static void Main(String[] args)
    {
        // With dependency injection.
        //var operationHandler = DependencyServiceProvider.Get().GetService<IOperationHandler>();

        var operationHandler = new OperationHandler(new BuySellOperationHandler());

        while (true)
        {
            var argument = Console.ReadLine();
            if (string.IsNullOrEmpty(argument))
            {
                break;
            }
            if (argument.ToUpper() == OperationType.Print)
            {
                operationHandler.Print();
            }
            else
            {
                var operation = OperationsFactory.Get(argument);
                operationHandler.Process(operation);
            }
        }
    }