Food Ordering System: OOD for Menu, Cart, and Order Lifecycle Management

Question

## Round 1 - Coding

## Problem

Design and implement a food ordering system for a single restaurant. Your system must support:

1. A `Menu` that holds `Item(name, price, category, available)`. Items can be enabled/disabled.
2. A `Cart` per user: `add_item`, `remove_item`, `update_quantity`, `get_total`.
3. An `Order` created from a cart: transitions through states `PLACED -> PREPARING -> OUT_FOR_DELIVERY -> DELIVERED`. Cancellation only allowed before `PREPARING`.

```python
class Item:
    def __init__(self, name: str, price: float, category: str): ...

class Cart:
    def add_item(self, item: Item, qty: int) -> None: ...
    def remove_item(self, item_name: str) -> None: ...
    def get_total(self) -> float: ...

class Order:
    def advance_state(self) -> None: ...
    def cancel(self) -> bool: ...
    def get_receipt(self) -> str: ...
```

```
Item("Burger", 9.99, "Mains")
cart.add_item(burger, 2)
cart.get_total() -> 19.98
order = Order(cart)
order.advance_state()  # PREPARING
order.cancel()         -> False (too late)
```

## Follow-ups

1. How would you apply a discount code that takes 10% off orders above $30?
2. Support multiple restaurants — how does your design change?
3. Where would you add tax calculation, and should it live in `Cart` or `Order`?
4. How do you handle an item becoming unavailable after it's already in a customer's cart?

Food Ordering System: OOD for Menu, Cart, and Order Lifecycle Management

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