using System;
using System.Buffers.Binary;
using System.Collections.Generic;
using System.ComponentModel;
using System.Globalization;
using System.IO;
using System.IO.Compression;
using System.Linq;
using System.Net;
using System.Net.Sockets;
using System.Reflection;
using System.Security.Cryptography;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Web;
using TL;
using static WTelegram.Encryption;

namespace WTelegram
{
	public partial class Client : IDisposable
	{
		/// <summary>This event will be called when unsollicited updates/messages are sent by Telegram servers</summary>
		/// <remarks>Make your handler <see langword="async"/>, or return <see cref="Task.CompletedTask"></see><br/>See <see href="https://github.com/wiz0u/WTelegramClient/blob/master/Examples/Program_ListenUpdates.cs">Examples/Program_ListenUpdate.cs</see> for how to use this</remarks>
		public event Func<IObject, Task> OnUpdate;
		/// <summary>Used to create a TcpClient connected to the given address/port, or throw an exception on failure</summary>
		public TcpFactory TcpHandler { get; set; } = DefaultTcpHandler;
		public delegate Task<TcpClient> TcpFactory(string host, int port);
		/// <summary>Url for using a MTProxy. https://t.me/proxy?server=... </summary>
		public string MTProxyUrl { get; set; }
		/// <summary>Telegram configuration, obtained at connection time</summary>
		public Config TLConfig { get; private set; }
		/// <summary>Number of automatic reconnections on connection/reactor failure</summary>
		public int MaxAutoReconnects { get; set; } = 5;
		/// <summary>Number of attempts in case of wrong verification_code or password</summary>
		public int MaxCodePwdAttempts { get; set; } = 3;
		/// <summary>Number of seconds under which an error 420 FLOOD_WAIT_X will not be raised and your request will instead be auto-retried after the delay</summary>
		public int FloodRetryThreshold { get; set; } = 60;
		/// <summary>Number of seconds between each keep-alive ping. Increase this if you have a slow connection or you're debugging your code</summary>
		public int PingInterval { get; set; } = 60;
		/// <summary>Size of chunks when uploading/downloading files. Reduce this if you don't have much memory</summary>
		public int FilePartSize { get; set; } = 512 * 1024;
		/// <summary>Is this Client instance the main or a secondary DC session</summary>
		public bool IsMainDC => (_dcSession?.DataCenter?.id ?? 0) == _session.MainDC;
		/// <summary>Has this Client established connection been disconnected?</summary>
		public bool Disconnected => _tcpClient != null && !(_tcpClient.Client?.Connected ?? false);
		/// <summary>ID of the current logged-in user or 0</summary>
		public long UserId => _session.UserId;

		private readonly Func<string, string> _config;
		private readonly Session _session;
		private string _apiHash;
		private Session.DCSession _dcSession;
		private TcpClient _tcpClient;
		private Stream _networkStream;
		private IObject _lastSentMsg;
		private long _lastRecvMsgId;
		private readonly List<long> _msgsToAck = new();
		private readonly Random _random = new();
		private int _saltChangeCounter;
		private Task _reactorTask;
		private Rpc _bareRpc;
		private readonly Dictionary<long, Rpc> _pendingRpcs = new();
		private SemaphoreSlim _sendSemaphore = new(0);
		private readonly SemaphoreSlim _semaphore = new(1);
		private Task _connecting;
		private CancellationTokenSource _cts;
		private int _reactorReconnects = 0;
		private const string ConnectionShutDown = "Could not read payload length : Connection shut down";
		private readonly SemaphoreSlim _parallelTransfers = new(10); // max parallel part uploads/downloads
		private readonly SHA256 _sha256 = SHA256.Create();
		private readonly SHA256 _sha256Recv = SHA256.Create();
#if OBFUSCATION
		private AesCtr _sendCtr, _recvCtr;
#endif
		private bool _paddedMode;

		/// <summary>Welcome to WTelegramClient! 🙂</summary>
		/// <param name="configProvider">Config callback, is queried for: <b>api_id</b>, <b>api_hash</b>, <b>session_pathname</b></param>
		/// <param name="sessionStore">if specified, must support initial Length &amp; Read() of a session, then calls to Write() the updated session. Other calls can be ignored</param>
		public Client(Func<string, string> configProvider = null, Stream sessionStore = null)
		{
			_config = configProvider ?? DefaultConfigOrAsk;
			sessionStore ??= new SessionStore(Config("session_pathname"));
			var session_key = _config("session_key") ?? (_apiHash = Config("api_hash"));
			_session = Session.LoadOrCreate(sessionStore, Convert.FromHexString(session_key));
			if (_session.ApiId == 0) _session.ApiId = int.Parse(Config("api_id"));
			if (_session.MainDC != 0) _session.DCSessions.TryGetValue(_session.MainDC, out _dcSession);
			_dcSession ??= new() { Id = Helpers.RandomLong() };
			_dcSession.Client = this;
			var version = Assembly.GetExecutingAssembly().GetCustomAttribute<AssemblyInformationalVersionAttribute>().InformationalVersion;
			Helpers.Log(1, $"WTelegramClient {version[..version.IndexOf('+')]} running under {System.Runtime.InteropServices.RuntimeInformation.FrameworkDescription}");
		}

		private Client(Client cloneOf, Session.DCSession dcSession)
		{
			_config = cloneOf._config;
			_session = cloneOf._session;
			TcpHandler = cloneOf.TcpHandler;
			MTProxyUrl = cloneOf.MTProxyUrl;
			PingInterval = cloneOf.PingInterval;
			_dcSession = dcSession;
		}

		internal Task<string> ConfigAsync(string what) => Task.Run(() => Config(what));
		internal string Config(string what)
			=> _config(what) ?? DefaultConfig(what) ?? throw new ApplicationException("You must provide a config value for " + what);

		/// <summary>Default config values, used if your Config callback returns <see langword="null"/></summary>
		public static string DefaultConfig(string what) => what switch
		{
			"session_pathname" => Path.Combine(
				Path.GetDirectoryName(Path.GetDirectoryName(AppDomain.CurrentDomain.BaseDirectory.TrimEnd(Path.DirectorySeparatorChar)))
				?? AppDomain.CurrentDomain.BaseDirectory, "WTelegram.session"),
#if DEBUG
			"server_address" => "149.154.167.40:443",	// Test DC 2
#else
			"server_address" => "149.154.167.50:443",	// DC 2
#endif
			"device_model" => Environment.Is64BitOperatingSystem ? "PC 64bit" : "PC 32bit",
			"system_version" => Helpers.GetSystemVersion(),
			"app_version" => Helpers.GetAppVersion(),
			"system_lang_code" => CultureInfo.InstalledUICulture.TwoLetterISOLanguageName,
			"lang_pack" => "",
			"lang_code" => CultureInfo.CurrentUICulture.TwoLetterISOLanguageName,
			"user_id" => "-1",
			"verification_code" or "password" => AskConfig(what),
			_ => null // api_id api_hash phone_number... it's up to you to reply to these correctly
		};

		internal static string DefaultConfigOrAsk(string config) => DefaultConfig(config) ?? AskConfig(config);

		private static string AskConfig(string config)
		{
			if (config == "session_key")
			{
				Console.WriteLine("Welcome! You can obtain your api_id/api_hash at https://my.telegram.org/apps");
				return null;
			}
			Console.Write($"Enter {config.Replace('_', ' ')}: ");
			return Console.ReadLine();
		}

