using System;

using System.Collections.Generic;

using System.Linq;

​

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        Product p1 = new Product("CD1234", 10);

        Product p2 = new Product("T1020", 20);

        var products = new List<Product>();

        products.Add(p1);

        products.Add(p2);

        Stock s1 = new Stock("CD1234", 100);

        Stock s2 = new Stock("T1020", 200);

        var stocks = new List<Stock>();

        stocks.Add(s1);

        stocks.Add(s2);

        // DoubleStocks(stocks);

        List<Stock> doubleStocks = DoubleThings<Stock>(stocks);

        PrintStocks(doubleStocks);

        List<Product> doubleProducts = DoubleThings<Product>(products);

        // PrintStocks(doubleStocks);

    }

    public static List<T> DoubleThings<T>(List<T> stocks) where T : class, new()

    {

        var result = new List<T>();

        foreach(var s in stocks){

            Console.WriteLine(s.GetType());

            if(s is Stock stock){

                stock.OnHand *= 2;

                Console.WriteLine($"I am stock {stock.Sku} {stock.OnHand}");

                result.Add((T)(object)stock);

            }else if(s is Product product){

                product.Price *= 2;

                Console.WriteLine($"I am product {product.Sku} {product.Price}");

                result.Add((T)(object)product);

            }

        }

        return result;

    }

    public static List<Stock> DoubleStocks(List<Stock> stocks)

    {

        var result = new List<Stock>();

        foreach(var s in stocks){

            s.OnHand *= 2;

            Console.WriteLine($"I am {s.Sku} {s.OnHand}");

            result.Add(s);

        }

        return result;

    }

    public static void PrintStocks(List<Stock> stocks)

    {

        Console.WriteLine($"\nPRINTING STOCKS:");

        foreach(var s in stocks){

            Console.WriteLine($"I am {s.Sku} {s.OnHand}");

        }

    }

    public class Product : ISku

    {

        public string Sku { get; set; }

        public int Price { get; set; }

        public Product(){}

        public Product(string sku, int price)

        {

            Sku = sku;

            Price = price;

        }

    }

    public class Stock : ISku

    {

        public string Sku { get; set; }

        public int OnHand { get; set; }

        public Stock(){}

        public Stock(string sku, int onHand)

        {

            Sku = sku;

            OnHand = onHand;

        }

    }

    interface ISku

    {

        string Sku { get; set; }

    }

}