StateKeeper.cs

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Telegram.Bot;
using Telegram.Bot.Types;
using Telegram.Bot.Types.Enums;
using Telegram.Bot.Types.ReplyMarkups;

namespace Tester
{
    class Program
    {

        private static readonly ITelegramBotClient telegramBotClient = 
            new TelegramBotClient("botToken");

        private static readonly ConcurrentDictionary<int, ConversationState> state =
            new ConcurrentDictionary<int, ConversationState>();

        private static readonly ConcurrentDictionary<int, UserInformation> userInfo =
            new ConcurrentDictionary<int, UserInformation>();

        #region ConstantStr

        private static readonly string[] Genders = new[] { "👩", "🧑" };
        private static readonly string[] Colors = new[] { "Red", "Blue", "Green", "Yellow", "Brown", "Black" };

        #endregion

        public static void Main(string[] args)
        {

            telegramBotClient.OnUpdate += async (sender, e) =>
            {
                await OnUpdate(e.Update);
            };

            telegramBotClient.StartReceiving(new[] { UpdateType.Message });

            Console.ReadLine();

        }

        private static async Task OnUpdate(Update up)
        {
            Message message = up.Message;
            int userid = message.From.Id;

            if (state.ContainsKey(userid))
            {
                if(message.Text == "back")
                {
                    state[userid]--;

                    switch (state[userid])
                    {
                        case ConversationState.WitingForGender:
                            {
                                await telegramBotClient.SendTextMessageAsync(
                                    userid,
                                    $"Select your gender",
                                    replyMarkup: new ReplyKeyboardMarkup(GetButtons(Genders, false), true));

                                break;
                            }
                        case ConversationState.WitingForName:
                            {
                                await telegramBotClient.SendTextMessageAsync(
                                    userid,
                                    $"Enter your name:",
                                    replyMarkup: new ReplyKeyboardMarkup(GetButtons(), true));

                                break;
                            }
                        case ConversationState.WitingForFamilyname:
                            {
                                await telegramBotClient.SendTextMessageAsync(
                                    userid,
                                    $"Enter your familyname",
                                    replyMarkup: new ReplyKeyboardMarkup(GetButtons(), true));

                                break;
                            }
                        case ConversationState.WitingForColor:
                            {
                                await telegramBotClient.SendTextMessageAsync(
                                    userid,
                                    $"Select colors",
                                    replyMarkup: new ReplyKeyboardMarkup(GetButtons(Colors, true), true));

                                break;
                            }
                    }

                    return;
                }

                switch (state[userid])
                {
                    case ConversationState.WitingForGender:
                        {
                            if (!Genders.Any(x => x == message.Text))
                            {
                                _ = await telegramBotClient.SendTextMessageAsync(
                                    userid,
                                    "Invalid gender!",
                                    replyMarkup: new ReplyKeyboardMarkup(GetButtons(Genders, false), true));

                                return;
                            }

                            await telegramBotClient.SendTextMessageAsync(
                                userid,
                                $"Ok you selected {message.Text}, now what's your name?",
                                replyMarkup: new ReplyKeyboardMarkup(GetButtons(), true));

                            state[userid] = ConversationState.WitingForName;

                            userInfo[userid].Gender = message.Text == "🧑";

                            return;
                        }

                    case ConversationState.WitingForName:
                        {
                            await telegramBotClient.SendTextMessageAsync(
                                userid,
                                $"Ok your name is {message.Text}, now what's your familyname?",
                                replyMarkup: new ReplyKeyboardMarkup(GetButtons(), true));

                            state[userid] = ConversationState.WitingForFamilyname;

                            userInfo[userid].Name = message.Text;

                            return;
                        }

                    case ConversationState.WitingForFamilyname:
                        {

                            await telegramBotClient.SendTextMessageAsync(
                                userid,
                                $"Ok your familyname is {message.Text}, now what's your Favorite colors?",
                                replyMarkup: new ReplyKeyboardMarkup(GetButtons(Colors), true));

                            state[userid] = ConversationState.WitingForColor;

                            userInfo[userid].Familyname = message.Text;

                            return;
                        }

                    case ConversationState.WitingForColor:
                        {
                            if (!Colors.Any(x => x == message.Text))
                            {
                                _ = await telegramBotClient.SendTextMessageAsync(
                                    userid,
                                    "Invalid color!",
                                    replyMarkup: new ReplyKeyboardMarkup(GetButtons(Colors), true));

                                return;
                            }

                            await telegramBotClient.SendTextMessageAsync(
                                userid,
                                $"Ok your Favorite colors is {message.Text}",
                                replyMarkup: new ReplyKeyboardMarkup(GetButtons(), true));

                            state[userid] = ConversationState.Done;

                            userInfo[userid].FavoriteColors = message.Text;

                            await telegramBotClient.SendTextMessageAsync(
                                userid,
                                userInfo[userid].ToString(),
                                replyMarkup: new ReplyKeyboardRemove());

                            return;
                        }

                    case ConversationState.Done:
                        {
                            await telegramBotClient.SendTextMessageAsync(
                                userid,
                                $"You are done here!",
                                replyMarkup: new ReplyKeyboardMarkup(GetButtons(), true));

                            await telegramBotClient.SendTextMessageAsync(
                                userid,
                                userInfo[userid].ToString(),
                                replyMarkup: new ReplyKeyboardRemove());

                            return;
                        }
                    default:
                        break;
                }
            }
            else
            {
                await telegramBotClient.SendTextMessageAsync(
                    userid,
                    "Please select your gender",
                    replyMarkup: new ReplyKeyboardMarkup(GetButtons(Genders, false), true)
                );

                userInfo.TryAdd(userid, new UserInformation(userid));

                state.TryAdd(userid, ConversationState.WitingForGender);
            }
        }


        private static IEnumerable<IEnumerable<KeyboardButton>> GetButtons(string[] vs = null,
            bool back = true)
        {
            if (vs == null)
            {
                return new KeyboardButton[][]
                {
                    new KeyboardButton[]
                    {
                        new KeyboardButton("back")
                    }
                };
            }

            var arraylenght = back ? vs.Length + 1 : vs.Length;

            KeyboardButton[][] buttons = new KeyboardButton[arraylenght][];

            for (int i = 0; i < vs.Length; i++)
            {
                buttons[i] = new KeyboardButton[] { new KeyboardButton(vs[i]) };
            }

            if (back)
            {
                buttons[^1] = new KeyboardButton[] { new KeyboardButton("back") };
            }

            return buttons;
        }

        private enum ConversationState
        {
            WitingForGender = 1,
            WitingForName,
            WitingForFamilyname,
            WitingForColor,
            Done
        }

        private class UserInformation
        {
            public override string ToString()
            {
                return $"{Name} {Familyname}\nGender: {Gender}\nColor: {FavoriteColors}";
            }

            public UserInformation(int userid)
            {
                Userid = userid;
            }

            public int Userid { get; set; }

            public bool Gender { get; set; }

            public string Name { get; set; }

            public string Familyname { get; set; }

            public string FavoriteColors { get; set; }
        }
    }
}