using System;
using System.Security.Cryptography;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using RR.Game2D.Core.Managers;
using UnityEngine;

namespace RR.Common.Controls
{
    internal sealed class ComDeviceClient
    {
        private const string RequestInput = "91";
        private const string DefaultInputBits = "11111111111111111111111111";
        private const long CoinDebounceMs = 250;

        private static readonly byte[] AesEncryptedKey =
        {
            0x69, 0x40, 0xC7, 0x0E, 0xF2, 0xC7, 0x45, 0x70,
            0x72, 0xCD, 0x28, 0x58, 0x99, 0x8F, 0x73, 0xA8,
            0x5F, 0x5F, 0xED, 0xB4, 0xC1, 0x62, 0xB4, 0x24,
            0xAC, 0xD7, 0xA3, 0xD6, 0xD8, 0x0B, 0x50, 0x37
        };

        private readonly object _ioLock = new object();

        private readonly bool _enableEncryptedHandshake;
        private readonly int _handshakeTimeoutMs;
        private readonly bool _keepAlive;
        private readonly string _roleRequestCommand;
        private readonly string _roleResponsePrefix;
        private readonly int _roleRequestTimeoutMs;

        private CancellationTokenSource _lifecycleCts;
        private Task _pollTask;
        private Task _keepAliveTask;

        private int _handle;
        private long _lastCoinTime;
        private int _inputToggle;
        private int _missedInputResponses;

        private bool _isAuthorized;
        private bool _isOperational;
        private bool _handshakeInProgress;

        private string _requestHex = string.Empty;
        private string _lastHandshakeResponse = string.Empty;
        private string _lastInputBits = DefaultInputBits;
        private byte[] _aesKey32;

        private HandshakeStage _handshakeStage = HandshakeStage.None;
        private TaskCompletionSource<bool> _handshakeCompletion;
        private TaskCompletionSource<bool> _chalReceivedCompletion;
        private TaskCompletionSource<string> _roleCompletion;
        private TaskCompletionSource<string> _macCompletion;

        private enum HandshakeStage
        {
            None,
            WaitingChal,
            WaitingRaes,
            Completed,
            Failed
        }

        public string DeviceId { get; }
        public string PortName { get; }

        public bool IsOperational => _isOperational;
        public string LastInputBits => _lastInputBits;
        public string ControllerRole { get; private set; } = string.Empty;
        public string MacAddress { get; private set; } = string.Empty;

        public event Action<string> CoinAccepted;
        public event Action<string, string> InputReceived;
        public event Action<string, string> RawLineReceived;
        public event Action<string> Authorized;
        public event Action<string> Disconnected;
        public event Action<string> ConnectionLost;

        public ComDeviceClient(
            string portName,
            bool enableEncryptedHandshake,
            int handshakeTimeoutMs,
            bool keepAlive,
            string roleRequestCommand,
            string roleResponsePrefix,
            int roleRequestTimeoutMs)
        {
            PortName = portName;
            DeviceId = portName;
            _enableEncryptedHandshake = enableEncryptedHandshake;
            _handshakeTimeoutMs = Math.Max(500, handshakeTimeoutMs);
            _keepAlive = keepAlive;
            _roleRequestCommand = roleRequestCommand?.Trim() ?? string.Empty;
            _roleResponsePrefix = string.IsNullOrWhiteSpace(roleResponsePrefix) ? "ROLE" : roleResponsePrefix.Trim();
            _roleRequestTimeoutMs = Math.Max(200, roleRequestTimeoutMs);

            if (_enableEncryptedHandshake)
            {
                _aesKey32 = BuildAesKey();
            }
        }

        public bool Start()
        {
            if (!OpenPort()) return false;

            _lifecycleCts = new CancellationTokenSource();
            _pollTask = Task.Run(() => PollLoopAsync(_lifecycleCts.Token), _lifecycleCts.Token);

            if (_enableEncryptedHandshake)
            {
                _ = RunHandshakeAsync(_lifecycleCts.Token);
            }
            else
            {
                MarkOperational();
            }

            return true;
        }

        public void Stop(bool sendShutdownCommands)
        {
            try
            {
                _lifecycleCts?.Cancel();
            }
            catch
            {
                // ignored
            }

            if (sendShutdownCommands)
            {
                SendRaw("2170", true);
                SendRaw("2130", true);
            }

            lock (_ioLock)
            {
                if (_handle > 0)
                {
                    ComNativeWrapper.Serial_Close(_handle);
                    _handle = 0;
                }
            }

