error handling

Annex.hs

@@ -45,10 +45,9 @@ startAnnex = do
  - the annex directory and setting up the symlink pointing to its content. -}
 annexFile :: State -> FilePath -> IO ()
 annexFile state file = do
-	-- TODO check if already annexed
-	let alreadyannexed = Nothing
-	case (alreadyannexed) of
-		Just _ -> error $ "already annexed: " ++ file
+	r <- lookupFile file
+	case (r) of
+		Just _ -> error $ "already annexed " ++ file
 		Nothing -> do
 			checkLegal file
 			stored <- storeFile state file
@@ -84,16 +83,14 @@ annexFile state file = do
 {- Inverse of annexFile. -}
 unannexFile :: State -> FilePath -> IO ()
 unannexFile state file = do
-	-- TODO check if already annexed
-	let alreadyannexed = Just 1
-	case (alreadyannexed) of
+	r <- lookupFile file
+	case (r) of
 		Nothing -> error $ "not annexed " ++ file
-		Just _ -> do
-			key <- fileKey file
-			dropped <- dropFile state key
-			case (dropped) of
-				Nothing -> return ()
 		Just (key, backend) -> do
+			dropped <- dropFile state backend key
+			if (not dropped)
+				then error $ "backend refused to drop " ++ file
+				else do
 					let src = annexLocation state backend key
 					removeFile file
 					gitRun (repo state) ["rm", file]
@@ -110,20 +107,17 @@ unannexFile state file = do
 {- Transfers the file from a remote. -}
 annexGetFile :: State -> FilePath -> IO ()
 annexGetFile state file = do
-	-- TODO check if already annexed
-	let alreadyannexed = Just 1
-	case (alreadyannexed) of
+	r <- lookupFile file
+	case (r) of
 		Nothing -> error $ "not annexed " ++ file
-		Just _ -> do
-			key <- fileKey file
-			backend <- fileBackend file
+		Just (key, backend) -> do
 			inannex <- inAnnex state backend key
 			if (inannex)
 				then return ()
 				else do
 					let dest = annexLocation state backend key
 					createDirectoryIfMissing True (parentDir dest)
-					success <- retrieveFile state key dest
+					success <- retrieveFile state backend key dest
 					if (success)
 						then do
 							logStatus state key ValuePresent

Backend.hs

@@ -14,14 +14,13 @@
  - -}
 
 module Backend (
-	lookupBackend,
 	storeFile,
 	dropFile,
 	retrieveFile,
-	fileKey,
-	fileBackend
+	lookupFile
 ) where
 
+import Control.Exception
 import System.Directory
 import System.FilePath
 import Data.String.Utils
@@ -51,50 +50,24 @@ storeFile' (b:bs) state file = do
 
 {- Attempts to retrieve an key from one of the backends, saving it to
  - a specified location. -}
-retrieveFile :: State -> Key -> FilePath -> IO Bool
-retrieveFile state key dest = do
-	result <- lookupBackend state key
-	case (result) of
-		Nothing -> return False
-		Just backend -> (retrieveKeyFile backend) state key dest
+retrieveFile :: State -> Backend -> Key -> FilePath -> IO Bool
+retrieveFile state backend key dest = (retrieveKeyFile backend) state key dest
 
-{- Drops a key from the backend that has it. -}
-dropFile :: State -> Key -> IO (Maybe (Key, Backend))
-dropFile state key = do
-	result <- lookupBackend state key
-	case (result) of
-		Nothing -> return Nothing
-		Just backend -> do
-			(removeKey backend) state key
-			return $ Just (key, backend)
+{- Drops a key from a backend. -}
+dropFile :: State -> Backend -> Key -> IO Bool
+dropFile state backend key = (removeKey backend) state key
 
-{- Looks up the backend that has a key. -}
-lookupBackend :: State -> Key -> IO (Maybe Backend)
-lookupBackend state key = lookupBackend' (backends state) state key
-lookupBackend' [] _ _ = return Nothing
-lookupBackend' (b:bs) state key = do
-	present <- checkBackend b state key
-	if present
-		then
-			return $ Just b
-		else
-			lookupBackend' bs state key
-
-{- Checks if a key is available via a given backend. -}
-checkBackend :: Backend -> State -> Key -> IO (Bool)
-checkBackend backend state key = 
-	doesFileExist $ annexLocation state backend key
-
-{- Looks up the key corresponding to an annexed file,
+{- Looks up the key and backend corresponding to an annexed file,
  - by examining what the file symlinks to. -}
-fileKey :: FilePath -> IO Key
-fileKey file = do
-	l <- readSymbolicLink (file)
-	return $ Key $ takeFileName $ l
-
-{- Looks up the backend corresponding to an annexed file,
- - by examining what the file symlinks to. -}
-fileBackend :: FilePath -> IO Backend
-fileBackend file = do
-	l <- readSymbolicLink (file)
-	return $ lookupBackendName $ takeFileName $ parentDir $ l
+lookupFile :: FilePath -> IO (Maybe (Key, Backend))
+lookupFile file = do
+	result <- try (lookup)::IO (Either SomeException (Maybe (Key, Backend)))
+	case (result) of
+		Left err -> return Nothing
+		Right succ -> return succ
+	where 
+		lookup = do
+			l <- readSymbolicLink file
+			return $ Just (k l, b l)
+		k l = Key $ takeFileName $ l
+		b l = lookupBackendName $ takeFileName $ parentDir $ l