Level Level Design: Vending Machine System

Design a vending machine system that allows users to select a product from a list of available items and purchase it by inserting cash.

Functional Requirements

The vendoring machine should support for the following operations:

1. Display all available products along with important details like name, price and the quantity available in stock.

2. Allow users to select a product and insert coins or notes as payment. Once the inserted amount is sufficient, the machine should dispense the product and return the change.

3. Manage product inventory by updating the available stock after every successful purchase to ensure accurate inventory tracking.

Primary Use Cases

The primary use case for the vending machine system is to allow users to select a product and purchase it by inserting coins or notes as payment. Here's how its workflow looks like:

1. User selects a Product and inserts coins or notes as Payment.

2. The VendingMachine validates the insertedAmount against the productPrice and dispenses the Product and returns the change if the Payment is greater than the productPrice.

3. Finally, the VendingMachine updates the Inventory after every successful purchase to keep track of the available stock.

Object Model Design

The primary entities in the system include:

VendingMachine

Serves as the central controller for the system, handling product selection and dispensing, managing product inventory and processing cash payments.

To prevent the VendingMachine from becoming a God Object (a class with too many responsibilities), it can act as a facade and delegate the responsibility of managing the product inventory and processing cash payments to specialized components.

class VendingMachine {

    private Inventory inventory;

    public void selectProduct(Product product) {

    }

    public void processPayment(Payment payment) {

    }

    public void dispenseProduct(Product product, int quantity) {
        inventory.removeProduct(product, quantity);
    }

}

The VendingMachine should provide feedback at each stage to guide the user. For instance, it should display messages like "Insert money to proceed", "Select a product", or "Please collect your change". To handle this, we can use the State Pattern. ????

Inventory

class Inventory {

    private Map<Product, Integer> stock;
    
    public void addProduct(Product product, int quantity) {
        stock.put(product, stock.getOrDefault(product, 0) + quantity);
    }

    public void removeProduct(Product product, int quantity) {
        if (stock.containsKey(product)) {
            int currentStock = stock.get(product);
            if (currentStock >= quantity) {
                stock.put(product, currentStock - quantity);
            } else {
                throw new InsufficientStockException();
            }
        } else {
            throw new ProductNotFoundException();
        }
    }
}

Product

class Product {

    private String name;
    private double price;


    public Product(String name, double price) {
        this.name = name;
        this.price = price;
    }

    public double getPrice() {
        return price;
    }
    
}