content: module Data.Time.Calendar.Julian
  (
  	module Data.Time.Calendar.JulianYearDay,
  
  	toJulian,fromJulian,fromJulianValid,showJulian,julianMonthLength,
  
  	-- calendrical arithmetic
      -- e.g. "one month after March 31st"
  	addJulianMonthsClip,addJulianMonthsRollOver,
  	addJulianYearsClip,addJulianYearsRollOver
  ) where
  
  import Data.Time.Calendar.MonthDay
  import Data.Time.Calendar.JulianYearDay
  import Data.Time.Calendar.Days
  import Data.Time.Calendar.Private
  
  -- | convert to proleptic Julian calendar. First element of result is year, second month number (1-12), third day (1-31).
  toJulian :: Day -> (Integer,Int,Int)
  toJulian date = (year,month,day) where
  	(year,yd) = toJulianYearAndDay date
  	(month,day) = dayOfYearToMonthAndDay (isJulianLeapYear year) yd
  
  -- | convert from proleptic Julian 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.
  fromJulian :: Integer -> Int -> Int -> Day
  fromJulian year month day = fromJulianYearAndDay year (monthAndDayToDayOfYear (isJulianLeapYear year) month day)
  
  -- | convert from proleptic Julian calendar. First argument is year, second month number (1-12), third day (1-31).
  -- Invalid values will return Nothing.
  fromJulianValid :: Integer -> Int -> Int -> Maybe Day
  fromJulianValid year month day = do
  	doy <- monthAndDayToDayOfYearValid (isJulianLeapYear year) month day
  	fromJulianYearAndDayValid year doy
  
  -- | show in ISO 8601 format (yyyy-mm-dd)
  showJulian :: Day -> String
  showJulian date = (show4 (Just '0') y) ++ "-" ++ (show2 (Just '0') m) ++ "-" ++ (show2 (Just '0') d) where
  	(y,m,d) = toJulian date
  
  -- | The number of days in a given month according to the proleptic Julian calendar. First argument is year, second is month.
  julianMonthLength :: Integer -> Int -> Int
  julianMonthLength year = monthLength (isJulianLeapYear year)
  
  rolloverMonths :: (Integer,Integer) -> (Integer,Int)
  rolloverMonths (y,m) = (y + (div (m - 1) 12),fromIntegral (mod (m - 1) 12) + 1)
  
  addJulianMonths :: Integer -> Day -> (Integer,Int,Int)
  addJulianMonths n day = (y',m',d) where
  	(y,m,d) = toJulian 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.
  addJulianMonthsClip :: Integer -> Day -> Day
  addJulianMonthsClip n day = fromJulian y m d where
  	(y,m,d) = addJulianMonths 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.
  addJulianMonthsRollOver :: Integer -> Day -> Day
  addJulianMonthsRollOver n day = addDays (fromIntegral d - 1) (fromJulian y m 1) where
  	(y,m,d) = addJulianMonths 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.
  addJulianYearsClip :: Integer -> Day -> Day
  addJulianYearsClip n = addJulianMonthsClip (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.
  addJulianYearsRollOver :: Integer -> Day -> Day
  addJulianYearsRollOver n = addJulianMonthsRollOver (n * 12)
  