module HW1.T1
  ( Day (..)
  , afterDays
  , daysToParty
  , isWeekend
  , nextDay
  ) where

import Numeric.Natural (Natural)

data Day
  = Monday
  | Tuesday
  | Wednesday
  | Thursday
  | Friday
  | Saturday
  | Sunday
  deriving Show

nextDay :: Day -> Day
nextDay Monday = Tuesday
nextDay Tuesday = Wednesday
nextDay Wednesday = Thursday
nextDay Thursday = Friday
nextDay Friday = Saturday
nextDay Saturday = Sunday
nextDay Sunday = Monday

afterDays :: Natural -> Day -> Day
afterDays 0 day = day
afterDays n day = afterDays (n - 1) (nextDay day)

isWeekend :: Day -> Bool
isWeekend Saturday = True
isWeekend Sunday = True
isWeekend _ = False


counterForDays :: Day -> Natural -> Natural
counterForDays Friday n = n
counterForDays day n = counterForDays (nextDay day) (n + 1)

daysToParty :: Day -> Natural
daysToParty Friday = 0
daysToParty day = counterForDays day 0