypes[t];
        }

        internal object GetOwner()
        {
            return m_Owner;
        }

        internal void SetLocalClientId(ulong id)
        {
            m_LocalClientId = id;
        }

        public const int DefaultNonFragmentedMessageMaxSize = 1300 & ~7; // Round down to nearest word aligned size (1296)
        public int NonFragmentedMessageMaxSize = DefaultNonFragmentedMessageMaxSize;
        public int FragmentedMessageMaxSize = int.MaxValue;

        public Dictionary<ulong, int> PeerMTUSizes = new Dictionary<ulong, int>();

        internal struct MessageWithHandler
        {
            public Type MessageType;
            public MessageHandler Handler;
            public VersionGetter GetVersion;
        }

        public NetworkMessageManager(INetworkMessageSender sender, object owner, INetworkMessageProvider provider = null)
        {
            try
            {
                m_Sender = sender;
                m_Owner = owner;
                if (provider == null)
                {
                    provider = new ILPPMessageProvider();
                }

                // Get the presorted message types returned by the provider
                var allowedTypes = provider.GetMessages();

                foreach (var type in allowedTypes)
                {
                    RegisterMessageType(type);
                }

#if UNITY_EDITOR
                if (EnableMessageOrderConsoleLog)
                {
                    // DANGO-TODO: Remove this when we have some form of message type indices stability in place
                    // For now, just log the messages and their assigned types for reference purposes.
                    var networkManager = m_Owner as NetworkManager;
                    if (networkManager != null)
                    {
                        if (networkManager.DistributedAuthorityMode)
                        {
                            var messageListing = new StringBuilder();
                            messageListing.AppendLine("NGO Message Index to Type Listing:");
                            foreach (var message in m_MessageTypes)
                            {
                                messageListing.AppendLine($"[{message.Value}][{message.Key.Name}]");
                            }
                            Debug.Log(messageListing);
                        }
                    }
                }
#endif
            }
            catch (Exception)
            {
                Dispose();
                throw;
            }
        }

        internal static bool EnableMessageOrderConsoleLog = false;

        public void Dispose()
        {
            if (m_Disposed)
            {
                return;
            }

            // Can't just iterate SendQueues or SendQueues.Keys because ClientDisconnected removes from the queue.
            foreach (var kvp in m_SendQueues)
            {
                ClientDisconnected(kvp.Key);
            }

            CleanupDisconnectedClients();

            for (var queueIndex = 0; queueIndex < m_IncomingMessageQueue.Length; ++queueIndex)
            {
                // Avoid copies...
                ref var item = ref m_IncomingMessageQueue.ElementAt(queueIndex);
                item.Reader.Dispose();
            }

            m_IncomingMessageQueue.Dispose();
            m_Disposed = true;
        }

        ~NetworkMessageManager()
        {
            Dispose();
        }

        public void Hook(INetworkHooks hooks)
        {
            m_Hooks.Add(hooks);
        }

        public void Unhook(INetworkHooks hooks)
        {
            m_Hooks.Remove(hooks);
        }

        private void RegisterMessageType(MessageWithHandler messageWithHandler)
        {
            // If we are out of space, perform amortized linear growth
            if (m_HighMessageType == m_MessageHandlers.Length)
            {
                Array.Resize(ref m_MessageHandlers, 2 * m_MessageHandlers.Length);
                Array.Resize(ref m_ReverseTypeMap, 2 * m_ReverseTypeMap.Length);
            }

            m_MessageHandlers[m_HighMessageType] = messageWithHandler.Handler;
            m_ReverseTypeMap[m_HighMessageType] = messageWithHandler.MessageType;
            m_MessagesByHash[XXHash.Hash32(messageWithHandler.MessageType.FullName)] = messageWithHandler.MessageType;
            m_MessageTypes[messageWithHandler.MessageType] = m_HighMessageType++;
            m_LocalVersions[messageWithHandler.MessageType] = messageWithHandler.GetVersion();
        }

        public int GetLocalVersion(Type messageType)
        {
            return m_LocalVersions[messageType];
        }