            _isOperational = false;
            _isAuthorized = false;
            _handshakeInProgress = false;
            _handshakeStage = HandshakeStage.None;
            _handshakeCompletion?.TrySetCanceled();
            _chalReceivedCompletion?.TrySetCanceled();
            _roleCompletion?.TrySetCanceled();
            _macCompletion?.TrySetCanceled();
            ControllerRole = string.Empty;
            _keepAliveTask = null;

            Disconnected?.Invoke(DeviceId);

            _lifecycleCts?.Dispose();
            _lifecycleCts = null;
        }

        public void Send(string message)
        {
            SendRaw(message, false);
        }

        private bool OpenPort()
        {
            int handle = ComNativeWrapper.Serial_Open(PortName, 115200, 8, 0, 1, 5, 10);
            if (handle <= 0)
            {
                GameManager.Logger?.LogError("ComDeviceClient", $"[{DeviceId}] Open failed: {ComNativeWrapper.GetLastError()}");
                return false;
            }

            lock (_ioLock)
            {
                _handle = handle;
            }

            _lastCoinTime = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds();
            FlushPortBuffer();
            return true;
        }

        private async Task PollLoopAsync(CancellationToken token)
        {
            while (!token.IsCancellationRequested)
            {
                try
                {
                    await Task.Delay(1, token);
                    string line = ReadBufferLine();
                    if (string.IsNullOrEmpty(line)) continue;
                    ProcessLine(line);
                }
                catch (OperationCanceledException)
                {
                    break;
                }
                catch (Exception e)
                {
                    GameManager.Logger?.LogError("ComDeviceClient", $"[{DeviceId}] Poll error: {e.Message}");
                }
            }
        }

        private void ProcessLine(string line)
        {
            line = line.Trim();
            if (string.IsNullOrEmpty(line)) return;

            if (_handshakeInProgress)
            {
                TryProcessHandshakeLine(line);
                return;
            }

            if (!_isOperational) return;

            if (TryHandleRoleLine(line))
            {
                return;
            }

            if (TryHandleMacLine(line))
            {
                return;
            }

            if (line.StartsWith("INPUT", StringComparison.Ordinal))
            {
                _inputToggle = 1;
                if (line.Length <= 5) return;

                string rawData = line.Substring(5);
                if (string.IsNullOrWhiteSpace(rawData)) return;

                // Проверяем датчик хоппера: 2-й бит с начала в нормальном двоичном представлении
                if (long.TryParse(rawData, out long rawValue))
                {
                    string rawBinary = Convert.ToString(rawValue, 2);
                    if (rawBinary.Length >= 2 && rawBinary[1] == '0')
                        PrizeSystem.SignalPrizeGiven();
                }

                string bits = DecimalToBinary(rawData);
                _lastInputBits = bits;
                InputReceived?.Invoke(DeviceId, bits);
                return;
            }

            RawLineReceived?.Invoke(DeviceId, line);
        }

        private async Task RunHandshakeAsync(CancellationToken token)
        {
            _handshakeInProgress = true;
            _isAuthorized = false;
            _isOperational = false;
            _handshakeStage = HandshakeStage.WaitingChal;
            _lastHandshakeResponse = string.Empty;
            _handshakeCompletion = new TaskCompletionSource<bool>(TaskCreationOptions.RunContinuationsAsynchronously);
            _chalReceivedCompletion = new TaskCompletionSource<bool>(TaskCreationOptions.RunContinuationsAsynchronously);
            Debug.Log($"[COM AUTH][{DeviceId}] Handshake started. Stage={_handshakeStage}");

            _requestHex = GenerateRandomBlock16Hex();
            // Порядок handshake по протоколу платы:
            // PC -> 07[random], board -> CHAL, PC -> 08[enc(CHAL)], board -> RAES, board -> AUTH_CNT_OK.
            SendRaw("07" + _requestHex, true);
            Debug.Log($"[COM AUTH][{DeviceId}] -> 07{_requestHex}");

            // Если на 07 не получили ожидаемый CHAL быстро, сразу пропускаем устройство.
            int chalFastTimeoutMs = Math.Min(1200, Math.Max(250, _handshakeTimeoutMs / 4));
            Task chalFastTimeoutTask = Task.Delay(chalFastTimeoutMs, token);
            Task chalFastFinished = await Task.WhenAny(_chalReceivedCompletion.Task, chalFastTimeoutTask);
            if (chalFastFinished != _chalReceivedCompletion.Task)
            {
                Debug.LogWarning($"[COM AUTH][{DeviceId}] No CHAL after 07 in {chalFastTimeoutMs}ms. Skipping device.");
                FailHandshake($"Нет ожидаемого CHAL на 07 за {chalFastTimeoutMs}ms");
                return;
            }