		/// <summary>Load a specific Telegram server public key</summary>
		/// <param name="pem">A string starting with <c>-----BEGIN RSA PUBLIC KEY-----</c></param>
		public static void LoadPublicKey(string pem) => Encryption.LoadPublicKey(pem);

		/// <summary>Builds a structure that is used to validate a 2FA password</summary>
		/// <param name="accountPassword">Password validation configuration. You can obtain this via <c>Account_GetPassword</c> or through OnUpdate as part of the login process</param>
		/// <param name="password">The password to validate</param>
		public static Task<InputCheckPasswordSRP> InputCheckPassword(Account_Password accountPassword, string password)
			=> Check2FA(accountPassword, () => Task.FromResult(password));

		public void Dispose()
		{
			Helpers.Log(2, $"{_dcSession.DcID}>Disposing the client");
			Reset(false, IsMainDC);
			_networkStream = null;
			if (IsMainDC) _session.Dispose();
			GC.SuppressFinalize(this);
		}

		public void DisableUpdates(bool disable = true) => _dcSession.DisableUpdates(disable);

		/// <summary>Disconnect from Telegram <i>(shouldn't be needed in normal usage)</i></summary>
		/// <param name="resetUser">Forget about logged-in user</param>
		/// <param name="resetSessions">Disconnect secondary sessions with other DCs</param>
		public void Reset(bool resetUser = true, bool resetSessions = true)
		{
			try
			{
				if (CheckMsgsToAck() is MsgsAck msgsAck)
					SendAsync(msgsAck, false).Wait(1000);
			}
			catch { }
			_cts?.Cancel();
			_sendSemaphore = new(0);	// initially taken, first released during DoConnectAsync
			try
			{
				_reactorTask?.Wait(1000);
			}
			catch { }
			_reactorTask = null;
			_networkStream?.Close();
			_tcpClient?.Dispose();
#if OBFUSCATION
			_sendCtr?.Dispose();
			_recvCtr?.Dispose();
#endif
			_paddedMode = false;
			_connecting = null;
			if (resetSessions)
			{
				foreach (var altSession in _session.DCSessions.Values)
					if (altSession.Client != null && altSession.Client != this)
					{
						altSession.Client.Dispose();
						altSession.Client = null;
					}
			}
			if (resetUser)
				_session.UserId = 0;
		}

		private Session.DCSession GetOrCreateDCSession(int dcId, DcOption.Flags flags)
		{
			if (_session.DCSessions.TryGetValue(dcId, out var dcSession))
				if (dcSession.Client != null || dcSession.DataCenter.flags == flags)
					return dcSession; // if we have already a session with this DC and we are connected or it is a perfect match, use it
			// try to find the most appropriate DcOption for this DC
			if ((dcSession?.AuthKeyID ?? 0) == 0) // we will need to negociate an AuthKey => can't use media_only DC
				flags &= ~DcOption.Flags.media_only;
			var dcOptions = _session.DcOptions.Where(dc => dc.id == dcId).OrderBy(dc => dc.flags ^ flags);
			var dcOption = dcOptions.FirstOrDefault() ?? throw new ApplicationException($"Could not find adequate dc_option for DC {dcId}");
			dcSession ??= new Session.DCSession { Id = Helpers.RandomLong() }; // create new session only if not already existing
			dcSession.DataCenter = dcOption;
			return _session.DCSessions[dcId] = dcSession;
		}

		/// <summary>Obtain/create a Client for a secondary session on a specific Data Center</summary>
		/// <param name="dcId">ID of the Data Center</param>
		/// <param name="media_only">Session will be used only for transferring media</param>
		/// <param name="connect">Connect immediately</param>
		/// <returns>Client connected to the selected DC</returns>
		public async Task<Client> GetClientForDC(int dcId, bool media_only = true, bool connect = true)
		{
			if (_dcSession.DataCenter?.id == dcId) return this;
			Session.DCSession altSession;
			lock (_session)
			{
				altSession = GetOrCreateDCSession(dcId, _dcSession.DataCenter.flags | (media_only ? DcOption.Flags.media_only : 0));
				if (altSession.Client?.Disconnected ?? false) { altSession.Client.Dispose(); altSession.Client = null; }
				altSession.Client ??= new Client(this, altSession);
			}
			Helpers.Log(2, $"Requested connection to DC {dcId}...");
			if (connect)
			{
				await _semaphore.WaitAsync();
				try
				{
					Auth_ExportedAuthorization exported = null;
					if (_session.UserId != 0 && IsMainDC && altSession.UserId != _session.UserId)
						exported = await this.Auth_ExportAuthorization(dcId);
					await altSession.Client.ConnectAsync();
					if (exported != null)
					{
						var authorization = await altSession.Client.Auth_ImportAuthorization(exported.id, exported.bytes);
						if (authorization is not Auth_Authorization { user: User user })
							throw new ApplicationException("Failed to get Authorization: " + authorization.GetType().Name);
						altSession.UserId = user.id;
					}
				}
				finally
				{
					_semaphore.Release();
				}
			}
			return altSession.Client;
		}