        internal static string ByteArrayToString(byte[] ba, int offset, int count)
        {
            var hex = new StringBuilder(ba.Length * 2);
            for (int i = offset; i < offset + count; ++i)
            {
                hex.AppendFormat("{0:x2} ", ba[i]);
            }

            return hex.ToString();
        }

        internal void HandleIncomingData(ulong clientId, ArraySegment<byte> data, float receiveTime)
        {
            unsafe
            {
                fixed (byte* dataPtr = data.Array)
                {
                    var batchReader = new FastBufferReader(dataPtr + data.Offset, Allocator.None, data.Count);
                    if (!batchReader.TryBeginRead(sizeof(NetworkBatchHeader)))
                    {
                        NetworkLog.LogError("Received a packet too small to contain a BatchHeader. Ignoring it.");
                        return;
                    }

                    batchReader.ReadValue(out NetworkBatchHeader batchHeader);

                    if (batchHeader.Magic != NetworkBatchHeader.MagicValue)
                    {
                        NetworkLog.LogError($"Received a packet with an invalid Magic Value. Please report this to the Netcode for GameObjects team at https://github.com/Unity-Technologies/com.unity.netcode.gameobjects/issues and include the following data: Offset: {data.Offset}, Size: {data.Count}, Full receive array: {ByteArrayToString(data.Array, 0, data.Array.Length)}");
                        return;
                    }

                    if (batchHeader.BatchSize != data.Count)
                    {
                        NetworkLog.LogError($"Received a packet with an invalid Batch Size Value. Please report this to the Netcode for GameObjects team at https://github.com/Unity-Technologies/com.unity.netcode.gameobjects/issues and include the following data: Offset: {data.Offset}, Size: {data.Count}, Expected Size: {batchHeader.BatchSize}, Full receive array: {ByteArrayToString(data.Array, 0, data.Array.Length)}");
                        return;
                    }

                    var hash = XXHash.Hash64(batchReader.GetUnsafePtrAtCurrentPosition(), batchReader.Length - batchReader.Position);

                    if (hash != batchHeader.BatchHash)
                    {
                        NetworkLog.LogError($"Received a packet with an invalid Hash Value. Please report this to the Netcode for GameObjects team at https://github.com/Unity-Technologies/com.unity.netcode.gameobjects/issues and include the following data: Received Hash: {batchHeader.BatchHash}, Calculated Hash: {hash}, Offset: {data.Offset}, Size: {data.Count}, Full receive array: {ByteArrayToString(data.Array, 0, data.Array.Length)}");
                        return;
                    }

                    for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
                    {
                        m_Hooks[hookIdx].OnBeforeReceiveBatch(clientId, batchHeader.BatchCount, batchReader.Length);
                    }

                    for (var messageIdx = 0; messageIdx < batchHeader.BatchCount; ++messageIdx)
                    {
                        var messageHeader = new NetworkMessageHeader();
                        var position = batchReader.Position;
                        try
                        {
                            ByteUnpacker.ReadValueBitPacked(batchReader, out messageHeader.MessageType);
                            ByteUnpacker.ReadValueBitPacked(batchReader, out messageHeader.MessageSize);
                        }
                        catch (OverflowException)
                        {
                            NetworkLog.LogError("Received a batch that didn't have enough data for all of its batches, ending early!");
                            throw;
                        }

                        var receivedHeaderSize = batchReader.Position - position;

                        if (!batchReader.TryBeginRead((int)messageHeader.MessageSize))
                        {
                            NetworkLog.LogError("Received a message that claimed a size larger than the packet, ending early!");
                            return;
                        }

