Source code for app.discount_strategy

from abc import ABC, abstractmethod




class DiscountStrategy(ABC):
    """Abstract base class for discount calculation strategies."""



    @abstractmethod
    def calculate_discount(self, subtotal: float) -> float:
        """
        Calculate the discount amount for a given subtotal.

        Args:
            subtotal: The subtotal before discount

        Returns:
            float: The discount amount (positive value)
        """
        ...






class NoDiscount(DiscountStrategy):
    """No discount applied."""



    def calculate_discount(self, subtotal: float) -> float:
        return 0.0






class PercentageDiscount(DiscountStrategy):
    """Apply a percentage discount."""

    def __init__(self, percentage: float):
        """
        Initialize the percentage discount strategy.

        Args:
            percentage: Discount percentage (e.g., 10 for 10%)

        Raises:
            ValueError: If percentage is negative or greater than 100
        """
        if percentage < 0 or percentage > 100:
            raise ValueError("Percentage must be between 0 and 100")
        self.percentage = percentage



    def calculate_discount(self, subtotal: float) -> float:
        return round(subtotal * (self.percentage / 100), 2)






class ThresholdFixedDiscount(DiscountStrategy):
    """Apply a fixed discount if a threshold is reached."""

    def __init__(self, threshold: float, amount: float):
        """
        Initialize the threshold-based discount strategy.

        Args:
            threshold: Minimum subtotal required for discount
            amount: Fixed discount amount to apply

        Raises:
            ValueError: If threshold or amount is negative
        """
        if threshold < 0:
            raise ValueError("Threshold must be non-negative")
        if amount < 0:
            raise ValueError("Amount must be non-negative")
        self.threshold = threshold
        self.amount = amount



    def calculate_discount(self, subtotal: float) -> float:
        if subtotal >= self.threshold:
            return round(min(subtotal, self.amount), 2)
        return 0.0