		private async Task Reactor(Stream stream, CancellationTokenSource cts)
		{
			const int MinBufferSize = 1024;
			var data = new byte[MinBufferSize];
			while (!cts.IsCancellationRequested)
			{
				IObject obj = null;
				try
				{
					if (await stream.FullReadAsync(data, 4, cts.Token) != 4)
						throw new ApplicationException(ConnectionShutDown);
#if OBFUSCATION
					_recvCtr.EncryptDecrypt(data, 4);
#endif
					int payloadLen = BinaryPrimitives.ReadInt32LittleEndian(data);
					if (payloadLen <= 0)
						throw new ApplicationException("Could not read frame data : Invalid payload length");
					else if (payloadLen > data.Length)
						data = new byte[payloadLen];
					else if (Math.Max(payloadLen, MinBufferSize) < data.Length / 4)
						data = new byte[Math.Max(payloadLen, MinBufferSize)];
					if (await stream.FullReadAsync(data, payloadLen, cts.Token) != payloadLen)
						throw new ApplicationException("Could not read frame data : Connection shut down");
#if OBFUSCATION
					_recvCtr.EncryptDecrypt(data, payloadLen);
#endif
					obj = ReadFrame(data, payloadLen);
				}
				catch (Exception ex) // an exception in RecvAsync is always fatal
				{
					if (cts.IsCancellationRequested) return;
					Helpers.Log(5, $"{_dcSession.DcID}>An exception occured in the reactor: {ex}");
					var oldSemaphore = _sendSemaphore;
					await oldSemaphore.WaitAsync(cts.Token); // prevent any sending while we reconnect
					var reactorError = new ReactorError { Exception = ex };
					try
					{
						lock (_msgsToAck) _msgsToAck.Clear();
						Reset(false, false);
						_reactorReconnects = (_reactorReconnects + 1) % MaxAutoReconnects;
						if (!IsMainDC && _pendingRpcs.Count <= 1 && ex is ApplicationException { Message: ConnectionShutDown } or IOException { InnerException: SocketException })
							if (_pendingRpcs.Values.FirstOrDefault() is not Rpc rpc || rpc.type == typeof(Pong))
								_reactorReconnects = 0;
						if (_reactorReconnects != 0)
						{
							await Task.Delay(5000);
							if (_networkStream == null) return; // Dispose has been called in-between
							await ConnectAsync(); // start a new reactor after 5 secs
							lock (_pendingRpcs) // retry all pending requests
							{
								foreach (var rpc in _pendingRpcs.Values)
									rpc.tcs.SetResult(reactorError); // this leads to a retry (see Invoke<T> method)
								_pendingRpcs.Clear();
								_bareRpc = null;
							}
							// TODO: implement an Updates gaps handling system? https://core.telegram.org/api/updates
							if (IsMainDC)
							{
								var updatesState = await this.Updates_GetState(); // this call reenables incoming Updates
								RaiseUpdate(updatesState);
							}
						}
						else
							throw;
					}
					catch
					{
						RaiseUpdate(reactorError);
						lock (_pendingRpcs) // abort all pending requests
						{
							foreach (var rpc in _pendingRpcs.Values)
								rpc.tcs.SetException(ex);
							_pendingRpcs.Clear();
							_bareRpc = null;
						}
					}
					finally
					{
						oldSemaphore.Release();
					}
				}
				if (obj != null)
					await HandleMessageAsync(obj);
			}
		}

		internal DateTime MsgIdToStamp(long serverMsgId)
			=> new((serverMsgId >> 32) * 10000000 - _dcSession.ServerTicksOffset + 621355968000000000L, DateTimeKind.Utc);

		internal IObject ReadFrame(byte[] data, int dataLen)
		{
			if (dataLen < 8 && data[3] == 0xFF)
			{
				int error_code = -BinaryPrimitives.ReadInt32LittleEndian(data);
				throw new RpcException(error_code, TransportError(error_code));
			}
			if (dataLen < 24) // authKeyId+msgId+length+ctorNb | authKeyId+msgKey
				throw new ApplicationException($"Packet payload too small: {dataLen}");

			long authKeyId = BinaryPrimitives.ReadInt64LittleEndian(data);
			if (authKeyId != _dcSession.AuthKeyID)
				throw new ApplicationException($"Received a packet encrypted with unexpected key {authKeyId:X}");
			if (authKeyId == 0) // Unencrypted message
			{
				using var reader = new TL.BinaryReader(new MemoryStream(data, 8, dataLen - 8), this);
				long msgId = _lastRecvMsgId = reader.ReadInt64();
				if ((msgId & 1) == 0) throw new ApplicationException($"Invalid server msgId {msgId}");
				int length = reader.ReadInt32();
				dataLen -= 20;
				if (length > dataLen || length < dataLen - (_paddedMode ? 15 : 0))
					throw new ApplicationException($"Unexpected unencrypted length {length} != {dataLen}");

				var obj = reader.ReadTLObject();
				Helpers.Log(1, $"{_dcSession.DcID}>Receiving {obj.GetType().Name,-40} {MsgIdToStamp(msgId):u} clear{((msgId & 2) == 0 ? "" : " NAR")}");
				return obj;
			}
			else
			{
				byte[] decrypted_data = EncryptDecryptMessage(data.AsSpan(24, (dataLen - 24) & ~0xF), false, _dcSession.AuthKey, data, 8, _sha256Recv);
				if (decrypted_data.Length < 36) // header below+ctorNb
					throw new ApplicationException($"Decrypted packet too small: {decrypted_data.Length}");
				_sha256Recv.TransformBlock(_dcSession.AuthKey, 96, 32, null, 0);
				_sha256Recv.TransformFinalBlock(decrypted_data, 0, decrypted_data.Length);
				if (!data.AsSpan(8, 16).SequenceEqual(_sha256Recv.Hash.AsSpan(8, 16)))
					throw new ApplicationException($"Mismatch between MsgKey & decrypted SHA256");
				_sha256Recv.Initialize();
				using var reader = new TL.BinaryReader(new MemoryStream(decrypted_data), this);
				var serverSalt = reader.ReadInt64();    // int64 salt
				var sessionId = reader.ReadInt64();     // int64 session_id
				var msgId = reader.ReadInt64();         // int64 message_id
				var seqno = reader.ReadInt32();         // int32 msg_seqno
				var length = reader.ReadInt32();        // int32 message_data_length
				
				if (length < 0 || length % 4 != 0) throw new ApplicationException($"Invalid message_data_length: {length}");
				if (decrypted_data.Length - 32 - length is < 12 or > 1024) throw new ApplicationException($"Invalid message padding length: {decrypted_data.Length - 32}-{length}");
				if (sessionId != _dcSession.Id) throw new ApplicationException($"Unexpected session ID: {sessionId} != {_dcSession.Id}");
				if ((msgId & 1) == 0) throw new ApplicationException($"msg_id is not odd: {msgId}");
				if (!_dcSession.CheckNewMsgId(msgId))
				{
					Helpers.Log(3, $"{_dcSession.DcID}>Ignoring duplicate or old msg_id {msgId}");
					return null;
				}
				if (_lastRecvMsgId == 0) // resync ServerTicksOffset on first message
					_dcSession.ServerTicksOffset = (msgId >> 32) * 10000000 - DateTime.UtcNow.Ticks + 621355968000000000L;
				var msgStamp = MsgIdToStamp(_lastRecvMsgId = msgId);

				if (serverSalt != _dcSession.Salt) // salt change happens every 30 min
				{
					Helpers.Log(2, $"{_dcSession.DcID}>Server salt has changed: {_dcSession.Salt:X} -> {serverSalt:X}");
					_dcSession.Salt = serverSalt;
					_saltChangeCounter += 20; // counter is decreased by KeepAlive every minute (we have margin of 10)
					if (_saltChangeCounter >= 30)
						throw new ApplicationException($"Server salt changed too often! Security issue?");
				}
				if ((seqno & 1) != 0) lock (_msgsToAck) _msgsToAck.Add(msgId);