                        m_IncomingMessageQueue.Add(new ReceiveQueueItem
                        {
                            Header = messageHeader,
                            SenderId = clientId,
                            Timestamp = receiveTime,
                            // Copy the data for this message into a new FastBufferReader that owns that memory.
                            // We can't guarantee the memory in the ArraySegment stays valid because we don't own it, so we must move it to memory we do own.
                            Reader = new FastBufferReader(batchReader.GetUnsafePtrAtCurrentPosition(), Allocator.TempJob, (int)messageHeader.MessageSize),
                            MessageHeaderSerializedSize = receivedHeaderSize,
                        });
                        batchReader.Seek(batchReader.Position + (int)messageHeader.MessageSize);
                    }

                    for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
                    {
                        m_Hooks[hookIdx].OnAfterReceiveBatch(clientId, batchHeader.BatchCount, batchReader.Length);
                    }
                }
            }
        }

        private bool CanReceive(ulong clientId, Type messageType, FastBufferReader messageContent, ref NetworkContext context)
        {
            for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
            {
                if (!m_Hooks[hookIdx].OnVerifyCanReceive(clientId, messageType, messageContent, ref context))
                {
                    return false;
                }
            }

            return true;
        }

        internal Type GetMessageForHash(uint messageHash)
        {
            if (!m_MessagesByHash.ContainsKey(messageHash))
            {
                return null;
            }

            return m_MessagesByHash[messageHash];
        }

        internal void SetVersion(ulong clientId, uint messageHash, int version)
        {
            if (!m_MessagesByHash.ContainsKey(messageHash))
            {
                return;
            }

            var messageType = m_MessagesByHash[messageHash];

            if (!m_PerClientMessageVersions.ContainsKey(clientId))
            {
                m_PerClientMessageVersions[clientId] = new Dictionary<Type, int>();
            }

            m_PerClientMessageVersions[clientId][messageType] = version;
        }

        internal void SetServerMessageOrder(NativeArray<uint> messagesInIdOrder)
        {
            var oldHandlers = m_MessageHandlers;
            var oldTypes = m_MessageTypes;
            m_ReverseTypeMap = new Type[messagesInIdOrder.Length];
            m_MessageHandlers = new MessageHandler[messagesInIdOrder.Length];
            m_MessageTypes = new Dictionary<Type, uint>();

            for (var i = 0; i < messagesInIdOrder.Length; ++i)
            {
                if (!m_MessagesByHash.ContainsKey(messagesInIdOrder[i]))
                {
                    continue;
                }

                var messageType = m_MessagesByHash[messagesInIdOrder[i]];
                var oldId = oldTypes[messageType];
                var handler = oldHandlers[oldId];
                var newId = (uint)i;
                m_MessageTypes[messageType] = newId;
                m_MessageHandlers[newId] = handler;
                m_ReverseTypeMap[newId] = messageType;
            }
        }

        public void HandleMessage(in NetworkMessageHeader header, FastBufferReader reader, ulong senderId, float timestamp, int serializedHeaderSize)
        {
            using (reader)
            {
                if (header.MessageType >= m_HighMessageType)
                {
                    Debug.LogWarning($"Received a message with invalid message type value {header.MessageType}");
                    return;
                }

                var context = new NetworkContext
                {
                    SystemOwner = m_Owner,
                    SenderId = senderId,
                    Timestamp = timestamp,
                    Header = header,
                    SerializedHeaderSize = serializedHeaderSize,
                    MessageSize = header.MessageSize,
                };

                var type = m_ReverseTypeMap[header.MessageType];
                if (!CanReceive(senderId, type, reader, ref context))
                {
                    return;
                }

                var handler = m_MessageHandlers[header.MessageType];
                for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
                {
                    m_Hooks[hookIdx].OnBeforeReceiveMessage(senderId, type, reader.Length + FastBufferWriter.GetWriteSize<NetworkMessageHeader>());
                }

                // This will also log an exception is if the server knows about a message type the client doesn't know about.
                // In this case the handler will be null. It is still an issue the user must deal with:
                // If the two connecting builds know about different messages, the server should not send a message to a client that doesn't know about it
                if (handler == null)
                {
                    Debug.LogException(new HandlerNotRegisteredException(header.MessageType.ToString()));
                }
                else
                {
                    // No user-land message handler exceptions should escape the receive loop.
                    // If an exception is throw, the message is ignored.
                    // Example use case: A bad message is received that can't be deserialized and throws an OverflowException because it specifies a length greater than the number of bytes in it for some dynamic-length value.
                    try
                    {
                        handler.Invoke(reader, ref context, this);
                    }
                    catch (Exception e)
                    {
                        Debug.LogException(e);
                    }
                }

