using System;

using System.Collections.Generic;   

​

public class Program

{

    public static void Main()

    {

        List<string> toDoContainer = new List<string>();

        bool isRunnng = true;

        int counter = 0;

        Console.WriteLine("Hello!");

        Options();

        while(isRunnng)

        {

            string userOption = Console.ReadLine().ToLower();

            switch(userOption)

            {

                case "s":

                    if(toDoContainer.Count == 0)

                    {

                        Console.WriteLine("No TODOs have been added yet!");

                        Options();

                        Console.WriteLine("Hello!");

                    }

                    else 

                    {

                        foreach(var item in toDoContainer)

                        {

                            counter++;

                            Console.WriteLine($"\n{counter}.{item}");

                        }

                        Options();

                    }

                break;

                case "a":

                    Console.WriteLine($"Enter the TODO description:");

                    string toDo = Console.ReadLine();

                    if(toDo == "")

                    {

                        Console.WriteLine($"The description cannot be empty.");

                        Console.WriteLine($"Enter the TODO description:");

                    }

                    else

                    {

                        if(!toDoContainer.Contains(toDo))

                        {

                            Console.WriteLine($"TODO successfully added: [{toDo}]");

                            toDoContainer.Add(toDo);

                        } 

                        else 

                        {

                            Console.WriteLine($"The description must be unique..");

                            Console.WriteLine($"Enter the TODO description");

                        }

                    }

                break;

                case "e":

                    isRunnng = false;

                break;

                default:

                    Console.WriteLine("Incorrect input!");

                    Options();

                break;

            }

        }

    }

    static void Options()

    {

        Console.WriteLine("\nWhat do you want to do?");

        Console.WriteLine("[S]ee all TODOs");

        Console.WriteLine("[A]dd a TODO");

        Console.WriteLine("[R]emove a TODO");

        Console.WriteLine("[E]xit");

    }

}