-- | The module containing the functions directly related to the month calculations, and exposed in the library.
module Months where

import Helpers

-- | Computes the average of the number of days in a months by folding the list given by monthLengthList
meanMonth :: Double
meanMonth = let months = map realToFrac monthLengthList
              in mean months

-- | Returns a list of Ints containing the lengths of every month in a Gregorian Cycle.
-- A Gregorian cycle (or whatever it is called) is made of 400 years.
-- Each year has 12 months,
-- Of which:
-- 7 have 31 days,
-- 4 have 30 days,
-- and 1 has either 28 days, or 29 days if the year is bissextile.
-- In the gregorian calendar, a year is bissextile if its number is dividable by 4,
-- except when it is dividable by 100, but it is bissextile when it is dividable by 400.
monthLengthList :: [Int]
monthLengthList = longMonths ++ shortMonths ++ febIntercalary ++ febBissextile
                    where longMonths = [31 | x <- [1..(7 * 400)]] -- 7 31-day months a year on a 400-year cycle
                          shortMonths = [30 | x <- [1..(4 * 400)]] -- 4 30-day months a year on the same cycle
                          febIntercalary = [28 | x <- [1..400], not (bissextile x)]
                          febBissextile = [29 | x <- [1..400], bissextile x]

-- | Tells whether a year is bissextile
bissextile :: Int -> Bool
bissextile x = ((x `dividableBy` 4) && not (x `dividableBy` 100)) || (x == 400)