            Task timeoutTask = Task.Delay(_handshakeTimeoutMs, token);
            Task finished = await Task.WhenAny(_handshakeCompletion.Task, timeoutTask);

            if (finished == _handshakeCompletion.Task && _handshakeCompletion.Task.Result)
            {
                Debug.Log($"[COM AUTH][{DeviceId}] Handshake completed successfully");
                MarkOperational();
                return;
            }

            GameManager.Logger.LogWarning($"COM AUTH [{DeviceId}]", $"Handshake timeout. Last board response: {_lastHandshakeResponse}");
            FailHandshake($"Таймаут рукопожатия. Последний ответ платы: {_lastHandshakeResponse}");
        }

        private void TryProcessHandshakeLine(string line)
        {
            Debug.Log($"[COM AUTH][{DeviceId}] <- {line}; stage={_handshakeStage}");
            _lastHandshakeResponse = line;

            // Во время handshake обрабатываем только ожидаемые сообщения:
            // WaitingChal -> CHAL
            // WaitingRaes -> RAES
            // Все остальные строки игнорируем.
            if (_handshakeStage == HandshakeStage.WaitingChal)
            {
                if (line.StartsWith("CHAL", StringComparison.Ordinal))
                {
                    HandleChal(line);
                }
                else
                {
                    Debug.Log($"[COM AUTH][{DeviceId}] Ignored while WaitingChal: {line}");
                }

                return;
            }

            if (_handshakeStage == HandshakeStage.WaitingRaes)
            {
                if (line.StartsWith("RAES", StringComparison.Ordinal))
                {
                    HandleRaes(line);
                }
                else
                {
                    Debug.Log($"[COM AUTH][{DeviceId}] Ignored while WaitingRaes: {line}");
                }

                return;
            }

            Debug.Log($"[COM AUTH][{DeviceId}] Ignored in stage {_handshakeStage}: {line}");
        }

        private void HandleRaes(string line)
        {
            try
            {
                Debug.Log($"[COM AUTH][{DeviceId}] Handling RAES...");
                if (_handshakeStage != HandshakeStage.WaitingRaes)
                {
                    FailHandshake($"RAES в неверной фазе: {_handshakeStage}");
                    return;
                }

                if (line.Length < 36)
                {
                    FailHandshake("Некорректная длина RAES");
                    return;
                }

                string hex = line.Substring(4, 32);
                if (!IsHexString(hex, 32))
                {
                    FailHandshake("RAES содержит некорректный HEX");
                    return;
                }

                string decrypted = DecryptHexBlock16(hex);
                if (!string.Equals(decrypted, _requestHex, StringComparison.OrdinalIgnoreCase))
                {
                    FailHandshake("RAES не совпадает с запросом 07");
                    return;
                }

                _handshakeStage = HandshakeStage.Completed;
                _isAuthorized = true;
                Debug.Log($"[COM AUTH][{DeviceId}] RAES verified. Raw RAES={line}; decrypted={decrypted}; handshake complete");
                _handshakeCompletion?.TrySetResult(true);
            }
            catch (Exception e)
            {
                FailHandshake($"Ошибка RAES: {e.Message}");
            }
        }

        private void HandleChal(string line)
        {
            try
            {
                Debug.Log($"[COM AUTH][{DeviceId}] Handling CHAL...");
                if (_handshakeStage != HandshakeStage.WaitingChal)
                {
                    FailHandshake($"CHAL в неверной фазе: {_handshakeStage}");
                    return;
                }

                _chalReceivedCompletion?.TrySetResult(true);

                if (line.Length < 36)
                {
                    FailHandshake("Некорректная длина CHAL");
                    return;
                }

                string hex = line.Substring(4, 32);
                if (!IsHexString(hex, 32))
                {
                    FailHandshake("CHAL содержит некорректный HEX");
                    return;
                }

                string encrypted = EncryptHexBlock16(hex);
                SendRaw("08" + encrypted, true);
                _handshakeStage = HandshakeStage.WaitingRaes;
                Debug.Log($"[COM AUTH][{DeviceId}] -> 08{encrypted}; stage={_handshakeStage}");
            }
            catch (Exception e)
            {
                FailHandshake($"Ошибка CHAL: {e.Message}");
            }
        }

        private void MarkOperational()
        {
            _handshakeInProgress = false;
            _isAuthorized = true;
            _isOperational = true;
            _handshakeStage = HandshakeStage.Completed;
            ControllerRole = string.Empty;
            _missedInputResponses = 0;
            Debug.Log($"[COM AUTH][{DeviceId}] Device marked operational");