				var ctorNb = reader.ReadUInt32();
				if (ctorNb != Layer.BadMsgCtor && (msgStamp - DateTime.UtcNow).Ticks / TimeSpan.TicksPerSecond is > 30 or < -300)
				{   // msg_id values that belong over 30 seconds in the future or over 300 seconds in the past are to be ignored.
					Helpers.Log(1, $"{_dcSession.DcID}>Ignoring  0x{ctorNb:X8} because of wrong timestamp    {msgStamp:u} (svc)");
					return null;
				}
				if (ctorNb == Layer.MsgContainerCtor)
				{
					Helpers.Log(1, $"{_dcSession.DcID}>Receiving {"MsgContainer",-40} {msgStamp:u} (svc)");
					return ReadMsgContainer(reader);
				}
				else if (ctorNb == Layer.RpcResultCtor)
				{
					Helpers.Log(1, $"{_dcSession.DcID}>Receiving {"RpcResult",-40} {msgStamp:u}");
					return ReadRpcResult(reader);
				}
				else
				{
					var obj = reader.ReadTLObject(ctorNb);
					Helpers.Log(1, $"{_dcSession.DcID}>Receiving {obj.GetType().Name,-40} {msgStamp:u} {((seqno & 1) != 0 ? "" : "(svc)")} {((msgId & 2) == 0 ? "" : "NAR")}");
					return obj;
				}
			}

			static string TransportError(int error_code) => error_code switch
			{
				404 => "Auth key not found",
				429 => "Transport flood",
				444 => "Invalid DC",
				_ => Enum.GetName(typeof(HttpStatusCode), error_code) ?? "Transport error"
			};
		}

		internal MsgContainer ReadMsgContainer(TL.BinaryReader reader)
		{
			int count = reader.ReadInt32();
			var array = new _Message[count];
			for (int i = 0; i < count; i++)
			{
				var msg = array[i] = new _Message(reader.ReadInt64(), reader.ReadInt32(), null) { bytes = reader.ReadInt32() };
				if ((msg.seqno & 1) != 0) lock (_msgsToAck) _msgsToAck.Add(msg.msg_id);
				var pos = reader.BaseStream.Position;
				try
				{
					var ctorNb = reader.ReadUInt32();
					if (ctorNb == Layer.RpcResultCtor)
					{
						Helpers.Log(1, $"            → {"RpcResult",-38} {MsgIdToStamp(msg.msg_id):u}");
						msg.body = ReadRpcResult(reader);
					}
					else
					{
						var obj = msg.body = reader.ReadTLObject(ctorNb);
						Helpers.Log(1, $"            → {obj.GetType().Name,-38} {MsgIdToStamp(msg.msg_id):u} {((msg.seqno & 1) != 0 ? "" : "(svc)")} {((msg.msg_id & 2) == 0 ? "" : "NAR")}");
					}
				}
				catch (Exception ex)
				{
					Helpers.Log(4, "While deserializing vector<%Message>: " + ex.ToString());
				}
				reader.BaseStream.Position = pos + array[i].bytes;
			}
			return new MsgContainer { messages = array };
		}

		private RpcResult ReadRpcResult(TL.BinaryReader reader)
		{
			long msgId = reader.ReadInt64();
			var rpc = PullPendingRequest(msgId);
			object result;
			if (rpc != null)
			{
				try
				{
					if (!rpc.type.IsArray)
						result = reader.ReadTLValue(rpc.type);
					else
					{
						var peek = reader.ReadUInt32();
						if (peek == Layer.RpcErrorCtor)
							result = reader.ReadTLObject(Layer.RpcErrorCtor);
						else if (peek == Layer.GZipedCtor)
							using (var gzipReader = new TL.BinaryReader(new GZipStream(new MemoryStream(reader.ReadTLBytes()), CompressionMode.Decompress), reader.Client))
								result = gzipReader.ReadTLValue(rpc.type);
						else
						{
							reader.BaseStream.Position -= 4;
							result = reader.ReadTLValue(rpc.type);
						}
					}
					if (rpc.type.IsEnum) result = Enum.ToObject(rpc.type, result);
					if (result is RpcError rpcError)
						Helpers.Log(4, $"             → RpcError {rpcError.error_code,3} {rpcError.error_message,-24} #{(short)msgId.GetHashCode():X4}");
					else
						Helpers.Log(1, $"             → {result?.GetType().Name,-37} #{(short)msgId.GetHashCode():X4}");
					rpc.tcs.SetResult(result);
				}
				catch (Exception ex)
				{
					rpc.tcs.SetException(ex);
					throw;
				}
			}
			else
			{
				var ctorNb = reader.ReadUInt32();
				if (ctorNb == Layer.VectorCtor)
				{
					reader.BaseStream.Position -= 4;
					result = reader.ReadTLVector(typeof(IObject[]));
				}
				else if (ctorNb == (uint)Bool.False) result = false;
				else if (ctorNb == (uint)Bool.True) result = true;
				else result = reader.ReadTLObject(ctorNb);
				var typeName = result?.GetType().Name;
				if (MsgIdToStamp(msgId) >= _session.SessionStart)
					Helpers.Log(4, $"             → {typeName,-37} for unknown msgId #{(short)msgId.GetHashCode():X4}");
				else
					Helpers.Log(1, $"             → {typeName,-37} for past msgId #{(short)msgId.GetHashCode():X4}");
			}
			return new RpcResult { req_msg_id = msgId, result = result };
		}

		class Rpc
		{
			public Type type;
			public TaskCompletionSource<object> tcs = new(TaskCreationOptions.RunContinuationsAsynchronously);
			public long msgId;
			public Task<object> Task => tcs.Task;
		}

		private Rpc PullPendingRequest(long msgId)
		{
			Rpc request;
			lock (_pendingRpcs)
				if (_pendingRpcs.TryGetValue(msgId, out request))
					_pendingRpcs.Remove(msgId);
			return request;
		}