                for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
                {
                    m_Hooks[hookIdx].OnAfterReceiveMessage(senderId, type, reader.Length + FastBufferWriter.GetWriteSize<NetworkMessageHeader>());
                }
            }
        }

        internal void ProcessIncomingMessageQueue()
        {
            if (StopProcessing)
            {
                return;
            }

            for (var index = 0; index < m_IncomingMessageQueue.Length; ++index)
            {
                // Avoid copies...
                ref var item = ref m_IncomingMessageQueue.ElementAt(index);
                HandleMessage(item.Header, item.Reader, item.SenderId, item.Timestamp, item.MessageHeaderSerializedSize);
                if (m_Disposed)
                {
                    return;
                }
            }

            m_IncomingMessageQueue.Clear();
        }

        internal void ClientConnected(ulong clientId)
        {
            if (m_SendQueues.ContainsKey(clientId))
            {
                return;
            }

            m_SendQueues[clientId] = new NativeList<SendQueueItem>(16, Allocator.Persistent);
        }

        internal void ClientDisconnected(ulong clientId)
        {
            m_DisconnectedClients.Add(clientId);
        }

        private void CleanupDisconnectedClient(ulong clientId)
        {
            if (!m_SendQueues.ContainsKey(clientId))
            {
                return;
            }

            var queue = m_SendQueues[clientId];
            for (var i = 0; i < queue.Length; ++i)
            {
                queue.ElementAt(i).Writer.Dispose();
            }

            queue.Dispose();
            m_SendQueues.Remove(clientId);

            m_PerClientMessageVersions.Remove(clientId);
            PeerMTUSizes.Remove(clientId);
        }

        internal void CleanupDisconnectedClients()
        {
            foreach (var clientId in m_DisconnectedClients)
            {
                CleanupDisconnectedClient(clientId);
            }

            m_DisconnectedClients.Clear();
        }

        public static int CreateMessageAndGetVersion<T>() where T : INetworkMessage, new()
        {
            return new T().Version;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        internal int GetMessageVersion(Type type, ulong clientId, bool forReceive = false)
        {
            if (!m_PerClientMessageVersions.TryGetValue(clientId, out var versionMap))
            {
                var networkManager = NetworkManager.Singleton;
                if (networkManager != null && networkManager.LogLevel == LogLevel.Developer)
                {
                    if (forReceive)
                    {
                        NetworkLog.LogWarning($"Trying to receive {type.Name} from client {clientId} which is not in a connected state.");
                    }
                    else
                    {
                        NetworkLog.LogWarning($"Trying to send {type.Name} to client {clientId} which is not in a connected state.");
                    }
                }
                return -1;
            }

            if (!versionMap.TryGetValue(type, out var messageVersion))
            {
                return -1;
            }

            return messageVersion;
        }



        public static void ReceiveMessage<T>(FastBufferReader reader, ref NetworkContext context, NetworkMessageManager manager) where T : INetworkMessage, new()
        {
            var messageType = typeof(T);
            var message = new T();
            var messageVersion = 0;

            // Special cases because these are the messages that carry the version info - thus the version info isn't
            // populated yet when we get these. The first part of these messages always has to be the version data
            // and can't change.
            if (messageType != s_ConnectionRequestType && messageType != s_ConnectionApprovedType && messageType != s_DisconnectReasonType && context.SenderId != manager.m_LocalClientId)
            {
                messageVersion = manager.GetMessageVersion(messageType, context.SenderId, true);
                if (messageVersion < 0)
                {
                    return;
                }
            }

            if (message.Deserialize(reader, ref context, messageVersion))
            {
                for (var hookIdx = 0; hookIdx < manager.m_Hooks.Count; ++hookIdx)
                {
                    manager.m_Hooks[hookIdx].OnBeforeHandleMessage(ref message, ref context);
                }

                message.Handle(ref context);

