interface DiscountRule {
  threshold: number,
  discount: number
}

type CarCategory = 'economy' | 'standard' | 'premium'

const MIN_ECONOMY_RATE_VALUE = 35
const MIN_STANDARD_RATE_VALUE = 55
const MIN_PREMIUM_RATE_VALUE = 90

const MIN_INSURANCE_DAYS = 15
const MIN_DAY_VALUE = 0

const RATE_BY_CAR_CATEGORY: Record<CarCategory, number> = {
  'economy': MIN_ECONOMY_RATE_VALUE,
  'standard': MIN_STANDARD_RATE_VALUE,
  'premium': MIN_PREMIUM_RATE_VALUE
}

const MIN_DISCOUNT_THRESHOLD_ONE = 14
const MIN_DISCOUNT_THRESHOLD_TWO = 7

const DISCOUNT_VALUE_ONE = 0.2
const DISCOUNT_VALUE_TWO = 0.1

const DEFAULT_INVALID_VALUE = -1

const DISCOUNT_RULES: DiscountRule[] = [
  { threshold: MIN_DISCOUNT_THRESHOLD_ONE, discount: DISCOUNT_VALUE_ONE },
  { threshold: MIN_DISCOUNT_THRESHOLD_TWO, discount: DISCOUNT_VALUE_TWO },
]

export function calculateCarRentalCost(days: number, category: CarCategory, hasInsurance: boolean): number {
  if (!isValidDay(days)) return DEFAULT_INVALID_VALUE
  if (!isValidCarCategory(category)) return DEFAULT_INVALID_VALUE

  const rate = calculateRateByCarCategory(category)
  const subTotal = calculateDiscountForRentedDays(rate * days, days)

  return hasInsurance ? subTotal + insuranceCost(days) : subTotal
}

function calculateRateByCarCategory(category: CarCategory) {  
  return RATE_BY_CAR_CATEGORY[category] ?? DEFAULT_INVALID_VALUE
}

function isValidDay(day: number) {
  return day > MIN_DAY_VALUE
}

function calculateDiscountForRentedDays(subTotal: number, days: number) {
  const discountRule = DISCOUNT_RULES.find(({ threshold }) => days >= threshold)

  if (!discountRule) return subTotal

  return subTotal * (1 - discountRule.discount)
}

function insuranceCost(days: number) {
  return MIN_INSURANCE_DAYS * days
}

function isValidCarCategory(category: CarCategory) {
  return RATE_BY_CAR_CATEGORY[category]
}