    {-# OPTIONS -ffi -Wall -Werror #-}

    -- #hide
    module Data.Time.LocalTime.TimeZone
    (
    	-- * Time zones
    	TimeZone(..),timeZoneOffsetString,minutesToTimeZone,hoursToTimeZone,utc,

    	-- getting the locale time zone
    	getTimeZone,getCurrentTimeZone
    ) where

    --import System.Time.Calendar.Format
    import Data.Time.Calendar.Private
    import Data.Time.Clock
    import Data.Time.Clock.POSIX

    import Foreign
    import Foreign.C

    -- | A TimeZone is a whole number of minutes offset from UTC, together with a name and a \"just for summer\" flag.
    data TimeZone = TimeZone {
    	-- | The number of minutes offset from UTC. Positive means local time will be later in the day than UTC.
    	timeZoneMinutes :: Int,
    	-- | Is this time zone just persisting for the summer?
    	timeZoneSummerOnly :: Bool,
    	-- | The name of the zone, typically a three- or four-letter acronym.
    	timeZoneName :: String
    } deriving (Eq,Ord)

    -- | Create a nameless non-summer timezone for this number of minutes
    minutesToTimeZone :: Int -> TimeZone
    minutesToTimeZone m = TimeZone m False ""

    -- | Create a nameless non-summer timezone for this number of hours
    hoursToTimeZone :: Int -> TimeZone
    hoursToTimeZone i = minutesToTimeZone (60 * i)

    showT :: Int -> String
    showT t = (show2 (div t 60)) ++ (show2 (mod t 60))

    -- | Text representing the offset of this timezone, such as \"-0800\" or \"+0400\" (like %z in formatTime)
    timeZoneOffsetString :: TimeZone -> String
    timeZoneOffsetString (TimeZone t _ _) | t < 0 = '-':(showT (negate t))
    timeZoneOffsetString (TimeZone t _ _) = '+':(showT t)

    instance Show TimeZone where
    	show zone@(TimeZone _ _ "") = timeZoneOffsetString zone
    	show (TimeZone _ _ name) = name

    -- | The UTC time zone
    utc :: TimeZone
    utc = TimeZone 0 False "UTC"

    {-# CFILES cbits/HsTime.c #-}
    foreign import ccall unsafe "HsTime.h get_current_timezone_seconds" get_current_timezone_seconds :: CTime -> Ptr CInt -> Ptr CString -> IO CLong

    posixToCTime :: POSIXTime -> CTime
    posixToCTime  = fromInteger . floor

    -- | Get the local time-zone for a given time (varying as per summertime adjustments)
    getTimeZone :: UTCTime -> IO TimeZone
    getTimeZone time = with 0 (\pdst -> with nullPtr (\pcname -> do
    	secs <- get_current_timezone_seconds (posixToCTime (utcTimeToPOSIXSeconds time)) pdst pcname
    	case secs of
    		0x80000000 -> fail "localtime_r failed"
    		_ -> do
    			dst <- peek pdst
    			cname <- peek pcname
    			name <- peekCString cname
    			return (TimeZone (div (fromIntegral secs) 60) (dst == 1) name)
    	))

    -- | Get the current time-zone
    getCurrentTimeZone :: IO TimeZone
    getCurrentTimeZone = getCurrentTime >>= getTimeZone