from langchain.tools import tool


@tool
def calculate_discount(price: float, discount_percent: float) -> str:
    """Calculate the final price after a percentage discount."""
    if price < 0:
        return "Price must be greater than or equal to 0."
    if discount_percent < 0 or discount_percent > 100:
        return "Discount percent must be between 0 and 100."

    final_price = price * (1 - discount_percent / 100)
    return f"Final price: ${final_price:.2f}"


print(calculate_discount.name)
print(calculate_discount.description)
print(calculate_discount.invoke({"price": 120, "discount_percent": 25}))