            SendRaw("2171", true);
            SendRaw("890003", true);
            SendRaw("8600", true);

            if (_keepAlive && (_keepAliveTask == null || _keepAliveTask.IsCompleted))
            {
                _keepAliveTask = Task.Run(() => KeepAliveLoopAsync(_lifecycleCts.Token), _lifecycleCts.Token);
            }

            _ = Task.Run(() => ResolveRoleAfterAuthorizationAsync(_lifecycleCts.Token), _lifecycleCts.Token);
        }

        private void FailHandshake(string message)
        {
            _isAuthorized = false;
            _isOperational = false;
            _handshakeInProgress = false;
            _handshakeStage = HandshakeStage.Failed;
            _handshakeCompletion?.TrySetResult(false);
            Debug.LogWarning($"[COM AUTH][{DeviceId}] Handshake failed: {message}");
            GameManager.Logger?.LogWarning("ComDeviceClient", $"[{DeviceId}] {message}");

            // Если порт отвечает не по ожидаемому протоколу платы,
            // отключаем устройство, чтобы менеджер выбрал другой порт.
            Stop(false);
        }

        private async Task KeepAliveLoopAsync(CancellationToken token)
        {
            while (!token.IsCancellationRequested)
            {
                try
                {
                    await Task.Delay(2000, token);

                    if (!_isOperational)
                    {
                        await Task.Delay(8000, token);
                        continue;
                    }

                    SendRaw(RequestInput, false);
                    _inputToggle = 0;

                    await Task.Delay(1000, token);
                    if (_inputToggle == 0)
                    {
                        _missedInputResponses++;
                        if (_missedInputResponses >= 3)
                        {
                            GameManager.Logger?.LogWarning("ComDeviceClient",
                                $"[{DeviceId}] Нет INPUT-ответа {_missedInputResponses} цикла подряд, выполняю reconnect");
                            _missedInputResponses = 0;
                            await ReconnectAsync(token);
                        }
                    }
                    else
                    {
                        _missedInputResponses = 0;
                    }

                    await Task.Delay(7000, token);
                }
                catch (OperationCanceledException)
                {
                    break;
                }
                catch (Exception e)
                {
                    GameManager.Logger?.LogError("ComDeviceClient", $"[{DeviceId}] KeepAlive error: {e.Message}");
                }
            }
        }

        private async Task ReconnectAsync(CancellationToken token)
        {
            _isOperational = false;
            _isAuthorized = false;
            _handshakeInProgress = false;
            _handshakeStage = HandshakeStage.None;
            _lastInputBits = DefaultInputBits;
            _inputToggle = 0;
            ControllerRole = string.Empty;
            MacAddress = string.Empty;

            ConnectionLost?.Invoke(DeviceId);

            lock (_ioLock)
            {
                if (_handle > 0)
                {
                    ComNativeWrapper.Serial_Close(_handle);
                    _handle = 0;
                }
            }

            if (!OpenPort())
            {
                // Порт недоступен при переподключении: отключаем устройство и даем менеджеру
                // переключиться на другие доступные порты.
                Stop(false);
                return;
            }

            if (_enableEncryptedHandshake)
            {
                await RunHandshakeAsync(token);
            }
            else
            {
                MarkOperational();
            }
        }

        private void FlushPortBuffer()
        {
            lock (_ioLock)
            {
                if (_handle <= 0) return;

                byte[] localBuf = new byte[1024];
                int flushedCount = 0;

                int read;
                while ((read = ComNativeWrapper.Serial_ReadLineUTF8_bytes(_handle, localBuf, localBuf.Length)) > 0)
                {
                    flushedCount++;
                    if (flushedCount > 100) break;
                }
            }
        }

        private string ReadBufferLine()
        {
            lock (_ioLock)
            {
                if (_handle <= 0) return string.Empty;

                byte[] localBuf = new byte[1024];
                int read = ComNativeWrapper.Serial_ReadLineUTF8_bytes(_handle, localBuf, localBuf.Length);
                if (read <= 0) return string.Empty;

                if (read > localBuf.Length) read = localBuf.Length;

                string line = Encoding.UTF8.GetString(localBuf, 0, read).Trim();
                if (line != "COIN") return line;

                long now = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds();
                if (now - _lastCoinTime < CoinDebounceMs) return string.Empty;

