ELECTRONICS_DISCOUNT = 0.15
CLOTHING_DISCOUNT = 0.20
FOOD_DISCOUNT = 0.05
DEFAULT_DISCOUNT = 0.0
TAX_RATE = 0.21

def get_discount_rate(category: str ) -> float:
    if category == "electronics":
        return ELECTRONICS_DISCOUNT
    elif category == "clothing":
        return CLOTHING_DISCOUNT
    elif category == "food":
        return FOOD_DISCOUNT
    else:
        return DEFAULT_DISCOUNT

def get_product_final_price(price: float, category: str, stock: int) -> float:
    if stock <= 0 or price <= 0:
        return -1

    discount_rate = get_discount_rate(category)
    price_after_discount = price * (1 - discount_rate)

    final_price = price_after_discount * (1 + TAX_RATE)

    return round(final_price, 2)

exports = get_product_final_price