PaymentsSystem.cs

using System.Text;

namespace PaymentSystems
{
    internal class Program
    {
        private static void Main(string[] args)
        {
            Order order = new(10, 500);

            string secretKey = "waflyaaa";

            MD5HashConverter md5Converter = new();
            SHA1HashConverter sha1Converter = new();

            System1PaymentProvider md5PaymentSystem = new(md5Converter);
            System2PaymentProvider amountMd5PaymentSystem = new(md5Converter);
            System3PaymentProvider sha1SecretKeyPaymentSystem = new(sha1Converter, secretKey);

            Console.WriteLine(md5PaymentSystem.GetPayingLink(order));
            Console.WriteLine(amountMd5PaymentSystem.GetPayingLink(order));
            Console.WriteLine(sha1SecretKeyPaymentSystem.GetPayingLink(order));
        }
    }

    public interface IPaymentSystem
    {
        public string GetPayingLink(Order order);
    }

    public interface IHashConverter
    {
        public string ComputeHash(string data);
    }

    public sealed class Order
    {
        public readonly int Id;
        public readonly int Amount;

        public Order(int id, int amount)
        {
            ArgumentOutOfRangeException.ThrowIfNegative(id);
            ArgumentOutOfRangeException.ThrowIfNegative(amount);

            Id = id;
            Amount = amount;
        }
    }

    public sealed class MD5HashConverter : IHashConverter
    {
        public string ComputeHash(string data)
        {
            using (System.Security.Cryptography.MD5 md5 = System.Security.Cryptography.MD5.Create())
            {
                byte[] bytes = Encoding.ASCII.GetBytes(data);
                byte[] hashBytes = md5.ComputeHash(bytes);
                return Convert.ToHexString(hashBytes);
            }
        }
    }

    public sealed class SHA1HashConverter : IHashConverter
    {
        public string ComputeHash(string data)
        {
            using (System.Security.Cryptography.SHA1 sha1 = System.Security.Cryptography.SHA1.Create())
            {
                byte[] bytes = Encoding.ASCII.GetBytes(data);
                byte[] hashBytes = sha1.ComputeHash(bytes);
                return Convert.ToHexString(hashBytes);
            }
        }
    }

    public abstract class PaymentSystem : IPaymentSystem
    {
        protected IHashConverter Converter;

        public PaymentSystem(IHashConverter converter)
        {
            Converter = converter ?? throw new ArgumentNullException(nameof(converter));
        }

        public abstract string GetPayingLink(Order order);
    }

    public sealed class System1PaymentProvider : PaymentSystem
    {
        private readonly string _link = "pay.system1.ru/order?amount=12000RUB&hash=";

        public System1PaymentProvider(IHashConverter converter) : base(converter)
        {
        }

        public override string GetPayingLink(Order order)
        {
            return _link + Converter.ComputeHash(order.Id.ToString());
        }
    }

    public sealed class System2PaymentProvider : PaymentSystem
    {
        private readonly string _link = "order.system2.ru/pay?hash=";

        public System2PaymentProvider(IHashConverter converter) : base(converter)
        {
        }

        public override string GetPayingLink(Order order)
        {
            return _link + Converter.ComputeHash(order.Id.ToString() + order.Amount);
        }
    }

    public sealed class System3PaymentProvider : PaymentSystem
    {
        private readonly string _link = "system3.com/pay?amount=12000&curency=RUB&hash=";
        private readonly string _secretKey;

        public System3PaymentProvider(IHashConverter converter, string secretKey) : base(converter)
        {
            if (string.IsNullOrEmpty(secretKey))
                throw new ArgumentNullException(nameof(secretKey));

            _secretKey = secretKey;
        }

        public override string GetPayingLink(Order order)
        {
            return _link + Converter.ComputeHash(order.Id.ToString() + order.Amount + _secretKey);
        }
    }
}