                _lastCoinTime = now;

                if (_isOperational)
                {
                    ComNativeWrapper.Serial_WriteStringUTF8(_handle, "10", 1);
                    CoinAccepted?.Invoke(DeviceId);
                }

                return string.Empty;
            }
        }

        private void SendRaw(string message, bool bypassAuthorization)
        {
            if (string.IsNullOrWhiteSpace(message)) return;
            if (!bypassAuthorization && !_isOperational) return;

            lock (_ioLock)
            {
                if (_handle <= 0) return;
                ComNativeWrapper.Serial_WriteStringUTF8(_handle, message, 1);
            }
        }

        private bool TryHandleRoleLine(string line)
        {
            if (_roleCompletion == null) return false;
            if (!_roleCompletion.Task.IsCompleted && TryExtractRole(line, out string role))
            {
                ControllerRole = role;
                _roleCompletion.TrySetResult(role);
                return true;
            }

            return false;
        }

        private bool TryHandleMacLine(string line)
        {
            if (_macCompletion == null) return false;
            if (!_macCompletion.Task.IsCompleted && TryExtractMac(line, out string mac))
            {
                MacAddress = mac;
                _macCompletion.TrySetResult(mac);
                return true;
            }

            return false;
        }

        private static bool TryExtractMac(string line, out string mac)
        {
            mac = string.Empty;
            if (string.IsNullOrWhiteSpace(line)) return false;

            string trimmed = line.Trim();

            // Ответ на "06" — голый MAC без двоеточий, 12 hex-символов
            if (trimmed.Length == 12 && IsHexString(trimmed))
            {
                mac = trimmed.ToUpperInvariant();
                return true;
            }

            return false;
        }

        private static bool IsHexString(string s)
        {
            for (int i = 0; i < s.Length; i++)
            {
                char c = s[i];
                if (!((c >= '0' && c <= '9') || (c >= 'a' && c <= 'f') || (c >= 'A' && c <= 'F')))
                    return false;
            }
            return true;
        }

        private async Task ResolveRoleAfterAuthorizationAsync(CancellationToken token)
        {
            // Роль и MAC считываем только после завершенной авторизации рукопожатия.
            if (!_enableEncryptedHandshake || !_isAuthorized || string.IsNullOrWhiteSpace(_roleRequestCommand))
            {
                Authorized?.Invoke(DeviceId);
                return;
            }

            try
            {
                // --- Запрос роли ---
                _roleCompletion = new TaskCompletionSource<string>(TaskCreationOptions.RunContinuationsAsynchronously);
                SendRaw(_roleRequestCommand, false);

                Task timeoutTask = Task.Delay(_roleRequestTimeoutMs, token);
                Task finished = await Task.WhenAny(_roleCompletion.Task, timeoutTask);
                if (finished == _roleCompletion.Task &&
                    _roleCompletion.Task.IsCompletedSuccessfully &&
                    !string.IsNullOrWhiteSpace(_roleCompletion.Task.Result))
                {
                    ControllerRole = _roleCompletion.Task.Result;
                }
                else
                {
                    GameManager.Logger?.LogWarning("ComDeviceClient",
                        $"[{DeviceId}] Не удалось получить роль контроллера за {_roleRequestTimeoutMs}ms");
                }

                // --- Запрос MAC-адреса ---
                _macCompletion = new TaskCompletionSource<string>(TaskCreationOptions.RunContinuationsAsynchronously);
                SendRaw("06", false);

                Task macTimeoutTask = Task.Delay(_roleRequestTimeoutMs, token);
                Task macFinished = await Task.WhenAny(_macCompletion.Task, macTimeoutTask);
                if (macFinished == _macCompletion.Task &&
                    _macCompletion.Task.IsCompletedSuccessfully &&
                    !string.IsNullOrWhiteSpace(_macCompletion.Task.Result))
                {
                    MacAddress = _macCompletion.Task.Result;
                    GameManager.Logger?.Log("ComDeviceClient",
                        $"[{DeviceId}] MAC-адрес: {MacAddress}");
                }
                else
                {
                    GameManager.Logger?.LogWarning("ComDeviceClient",
                        $"[{DeviceId}] Не удалось получить MAC-адрес за {_roleRequestTimeoutMs}ms");
                }
            }
            catch (OperationCanceledException)
            {
                // ignore
            }
            catch (Exception e)
            {
                GameManager.Logger?.LogError("ComDeviceClient", $"[{DeviceId}] Role/MAC resolve error: {e.Message}");
            }
            finally
            {
                Authorized?.Invoke(DeviceId);
            }
        }

