Home work - anarchy in the hospital

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

namespace Home_Work
{
    class Program
    {
        static void Main()
        {
            Database database = new Database();
            database.Work();
        }
    }

    class Database
    {
        private List<Patient> _patients;

        public Database()
        {
            _patients = new List<Patient>();
            Fill();
        }

        public void Work()
        {
            bool isWorking = true;
            List<Patient> patients = _patients;
            int number;

            while (isWorking == true)
            {
                Console.WriteLine("Больные: ");
                ShowSelection(patients);
                Console.WriteLine("\n1. Отсортировать по ФИО.\n2. Отсортировать по возрасту.\n3. Отсортировать по болезни.\n4. Выход.");
                Console.Write("Введите команду: ");
                number = GetNumber();

                switch (number)
                {
                    case 1:
                        patients = GetSortByFullName();
                        break;

                    case 2:
                        patients = GetSortByAge();
                        break;

                    case 3:
                        patients = GetSortByDisease();
                        break;

                    case 4:
                        isWorking = false;
                        break;

                    default:
                        Console.WriteLine("Неверная команда.");
                        break;
                }

                Console.ReadKey();
                Console.Clear();
            }
        }

        private int GetNumber()
        {
            bool isConverted = false;
            int number = 0;
            string userInput;

            while (isConverted == false)
            {
                userInput = Console.ReadLine();
                isConverted = Int32.TryParse(userInput, out number);
            }

            return number;
        }

        private List<Patient> GetSortByFullName()
        {
            return _patients.OrderBy(patient => patient.FullName).ToList();
        }

        private List<Patient> GetSortByAge()
        {
            return _patients.OrderBy(patient => patient.Age).ToList();
        }

        private List<Patient> GetSortByDisease()
        {
            Disease disease = GetDisease();

            return _patients.Where(patient => patient.Disease == disease).ToList();
        }

        private Disease GetDisease()
        {
            bool isSelected = false;
            int nationalCount = Enum.GetNames(typeof(Disease)).Length;
            int number = 0;

            for (int i = 0; i < nationalCount; i++)
            {
                Console.WriteLine($"{i + 1}. {(Disease)i}.");
            }

            while (isSelected == false)
            {
                number = GetNumber() - 1;

                if (number >= 0 && number < nationalCount)
                {
                    isSelected = true;
                }
                else
                {
                    Console.WriteLine("Введите номер болезни.");
                }
            }

            return (Disease)number;
        }

        private void ShowSelection(List<Patient> criminals)
        {
            foreach (Patient patient in _patients)
            {
                patient.ShowInfo();
            }
        }

        private void Fill()
        {
            _patients.Add(new Patient("Черёмушко Алексей Алексеевич", (Disease)0));
            _patients.Add(new Patient("Чер Дмитрий Алексеевич", (Disease)0));
            _patients.Add(new Patient("Альанах Алексей Дмитриевич", (Disease)1));
            _patients.Add(new Patient("Вассерман Анатолий Акашанович", (Disease)2));
            _patients.Add(new Patient("Шерлок Ди Холмс", (Disease)0));
            _patients.Add(new Patient("Макуночи Но Ипо", (Disease)1));
            _patients.Add(new Patient("Грозный Иван Васильевич", (Disease)1));
            _patients.Add(new Patient("Борн Дмитрий Анатольевич", (Disease)0));
            _patients.Add(new Patient("Навальный Владимир Владиславович", (Disease)2));
            _patients.Add(new Patient("Евпатий Калодратий", (Disease)0));
            _patients.Add(new Patient("Никто", (Disease)1));
            _patients.Add(new Patient("Андерсон Джон Викторович", (Disease)0));
            _patients.Add(new Patient("Самураев Душнила Тёмович", (Disease)2));
        }
    }

    class Patient
    {
        private static Random _random;
        private string _fullName;
        private int _age;
        private Disease _disease;

        static Patient()
        {
            _random = new Random();
        }

        public Patient(string fullName, Disease disease)
        {
            int maxAge = 100;

            _fullName = fullName;
            _disease = disease;
            _age = _random.Next(maxAge);
        }

        public string FullName => _fullName;
        public int Age => _age;
        public Disease Disease => _disease;

        public void ShowInfo()
        {
            Console.WriteLine($"{_fullName}. Возраст: {_age}. Болезнь: {_disease}.");
        }
    }

    enum Disease
    {
        Covid19,
        AIDS,
        Pneumonia
    }
}