const INVALID_INPUT_RESULT = -1;

const LOCAL_ZONE = 'local';
const REGIONAL_ZONE = 'regional';
const NATIONAL_ZONE = 'nacional';

const LOCAL_BASE_RATE_PER_KG = 2;
const REGIONAL_BASE_RATE_PER_KG = 5;
const NATIONAL_BASE_RATE_PER_KG = 10;

const LOCAL_DISTANCE_SURCHARGE_RATE = 0.10;
const REGIONAL_DISTANCE_SURCHARGE_RATE = 0.05;
const NATIONAL_DISTANCE_SURCHARGE_RATE = 0.02;

const HEAVY_PACKAGE_WEIGHT_THRESHOLD = 20;
const HEAVY_PACKAGE_DISCOUNT_MULTIPLIER = 0.90;

const ROUNDING_FACTOR = 100;

export function calculateShippingCost(
  weight: number,
  distance: number,
  zone: string
): number {
  if (!isValidInput(weight, distance)) {
    return INVALID_INPUT_RESULT;
  }

  const { baseCost, distanceSurcharge } = calculateZoneCosts(
    weight,
    distance,
    zone
  );

  let totalCost = baseCost + distanceSurcharge;

  if (weight > HEAVY_PACKAGE_WEIGHT_THRESHOLD) {
    totalCost *= HEAVY_PACKAGE_DISCOUNT_MULTIPLIER;
  }

  return Math.round(totalCost * ROUNDING_FACTOR) / ROUNDING_FACTOR;
}

function isValidInput(weight: number, distance: number): boolean {
  return weight > 0 && distance > 0;
}

function calculateZoneCosts(
  weight: number,
  distance: number,
  zone: string
): { baseCost: number; distanceSurcharge: number } {
  if (zone === LOCAL_ZONE) {
    return {
      baseCost: weight * LOCAL_BASE_RATE_PER_KG,
      distanceSurcharge: distance * LOCAL_DISTANCE_SURCHARGE_RATE,
    };
  }

  if (zone === REGIONAL_ZONE) {
    return {
      baseCost: weight * REGIONAL_BASE_RATE_PER_KG,
      distanceSurcharge: distance * REGIONAL_DISTANCE_SURCHARGE_RATE,
    };
  }

  if (zone === NATIONAL_ZONE) {
    return {
      baseCost: weight * NATIONAL_BASE_RATE_PER_KG,
      distanceSurcharge: distance * NATIONAL_DISTANCE_SURCHARGE_RATE,
    };
  }

  return {
    baseCost: 0,
    distanceSurcharge: 0,
  };
}