1 files changed, 83 insertions, 0 deletions
diff --git a/src/Hakyll/Core/Provider/Modified.hs b/src/Hakyll/Core/Provider/Modified.hs
new file mode 100644
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+++ b/src/Hakyll/Core/Provider/Modified.hs
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+--------------------------------------------------------------------------------
+module Hakyll.Core.Provider.Modified
+    ( resourceModified
+    , resourceModificationTime
+    ) where
+
+
+--------------------------------------------------------------------------------
+import           Control.Applicative                ((<$>), (<*>))
+import           Control.Monad                      (when)
+import qualified Crypto.Hash.MD5                    as MD5
+import qualified Data.ByteString                    as B
+import qualified Data.ByteString.Lazy               as BL
+import           Data.IORef
+import qualified Data.Map                           as M
+import           Data.Time                          (UTCTime)
+import           System.Directory                   (getModificationTime)
+
+
+--------------------------------------------------------------------------------
+import           Hakyll.Core.Identifier
+import           Hakyll.Core.Provider.Internal
+import           Hakyll.Core.Provider.MetadataCache
+import           Hakyll.Core.Store                  (Store)
+import qualified Hakyll.Core.Store                  as Store
+
+
+--------------------------------------------------------------------------------
+-- | A resource is modified if it or its metadata has changed
+resourceModified :: Provider -> Identifier -> IO Bool
+resourceModified rp r
+    | not exists = return False
+    | otherwise  = do
+        cache <- readIORef cacheRef
+        case M.lookup normalized cache of
+            Just m  -> return m
+            Nothing -> do
+                -- Check if the actual file was modified, and do a recursive
+                -- call to check if the metadata file was modified
+                m <- (||)
+                    <$> fileDigestModified store (toFilePath r)
+                    <*> resourceModified rp (resourceMetadataResource r)
+                modifyIORef cacheRef (M.insert normalized m)
+
+                -- Important! (But ugly)
+                when m $ resourceInvalidateMetadataCache rp r
+
+                return m
+  where
+    normalized = setVersion Nothing r
+    exists     = resourceExists rp r
+    store      = providerStore rp
+    cacheRef   = providerModifiedCache rp
+
+
+--------------------------------------------------------------------------------
+-- | Utility: Check if a the digest of a file was modified
+fileDigestModified :: Store -> FilePath -> IO Bool
+fileDigestModified store fp = do
+    -- Get the latest seen digest from the store, and calculate the current
+    -- digest for the
+    lastDigest <- Store.get store key
+    newDigest  <- fileDigest fp
+    if Store.Found newDigest == lastDigest
+        -- All is fine, not modified
+        then return False
+        -- Resource modified; store new digest
+        else do
+            Store.set store key newDigest
+            return True
+  where
+    key = ["Hakyll.Core.Resource.Provider.fileModified", fp]
+
+
+--------------------------------------------------------------------------------
+-- | Utility: Retrieve a digest for a given file
+fileDigest :: FilePath -> IO B.ByteString
+fileDigest = fmap MD5.hashlazy . BL.readFile
+
+
+--------------------------------------------------------------------------------
+resourceModificationTime :: Identifier -> IO UTCTime
+resourceModificationTime = getModificationTime . toFilePath