1 files changed, 57 insertions, 0 deletions
diff --git a/src/Storage/Internal.hs b/src/Storage/Internal.hs
new file mode 100644
index 0000000..6a86dea
--- /dev/null
+++ b/src/Storage/Internal.hs
@@ -0,0 +1,57 @@
+module Storage.Internal where
+
+import Control.Exception
+
+import Data.ByteString (ByteString)
+import qualified Data.ByteString as B
+import qualified Data.ByteString.Lazy as BL
+
+import System.Directory
+import System.FilePath
+import System.IO
+import System.Posix.Files
+import System.Posix.IO
+import System.Posix.Types
+
+data Storage = Storage FilePath
+    deriving (Eq, Ord)
+
+
+openFdParents :: FilePath -> OpenMode -> Maybe FileMode -> OpenFileFlags -> IO Fd
+openFdParents path omode fmode flags = do
+    createDirectoryIfMissing True (takeDirectory path)
+    openFd path omode fmode flags
+
+writeFileOnce :: FilePath -> BL.ByteString -> IO ()
+writeFileOnce file content = bracket
+    (fdToHandle =<< openFdParents locked WriteOnly (Just $ unionFileModes ownerReadMode ownerWriteMode) (defaultFileFlags { exclusive = True }))
+    hClose $ \h -> do
+        fileExist file >>= \case
+            True  -> removeLink locked
+            False -> do BL.hPut h content
+                        rename locked file
+    where locked = file ++ ".lock"
+
+writeFileChecked :: FilePath -> Maybe ByteString -> ByteString -> IO (Either (Maybe ByteString) ())
+writeFileChecked file prev content = bracket
+    (fdToHandle =<< openFdParents locked WriteOnly (Just $ unionFileModes ownerReadMode ownerWriteMode) (defaultFileFlags { exclusive = True }))
+    hClose $ \h -> do
+        (prev,) <$> fileExist file >>= \case
+            (Nothing, True) -> do
+                current <- B.readFile file
+                removeLink locked
+                return $ Left $ Just current
+            (Nothing, False) -> do B.hPut h content
+                                   rename locked file
+                                   return $ Right ()
+            (Just expected, True) -> do
+                current <- B.readFile file
+                if current == expected then do B.hPut h content
+                                               rename locked file
+                                               return $ return ()
+                                       else do removeLink locked
+                                               return $ Left $ Just current
+            (Just _, False) -> do
+                removeLink locked
+                return $ Left Nothing
+    where locked = file ++ ".lock"