                for (var hookIdx = 0; hookIdx < manager.m_Hooks.Count; ++hookIdx)
                {
                    manager.m_Hooks[hookIdx].OnAfterHandleMessage(ref message, ref context);
                }
            }
        }

        private bool CanSend(ulong clientId, Type messageType, NetworkDelivery delivery)
        {
            for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
            {
                if (!m_Hooks[hookIdx].OnVerifyCanSend(clientId, messageType, delivery))
                {
                    return false;
                }
            }

            return true;
        }

        internal int SendMessage<TMessageType, TClientIdListType>(ref TMessageType message, NetworkDelivery delivery, in TClientIdListType clientIds)
            where TMessageType : INetworkMessage
            where TClientIdListType : IReadOnlyList<ulong>
        {
            if (clientIds.Count == 0)
            {
                return 0;
            }

            var largestSerializedSize = 0;
            var sentMessageVersions = new NativeHashSet<int>(clientIds.Count, Allocator.Temp);
            for (var i = 0; i < clientIds.Count; ++i)
            {
                var messageVersion = 0;
                // Special case because this is the message that carries the version info - thus the version info isn't populated yet when we get this.
                // The first part of this message always has to be the version data and can't change.
                if (typeof(TMessageType) != s_ConnectionRequestType)
                {
                    messageVersion = GetMessageVersion(typeof(TMessageType), clientIds[i]);
                    if (messageVersion < 0)
                    {
                        // Client doesn't know this message exists, don't send it at all.
                        continue;
                    }
                }

                if (sentMessageVersions.Contains(messageVersion))
                {
                    continue;
                }

                sentMessageVersions.Add(messageVersion);

                var maxSize = delivery == NetworkDelivery.ReliableFragmentedSequenced ? FragmentedMessageMaxSize : NonFragmentedMessageMaxSize;

                using var tmpSerializer = new FastBufferWriter(NonFragmentedMessageMaxSize - FastBufferWriter.GetWriteSize<NetworkMessageHeader>(), Allocator.Temp, maxSize - FastBufferWriter.GetWriteSize<NetworkMessageHeader>());

                message.Serialize(tmpSerializer, messageVersion);

                var size = SendPreSerializedMessage(tmpSerializer, maxSize, ref message, delivery, clientIds, messageVersion);
                largestSerializedSize = size > largestSerializedSize ? size : largestSerializedSize;
            }

            sentMessageVersions.Dispose();

            return largestSerializedSize;
        }

        internal unsafe int SendPreSerializedMessage<TMessageType>(in FastBufferWriter tmpSerializer, int maxSize, ref TMessageType message, NetworkDelivery delivery, in IReadOnlyList<ulong> clientIds, int messageVersionFilter)
            where TMessageType : INetworkMessage
        {
            using var headerSerializer = new FastBufferWriter(FastBufferWriter.GetWriteSize<NetworkMessageHeader>(), Allocator.Temp);

            var header = new NetworkMessageHeader
            {
                MessageSize = (uint)tmpSerializer.Length,
                MessageType = m_MessageTypes[typeof(TMessageType)],
            };
            BytePacker.WriteValueBitPacked(headerSerializer, header.MessageType);
            BytePacker.WriteValueBitPacked(headerSerializer, header.MessageSize);

            for (var i = 0; i < clientIds.Count; ++i)
            {
                if (m_DisconnectedClients.Contains(clientIds[i]))
                {
                    continue;
                }

                // Special case because this is the message that carries the version info - thus the version info isn't populated yet when we get this.
                // The first part of this message always has to be the version data and can't change.
                if (typeof(TMessageType) != s_ConnectionRequestType)
                {
                    var messageVersion = GetMessageVersion(typeof(TMessageType), clientIds[i]);
                    if (messageVersion < 0)
                    {
                        // Client doesn't know this message exists, don't send it at all.
                        continue;
                    }

                    if (messageVersion != messageVersionFilter)
                    {
                        continue;
                    }
                }

                var clientId = clientIds[i];

                if (!CanSend(clientId, typeof(TMessageType), delivery))
                {
                    continue;
                }

