-- | TAI and leap-second maps for converting to UTC: most people won't need this module.
module Data.Time.Clock.Internal.AbsoluteTime
(
    -- TAI arithmetic
    AbsoluteTime,taiEpoch,addAbsoluteTime,diffAbsoluteTime,
    taiNominalDayStart,
) where

import Data.Typeable
import Data.Data
import Control.DeepSeq
import Data.Time.Calendar.Days
import Data.Time.Clock.Internal.DiffTime


-- | AbsoluteTime is TAI, time as measured by a clock.
newtype AbsoluteTime = MkAbsoluteTime DiffTime deriving (Eq,Ord,Data,Typeable)

instance NFData AbsoluteTime where
    rnf (MkAbsoluteTime a) = rnf a

-- | The epoch of TAI, which is 1858-11-17 00:00:00 TAI.
taiEpoch :: AbsoluteTime
taiEpoch = MkAbsoluteTime 0

taiNominalDayStart :: Day -> AbsoluteTime
taiNominalDayStart day = MkAbsoluteTime $ realToFrac $ (toModifiedJulianDay day) * 86400

-- | addAbsoluteTime a b = a + b
addAbsoluteTime :: DiffTime -> AbsoluteTime -> AbsoluteTime
addAbsoluteTime t (MkAbsoluteTime a) = MkAbsoluteTime (a + t)

-- | diffAbsoluteTime a b = a - b
diffAbsoluteTime :: AbsoluteTime -> AbsoluteTime -> DiffTime
diffAbsoluteTime (MkAbsoluteTime a) (MkAbsoluteTime b) = a - b