content: {-# OPTIONS -fno-warn-orphans #-}
  
  -- #hide
  module Data.Time.Calendar.Gregorian
  (
  	-- * Gregorian calendar
  	toGregorian,fromGregorian,fromGregorianValid,showGregorian,gregorianMonthLength,
  
  	-- calendrical arithmetic
      -- e.g. "one month after March 31st"
  	addGregorianMonthsClip,addGregorianMonthsRollOver,
  	addGregorianYearsClip,addGregorianYearsRollOver,
  
  	-- re-exported from OrdinalDate
  	isLeapYear
  ) where
  
  import Data.Time.Calendar.MonthDay
  import Data.Time.Calendar.OrdinalDate
  import Data.Time.Calendar.Days
  import Data.Time.Calendar.Private
  
  -- | convert to proleptic Gregorian calendar. First element of result is year, second month number (1-12), third day (1-31).
  toGregorian :: Day -> (Integer,Int,Int)
  toGregorian date = (year,month,day) where
  	(year,yd) = toOrdinalDate date
  	(month,day) = dayOfYearToMonthAndDay (isLeapYear year) yd
  
  -- | convert from proleptic Gregorian calendar. First argument is year, second month number (1-12), third day (1-31).
  -- Invalid values will be clipped to the correct range, month first, then day.
  fromGregorian :: Integer -> Int -> Int -> Day
  fromGregorian year month day = fromOrdinalDate year (monthAndDayToDayOfYear (isLeapYear year) month day)
  
  -- | convert from proleptic Gregorian calendar. First argument is year, second month number (1-12), third day (1-31).
  -- Invalid values will return Nothing
  fromGregorianValid :: Integer -> Int -> Int -> Maybe Day
  fromGregorianValid year month day = do
  	doy <- monthAndDayToDayOfYearValid (isLeapYear year) month day
  	fromOrdinalDateValid year doy
  
  -- | show in ISO 8601 format (yyyy-mm-dd)
  showGregorian :: Day -> String
  showGregorian date = (show4 (Just '0') y) ++ "-" ++ (show2 (Just '0') m) ++ "-" ++ (show2 (Just '0') d) where
  	(y,m,d) = toGregorian date
  
  -- | The number of days in a given month according to the proleptic Gregorian calendar. First argument is year, second is month.
  gregorianMonthLength :: Integer -> Int -> Int
  gregorianMonthLength year = monthLength (isLeapYear year)
  
  rolloverMonths :: (Integer,Integer) -> (Integer,Int)
  rolloverMonths (y,m) = (y + (div (m - 1) 12),fromIntegral (mod (m - 1) 12) + 1)
  
  addGregorianMonths :: Integer -> Day -> (Integer,Int,Int)
  addGregorianMonths n day = (y',m',d) where
  	(y,m,d) = toGregorian day
  	(y',m') = rolloverMonths (y,fromIntegral m + n)
  
  -- | Add months, with days past the last day of the month clipped to the last day.
  -- For instance, 2005-01-30 + 1 month = 2005-02-28.
  addGregorianMonthsClip :: Integer -> Day -> Day
  addGregorianMonthsClip n day = fromGregorian y m d where
  	(y,m,d) = addGregorianMonths n day
  
  -- | Add months, with days past the last day of the month rolling over to the next month.
  -- For instance, 2005-01-30 + 1 month = 2005-03-02.
  addGregorianMonthsRollOver :: Integer -> Day -> Day
  addGregorianMonthsRollOver n day = addDays (fromIntegral d - 1) (fromGregorian y m 1) where
  	(y,m,d) = addGregorianMonths n day
  
  -- | Add years, matching month and day, with Feb 29th clipped to Feb 28th if necessary.
  -- For instance, 2004-02-29 + 2 years = 2006-02-28.
  addGregorianYearsClip :: Integer -> Day -> Day
  addGregorianYearsClip n = addGregorianMonthsClip (n * 12)
  
  -- | Add years, matching month and day, with Feb 29th rolled over to Mar 1st if necessary.
  -- For instance, 2004-02-29 + 2 years = 2006-03-01.
  addGregorianYearsRollOver :: Integer -> Day -> Day
  addGregorianYearsRollOver n = addGregorianMonthsRollOver (n * 12)
  
  -- orphan instance
  instance Show Day where
  	show = showGregorian
  