OrdinalDate.hs

-- | ISO 8601 Ordinal Date format
module Data.Time.Calendar.OrdinalDate where

import Data.Time.Calendar.Days
import Data.Time.Calendar.Private

-- | Convert to ISO 8601 Ordinal Date format. First element of result is year (proleptic Gregoran calendar),
-- second is the day of the year, with 1 for Jan 1, and 365 (or 366 in leap years) for Dec 31.
toOrdinalDate :: Day -> (Integer, Int)
toOrdinalDate (ModifiedJulianDay mjd) = (year, yd)
  where
    a = mjd + 678575
    quadcent = div a 146097
    b = mod a 146097
    cent = min (div b 36524) 3
    c = b - (cent * 36524)
    quad = div c 1461
    d = mod c 1461
    y = min (div d 365) 3
    yd = fromInteger (d - (y * 365) + 1)
    year = quadcent * 400 + cent * 100 + quad * 4 + y + 1

-- | Convert from ISO 8601 Ordinal Date format.
-- Invalid day numbers will be clipped to the correct range (1 to 365 or 366).
fromOrdinalDate :: Integer -> Int -> Day
fromOrdinalDate year day = ModifiedJulianDay mjd
  where
    y = year - 1
    mjd =
        (fromIntegral
             (clip
                  1
                  (if isLeapYear year
                       then 366
                       else 365)
                  day)) +
        (365 * y) +
        (div y 4) -
        (div y 100) +
        (div y 400) -
        678576

-- | Convert from ISO 8601 Ordinal Date format.
-- Invalid day numbers return 'Nothing'
fromOrdinalDateValid :: Integer -> Int -> Maybe Day
fromOrdinalDateValid year day = do
    day' <-
        clipValid
            1
            (if isLeapYear year
                 then 366
                 else 365)
            day
    let
        y = year - 1
        mjd = (fromIntegral day') + (365 * y) + (div y 4) - (div y 100) + (div y 400) - 678576
    return (ModifiedJulianDay mjd)

-- | Show in ISO 8601 Ordinal Date format (yyyy-ddd)
showOrdinalDate :: Day -> String
showOrdinalDate date = (show4 y) ++ "-" ++ (show3 d)
  where
    (y, d) = toOrdinalDate date

-- | Is this year a leap year according to the proleptic Gregorian calendar?
isLeapYear :: Integer -> Bool
isLeapYear year = (mod year 4 == 0) && ((mod year 400 == 0) || not (mod year 100 == 0))

-- | Get the number of the Monday-starting week in the year and the day of the week.
-- The first Monday is the first day of week 1, any earlier days in the year are week 0 (as @%W@ in 'Data.Time.Format.formatTime').
-- Monday is 1, Sunday is 7 (as @%u@ in 'Data.Time.Format.formatTime').
mondayStartWeek :: Day -> (Int, Int)
mondayStartWeek date = (fromInteger ((div d 7) - (div k 7)), fromInteger (mod d 7) + 1)
  where
    yd = snd (toOrdinalDate date)
    d = (toModifiedJulianDay date) + 2
    k = d - (toInteger yd)

-- | Get the number of the Sunday-starting week in the year and the day of the week.
-- The first Sunday is the first day of week 1, any earlier days in the year are week 0 (as @%U@ in 'Data.Time.Format.formatTime').
-- Sunday is 0, Saturday is 6 (as @%w@ in 'Data.Time.Format.formatTime').
sundayStartWeek :: Day -> (Int, Int)
sundayStartWeek date = (fromInteger ((div d 7) - (div k 7)), fromInteger (mod d 7))
  where
    yd = snd (toOrdinalDate date)
    d = (toModifiedJulianDay date) + 3
    k = d - (toInteger yd)

