lifted out the kqueue and inotify to a generic DirWatcher interface

Kqueue code for dispatching events is not tested and probably doesn't
build.

Utility/DirWatcher.hs

@@ -0,0 +1,53 @@
+{- generic directory watching interface
+ -
+ - Uses either inotify or kqueue to watch a directory (and subdirectories)
+ - for changes, and runs hooks for different sorts of events as they occur.
+ -
+ - Copyright 2012 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+{-# LANGUAGE CPP #-}
+
+module Utility.DirWatcher where
+
+import Utility.Types.DirWatcher
+
+#if WITH_INOTIFY
+import qualified Utility.INotify as INotify
+import qualified System.INotify as INotify
+import Utility.ThreadScheduler
+#endif
+#if WITH_KQUEUE
+import qualified Utility.Kqueue as Kqueue
+#endif
+
+type Pruner = FilePath -> Bool
+
+canWatch :: Bool
+#if (WITH_INOTIFY || WITH_KQUEUE)
+canWatch = True
+#else
+#if defined linux_HOST_OS
+#warning "Building without inotify support"
+#endif
+canWatch = False
+#endif
+
+#if WITH_INOTIFY
+watchDir :: FilePath -> Pruner -> WatchHooks -> (IO () -> IO ()) -> IO ()
+watchDir dir prune hooks runstartup = INotify.withINotify $ \i -> do
+	runstartup $ INotify.watchDir i dir prune hooks
+	waitForTermination -- Let the inotify thread run.
+#else
+#if WITH_KQUEUE
+watchDir :: FilePath -> Pruner -> WatchHooks -> (IO Kqueue.Kqueue -> IO Kqueue.Kqueue) -> IO ()
+watchDir dir ignored hooks runstartup = do
+	kq <- runstartup $ Kqueue.initKqueue dir ignored
+	Kqueue.runHooks kq hooks
+#else
+watchDir :: FilePath -> Pruner -> WatchHooks -> (IO () -> IO ()) -> IO ()
+watchDir = undefined
+#endif
+#endif