using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var proxy = new CalculatorProxy();

        DoSomeRandomCalculations(proxy);

        Console.WriteLine($"Operations: {proxy.ResultHistory.Count}\n");

        Console.WriteLine("Results:");

        foreach(var result in proxy.ResultHistory)

        {

            Console.WriteLine(result);

        }

    }

    private static void DoSomeRandomCalculations(ICalculator calculator)

    {

        var random = new Random();

        foreach(var _ in Enumerable.Range(0, random.Next(5, 15)))

        {

            var operation = random.Next(2);

            var valueForOperation = random.Next(int.MaxValue);

            switch (operation)

            {

                case 0:

                    calculator.Add(valueForOperation);

                    break;

                case 1:

                    calculator.Subtract(valueForOperation);

                    break;

            }

        }

    }

}

​

public interface ICalculator

{

    int Result { get; }

    void Add(int value);

    void Subtract(int value);

}

​

public class RealCalculator : ICalculator

{

    public int Result { get; private set; }

    public void Add(int value)

    {

        this.Result += value;

    }

    public void Subtract(int value)

    {

        this.Result -= value;

    }

}

​

public class CalculatorProxy : ICalculator

{

    private readonly RealCalculator realCalculator;

    public CalculatorProxy()

    {

        this.realCalculator = new RealCalculator();

        this.ResultHistory = new List<int>();

    }

    public int Result

    {

        get

        {

            return this.realCalculator.Result;

        }

    }

    public List<int> ResultHistory { get; }

    public void Add(int value)

    {

        this.realCalculator.Add(value);

        this.ResultHistory.Add(this.realCalculator.Result);

    }

    public void Subtract(int value)

    {

        this.realCalculator.Subtract(value);

        this.ResultHistory.Add(this.realCalculator.Result);

    }

}