Challenge

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

namespace Challenge1
{
    class Program
    {
        static Dictionary<string, User> users = new Dictionary<string, User>();
        static void Main(string[] args)
        {
            Loadusers();
            Login();
        }
        static void Login()
        {
            Console.WriteLine("Username:");
            string username = Console.ReadLine();
            Console.WriteLine("Password:");
            string password = Console.ReadLine();
            foreach(KeyValuePair<string, User> u in users)
            {
                if (username == u.Value.Username && password == u.Value.Password)
                {
                    Console.WriteLine("Logged in as: " + username);
                    Commands();
                }
            }
            Console.WriteLine("Wrong username or password entered.");
            Login();

        }
        static void Loadusers()
        {
            if (File.Exists(AppDomain.CurrentDomain.BaseDirectory + "/users.txt"))
            {
                FileStream file = File.OpenRead(AppDomain.CurrentDomain.BaseDirectory + "/users.txt");
                TextReader reader = new StreamReader(file);
                int length = Int32.Parse(reader.ReadLine());
                users = new Dictionary<string, User>();
                for (int i=0; i<length; i++)
                {
                    string line = reader.ReadLine();
                    string[] parts = line.Split(';');
                    users.Add(parts[0],new User() { Username =parts[0], Password=parts[1], });
                }
                reader.Close();
            } else
            {
                users.Add("admin", new User() { Username = "admin", Password = "123", });
            }
        }
        static void Saveusers()
        {
            if (File.Exists(AppDomain.CurrentDomain.BaseDirectory + "/users.txt"))
            {
                File.Delete(AppDomain.CurrentDomain.BaseDirectory + "/users.txt");
            }
            FileStream file = File.OpenWrite(AppDomain.CurrentDomain.BaseDirectory + "/users.txt");
            TextWriter writer = new StreamWriter(file);
            writer.WriteLine(users.Count());
            foreach (KeyValuePair<string,User> u in users)
            {
                writer.WriteLine(u.Value.Username + ";" + u.Value.Password);
            }
            writer.Flush();
            writer.Close();
        }
        static void Commands()
        {
            string input = Console.ReadLine();
            switch(input)
            {
                default:
                    Console.WriteLine("Wrong command!");
                    Commands();
                    break;
                case "commands":
                    Console.WriteLine("adduser | showusers | deleteusers | saveusers | exit |");
                    Commands();
                    break;
                case "adduser":
                    Console.WriteLine("Enter Username:");
                    string username = Console.ReadLine();
                    Console.WriteLine("Enter password:");
                    string password = Console.ReadLine();
                    users.Add(username,new User() { Username = username, Password = password, });
                    Saveusers();
                    Console.WriteLine("User " + username + " has been added!");
                    Commands();
                    break;
                case "showusers":
                    Showusers();
                    Commands();
                    break;
                case "deleteuser":
                    Console.WriteLine("Enter the Username to be deleted");
                    Showusers();
                    input = Console.ReadLine();
                    if (users.ContainsKey(input))
                    {
                        users.Remove(input);
                        Saveusers();
                        Console.WriteLine("User with Username: " + input + " has been deleted.");
                    } else
                    {
                        Console.WriteLine("Wrong username entered.");
                    }
                    Commands();
                    break;
                case "exit":
                    break;
            }
        }
        static void Showusers()
        {
            foreach (KeyValuePair <string,User> u in users)
            {
                Console.WriteLine("Username: " + u.Value.Username + " Password: " + u.Value.Password);
            }
        }
    }
}