		private async Task HandleMessageAsync(IObject obj)
		{
			switch (obj)
			{
				case MsgContainer container:
					foreach (var msg in container.messages)
						if (msg.body != null)
							await HandleMessageAsync(msg.body);
					break;
				case MsgCopy msgCopy:
					if (msgCopy?.orig_message?.body != null)
						await HandleMessageAsync(msgCopy.orig_message.body);
					break;
				case TL.Methods.Ping ping:
					_ = SendAsync(new Pong { msg_id = _lastRecvMsgId, ping_id = ping.ping_id }, false);
					break;
				case Pong pong:
					SetResult(pong.msg_id, pong);
					break;
				case FutureSalts futureSalts:
					SetResult(futureSalts.req_msg_id, futureSalts);
					break;
				case RpcResult rpcResult:
					break; // SetResult was already done in ReadRpcResult
				case MsgsAck msgsAck:
					break; // we don't do anything with these, for now
				case BadMsgNotification badMsgNotification:
					await _sendSemaphore.WaitAsync();
					bool retryLast = badMsgNotification.bad_msg_id == _dcSession.LastSentMsgId;
					var lastSentMsg = _lastSentMsg;
					_sendSemaphore.Release();
					var logLevel = badMsgNotification.error_code == 48 ? 2 : 4;
					Helpers.Log(logLevel, $"BadMsgNotification {badMsgNotification.error_code} for msg #{(short)badMsgNotification.bad_msg_id.GetHashCode():X4}");
					switch (badMsgNotification.error_code)
					{
						case 16: // msg_id too low (most likely, client time is wrong; synchronize it using msg_id notifications and re-send the original message)
						case 17: // msg_id too high (similar to the previous case, the client time has to be synchronized, and the message re-sent with the correct msg_id)
							_dcSession.LastSentMsgId = 0;
							var localTime = DateTime.UtcNow;
							_dcSession.ServerTicksOffset = (_lastRecvMsgId >> 32) * 10000000 - localTime.Ticks + 621355968000000000L;
							Helpers.Log(1, $"Time offset: {_dcSession.ServerTicksOffset} | Server: {MsgIdToStamp(_lastRecvMsgId).AddTicks(_dcSession.ServerTicksOffset).TimeOfDay} UTC | Local: {localTime.TimeOfDay} UTC");
							break;
						case 32: // msg_seqno too low (the server has already received a message with a lower msg_id but with either a higher or an equal and odd seqno)
						case 33: // msg_seqno too high (similarly, there is a message with a higher msg_id but with either a lower or an equal and odd seqno)
							if (_dcSession.Seqno <= 1)
								retryLast = false;
							else
							{
								Reset(false, false);
								_dcSession.Renew();
								await ConnectAsync();
							}
							break;
						case 48: // incorrect server salt (in this case, the bad_server_salt response is received with the correct salt, and the message is to be re-sent with it)
							_dcSession.Salt = ((BadServerSalt)badMsgNotification).new_server_salt;
							break;
						default:
							retryLast = false;
							break;
					}
					if (retryLast)
					{
						Rpc prevRequest;
						lock (_pendingRpcs)
							_pendingRpcs.TryGetValue(badMsgNotification.bad_msg_id, out prevRequest);
						await SendAsync(lastSentMsg, true, prevRequest);
						lock (_pendingRpcs)
							_pendingRpcs.Remove(badMsgNotification.bad_msg_id);
					}
					else if (PullPendingRequest(badMsgNotification.bad_msg_id) is Rpc rpc)
					{
						if (_bareRpc?.msgId == badMsgNotification.bad_msg_id) _bareRpc = null;
						rpc.tcs.SetException(new ApplicationException($"BadMsgNotification {badMsgNotification.error_code}"));
					}
					else
						RaiseUpdate(obj);
					break;
				default:
					if (_bareRpc != null)
					{
						var rpc = PullPendingRequest(_bareRpc.msgId);
						if (rpc?.type.IsAssignableFrom(obj.GetType()) == true)
						{
							_bareRpc = null;
							rpc.tcs.SetResult(obj);
							break;
						}
						else
							Helpers.Log(4, $"Received a {obj.GetType()} incompatible with expected bare {rpc?.type}");
					}
					RaiseUpdate(obj);
					break;
			}

			void SetResult(long msgId, object result)
			{
				var rpc = PullPendingRequest(msgId);
				if (rpc != null)
					rpc.tcs.SetResult(result);
				else
					RaiseUpdate(obj);
			}
		}

		private async void RaiseUpdate(IObject obj)
		{
			try
			{
				var task = OnUpdate?.Invoke(obj);
				if (task != null) await task;
			}
			catch (Exception ex)
			{
				Helpers.Log(4, $"{nameof(OnUpdate)}({obj?.GetType().Name}) raised {ex}");
			}
		}

		static async Task<TcpClient> DefaultTcpHandler(string host, int port)
		{
			var tcpClient = new TcpClient();
			try
			{
				await tcpClient.ConnectAsync(host, port);
			}
			catch
			{
				tcpClient.Dispose();
				throw;
			}
			return tcpClient;
		}

		/// <summary>Establish connection to Telegram servers without negociating a user session</summary>
		/// <remarks>Usually you shouldn't need to call this method: Use <see cref="LoginUserIfNeeded">LoginUserIfNeeded</see> instead. <br/>Config callback is queried for: <b>server_address</b></remarks>
		/// <returns>Most methods of this class are async (Task), so please use <see langword="await"/></returns>
		public async Task ConnectAsync()
		{
			lock (this)
				_connecting ??= DoConnectAsync();
			await _connecting;
		}

		private async Task DoConnectAsync()
		{
			_cts = new();
			IPEndPoint endpoint = null;
			byte[] preamble, secret = null;
			int dcId = _dcSession?.DcID ?? 0;
			if (dcId == 0) dcId = 2;
			if (MTProxyUrl != null)
			{
#if OBFUSCATION
				if (_dcSession.DataCenter?.flags.HasFlag(DcOption.Flags.media_only) == true) dcId = -dcId;
				var parms = HttpUtility.ParseQueryString(MTProxyUrl[MTProxyUrl.IndexOf('?')..]);
				var server = parms["server"];
				int port = int.Parse(parms["port"]);
				var str = parms["secret"]; // can be hex or base64
				var secretBytes = secret = str.All("0123456789ABCDEFabcdef".Contains) ? Convert.FromHexString(str) :
					System.Convert.FromBase64String(str.Replace('_', '/').Replace('-', '+') + new string('=', (2147483644 - str.Length) % 4));
				var tlsMode = secret.Length >= 21 && secret[0] == 0xEE;
				if (tlsMode || (secret.Length == 17 && secret[0] == 0xDD))
				{
					_paddedMode = true;
					secret = secret[1..17];
				}
				else if (secret.Length != 16) throw new ArgumentException("Invalid/unsupported secret", nameof(secret));
				Helpers.Log(2, $"Connecting to DC {dcId} via MTProxy {server}:{port}...");
				_tcpClient = await TcpHandler(server, port);
				_networkStream = _tcpClient.GetStream();
				if (tlsMode)
					_networkStream = await TlsStream.HandshakeAsync(_networkStream, secret, secretBytes[17..], _cts.Token);
#else
				throw new Exception("Library was not compiled with OBFUSCATION symbol");
#endif
			}
			else
			{
				endpoint = _dcSession?.EndPoint ?? Compat.IPEndPoint_Parse(Config("server_address"));
				Helpers.Log(2, $"Connecting to {endpoint}...");
				TcpClient tcpClient = null;
				try
				{
					try
					{
						tcpClient = await TcpHandler(endpoint.Address.ToString(), endpoint.Port);
					}
					catch (SocketException ex) // cannot connect to target endpoint, try to find an alternate
					{
						Helpers.Log(4, $"SocketException {ex.SocketErrorCode} ({ex.ErrorCode}): {ex.Message}");
						if (_dcSession?.DataCenter == null) throw;
						var triedEndpoints = new HashSet<IPEndPoint> { endpoint };
						if (_session.DcOptions != null)
						{
							var altOptions = _session.DcOptions.Where(dco => dco.id == _dcSession.DataCenter.id && dco.flags != _dcSession.DataCenter.flags
								&& (dco.flags & (DcOption.Flags.cdn | DcOption.Flags.tcpo_only | DcOption.Flags.media_only)) == 0)
								.OrderBy(dco => dco.flags);
							// try alternate addresses for this DC
							foreach (var dcOption in altOptions)
							{
								endpoint = new(IPAddress.Parse(dcOption.ip_address), dcOption.port);
								if (!triedEndpoints.Add(endpoint)) continue;
								Helpers.Log(2, $"Connecting to {endpoint}...");
								try
								{
									tcpClient = await TcpHandler(endpoint.Address.ToString(), endpoint.Port);
									_dcSession.DataCenter = dcOption;
									break;
								}
								catch (SocketException) { }
							}
						}
						if (tcpClient == null)
						{
							endpoint = Compat.IPEndPoint_Parse(Config("server_address")); // re-ask callback for an address
							if (!triedEndpoints.Add(endpoint)) throw;
							_dcSession.Client = null;
							// is it address for a known DCSession?
							_dcSession = _session.DCSessions.Values.FirstOrDefault(dcs => dcs.EndPoint.Equals(endpoint));
							_dcSession ??= new() { Id = Helpers.RandomLong() };
							_dcSession.Client = this;
							Helpers.Log(2, $"Connecting to {endpoint}...");
							tcpClient = await TcpHandler(endpoint.Address.ToString(), endpoint.Port);
						}
					}
				}
				catch
				{
					tcpClient?.Dispose();
					throw;
				}
				_tcpClient = tcpClient;
				_networkStream = _tcpClient.GetStream();
			}