                var startSize = NonFragmentedMessageMaxSize;
                if (delivery != NetworkDelivery.ReliableFragmentedSequenced)
                {
                    if (PeerMTUSizes.TryGetValue(clientId, out var clientMaxSize))
                    {
                        maxSize = clientMaxSize;
                    }
                    startSize = maxSize;
                    if (tmpSerializer.Position >= maxSize)
                    {
                        Debug.LogError($"MTU size for {clientId} is too small to contain a message of type {typeof(TMessageType).FullName}");
                        continue;
                    }
                }

                for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
                {
                    m_Hooks[hookIdx].OnBeforeSendMessage(clientId, ref message, delivery);
                }

                var sendQueueItem = m_SendQueues[clientId];
                if (sendQueueItem.Length == 0)
                {
                    sendQueueItem.Add(new SendQueueItem(delivery, startSize, Allocator.TempJob, maxSize));
                    sendQueueItem.ElementAt(0).Writer.Seek(sizeof(NetworkBatchHeader));
                }
                else
                {
                    ref var lastQueueItem = ref sendQueueItem.ElementAt(sendQueueItem.Length - 1);
                    if (lastQueueItem.NetworkDelivery != delivery || lastQueueItem.Writer.MaxCapacity - lastQueueItem.Writer.Position < tmpSerializer.Length + headerSerializer.Length)
                    {
                        sendQueueItem.Add(new SendQueueItem(delivery, startSize, Allocator.TempJob, maxSize));
                        sendQueueItem.ElementAt(sendQueueItem.Length - 1).Writer.Seek(sizeof(NetworkBatchHeader));
                    }
                }

                ref var writeQueueItem = ref sendQueueItem.ElementAt(sendQueueItem.Length - 1);
                writeQueueItem.Writer.TryBeginWrite(tmpSerializer.Length + headerSerializer.Length);

                writeQueueItem.Writer.WriteBytes(headerSerializer.GetUnsafePtr(), headerSerializer.Length);
                writeQueueItem.Writer.WriteBytes(tmpSerializer.GetUnsafePtr(), tmpSerializer.Length);
                writeQueueItem.BatchHeader.BatchCount++;
                for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
                {
                    m_Hooks[hookIdx].OnAfterSendMessage(clientId, ref message, delivery, tmpSerializer.Length + headerSerializer.Length);
                }
            }

            return tmpSerializer.Length + headerSerializer.Length;
        }

        internal unsafe int SendPreSerializedMessage<TMessageType>(in FastBufferWriter tmpSerializer, int maxSize, ref TMessageType message, NetworkDelivery delivery, ulong clientId)
            where TMessageType : INetworkMessage
        {
            var messageVersion = 0;
            // Special case because this is the message that carries the version info - thus the version info isn't
            // populated yet when we get this. The first part of this message always has to be the version data
            // and can't change.
            if (typeof(TMessageType) != s_ConnectionRequestType)
            {
                messageVersion = GetMessageVersion(typeof(TMessageType), clientId);
                if (messageVersion < 0)
                {
                    // Client doesn't know this message exists, don't send it at all.
                    return 0;
                }
            }

            ulong* clientIds = stackalloc ulong[] { clientId };
            return SendPreSerializedMessage(tmpSerializer, maxSize, ref message, delivery, new PointerListWrapper<ulong>(clientIds, 1), messageVersion);
        }

        private struct PointerListWrapper<T> : IReadOnlyList<T>
            where T : unmanaged
        {
            private unsafe T* m_Value;
            private int m_Length;

            internal unsafe PointerListWrapper(T* ptr, int length)
            {
                m_Value = ptr;
                m_Length = length;
            }

            public int Count
            {
                [MethodImpl(MethodImplOptions.AggressiveInlining)]
                get => m_Length;
            }

            public unsafe T this[int index]
            {
                [MethodImpl(MethodImplOptions.AggressiveInlining)]
                get => m_Value[index];
            }

            public IEnumerator<T> GetEnumerator()
            {
                throw new NotImplementedException();
            }

