    {-# OPTIONS -Wall -Werror #-}

    -- #hide
    module Data.Time.Clock.Scale
    (
    	-- * Universal Time
    	-- | Time as measured by the earth.
    	UniversalTime(..),

    	-- * Absolute intervals
    	DiffTime,
            secondsToDiffTime, picosecondsToDiffTime
    ) where

    import Data.Ratio ((%))
    import Data.Fixed

    -- | The Modified Julian Date is the day with the fraction of the day, measured from UT midnight.
    -- It's used to represent UT1, which is time as measured by the earth's rotation, adjusted for various wobbles.
    newtype UniversalTime = ModJulianDate {getModJulianDate :: Rational} deriving (Eq,Ord)

    -- | This is a length of time, as measured by a clock.
    -- Conversion functions will treat it as seconds.
    -- It has an accuracy of 10^-12 s.
    newtype DiffTime = MkDiffTime Pico deriving (Eq,Ord)

    -- necessary because H98 doesn't have "cunning newtype" derivation
    instance Enum DiffTime where
    	succ (MkDiffTime a) = MkDiffTime (succ a)
    	pred (MkDiffTime a) = MkDiffTime (pred a)
    	toEnum = MkDiffTime . toEnum
    	fromEnum (MkDiffTime a) = fromEnum a
    	enumFrom (MkDiffTime a) = fmap MkDiffTime (enumFrom a)
    	enumFromThen (MkDiffTime a) (MkDiffTime b) = fmap MkDiffTime (enumFromThen a b)
    	enumFromTo (MkDiffTime a) (MkDiffTime b) = fmap MkDiffTime (enumFromTo a b)
    	enumFromThenTo (MkDiffTime a) (MkDiffTime b) (MkDiffTime c) = fmap MkDiffTime (enumFromThenTo a b c)

    instance Show DiffTime where
    	show (MkDiffTime t) = (showFixed True t) ++ "s"

    -- necessary because H98 doesn't have "cunning newtype" derivation
    instance Num DiffTime where
    	(MkDiffTime a) + (MkDiffTime b) = MkDiffTime (a + b)
    	(MkDiffTime a) - (MkDiffTime b) = MkDiffTime (a - b)
    	(MkDiffTime a) * (MkDiffTime b) = MkDiffTime (a * b)
    	negate (MkDiffTime a) = MkDiffTime (negate a)
    	abs (MkDiffTime a) = MkDiffTime (abs a)
    	signum (MkDiffTime a) = MkDiffTime (signum a)
    	fromInteger i = MkDiffTime (fromInteger i)

    -- necessary because H98 doesn't have "cunning newtype" derivation
    instance Real DiffTime where
    	toRational (MkDiffTime a) = toRational a

    -- necessary because H98 doesn't have "cunning newtype" derivation
    instance Fractional DiffTime where
    	(MkDiffTime a) / (MkDiffTime b) = MkDiffTime (a / b)
    	recip (MkDiffTime a) = MkDiffTime (recip a)
    	fromRational r = MkDiffTime (fromRational r)

    -- | Create a 'DiffTime' which represents an integral number of seconds.
    secondsToDiffTime :: Integer -> DiffTime
    secondsToDiffTime = fromInteger

    -- | Create a 'DiffTime' from a number of picoseconds.
    picosecondsToDiffTime :: Integer -> DiffTime
    picosecondsToDiffTime x = fromRational (x % 1000000000000)