/// <summary>
        /// Adding a product into order for customer can order multiple items
        /// </summary>
        /// <param name="product"> The customer product purchase </param>
        /// <param name="amount"> The number of product to be purchased </param>
        public bool AddProduct(Product product, int amount)
        {
            // SPECIAL CASE TO CONSIDER: IF THE RESTRICTED AMOUNT IS LESS THAN OR EQUAL TO 0, IT MEANS THERE IS NO LIMIT.
            if (product == null || amount <= 0 || (product.RestrictedAmount > 0 && product.RestrictedAmount < amount))
            {
                return(false);
            }

            ProductDetail.Add(product.Name, amount);
            ProductPrice.Add(product.Name, Math.Round(product.Price, 2));
            return(true);
        }