Final

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;

namespace ConsoleApp1
{
    class Program
    {
        static TODOList list = null;
        static void Main(string[] args)
        {
            Menu menu = new Menu(() =>
            {
                if (list != null)
                {
                    Console.WriteLine("=> Work with: " + list.Path);
                }
                return "";
            });
            menu.Add("newtodo", "create new todo file", () =>
            {
                Console.WriteLine("Name:");
                list = TODOList.Create(Console.ReadLine());
                return "Success";
            });
            menu.Add("addentity", "create new todo in todo list", () =>
            {
                OpenList().Add(NewEnityDialog());
                return "Success";
            });
            menu.Add("showtodo", "print todo by id", () =>
            {
                try
                {
                    Console.WriteLine(EntityById(OpenList()).ToString());
                    return "Success";
                }
                catch (Exception e)
                {
                    Console.WriteLine(e);
                    return "Fail";
                }
            });
            menu.Add("edittodo", "edit todo by id", () =>
            {
                try
                {
                    TODOList l = OpenList();
                    TODOEntity e = EntityById(l);
                    Console.WriteLine(e.ToString());
                    TODOEntity newEntity = NewEnityDialog();
                    newEntity.ID = e.ID;
                    
                    l.Update(newEntity);
                    l.Save();
                    return "Success";
                }
                catch (Exception e)
                {
                    Console.WriteLine(e);
                    return "Fail";
                }
            });
            menu.Add("deletetodo", "remove todo by id from list", () =>
            {
                try
                {
                    TODOList l = OpenList();
                    TODOEntity e = EntityById(l);
                    Console.WriteLine(e.ToString());
                    l.Remove(e);
                    l.Save();
                    return "Success";
                }
                catch (Exception e)
                {
                    Console.WriteLine(e);
                    return "Fail";
                }
            });
            menu.Add("showtasks", "show all task", () =>
            {
                try
                {
                    OpenList().Print();
                    return "Success";
                }
                catch (Exception e)
                {
                    Console.WriteLine(e);
                    return "Fail";
                }
            });
            menu.Start();
        }

        static public TODOList OpenList()
        {
            if (list == null)
            {
                Console.WriteLine("File name:");
                list = TODOList.Open(Console.ReadLine());
                return list;
            }
            return list;
        }
        static public TODOEntity EntityById(TODOList list)
        {
            Console.WriteLine("ID:");
            int.TryParse(Console.ReadLine(), out int id);
            if (id == 0)
            {
                throw new Exception("ID must a number");
            }
            return list.ReadById(id);
        }
        static public TODOEntity NewEnityDialog()
        {
            Console.WriteLine("Name:");
            string name = Console.ReadLine();
            Console.WriteLine("Status:");
            string status = Console.ReadLine();
            Console.WriteLine("Description:");
            string desc = Console.ReadLine();
            return new TODOEntity(0, name, status, desc);
        }
    }
}

class TODOList
{
    public string Path;
    public List<TODOEntity> List = new List<TODOEntity>();
    public TODOList(string path)
    {
        Path = path;
    }
    public static TODOList Create(string path)
    {
        if (!File.Exists(path))
        {
            File.Create(path).Close();
            return new TODOList(path);
        }
        throw new Exception("File exist");
    }
    public static TODOList Open(string path)
    {
        if (!File.Exists(path))
        {
            throw new Exception("File not exist");
        }
        TODOList list = new TODOList(path);
        list.Read();
        return list;
    }
    public void Add(string Name, string Status, string Description)
    {

        int ID = List.Count == 0 ? 1 : List.Last().ID + 1;
        List.Add(new TODOEntity(ID, Name, Status, Description));
    }
    public void Add(TODOEntity entity)
    {
        Add(entity.Name, entity.Status, entity.Description);
    }
    public void Read()
    {
        using (StreamReader sr = new StreamReader(Path))
        {
            while (!sr.EndOfStream)
            {
                List.Add(TODOEntity.FromString(sr.ReadLine()));
            }
        }
    }
    public void Save()
    {
        using (StreamWriter sw = new StreamWriter(Path, false))
        {
            foreach (TODOEntity entity in List)
            {
                sw.WriteLine(entity.ToString());
            }
        }
    }

    public TODOEntity ReadById(int id)
    {
        return List.Where((x) => x.ID == id).Single();
    }

    public void Print()
    {
        foreach(TODOEntity e in List)
        {
            Console.WriteLine(e);
        }
    }

    public void Remove(TODOEntity e)
    {
        List.Remove(e);
        Save();
    }

    public void Update(TODOEntity e)
    {
        TODOEntity u = List.Where(x => x.ID == e.ID).Single();
        u.Name = e.Name;
        u.Status = e.Status;
        u.Description = e.Description;
        Save();
    }
}
class TODOEntity
{
    public int ID;
    public string Status;
    public string Name;
    public string Description;
    private const char sep = '|';

    public TODOEntity(int id, string name, string status, string desc)
    {
        ID = id;
        Name = name;
        Status = status;
        Description = desc;
    }

    public override string ToString()
    {
        return ID.ToString() + sep + Name + sep + Status + sep + Description;
    }

    public static TODOEntity FromString(string str)
    {
        string[] vs = str.Split(sep);
        return new TODOEntity(int.Parse(vs[0]), vs[1], vs[2], vs[3]);
    }
}

delegate string Call();

class Menu
{
    List<Element> Elements = new List<Element>();
    public string ExitCommand = "exit";
    public Call Callback;

    public Menu(Call cb)
    {
        Callback = cb;
    }
    public void Start()
    {
        Console.WriteLine("------------------");
        Console.WriteLine("List of available commands:");
        if (Callback != null)
        {
            Callback();
        }
        foreach (Element e in Elements)
        {
            Console.WriteLine(e);
        }
        Console.WriteLine("Write '"+ExitCommand+"' for close the program.");
        string cmd = Console.ReadLine();
        if (cmd == ExitCommand)
        {
            Environment.Exit(0);
        }
        Console.WriteLine(Exec(cmd));
        Start();
    }
    public void Add(string name, string desc, Call call)
    {
        Elements.Add(new Element(name, desc, call));
    }

    public string Exec(string param)
    {
        foreach (Element el in Elements)
        {
            if (el.Name == param)
            {
                return el.Callback();
            }
        }
        return "";
    }
}

class Element
{
    public string Description;
    public string Name;
    public Call Callback;
    public Element(string name, string desc, Call call)
    {
        Description = desc;
        Name = name;
        Callback = call;
    }
    public override string ToString()
    {
        return Name + " — " + Description;
    }
}