            IEnumerator IEnumerable.GetEnumerator()
            {
                return GetEnumerator();
            }
        }

        internal unsafe int SendMessage<T>(ref T message, NetworkDelivery delivery,
            ulong* clientIds, int numClientIds)
            where T : INetworkMessage
        {
            return SendMessage(ref message, delivery, new PointerListWrapper<ulong>(clientIds, numClientIds));
        }

        internal unsafe int SendMessage<T>(ref T message, NetworkDelivery delivery, ulong clientId)
            where T : INetworkMessage
        {
            ulong* clientIds = stackalloc ulong[] { clientId };
            return SendMessage(ref message, delivery, new PointerListWrapper<ulong>(clientIds, 1));
        }

        internal unsafe int SendMessage<T>(ref T message, NetworkDelivery delivery, in NativeArray<ulong> clientIds)
            where T : INetworkMessage
        {
            return SendMessage(ref message, delivery, new PointerListWrapper<ulong>((ulong*)clientIds.GetUnsafePtr(), clientIds.Length));
        }

        internal unsafe int SendMessage<T>(ref T message, NetworkDelivery delivery, in NativeList<ulong> clientIds)
            where T : INetworkMessage
        {
#if UTP_TRANSPORT_2_0_ABOVE
            return SendMessage(ref message, delivery, new PointerListWrapper<ulong>(clientIds.GetUnsafePtr(), clientIds.Length));
#else
            return SendMessage(ref message, delivery, new PointerListWrapper<ulong>((ulong*)clientIds.GetUnsafePtr(), clientIds.Length));
#endif
        }

        internal unsafe void ProcessSendQueues()
        {
            if (StopProcessing)
            {
                return;
            }

            foreach (var kvp in m_SendQueues)
            {
                var clientId = kvp.Key;
                var sendQueueItem = kvp.Value;
                for (var i = 0; i < sendQueueItem.Length; ++i)
                {
                    ref var queueItem = ref sendQueueItem.ElementAt(i);
                    // This is checked at every iteration because
                    // 1) each writer needs to be disposed, so we have to do the full loop regardless, and
                    // 2) the call to m_MessageSender.Send() may result in calling ClientDisconnected(), so the result of this check may change partway through iteration
                    if (m_DisconnectedClients.Contains(clientId))
                    {
                        queueItem.Writer.Dispose();
                        continue;
                    }

                    if (queueItem.BatchHeader.BatchCount == 0)
                    {
                        queueItem.Writer.Dispose();
                        continue;
                    }

                    for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
                    {
                        m_Hooks[hookIdx].OnBeforeSendBatch(clientId, queueItem.BatchHeader.BatchCount, queueItem.Writer.Length, queueItem.NetworkDelivery);
                    }

                    queueItem.Writer.Seek(0);
#if UNITY_EDITOR || DEVELOPMENT_BUILD
                    // Skipping the Verify and sneaking the write mark in because we know it's fine.
                    queueItem.Writer.Handle->AllowedWriteMark = sizeof(NetworkBatchHeader);
#endif


                    var alignedLength = (queueItem.Writer.Length + 7) & ~7;
                    queueItem.Writer.TryBeginWrite(alignedLength);

                    queueItem.BatchHeader.BatchHash = XXHash.Hash64(queueItem.Writer.GetUnsafePtr() + sizeof(NetworkBatchHeader), alignedLength - sizeof(NetworkBatchHeader));

                    queueItem.BatchHeader.BatchSize = alignedLength;

                    queueItem.Writer.WriteValue(queueItem.BatchHeader);
                    queueItem.Writer.Seek(alignedLength);


                    try
                    {
                        m_Sender.Send(clientId, queueItem.NetworkDelivery, queueItem.Writer);

                        for (var hookIdx = 0; hookIdx < m_Hooks.Count; ++hookIdx)
                        {
                            m_Hooks[hookIdx].OnAfterSendBatch(clientId, queueItem.BatchHeader.BatchCount, queueItem.Writer.Length, queueItem.NetworkDelivery);
                        }
                    }
                    finally
                    {
                        queueItem.Writer.Dispose();
                    }
                }

                sendQueueItem.Clear();
            }
        }
    }
}