using ExtensionMethods;
using MAX.Models;
using Microsoft.Extensions.Logging;
using System;
using System.IO;
using System.Net.Sockets;
using System.Security.Cryptography;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Xml;

namespace MAX
{
    public class Client : IDisposable
    {
        private ILogger logger;
        private string host;
        private int port;
        private int vendorId;
        private string serialNumber;
        private int userId;
        private string username;
        private string password;

        private TcpClient connection = null;
        private NetworkStream connectionStream = null;
        private TripleDES des = null;

        private bool disposed = false;

        public Client(ILogger logger, string host, int port, int vendorId, string serialNumber, int userId, string username, string password)
        {
            this.logger = logger;
            this.host = host;
            this.port = port;
            this.vendorId = vendorId;
            this.serialNumber = serialNumber;
            this.userId = userId;
            this.username = username;
            this.password = password;

            ConnectTimeout = 10000;
            ReceiveTimeout = 10000;
            SendTimeout = 10000;
        }

        public void Close()
        {
            Dispose(true);
        }

        public async Task<User> ConnectAsync()
        {
            if (connection != null)
                throw new Exception("Already connected");

            connection = new TcpClient(AddressFamily.InterNetwork);
            connection.ReceiveTimeout = ReceiveTimeout;
            connection.SendTimeout = SendTimeout;

            // Connect to the server
            try
            {
                using (var cancellationSource = new CancellationTokenSource(ConnectTimeout))
                {
                    await connection.ConnectAsync(host, port).WithCancellation(cancellationSource.Token).ConfigureAwait(false);
                }
            }
            catch (OperationCanceledException)
            {
                throw new Exception("Connect timeout");
            }
            connectionStream = connection.GetStream();

            // Device authentication
            await WriteMessageAsync(new MessageBuilder()
                .Append("Hi ")
                .Append(serialNumber)
                .Append("|V")
                .Append(vendorId)
                .Append("|123451234512345||||||")).ConfigureAwait(false);

            var response = await ReadMessageAsync().ConfigureAwait(false);
            if (!response.StartsWith("Hi "))
            {
                logger.LogError("Device authentication failed: {0}", response);
                return null;
            }

            // Request server RSA key
            await WriteMessageAsync(new MessageBuilder().Append("PK")).ConfigureAwait(false);
            response = await ReadMessageAsync().ConfigureAwait(false);

            // Key exchange
            des = TripleDES.Create();
            des.IV = new byte[] { 0, 0, 0, 0, 0, 0, 0, 0 };
            await WriteMessageAsync(new MessageBuilder()
                .Append("3D ")
                .Append(EncryptRSA(response, BitConverter.ToString(des.Key).Replace("-", "")))).ConfigureAwait(false);

            response = await ReadMessageAsync().ConfigureAwait(false);
            if (!response.StartsWith("OK"))
            {
                throw new Exception(String.Format("Key exchange failed: {0}", response));
            }

            // User authentication
            await WriteMessageAsync(new MessageBuilder()
                .Append("User ")
                .Append(Encrypt(new StringBuilder()
                    .Append(userId)
                    .Append("|")
                    .Append(username)
                    .Append("|")
                    .Append(password).ToString()))).ConfigureAwait(false);

            response = Decrypt(await ReadMessageAsync().ConfigureAwait(false));
            if (response.StartsWith("OK"))
            {
                var parts = response.Split('|');
                var user = new User()
                {
                    Id = userId,
                    Username = username,
                    FirstName = parts[4],
                    Surname = parts[3],
                    Enabled = bool.Parse(parts[6]),
                    Level = (User.UserLevel)int.Parse(parts[1]),
                    System = int.Parse(parts[2]),
                    LastLogin = DateTime.Parse(parts[5])
                };

                if (user.Level == User.UserLevel.CustomUser)
                {
                    user.CanPrintOffline = bool.Parse(parts[7]);
                    user.OfflinePrintValue = decimal.Parse(parts[8]);
                    user.CanPrintOnline = bool.Parse(parts[9]);
                    user.OnlinePrintValue = decimal.Parse(parts[10]);
                    user.CanReprintOffline = bool.Parse(parts[11]);
                    user.OfflineReprintValue = decimal.Parse(parts[12]);
                    user.CanReprintOnline = bool.Parse(parts[13]);
                    user.OnlineReprintValue = decimal.Parse(parts[14]);
                }

                // Account information
                await WriteMessageAsync(new MessageBuilder().Append("Acc")).ConfigureAwait(false);
                response = Decrypt(await ReadMessageAsync().ConfigureAwait(false));
                if (response.StartsWith("OK"))
                {
                    parts = response.Split('|');
                    user.Account = new Account()
                    {
                        Id = int.Parse(parts[1]),
                        Name = parts[2],
                        Balance = decimal.Parse(parts[3]),
                        Status = (Account.AccountStatus)int.Parse(parts[4]),
                        Reference = parts[5],
                        Warehouse = new Warehouse()
                        {
                            Id = int.Parse(parts[6]),
                            Name = parts[7]
                        }
                    };
                    return user;
                }
                else if (response.StartsWith("ER"))
                {
                    logger.LogError("Error retrieving account information: {0}", response);
                    return null;
                }
                else
                {
                    throw new Exception(String.Format("Invalid account information response: {0}", response));
                }
            }
            else if (response.StartsWith("ER"))
            {
                logger.LogInformation("User authentication failed: {0}", response);
                return null;
            }
            else
            {
                throw new Exception(String.Format("Invalid user information response: {0}", response));
            }
        }

        public int ConnectTimeout { get; set; }

        protected virtual void Dispose(bool disposing)
        {
            if (disposed)
                return;

            disposed = true;

