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-- | Interval-based implementation of preview polling
--
{-# LANGUAGE CPP #-}
module Hakyll.Web.Preview.Poll
( previewPoll
) where
import Control.Applicative ((<$>))
import Control.Concurrent (threadDelay)
import Control.Monad (filterM)
#if MIN_VERSION_directory(1,2,0)
import Data.Time (getCurrentTime)
#else
import System.Time (getClockTime)
#endif
import System.Directory (getModificationTime, doesFileExist)
import Hakyll.Core.Configuration
-- | A preview thread that periodically recompiles the site.
--
previewPoll :: Configuration -- ^ Configuration
-> IO [FilePath] -- ^ Updating action
-> IO () -- ^ Can block forever
previewPoll _ update = do
#if MIN_VERSION_directory(1,2,0)
time <- getCurrentTime
#else
time <- getClockTime
#endif
loop time =<< update
where
delay = 1000000
loop time files = do
threadDelay delay
files' <- filterM doesFileExist files
filesTime <- case files' of
[] -> return time
_ -> maximum <$> mapM getModificationTime files'
if filesTime > time || files' /= files
then loop filesTime =<< update
else loop time files'
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