Add file utility module

2 files changed, 67 insertions, 24 deletions

diff --git a/src/Hakyll/Core/ResourceProvider/FileResourceProvider.hs b/src/Hakyll/Core/ResourceProvider/FileResourceProvider.hs
index b682634..442ae9a 100644
--- a/src/Hakyll/Core/ResourceProvider/FileResourceProvider.hs
+++ b/src/Hakyll/Core/ResourceProvider/FileResourceProvider.hs
@@ -5,13 +5,10 @@ module Hakyll.Core.ResourceProvider.FileResourceProvider
     ) where
 
 import Control.Applicative ((<$>))
-import Control.Monad (forM)
-
-import System.Directory (doesDirectoryExist, getDirectoryContents)
-import System.FilePath ((</>), normalise)
 
 import Hakyll.Core.ResourceProvider
 import Hakyll.Core.Identifier
+import Hakyll.Core.Util.File
 
 -- | Create a filesystem-based 'ResourceProvider'
 --
@@ -22,23 +19,3 @@ fileResourceProvider = do
         { resourceList   = list
         , resourceString = readFile . toFilePath
         }
-
--- | Get all contents of a directory. Note that files starting with a dot (.)
---   will be ignored.
---
-getRecursiveContents :: FilePath -> IO [FilePath]
-getRecursiveContents topdir = do
-    topdirExists <- doesDirectoryExist topdir
-    if topdirExists
-        then do names <- getDirectoryContents topdir
-                let properNames = filter isProper names
-                paths <- forM properNames $ \name -> do
-                    let path = topdir </> name
-                    isDirectory <- doesDirectoryExist path
-                    if isDirectory
-                        then getRecursiveContents path
-                        else return [normalise path]
-                return (concat paths)
-        else return []
-  where
-    isProper = not . (== '.') . head
diff --git a/src/Hakyll/Core/Util/File.hs b/src/Hakyll/Core/Util/File.hs
new file mode 100644
index 0000000..355eafb
--- /dev/null
+++ b/src/Hakyll/Core/Util/File.hs
@@ -0,0 +1,66 @@
+-- | A module containing various file utility functions
+--
+module Hakyll.Core.Util.File
+    ( makeDirectories
+    , getRecursiveContents
+    , isFileObsolete
+    ) where
+
+import System.FilePath (normalise, takeDirectory, (</>))
+import System.Time (ClockTime)
+import Control.Monad (forM)
+import System.Directory ( createDirectoryIfMissing, doesDirectoryExist
+                        , doesFileExist, getModificationTime
+                        , getDirectoryContents
+                        )
+
+-- | Given a path to a file, try to make the path writable by making
+--   all directories on the path.
+--
+makeDirectories :: FilePath -> IO ()
+makeDirectories = createDirectoryIfMissing True . takeDirectory
+
+-- | Get all contents of a directory. Note that files starting with a dot (.)
+--   will be ignored.
+--
+getRecursiveContents :: FilePath -> IO [FilePath]
+getRecursiveContents topdir = do
+    topdirExists <- doesDirectoryExist topdir
+    if topdirExists
+        then do names <- getDirectoryContents topdir
+                let properNames = filter isProper names
+                paths <- forM properNames $ \name -> do
+                    let path = topdir </> name
+                    isDirectory <- doesDirectoryExist path
+                    if isDirectory
+                        then getRecursiveContents path
+                        else return [normalise path]
+                return (concat paths)
+        else return []
+  where
+    isProper = not . (== ".") . take 1
+
+-- | Check if a timestamp is obsolete compared to the timestamps of a number of
+-- files. When they are no files, it is never obsolete.
+--
+isObsolete :: ClockTime    -- ^ The time to check.
+           -> [FilePath]   -- ^ Dependencies of the cached file.
+           -> IO Bool
+isObsolete _ [] = return False
+isObsolete timeStamp depends = do
+    dependsModified <- mapM getModificationTime depends
+    return (timeStamp < maximum dependsModified)
+
+-- | Check if a file is obsolete, given it's dependencies. When the file does
+-- not exist, it is always obsolete. Other wise, it is obsolete if any of it's
+-- dependencies has a more recent modification time than the file.
+--
+isFileObsolete :: FilePath    -- ^ The cached file
+               -> [FilePath]  -- ^ Dependencies of the cached file
+               -> IO Bool
+isFileObsolete file depends = do
+    exists <- doesFileExist file
+    if not exists
+        then return True
+        else do timeStamp <- getModificationTime file
+                isObsolete timeStamp depends