            // No unmanaged resources are disposed so we don't need the full finalisation pattern.
            if (disposing)
            {
                if (des != null)
                {
                    des.Dispose();
                    des = null;
                }
                if (connectionStream != null)
                {
                    connectionStream.Dispose();
                    connectionStream = null;
                }
                if (connection != null)
                {
                    connection.Dispose();
                    connection = null;
                }
            }
        }

        public void Dispose()
        {
            Dispose(true);
        }

        private string Decrypt(string cipherText)
        {
            using (var decryptor = des.CreateDecryptor(des.Key, des.IV))
            {
                return Encoding.UTF8.GetString(Transform(decryptor, Convert.FromBase64String(cipherText)));
            }
        }

        private string Encrypt(string plainText)
        {
            using (var encryptor = des.CreateEncryptor(des.Key, des.IV))
            {
                return Convert.ToBase64String(Transform(encryptor, Encoding.UTF8.GetBytes(plainText)));
            }
        }

        private string EncryptRSA(string publicKey, string plainText)
        {
            RSAParameters parameters = new RSAParameters();

            var xml = new XmlDocument();
            xml.LoadXml(publicKey);
            if (! xml.DocumentElement.Name.Equals("RSAKeyValue"))
                throw new Exception("Invalid RSA key");

            foreach (XmlNode node in xml.DocumentElement.ChildNodes)
            {
                switch (node.Name)
                {
                    case "Modulus": parameters.Modulus = Convert.FromBase64String(node.InnerText); break;
                    case "Exponent": parameters.Exponent = Convert.FromBase64String(node.InnerText); break;
                    case "P": parameters.P = Convert.FromBase64String(node.InnerText); break;
                    case "Q": parameters.Q = Convert.FromBase64String(node.InnerText); break;
                    case "DP": parameters.DP = Convert.FromBase64String(node.InnerText); break;
                    case "DQ": parameters.DQ = Convert.FromBase64String(node.InnerText); break;
                    case "InverseQ": parameters.InverseQ = Convert.FromBase64String(node.InnerText); break;
                    case "D": parameters.D = Convert.FromBase64String(node.InnerText); break;
                }
            }

            using (var rsa = RSA.Create())
            {
                rsa.ImportParameters(parameters);
                var blockSize = rsa.KeySize / 8 - 42;
                var offset = 0;
                var input = Encoding.UTF32.GetBytes(plainText);
                StringBuilder output = new StringBuilder();
                while (offset < input.Length)
                {
                    var length = input.Length - offset;
                    if (length > blockSize)
                        length = blockSize;
                    var block = new byte[length];
                    Array.Copy(input, offset, block, 0, length);
                    var cipherText = rsa.Encrypt(block, RSAEncryptionPadding.OaepSHA1);
                    Array.Reverse(cipherText);
                    output.Append(Convert.ToBase64String(cipherText));
                    offset += length;
                }
                return output.ToString();
            }
        }

        private async Task<byte[]> ReadBytesAsync(int count)
        {
            int totalBytesRead = 0;
            byte[] buffer = new byte[count];
            while (totalBytesRead < count)
            {
                int bytesRead = await connectionStream.ReadAsync(buffer, totalBytesRead, count - totalBytesRead).ConfigureAwait(false);
                if (bytesRead == 0)
                    throw new Exception("Connection closed unexpectedly");
                totalBytesRead += bytesRead;
            }
            return buffer;
        }

        private async Task<string> ReadMessageAsync()
        {
            byte[] buffer = await ReadBytesAsync(2).ConfigureAwait(false);
            int size = buffer[0] * 256 + buffer[1];
            return Encoding.ASCII.GetString(await ReadBytesAsync(size).ConfigureAwait(false));
        }

        public int ReceiveTimeout { get; set; }

        public int SendTimeout { get; set; }

        private byte[] Transform(ICryptoTransform transform, byte[] input)
        {
            using (var memoryStream = new MemoryStream())
            using (var cryptoStream = new CryptoStream(memoryStream, transform, CryptoStreamMode.Write))
            {
                cryptoStream.Write(input, 0, input.Length);
                cryptoStream.FlushFinalBlock();
                return memoryStream.ToArray();
            }
        }

        private async Task WriteMessageAsync(MessageBuilder message)
        {
            byte[] data = message.GetBytes();
            await connectionStream.WriteAsync(data, 0, data.Length).ConfigureAwait(false);
        }
    }
}