-- | The inverse of 'mondayStartWeek'. Get a 'Day' given the year,
-- the number of the Monday-starting week, and the day of the week.
-- The first Monday is the first day of week 1, any earlier days in the year
-- are week 0 (as @%W@ in 'Data.Time.Format.formatTime').
fromMondayStartWeek ::
       Integer -- ^ Year.
    -> Int -- ^ Monday-starting week number (as @%W@ in 'Data.Time.Format.formatTime').
    -> Int -- ^ Day of week.
                               -- Monday is 1, Sunday is 7 (as @%u@ in 'Data.Time.Format.formatTime').
    -> Day
fromMondayStartWeek year w d = let
    -- first day of the year
    firstDay = fromOrdinalDate year 1
    -- 0-based year day of first monday of the year
    zbFirstMonday = (5 - toModifiedJulianDay firstDay) `mod` 7
    -- 0-based week of year
    zbWeek = w - 1
    -- 0-based day of week
    zbDay = d - 1
    -- 0-based day in year
    zbYearDay = zbFirstMonday + 7 * toInteger zbWeek + toInteger zbDay
    in addDays zbYearDay firstDay

fromMondayStartWeekValid ::
       Integer -- ^ Year.
    -> Int -- ^ Monday-starting week number (as @%W@ in 'Data.Time.Format.formatTime').
    -> Int -- ^ Day of week.
                               -- Monday is 1, Sunday is 7 (as @%u@ in 'Data.Time.Format.formatTime').
    -> Maybe Day
fromMondayStartWeekValid year w d = do
    d' <- clipValid 1 7 d
    let
        -- first day of the year
        firstDay = fromOrdinalDate year 1
        -- 0-based week of year
        zbFirstMonday = (5 - toModifiedJulianDay firstDay) `mod` 7
        -- 0-based week number
        zbWeek = w - 1
        -- 0-based day of week
        zbDay = d' - 1
        -- 0-based day in year
        zbYearDay = zbFirstMonday + 7 * toInteger zbWeek + toInteger zbDay
    zbYearDay' <-
        clipValid
            0
            (if isLeapYear year
                 then 365
                 else 364)
            zbYearDay
    return $ addDays zbYearDay' firstDay

-- | The inverse of 'sundayStartWeek'. Get a 'Day' given the year and
-- the number of the day of a Sunday-starting week.
-- The first Sunday is the first day of week 1, any earlier days in the
-- year are week 0 (as @%U@ in 'Data.Time.Format.formatTime').
fromSundayStartWeek ::
       Integer -- ^ Year.
    -> Int -- ^ Sunday-starting week number (as @%U@ in 'Data.Time.Format.formatTime').
    -> Int -- ^ Day of week
                               -- Sunday is 0, Saturday is 6 (as @%w@ in 'Data.Time.Format.formatTime').
    -> Day
fromSundayStartWeek year w d = let
    -- first day of the year
    firstDay = fromOrdinalDate year 1
    -- 0-based year day of first monday of the year
    zbFirstSunday = (4 - toModifiedJulianDay firstDay) `mod` 7
    -- 0-based week of year
    zbWeek = w - 1
    -- 0-based day of week
    zbDay = d
    -- 0-based day in year
    zbYearDay = zbFirstSunday + 7 * toInteger zbWeek + toInteger zbDay
    in addDays zbYearDay firstDay

fromSundayStartWeekValid ::
       Integer -- ^ Year.
    -> Int -- ^ Sunday-starting week number (as @%U@ in 'Data.Time.Format.formatTime').
    -> Int -- ^ Day of week.
                               -- Sunday is 0, Saturday is 6 (as @%w@ in 'Data.Time.Format.formatTime').
    -> Maybe Day
fromSundayStartWeekValid year w d = do
    d' <- clipValid 0 6 d
    let
        -- first day of the year
        firstDay = fromOrdinalDate year 1
        -- 0-based week of year
        zbFirstSunday = (4 - toModifiedJulianDay firstDay) `mod` 7
        -- 0-based week number
        zbWeek = w - 1
        -- 0-based day of week
        zbDay = d'
        -- 0-based day in year
        zbYearDay = zbFirstSunday + 7 * toInteger zbWeek + toInteger zbDay
    zbYearDay' <-
        clipValid
            0
            (if isLeapYear year
                 then 365
                 else 364)
            zbYearDay
    return $ addDays zbYearDay' firstDay