        private bool TryExtractRole(string line, out string role)
        {
            role = string.Empty;
            if (string.IsNullOrWhiteSpace(line)) return false;

            string trimmed = line.Trim();
            if (!trimmed.StartsWith(_roleResponsePrefix, StringComparison.OrdinalIgnoreCase))
            {
                return false;
            }

            string tail = trimmed.Substring(_roleResponsePrefix.Length).Trim();
            if (tail.StartsWith(":") || tail.StartsWith("="))
            {
                tail = tail.Substring(1).Trim();
            }

            if (string.IsNullOrWhiteSpace(tail)) return false;
            role = tail;
            return true;
        }

        private static string DecimalToBinary(string decimalString)
        {
            try
            {
                if (!long.TryParse(decimalString, out long value)) return DefaultInputBits;

                string binary = Convert.ToString(value, 2);
                char[] chars = binary.ToCharArray();
                Array.Reverse(chars);
                return new string(chars);
            }
            catch
            {
                return DefaultInputBits;
            }
        }

        private static byte[] BuildAesKey()
        {
            byte[] key = new byte[32];
            for (int i = 0; i < key.Length; i++)
            {
                key[i] = (byte)(AesEncryptedKey[i] ^ 0x37);
            }

            return key;
        }

        private string EncryptHexBlock16(string plainHex)
        {
            byte[] plain = HexToBytes(plainHex);
            if (plain.Length != 16) throw new InvalidOperationException("Plain must be 16 bytes.");
            return BytesToHex(Aes256EcbEncrypt(plain));
        }

        private string DecryptHexBlock16(string cipherHex)
        {
            byte[] cipher = HexToBytes(cipherHex);
            if (cipher.Length != 16) throw new InvalidOperationException("Cipher must be 16 bytes.");
            return BytesToHex(Aes256EcbDecrypt(cipher));
        }

        private byte[] Aes256EcbEncrypt(byte[] data)
        {
            using (Aes aes = Aes.Create())
            {
                aes.Key = _aesKey32;
                aes.Mode = CipherMode.ECB;
                aes.Padding = PaddingMode.None;

                using (ICryptoTransform encryptor = aes.CreateEncryptor())
                {
                    return encryptor.TransformFinalBlock(data, 0, data.Length);
                }
            }
        }

        private byte[] Aes256EcbDecrypt(byte[] data)
        {
            using (Aes aes = Aes.Create())
            {
                aes.Key = _aesKey32;
                aes.Mode = CipherMode.ECB;
                aes.Padding = PaddingMode.None;

                using (ICryptoTransform decryptor = aes.CreateDecryptor())
                {
                    return decryptor.TransformFinalBlock(data, 0, data.Length);
                }
            }
        }

        private static string GenerateRandomBlock16Hex()
        {
            byte[] buffer = new byte[16];
            RandomNumberGenerator.Fill(buffer);
            return BytesToHex(buffer);
        }

        private static byte[] HexToBytes(string hex)
        {
            if (hex == null) throw new ArgumentNullException(nameof(hex));
            hex = hex.Trim();

            if (hex.Length % 2 != 0)
            {
                throw new InvalidOperationException("Hex string length must be even.");
            }

            byte[] result = new byte[hex.Length / 2];
            for (int i = 0; i < result.Length; i++)
            {
                result[i] = Convert.ToByte(hex.Substring(i * 2, 2), 16);
            }

            return result;
        }

        private static string BytesToHex(byte[] bytes)
        {
            StringBuilder builder = new StringBuilder(bytes.Length * 2);
            for (int i = 0; i < bytes.Length; i++)
            {
                builder.AppendFormat("{0:X2}", bytes[i]);
            }

            return builder.ToString();
        }

        private static bool IsHexString(string value, int expectedLength)
        {
            if (string.IsNullOrWhiteSpace(value) || value.Length != expectedLength)
            {
                return false;
            }

            for (int i = 0; i < value.Length; i++)
            {
                if (!Uri.IsHexDigit(value[i]))
                {
                    return false;
                }
            }

            return true;
        }
    }
}