using System.Collections.Generic;
using static System.Console;

namespace NotificationPattern
{
    class Program
    {
        static void Main()
        {
            var userWithoutEmailAndPassword = new User(null, null);
            var userWithoutPassword = new User("user@gmail.com", null);
            var userWithoutEmail = new User(null, "duvidei_descobrir_minha_senha_HAHAHAHAHA");
            var user = new User("user@gmail.com", "duvidei_descobrir_minha_senha_HAHAHAHAHA");

            if (!userWithoutEmailAndPassword.IsValid())
            {
                WriteLine($"userWithoutEmailAndPassword = {string.Join("; ", userWithoutEmailAndPassword.Notifications)}");
            }

            if (!userWithoutPassword.IsValid())
            {
                WriteLine($"userWithoutPassword = {string.Join("; ", userWithoutPassword.Notifications)}");
            }

            if (!userWithoutEmail.IsValid())
            {
                WriteLine($"userWithoutEmail = {string.Join("; ", userWithoutEmail.Notifications)}");
            }

            if (user.IsValid())
            {
                WriteLine($"User is valid!");
            }

            ReadKey();
        }
    }

    public class Notification
    {
        public Notification(string code, string message)
        {
            Code = code;
            Message = message;
        }

        public string Code { get; }

        public string Message { get; }

        public override string ToString() => Message;
    }

    public abstract class Notifiable
    {
        private List<Notification> _notifications;

        public IReadOnlyCollection<Notification> Notifications => InternalNotifications;

        private List<Notification> InternalNotifications
        {
            get
            {
                if (_notifications == null)
                {
                    _notifications = new List<Notification>();
                }

                return _notifications;
            }
        }

        public void AddNotification(Notification notification)
        {
            if (notification != null)
                InternalNotifications.Add(notification);
        }

        public void ClearNotifications() => _notifications = null;

        public bool IsValid() => InternalNotifications.Count == 0;
    }

    public class User : Notifiable
    {
        public User(string email, string password)
        {
            Email = email;
            Password = password;

            if (string.IsNullOrEmpty(Email))
            {
                AddNotification(new Notification("USU-01", "Email must be informed."));
            }

            if (string.IsNullOrEmpty(Password))
            {
                AddNotification(new Notification("USU-02", "Password must be informed."));
            }
        }

        public string Email { get; private set; }

        public string Password { get; private set; }
    }
}