{-# LANGUAGE Safe #-}

module Data.Time.Calendar.MonthDay
    ( MonthOfYear, DayOfMonth, DayOfYear
    , monthAndDayToDayOfYear
    , monthAndDayToDayOfYearValid
    , dayOfYearToMonthAndDay
    , monthLength
    ) where

import Data.Time.Calendar.Types
import Data.Time.Calendar.Private

-- | Convert month and day in the Gregorian or Julian calendars to day of year.
-- First arg is leap year flag.
monthAndDayToDayOfYear :: Bool -> MonthOfYear -> DayOfMonth -> DayOfYear
monthAndDayToDayOfYear isLeap month day = (div (367 * month'' - 362) 12) + k + day'
  where
    month' = clip 1 12 month
    day' = fromIntegral (clip 1 (monthLength' isLeap month') day)
    month'' = fromIntegral month'
    k =
        if month' <= 2
            then 0
            else if isLeap
                     then -1
                     else -2

-- | Convert month and day in the Gregorian or Julian calendars to day of year.
-- First arg is leap year flag.
monthAndDayToDayOfYearValid :: Bool -> MonthOfYear -> DayOfMonth -> Maybe DayOfYear
monthAndDayToDayOfYearValid isLeap month day = do
    month' <- clipValid 1 12 month
    day' <- clipValid 1 (monthLength' isLeap month') day
    let
        day'' = fromIntegral day'
        month'' = fromIntegral month'
        k =
            if month' <= 2
                then 0
                else if isLeap
                         then -1
                         else -2
    return ((div (367 * month'' - 362) 12) + k + day'')

-- | Convert day of year in the Gregorian or Julian calendars to month and day.
-- First arg is leap year flag.
dayOfYearToMonthAndDay :: Bool -> DayOfYear -> (MonthOfYear, DayOfMonth)
dayOfYearToMonthAndDay isLeap yd =
    findMonthDay
        (monthLengths isLeap)
        (clip
             1
             (if isLeap
                  then 366
                  else 365)
             yd)

findMonthDay :: [Int] -> Int -> (Int, Int)
findMonthDay (n:ns) yd
    | yd > n = (\(m, d) -> (m + 1, d)) (findMonthDay ns (yd - n))
findMonthDay _ yd = (1, yd)

-- | The length of a given month in the Gregorian or Julian calendars.
-- First arg is leap year flag.
monthLength :: Bool -> MonthOfYear -> DayOfMonth
monthLength isLeap month' = monthLength' isLeap (clip 1 12 month')

monthLength' :: Bool -> MonthOfYear -> DayOfMonth
monthLength' isLeap month' = (monthLengths isLeap) !! (month' - 1)

monthLengths :: Bool -> [DayOfMonth]
monthLengths isleap =
    [ 31
    , if isleap
          then 29
          else 28
    , 31
    , 30
    , 31
    , 30
    , 31
    , 31
    , 30
    , 31
    , 30
    , 31
    ]
    --J        F                   M  A  M  J  J  A  S  O  N  D
