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-- | Fast access to the system clock.
module Data.Time.Clock.System
(
systemEpochDay,
SystemTime(..),
truncateSystemTimeLeapSecond,
getSystemTime,
systemToUTCTime,
utcToSystemTime,
systemToTAITime,
) where
import Data.Time.Clock.Internal.AbsoluteTime
import Data.Time.Clock.Internal.DiffTime
import Data.Time.Clock.Internal.SystemTime
import Data.Time.Clock.Internal.UTCTime
import Data.Time.Calendar.Days
import Data.Int (Int64)
-- | Map leap-second values to the start of the following second.
-- The resulting 'systemNanoseconds' will always be in the range 0 to 1E9-1.
truncateSystemTimeLeapSecond :: SystemTime -> SystemTime
truncateSystemTimeLeapSecond (MkSystemTime seconds nanoseconds) | nanoseconds >= 1000000000 = MkSystemTime (succ seconds) 0
truncateSystemTimeLeapSecond t = t
-- | Convert 'SystemTime' to 'UTCTime', matching zero 'SystemTime' to midnight of 'systemEpochDay' UTC.
systemToUTCTime :: SystemTime -> UTCTime
systemToUTCTime (MkSystemTime seconds nanoseconds) = let
days :: Int64
timeSeconds :: Int64
(days, timeSeconds) = seconds `divMod` 86400
day :: Day
day = addDays (fromIntegral days) systemEpochDay
timeNanoseconds :: Int64
timeNanoseconds = timeSeconds * 1000000000 + (fromIntegral nanoseconds)
timePicoseconds :: Int64
timePicoseconds = timeNanoseconds * 1000
time :: DiffTime
time = picosecondsToDiffTime $ fromIntegral timePicoseconds
in UTCTime day time
-- | Convert 'UTCTime' to 'SystemTime', matching zero 'SystemTime' to midnight of 'systemEpochDay' UTC.
utcToSystemTime :: UTCTime -> SystemTime
utcToSystemTime (UTCTime day time) = let
days :: Int64
days = fromIntegral $ diffDays day systemEpochDay
timePicoseconds :: Int64
timePicoseconds = fromIntegral $ diffTimeToPicoseconds time
timeNanoseconds :: Int64
timeNanoseconds = timePicoseconds `div` 1000
timeSeconds :: Int64
nanoseconds :: Int64
(timeSeconds,nanoseconds) = if timeNanoseconds >= 86400000000000 then (86399,timeNanoseconds - 86399000000000) else timeNanoseconds `divMod` 1000000000
seconds :: Int64
seconds = days * 86400 + timeSeconds
in MkSystemTime seconds $ fromIntegral nanoseconds
systemEpochAbsolute :: AbsoluteTime
systemEpochAbsolute = taiNominalDayStart systemEpochDay
-- | Convert 'SystemTime' to 'AbsoluteTime', matching zero 'SystemTime' to midnight of 'systemEpochDay' TAI.
systemToTAITime :: SystemTime -> AbsoluteTime
systemToTAITime (MkSystemTime s ns) = let
diff :: DiffTime
diff = (fromIntegral s) + (fromIntegral ns) * 1E-9
in addAbsoluteTime diff systemEpochAbsolute
-- | The day of the epoch of 'SystemTime', 1970-01-01
systemEpochDay :: Day
systemEpochDay = ModifiedJulianDay 40587
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