{-# LANGUAGE Safe #-}

-- | POSIX time, if you need to deal with timestamps and the like.
-- Most people won't need this module.
--
-- You can use 'POSIXTime' to obtain integer/word timestamps. For example:
--
-- > import Data.Time
-- > import Data.Time.Clock.POSIX
-- > import Data.Int
-- >
-- > nanosSinceEpoch :: UTCTime -> Int64
-- > nanosSinceEpoch =
-- >     floor . (1e9 *) . nominalDiffTimeToSeconds . utcTimeToPOSIXSeconds
-- >
-- > main :: IO ()
-- > main = do
-- >     u <- getCurrentTime
-- >     print $ nanosSinceEpoch u
module Data.Time.Clock.POSIX
    ( posixDayLength
    , POSIXTime
    , posixSecondsToUTCTime
    , utcTimeToPOSIXSeconds
    , getPOSIXTime
    , getCurrentTime
    , systemToPOSIXTime
    ) where

import Data.Fixed
import Data.Time.Calendar.Days
import Data.Time.Clock.Internal.POSIXTime
import Data.Time.Clock.Internal.UTCTime
import Data.Time.Clock.System

posixSecondsToUTCTime :: POSIXTime -> UTCTime
posixSecondsToUTCTime i = let
    (d, t) = divMod' i posixDayLength
    in UTCTime (addDays d systemEpochDay) (realToFrac t)

utcTimeToPOSIXSeconds :: UTCTime -> POSIXTime
utcTimeToPOSIXSeconds (UTCTime d t) =
    (fromInteger (diffDays d systemEpochDay) * posixDayLength) + min posixDayLength (realToFrac t)

systemToPOSIXTime :: SystemTime -> POSIXTime
systemToPOSIXTime (MkSystemTime s ns) = (fromIntegral s) + (fromIntegral ns) * 1E-9

-- | Get the current POSIX time from the system clock.
getPOSIXTime :: IO POSIXTime
getPOSIXTime = fmap systemToPOSIXTime getSystemTime

-- | Get the current 'UTCTime' from the system clock.
getCurrentTime :: IO UTCTime
getCurrentTime = systemToUTCTime `fmap` getSystemTime