import Data.Time
import Data.Time.Clock.POSIX

main :: IO ()
main = do
    -- We'll start by getting the current time.
    now <- getCurrentTime
    print now

    -- You can build a UTCTime by providing the year, month, day, etc.
    let then' = UTCTime (fromGregorian 2009 11 17) (timeOfDayToTime (TimeOfDay 20 34 58))
    print then'

    -- You can extract the various components of the time value as expected.
    print $ utctYear then'
    print $ utctMonth then'
    print $ utctDay then'
    print $ utctHour then'
    print $ utctMinute then'
    print $ utctSecond then'
    print $ utctDayOfWeek then'

    -- These functions compare two times, testing if the first occurs before, after,
    -- or at the same time as the second, respectively.
    print $ then' < now
    print $ then' > now
    print $ then' == now

    -- The diffUTCTime function returns a NominalDiffTime representing
    -- the interval between two times.
    let diff = diffUTCTime now then'
    print diff

    -- We can compute the length of the duration in various units.
    print $ nominalDiffTimeToSeconds diff / 3600  -- hours
    print $ nominalDiffTimeToSeconds diff / 60    -- minutes
    print $ nominalDiffTimeToSeconds diff         -- seconds

    -- You can use addUTCTime to advance a time by a given duration,
    -- or with a negative value to move backwards by a duration.
    print $ addUTCTime diff then'
    print $ addUTCTime (negate diff) then'

-- Helper functions to extract components from UTCTime
utctYear :: UTCTime -> Integer
utctYear = (\(y,_,_) -> y) . toGregorian . utctDay

utctMonth :: UTCTime -> Int
utctMonth = (\(_,m,_) -> m) . toGregorian . utctDay

utctDay :: UTCTime -> Int
utctDay = (\(_,_,d) -> d) . toGregorian . utctDay

utctHour :: UTCTime -> Int
utctHour = todHour . timeToTimeOfDay . utctDayTime

utctMinute :: UTCTime -> Int
utctMinute = todMin . timeToTimeOfDay . utctDayTime

utctSecond :: UTCTime -> Int
utctSecond = floor . todSec . timeToTimeOfDay . utctDayTime

utctDayOfWeek :: UTCTime -> String
utctDayOfWeek = show . dayOfWeek . utctDay