using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net.Sockets;
using System.Text;
using System.Threading.Tasks;

namespace Lab_SMTP
{
    public class SMTPClient
    {
        private bool _authRequest = false;
        private Socket _socket;

        public bool AuthRequest => _authRequest;

        public async Task<bool> Connect(string serverDomain)
        {
            Socket s = GetSocket(serverDomain, 25);
            if (s == null) return false;
            _socket = s;
            string hsResponse = await SendRequestWithResponse(_socket, "EHLO yandex.ru \r\n");
            _authRequest = hsResponse.Contains("AUTH LOGIN");
            return hsResponse.Contains("250");
        }

        public async Task<bool> SendAuth(string username, string password)
        {
            if (_socket == null || !_socket.Connected) return false;
            string response = await SendRequestWithResponse(_socket, "AUTH LOGIN\r\n");
            if (!response.Contains("334")) return false;
            string encodedUsername = Convert.ToBase64String(Encoding.UTF8.GetBytes(username));
            string encodedPassword = Convert.ToBase64String(Encoding.UTF8.GetBytes(password));
            response = await SendRequestWithResponse(_socket, $"{encodedUsername}\r\n");
            if (!response.Contains("334")) return false;
            response = await SendRequestWithResponse(_socket, $"{encodedPassword}\r\n");
            return response.Contains("235");
        }

        public async Task<bool> SendFrom(string from) {
            if (_socket == null || !_socket.Connected) return false;
            string response = await SendRequestWithResponse(_socket, $"MAIL FROM:<{from}>\r\n");
            return response.Contains("250");
        }

        public async Task<bool> SendTo(string to) {
            if (_socket == null || !_socket.Connected) return false;
            string response = await SendRequestWithResponse(_socket, $"RCPT TO:<{to}>\r\n");
            return response.Contains("250");
        }

        public async Task<bool> SendData(string data) {
            if (_socket == null || !_socket.Connected) return false;
            string response = await SendRequestWithResponse(_socket, "DATA \r\n");
            if (!response.Contains("354")) return false;
            StringReader reader = new StringReader(data);
            while (true)
            {
                string str = reader.ReadLine();
                if (str == null) break;
                await SendRequest(_socket, $"{str}\r\n");
            }
            response = await SendRequestWithResponse(_socket, ".\r\n");
            return response.Contains("250");
        }

        public async Task<bool> SendQuit(string to) {
            if (_socket == null || !_socket.Connected) return false;
            string response = await SendRequestWithResponse(_socket, $"QUIT\r\n");
            return response.Contains("250");
        }

        public static Socket GetSocket(string host, int port) {
            Socket s = null;
            var tempSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
            try {
                tempSocket.Connect(host, port);
            }
            catch (SocketException ex) {
                return null;
            }
            if (tempSocket.Connected)
                s = tempSocket;
            return s;
        }

        public static Task<int> ReceiveAsync(Socket socket, byte[] buffer, int offset, int size, SocketFlags socketFlags) {
            var tcs = new TaskCompletionSource<int>(socket);
            socket.BeginReceive(buffer, offset, size, socketFlags, iar =>
            {
                var t = (TaskCompletionSource<int>)iar.AsyncState;
                var s = (Socket)t.Task.AsyncState;
                try { t.TrySetResult(s.EndReceive(iar)); }
                catch (Exception exc) { t.TrySetException(exc); }
            }, tcs);
            return tcs.Task;
        }

        public static async Task SendRequest(Socket socket, string request) {
            Byte[] bytesSent = Encoding.Default.GetBytes(request);
            socket.Send(bytesSent, bytesSent.Length, 0);
            await Task.Delay(100);
        }

        public static async Task<string> SendRequestWithResponse(Socket socket, string request) {
            return await SendRequestWithResponse(socket, socket, request);
        }

        public static async Task<string> SendRequestWithResponse(Socket socketToSend, Socket socketToRecieve, string request) {
            Byte[] bytesReceived = new Byte[256];
            int bytes;
            string response = "";

            await SendRequest(socketToSend, request);

            do {
                bytes = await ReceiveAsync(socketToRecieve, bytesReceived, 0, bytesReceived.Length, 0);
                response = response + Encoding.Default.GetString(bytesReceived, 0, bytes);
                if (bytes < 255) break;
            }
            while (bytes > 0);
            return response;
        }
    }
}