from typing import Dict

MIN_VALUE_THRESHOLD: int = 0
HEAVY_PACKAGE_THRESHOLD: int = 20
HEAVY_PACKAGE_DISCOUNT: float = 0.10

ZONE_CONFIG: Dict = {
    "local" : {"base_per_kg": 2, "extra_per_km": 0.10},
    "regional": {"base_per_kg": 5, "extra_per_km": 0.05},
    "nacional": {"base_per_kg": 10, "extra_per_km": 0.02}
}

def is_valid_input(weight: float, distance: float) -> bool:
    return weight > MIN_VALUE_THRESHOLD and distance > MIN_VALUE_THRESHOLD

def calculate_raw_cost(weight: float, distance: float, zone: str) -> float:
    config: Dict = ZONE_CONFIG.get(zone.lower())

    if not config:
        return 0.0

    cost_from_weight: float = weight * config["base_per_kg"]
    cost_from_distance: float = distance * config["extra_per_km"]

    return cost_from_weight + cost_from_distance


def apply_discounts(total_cost: float, weight: float) -> float:
    if weight > HEAVY_PACKAGE_THRESHOLD:
        total_cost -= (total_cost * HEAVY_PACKAGE_DISCOUNT)

    return total_cost

def calculate_shipping_cost(weight: float, distance: float, zone: str) -> float:
    if not is_valid_input(weight, distance):
        return -1.0

    total_cost: float = calculate_raw_cost(weight, distance, zone)
    final_cost: float = apply_discounts(total_cost, weight)

    return round(final_cost, 2)

__all__ = ["calculate_shipping_cost"]