OCP.cs

namespace OCP
{
    internal class Program
    {
        private static void Main()
        {
            PaymentSystemFactory paymentSystemFactory = new PaymentSystemFactory();

            var orderForm = new OrderForm();

            try
            {
                IEnumerable<string> availableSystems = paymentSystemFactory.AvailablePaymentSystemIds;

                string systemId = orderForm.ShowForm(availableSystems);

                Func<IPaymentSystem> paymentSystemFactoryMethod = paymentSystemFactory.GetPaymentSystemFactory(systemId);

                var paymentHandler = new PaymentService(paymentSystemFactoryMethod);

                paymentHandler.ProcessPayment();
                paymentHandler.ShowPaymentResult();
            }
            catch (Exception exception)
            {
                Console.WriteLine($"Ошибка: {exception.Message}");
            }
        }
    }

    public class PaymentSystemFactory
    {
        private readonly Dictionary<string, Func<IPaymentSystem>> _paymentSystemFactories;

        public PaymentSystemFactory()
        {
            _paymentSystemFactories = new Dictionary<string, Func<IPaymentSystem>>();

            InitializePaymentSystemFactories();
        }

        public IEnumerable<string> AvailablePaymentSystemIds
        {
            get { return _paymentSystemFactories.Keys; }
        }

        public Func<IPaymentSystem> GetPaymentSystemFactory(string systemId)
        {
            if (string.IsNullOrWhiteSpace(systemId))
            {
                throw new ArgumentException("Идентификатор платежной системы не может быть пустым или содержать только пробелы.", nameof(systemId));
            }

            if (_paymentSystemFactories.TryGetValue(systemId, out Func<IPaymentSystem> factory))
            {
                return factory;
            }

            throw new NotSupportedException($"Платежная система с идентификатором '{systemId}' не поддерживается.");
        }

        private void InitializePaymentSystemFactories()
        {
            _paymentSystemFactories.Add(PaymentSystemIdentifiers.Qiwi, () => new QiwiPaymentSystem());
            _paymentSystemFactories.Add(PaymentSystemIdentifiers.WebMoney, () => new WebMoneyPaymentSystem());
            _paymentSystemFactories.Add(PaymentSystemIdentifiers.Card, () => new CardPaymentSystem());
            _paymentSystemFactories.Add(PaymentSystemIdentifiers.PayPal, () => new PayPalPaymentSystem());
        }
    }

    public static class PaymentSystemIdentifiers
    {
        public const string Qiwi = "qiwi";
        public const string WebMoney = "webmoney";
        public const string Card = "card";
        public const string PayPal = "paypal";
    }

    public interface IPaymentSystem
    {
        public string Id { get; }
        public void ProcessPayment();
        public void CheckPayment();
    }

    public class QiwiPaymentSystem : IPaymentSystem
    {
        public string Id => PaymentSystemIdentifiers.Qiwi;

        public void ProcessPayment()
        {
            Console.WriteLine("Перевод на страницу QIWI...");
        }

        public void CheckPayment()
        {
            Console.WriteLine("Проверка платежа через QIWI...");
        }
    }

    public class WebMoneyPaymentSystem : IPaymentSystem
    {
        public string Id => PaymentSystemIdentifiers.WebMoney;

        public void ProcessPayment()
        {
            Console.WriteLine("Вызов API WebMoney...");
        }

        public void CheckPayment()
        {
            Console.WriteLine("Проверка платежа через WebMoney...");
        }
    }

    public class CardPaymentSystem : IPaymentSystem
    {
        public string Id => PaymentSystemIdentifiers.Card;

        public void ProcessPayment()
        {
            Console.WriteLine("Вызов API банка эмитента карты...");
        }

        public void CheckPayment()
        {
            Console.WriteLine("Проверка платежа через карту...");
        }
    }

    public class PayPalPaymentSystem : IPaymentSystem
    {
        public string Id => PaymentSystemIdentifiers.PayPal;

        public void CheckPayment()
        {
            Console.WriteLine("Перевод на страницу PayPal...");
        }

        public void ProcessPayment()
        {
            Console.WriteLine("Проверка платежа через PayPal...");
        }
    }

    public class PaymentService
    {
        private readonly IPaymentSystem _paymentSystem;

        public PaymentService(Func<IPaymentSystem> paymentSystemFactory)
        {
            if (paymentSystemFactory == null)
            {
                throw new ArgumentNullException("Фабрика платёжных систем не может быть null.", nameof(paymentSystemFactory));
            }

            _paymentSystem = paymentSystemFactory();
        }

        public void ProcessPayment()
        {
            _paymentSystem.ProcessPayment();
        }

        public void ShowPaymentResult()
        {
            Console.WriteLine($"Вы оплатили с помощью {_paymentSystem.Id}");

            _paymentSystem.CheckPayment();

            Console.WriteLine("Оплата прошла успешно!");
        }
    }

    public class OrderForm
    {
        public string ShowForm(IEnumerable<string> paymentSystemId)
        {
            if (paymentSystemId == null || paymentSystemId.Any() == false)
            {
                throw new ArgumentException("Список платёжных систем не может быть пустым.", nameof(paymentSystemId));
            }

            Console.WriteLine("Мы принимаем: " + string.Join(", ", paymentSystemId));
            Console.WriteLine("Какой системой вы хотите совершить оплату?");

            string systemId = Console.ReadLine();

            if (string.IsNullOrWhiteSpace(systemId))
            {
                throw new ArgumentException("Идентификатор платежной системы не может быть пустым.", nameof(systemId));
            }

            return systemId.Trim().ToLower();
        }
    }
}