			byte protocolId = (byte)(_paddedMode ? 0xDD : 0xEE);
#if OBFUSCATION
			(_sendCtr, _recvCtr, preamble) = InitObfuscation(secret, protocolId, dcId);
#else
			preamble = new byte[] { protocolId, protocolId, protocolId, protocolId };
#endif
			await _networkStream.WriteAsync(preamble, 0, preamble.Length, _cts.Token);

			_saltChangeCounter = 0;
			_reactorTask = Reactor(_networkStream, _cts);
			_sendSemaphore.Release();

			try
			{
				if (_dcSession.AuthKeyID == 0)
					await CreateAuthorizationKey(this, _dcSession);

				var keepAliveTask = KeepAlive(_cts.Token);
				TLConfig = await this.InvokeWithLayer(Layer.Version,
					new TL.Methods.InitConnection<Config>
					{
						api_id = _session.ApiId,
						device_model = Config("device_model"),
						system_version = Config("system_version"),
						app_version = Config("app_version"),
						system_lang_code = Config("system_lang_code"),
						lang_pack = Config("lang_pack"),
						lang_code = Config("lang_code"),
						query = new TL.Methods.Help_GetConfig()
					});
				_session.DcOptions = TLConfig.dc_options;
				_saltChangeCounter = 0;
				if (_dcSession.DataCenter == null)
				{
					_dcSession.DataCenter = _session.DcOptions.Where(dc => dc.id == TLConfig.this_dc)
						.OrderByDescending(dc => dc.ip_address == endpoint?.Address.ToString())
						.ThenByDescending(dc => dc.port == endpoint?.Port)
						.ThenByDescending(dc => dc.flags == (endpoint?.AddressFamily == AddressFamily.InterNetworkV6 ? DcOption.Flags.ipv6 : 0))
						.First();
					_session.DCSessions[TLConfig.this_dc] = _dcSession;
				}
				if (_session.MainDC == 0) _session.MainDC = TLConfig.this_dc;
			}
			finally
			{
				lock (_session) _session.Save();
			}
			Helpers.Log(2, $"Connected to {(TLConfig.test_mode ? "Test DC" : "DC")} {TLConfig.this_dc}... {TLConfig.flags & (Config.Flags)~0xE00U}");
		}

		private async Task KeepAlive(CancellationToken ct)
		{
			int ping_id = _random.Next();
			while (!ct.IsCancellationRequested)
			{
				await Task.Delay(Math.Abs(PingInterval) * 1000, ct);
				if (_saltChangeCounter > 0) --_saltChangeCounter;
				if (PingInterval <= 0)
					await this.Ping(ping_id++);
				else // see https://core.telegram.org/api/optimisation#grouping-updates
#if DEBUG
					await this.PingDelayDisconnect(ping_id++, PingInterval * 5);
#else
					await this.PingDelayDisconnect(ping_id++, PingInterval * 5 / 4);
#endif
			}
		}

		/// <summary>Login as a bot (if not already logged-in).</summary>
		/// <remarks>Config callback is queried for: <b>bot_token</b>
		/// <br/>Bots can only call API methods marked with [bots: ✓] in their documentation. </remarks>
		/// <returns>Detail about the logged-in bot</returns>
		public async Task<User> LoginBotIfNeeded()
		{
			await ConnectAsync();
			string botToken = Config("bot_token");
			if (_session.UserId != 0) // a user is already logged-in
			{
				try
				{
					var users = await this.Users_GetUsers(new[] { InputUser.Self }); // this calls also reenable incoming Updates
					var self = users[0] as User;
					if (self.id == long.Parse(botToken.Split(':')[0]))
					{
						_session.UserId = _dcSession.UserId = self.id;
						return self;
					}
					Helpers.Log(3, $"Current logged user {self.id} mismatched bot_token. Logging out and in...");
				}
				catch (Exception ex)
				{
					Helpers.Log(4, $"Error while verifying current bot! ({ex.Message}) Proceeding to login...");
				}
				await this.Auth_LogOut();
				_session.UserId = _dcSession.UserId = 0;
			}
			var authorization = await this.Auth_ImportBotAuthorization(0, _session.ApiId, _apiHash ??= Config("api_hash"), botToken);
			return LoginAlreadyDone(authorization);
		}

