git-annex/Utility/TimeStamp.hs

{- timestamp parsing and formatting
 -
 - Copyright 2015-2019 Joey Hess <id@joeyh.name>
 -
 - License: BSD-2-clause
 -}

module Utility.TimeStamp (
	parserPOSIXTime,
	parsePOSIXTime,
	formatPOSIXTime,
) where

import Utility.Data

import Data.Time.Clock.POSIX
import Data.Time
import Data.Ratio
import Control.Applicative
import qualified Data.ByteString as B
import qualified Data.ByteString.Char8 as B8
import qualified Data.Attoparsec.ByteString as A
import Data.Attoparsec.ByteString.Char8 (char, decimal, signed, isDigit_w8)

{- Parses how POSIXTime shows itself: "1431286201.113452s"
 - (The "s" is included for historical reasons and is optional.)
 - Also handles the format with no decimal seconds. -}
parserPOSIXTime :: A.Parser POSIXTime
parserPOSIXTime = mkPOSIXTime
	<$> signed decimal
	<*> (declen <|> pure (0, 0))
	<* optional (char 's')
  where
	declen :: A.Parser (Integer, Int)
	declen = do
		_ <- char '.'
		b <- A.takeWhile isDigit_w8
		let len = B.length b
		d <- either fail pure $
			A.parseOnly (decimal <* A.endOfInput) b
		return (d, len)

parsePOSIXTime :: String -> Maybe POSIXTime
parsePOSIXTime s = eitherToMaybe $ 
	A.parseOnly (parserPOSIXTime <* A.endOfInput) (B8.pack s)

{- This implementation allows for higher precision in a POSIXTime than
 - supported by the system's Double, and avoids the complications of
 - floating point. -}
mkPOSIXTime :: Integer -> (Integer, Int) -> POSIXTime
mkPOSIXTime n (d, dlen)
	| n < 0 = fromIntegral n - fromRational r
	| otherwise = fromIntegral n + fromRational r
  where
	r = d % (10 ^ dlen)

formatPOSIXTime :: String -> POSIXTime -> String
formatPOSIXTime fmt t = formatTime defaultTimeLocale fmt (posixSecondsToUTCTime t)