Structure a Pizza-Ordering System with Four Discount Policies

Problem Statement

Design the core pricing and order engine for a pizza-ordering service. Your system must represent individual pizzas, handle order composition, apply four distinct discount policies in a well-defined sequence, and output a detailed breakdown explaining how the final total was calculated.

Data Models

1. Pizza:

   • size: "Small" ($8.00), "Medium" ($12.00), "Large" ($16.00).
   • toppings: List of topping names (strings). Each topping costs $1.50.
   • Base price of a pizza = size_price + (len(toppings) * 1.50).

2. Order:

   • A collection of Pizza items and optional metadata (e.g., coupon codes).

Discount Policies

Discounts are evaluated and applied in the following strict precedence order. No discount can reduce any intermediate or final balance below $0.00.

1. Policy A (Buy-X-Get-One-Free): For every 3 pizzas ordered, the cheapest pizza in that set of 3 is free (100% discount on that pizza's total price). If there are 6 pizzas, the 2 cheapest are free, etc.
2. Policy B (Topping Special): If an order contains 2 or more "Large" pizzas, all toppings across the entire order receive a 50% discount (deduct total_topping_count * 0.75).
3. Policy C (Order Tier Percentage Discount): If the subtotal after Policies A and B is at least $50.00, apply a 10% discount on that remaining balance.
4. Policy D (Fixed Coupon Code): If the coupon code "SAVE5" is provided, deduct $5.00 from the remaining balance after Policy C.

Class Interface

Implement the following classes in Python:

class Pizza:
    def __init__(self, size: str, toppings: list[str]):
        pass

    def get_price(self) -> float:
        pass

class Order:
    def __init__(self, coupon_code: str = None):
        pass

    def add_pizza(self, pizza: Pizza) -> None:
        pass

    def calculate_receipt(self) -> dict:
        """
        Returns a dictionary with:
        - "subtotal": float (sum of original pizza prices)
        - "discounts": list of dicts, each with {"policy": str, "amount": float}
          (only include discounts that provided an amount > 0)
        - "total": float (final amount owed, rounded to 2 decimal places)
        """
        pass

Constraints

• size is always one of "Small", "Medium", or "Large".
• len(toppings) >= 0.
• Order contains 0 <= n <= 100 pizzas.
• All monetary amounts in the returned dictionary should be rounded to 2 decimal places.

Example

order = Order(coupon_code="SAVE5")
order.add_pizza(Pizza("Large", ["pepperoni", "mushrooms"]))  # 16 + 3.00 = 19.00
order.add_pizza(Pizza("Large", ["extra cheese"]))             # 16 + 1.50 = 17.50
order.add_pizza(Pizza("Small", []))                           # 8.00

receipt = order.calculate_receipt()
# Initial subtotal: 19.00 + 17.50 + 8.00 = 44.50
# Policy A: 3 pizzas -> cheapest is Small ($8.00) -> discount = 8.00 (subtotal -> 36.50)
# Policy B: 2 Large pizzas -> 3 total toppings * 0.75 = 2.25 discount (subtotal -> 34.25)
# Policy C: Subtotal (34.25)  not applied ($0.00)
# Policy D: "SAVE5" applied -> 5.00 discount (subtotal -> 29.25)
# Total: 29.25