		/// <summary>Login as a user (if not already logged-in).
		/// <br/><i>(this method calls <see cref="ConnectAsync">ConnectAsync</see> if necessary)</i></summary>
		/// <remarks>Config callback is queried for: <b>phone_number</b>, <b>verification_code</b> <br/>and eventually <b>first_name</b>, <b>last_name</b> (signup required), <b>password</b> (2FA auth), <b>user_id</b> (alt validation)</remarks>
		/// <param name="settings">(optional) Preference for verification_code sending</param>
		/// <param name="reloginOnFailedResume">Proceed to logout and login if active user session cannot be resumed successfully</param>
		/// <returns>Detail about the logged-in user
		/// <br/>Most methods of this class are async (Task), so please use <see langword="await"/> to get the result</returns>
		public async Task<User> LoginUserIfNeeded(CodeSettings settings = null, bool reloginOnFailedResume = true)
		{
			await ConnectAsync();
			string phone_number = null;
			if (_session.UserId != 0) // a user is already logged-in
			{
				try
				{
					var users = await this.Users_GetUsers(new[] { InputUser.Self }); // this call also reenable incoming Updates
					var self = users[0] as User;
					// check user_id or phone_number match currently logged-in user
					if ((long.TryParse(_config("user_id"), out long id) && (id == -1 || self.id == id)) ||
						self.phone == string.Concat((phone_number = Config("phone_number")).Where(char.IsDigit)))
					{
						_session.UserId = _dcSession.UserId = self.id;
						return self;
					}
					var mismatch = $"Current logged user {self.id} mismatched user_id or phone_number";
					Helpers.Log(3, mismatch);
					if (!reloginOnFailedResume) throw new ApplicationException(mismatch);
				}
				catch (RpcException ex) when (reloginOnFailedResume)
				{
					Helpers.Log(4, $"Error while fetching current user! ({ex.Message})");
				}
				Helpers.Log(3, $"Proceeding to logout and login...");
				await this.Auth_LogOut();
				_session.UserId = _dcSession.UserId = 0;
			}
			phone_number ??= Config("phone_number");
			Auth_SentCode sentCode;
#pragma warning disable CS0618 // Auth_* methods are marked as obsolete
			try
			{
				sentCode = await this.Auth_SendCode(phone_number, _session.ApiId, _apiHash ??= Config("api_hash"), settings ??= new());
			}
			catch (RpcException ex) when (ex.Code == 500 && ex.Message == "AUTH_RESTART")
			{
				sentCode = await this.Auth_SendCode(phone_number, _session.ApiId, _apiHash, settings);
			}
			Auth_AuthorizationBase authorization = null;
			try
			{
			resent:
				var timeout = DateTime.UtcNow + TimeSpan.FromSeconds(sentCode.timeout);
				RaiseUpdate(sentCode);
				Helpers.Log(3, $"A verification code has been sent via {sentCode.type.GetType().Name[17..]}");
				for (int retry = 1; authorization == null; retry++)
					try
					{
						var verification_code = await ConfigAsync("verification_code");
						if (verification_code == "" && sentCode.next_type != 0)
						{
							var mustWait = timeout - DateTime.UtcNow;
							if (mustWait.Ticks > 0)
							{
								Helpers.Log(3, $"You must wait {(int)(mustWait.TotalSeconds + 0.5)} more seconds before requesting the code to be sent via {sentCode.next_type}");
								continue;
							}
							sentCode = await this.Auth_ResendCode(phone_number, sentCode.phone_code_hash);
							goto resent;
						}
						authorization = await this.Auth_SignIn(phone_number, sentCode.phone_code_hash, verification_code);
					}
					catch (RpcException e) when (e.Code == 400 && e.Message == "PHONE_CODE_INVALID")
					{
						Helpers.Log(4, "Wrong verification code!");
						if (retry == MaxCodePwdAttempts) throw;
					}
					catch (RpcException e) when (e.Code == 401 && e.Message == "SESSION_PASSWORD_NEEDED")
					{
						for (int pwdRetry = 1; authorization == null; pwdRetry++)
							try
							{
								var accountPassword = await this.Account_GetPassword();
								RaiseUpdate(accountPassword);
								var checkPasswordSRP = await Check2FA(accountPassword, () => ConfigAsync("password"));
								authorization = await this.Auth_CheckPassword(checkPasswordSRP);
							}
							catch (RpcException pe) when (pe.Code == 400 && pe.Message == "PASSWORD_HASH_INVALID")
							{
								Helpers.Log(4, "Wrong password!");
								if (pwdRetry == MaxCodePwdAttempts) throw;
							}
					}
			}
			catch
			{
				await this.Auth_CancelCode(phone_number, sentCode.phone_code_hash);
				throw;
			}
			if (authorization is Auth_AuthorizationSignUpRequired signUpRequired)
			{
				var waitUntil = DateTime.UtcNow.AddSeconds(3);
				RaiseUpdate(signUpRequired); // give caller the possibility to read and accept TOS
				var first_name = Config("first_name");
				var last_name = Config("last_name");
				var wait = waitUntil - DateTime.UtcNow;
				if (wait > TimeSpan.Zero) await Task.Delay(wait); // we get a FLOOD_WAIT_3 if we SignUp too fast
				authorization = await this.Auth_SignUp(phone_number, sentCode.phone_code_hash, first_name, last_name);
			}
#pragma warning restore CS0618
			return LoginAlreadyDone(authorization);
		}

		/// <summary><b>[Not recommended]</b> You can use this if you have already obtained a login authorization manually</summary>
		/// <param name="authorization">if this was not a successful Auth_Authorization, an exception is thrown</param>
		/// <returns>the User that was authorized</returns>
		/// <remarks>This approach is not recommended because you likely didn't properly handle all aspects of the login process
		/// <br/>(transient failures, unnecessary login, 2FA, sign-up required, slowness to respond, verification code resending, encryption key safety, etc..)
		/// <br/>Methods <c>LoginUserIfNeeded</c> and <c>LoginBotIfNeeded</c> handle these automatically for you</remarks>
		[EditorBrowsable(EditorBrowsableState.Never)]
		public User LoginAlreadyDone(Auth_AuthorizationBase authorization)
		{
			if (authorization is not Auth_Authorization { user: User user })
				throw new ApplicationException("Failed to get Authorization: " + authorization.GetType().Name);
			_session.UserId = _dcSession.UserId = user.id;
			lock (_session) _session.Save();
			return user;
		}

		private MsgsAck CheckMsgsToAck()
		{
			lock (_msgsToAck)
			{
				if (_msgsToAck.Count == 0) return null;
				var msgsAck = new MsgsAck { msg_ids = _msgsToAck.ToArray() };
				_msgsToAck.Clear();
				return msgsAck;
			}
		}

		internal (long msgId, int seqno) NewMsgId(bool isContent)
		{
			int seqno;
			long msgId = DateTime.UtcNow.Ticks + _dcSession.ServerTicksOffset - 621355968000000000L;
			msgId = msgId * 428 + (msgId >> 24) * 25110956; // approximately unixtime*2^32 and divisible by 4
			lock (_session)
			{
				if (msgId <= _dcSession.LastSentMsgId) msgId = _dcSession.LastSentMsgId += 4; else _dcSession.LastSentMsgId = msgId;
				seqno = isContent ? _dcSession.Seqno++ * 2 + 1 : _dcSession.Seqno * 2;
				_session.Save();
			}
			return (msgId, seqno);
		}

		private async Task SendAsync(IObject msg, bool isContent, Rpc rpc = null)
		{
			if (_reactorTask == null) throw new ApplicationException("You must connect to Telegram first");
			isContent &= _dcSession.AuthKeyID != 0;
			(long msgId, int seqno) = NewMsgId(isContent);
			if (rpc != null)
				lock (_pendingRpcs)
					_pendingRpcs[rpc.msgId = msgId] = rpc;
			if (isContent && CheckMsgsToAck() is MsgsAck msgsAck)
			{
				var (ackId, ackSeqno) = NewMsgId(false);
				var container = new MsgContainer { messages = new _Message[] { new(msgId, seqno, msg), new(ackId, ackSeqno, msgsAck) } };
				await SendAsync(container, false);
				return;
			}
			await _sendSemaphore.WaitAsync();
			try
			{
				using var memStream = new MemoryStream(1024);
				using var writer = new BinaryWriter(memStream, Encoding.UTF8);
				writer.Write(0);                // int32 payload_len (to be patched with payload length)

