Select a pattern for the given scenario, and design your suggested solution. Provide an explanatory justification

Consider Amazon online shopping application where the users can login and purchase various items. There are two people, Ahmed and Ali, trying to buy a specific phone but it is out of stock now. There is a guide option “notify me when product is available”. Customers can register on that; receive a notification message when this product is available. Select a pattern for the given scenario, and design your suggested solution. Provide an explanatory justification. Also, indicate the category of the selected pattern. design patterns