				if (_dcSession.AuthKeyID == 0) // send unencrypted message
				{
					writer.Write(0L);						// int64 auth_key_id = 0 (Unencrypted)
					writer.Write(msgId);					// int64 message_id
					writer.Write(0);						// int32 message_data_length (to be patched)
					Helpers.Log(1, $"{_dcSession.DcID}>Sending   {msg.GetType().Name.TrimEnd('_')}...");
					writer.WriteTLObject(msg);				// bytes message_data
					BinaryPrimitives.WriteInt32LittleEndian(memStream.GetBuffer().AsSpan(20), (int)memStream.Length - 24);    // patch message_data_length
				}
				else
				{
					using var clearStream = new MemoryStream(1024);
					using var clearWriter = new BinaryWriter(clearStream, Encoding.UTF8);
					clearWriter.Write(_dcSession.AuthKey, 88, 32);
					clearWriter.Write(_dcSession.Salt);		// int64 salt
					clearWriter.Write(_dcSession.Id);		// int64 session_id
					clearWriter.Write(msgId);				// int64 message_id
					clearWriter.Write(seqno);				// int32 msg_seqno
					clearWriter.Write(0);					// int32 message_data_length (to be patched)
					if ((seqno & 1) != 0)
						Helpers.Log(1, $"{_dcSession.DcID}>Sending   {msg.GetType().Name.TrimEnd('_'),-40} #{(short)msgId.GetHashCode():X4}");
					else
						Helpers.Log(1, $"{_dcSession.DcID}>Sending   {msg.GetType().Name.TrimEnd('_'),-40} {MsgIdToStamp(msgId):u} (svc)");
					clearWriter.WriteTLObject(msg);			// bytes message_data
					int clearLength = (int)clearStream.Length - 32;  // length before padding (= 32 + message_data_length)
					int padding = (0x7FFFFFF0 - clearLength) % 16;
					padding += _random.Next(1, 64) * 16;		// MTProto 2.0 padding must be between 12..1024 with total length divisible by 16
					clearStream.SetLength(32 + clearLength + padding);
					byte[] clearBuffer = clearStream.GetBuffer();
					BinaryPrimitives.WriteInt32LittleEndian(clearBuffer.AsSpan(60), clearLength - 32);    // patch message_data_length
					RNG.GetBytes(clearBuffer, 32 + clearLength, padding);
					var msgKeyLarge = _sha256.ComputeHash(clearBuffer, 0, 32 + clearLength + padding);
					const int msgKeyOffset = 8; // msg_key = middle 128-bits of SHA256(authkey_part+plaintext+padding)
					byte[] encrypted_data = EncryptDecryptMessage(clearBuffer.AsSpan(32, clearLength + padding), true, _dcSession.AuthKey, msgKeyLarge, msgKeyOffset, _sha256);

					writer.Write(_dcSession.AuthKeyID);				// int64 auth_key_id
					writer.Write(msgKeyLarge, msgKeyOffset, 16);	// int128 msg_key
					writer.Write(encrypted_data);					// bytes encrypted_data
				}
				if (_paddedMode) // Padded intermediate mode => append random padding
				{
					var padding = new byte[_random.Next(16)];
					RNG.GetBytes(padding);
					writer.Write(padding);
				}
				var buffer = memStream.GetBuffer();
				int frameLength = (int)memStream.Length;
				BinaryPrimitives.WriteInt32LittleEndian(buffer, frameLength - 4); // patch payload_len with correct value
#if OBFUSCATION
				_sendCtr.EncryptDecrypt(buffer, frameLength);
#endif
				await _networkStream.WriteAsync(buffer, 0, frameLength);
				_lastSentMsg = msg;
			}
			finally
			{
				_sendSemaphore.Release();
			}
		}

		internal async Task<T> InvokeBare<T>(IMethod<T> request)
		{
			if (_bareRpc != null) throw new ApplicationException("A bare request is already undergoing");
			_bareRpc = new Rpc { type = typeof(T) };
			await SendAsync(request, false, _bareRpc);
			return (T)await _bareRpc.Task;
		}

		/// <summary>Call the given TL method <i>(You shouldn't need to use this method directly)</i></summary>
		/// <typeparam name="T">Expected type of the returned object</typeparam>
		/// <param name="query">TL method structure</param>
		/// <returns>Wait for the reply and return the resulting object, or throws an RpcException if an error was replied</returns>
		public async Task<T> Invoke<T>(IMethod<T> query)
		{
			if (_dcSession.WithoutUpdates && query is not IMethod<Pong>)
				query = new TL.Methods.InvokeWithoutUpdates<T> { query = query };
			bool got503 = false;
		retry:
			var rpc = new Rpc { type = typeof(T) };
			await SendAsync(query, true, rpc);
			var result = await rpc.Task;
			switch (result)
			{
				case null: return default;
				case T resultT: return resultT;
				case RpcError { error_code: var code, error_message: var message }:
					int x = -1;
					for (int index = message.Length - 1; index > 0 && (index = message.LastIndexOf('_', index - 1)) >= 0;)
						if (message[index + 1] is >= '0' and <= '9')
						{
							int end = ++index;
							do end++; while (end < message.Length && message[end] is >= '0' and <= '9');
							x = int.Parse(message[index..end]);
							message = $"{message[0..index]}X{message[end..]}";
							break;
						}

					if (code == 303 && message.EndsWith("_MIGRATE_X"))
					{
						if (message != "FILE_MIGRATE_X")
						{
							// this is a hack to migrate _dcSession in-place (staying in same Client):
							Session.DCSession dcSession;
							lock (_session)
								dcSession = GetOrCreateDCSession(x, _dcSession.DataCenter.flags);
							Reset(false, false);
							_session.MainDC = x;
							_dcSession.Client = null;
							_dcSession = dcSession;
							_dcSession.Client = this;
							await ConnectAsync();
							goto retry;
						}
					}
					else if (code == 420 && (message.EndsWith("_WAIT_X") || message.EndsWith("_DELAY_X")))
					{
						if (x <= FloodRetryThreshold)
						{
							await Task.Delay(x * 1000);
							goto retry;
						}
					}
					else if (code == -503 && !got503)
					{
						got503 = true;
						goto retry;
					}
					else if (code == 500 && message == "AUTH_RESTART")
					{
						_session.UserId = 0; // force a full login authorization flow, next time
						lock (_session) _session.Save();
					}
					throw new RpcException(code, message, x);
				case ReactorError:
					goto retry;
				default:
					throw new ApplicationException($"{query.GetType().Name} call got a result of type {result.GetType().Name} instead of {typeof(T).Name}");
			}
		}
	}
}