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{- git-annex key/value backends
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 -
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 - Copyright 2010-2017 Joey Hess <id@joeyh.name>
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 -
 - Licensed under the GNU GPL version 3 or higher.
 -}
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module Backend (
	orderedList,
	genKey,
	getBackend,
	chooseBackend,
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	lookupBackendVariety,
	maybeLookupBackendVariety,
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	isStableKey,
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) where
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import qualified Annex
import Annex.CheckAttr
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import Types.Key
import Types.KeySource
import qualified Types.Backend as B

-- When adding a new backend, import it here and add it to the list.
import qualified Backend.Hash
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import qualified Backend.WORM
import qualified Data.Map as M

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list :: [Backend]
list = Backend.Hash.backends ++ Backend.WORM.backends ++ Backend.URL.backends
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{- List of backends in the order to try them when storing a new key. -}
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orderedList :: Annex [Backend]
orderedList = do
	l <- Annex.getState Annex.backends -- list is cached here
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	if not $ null l
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		then return l
		else do
			f <- Annex.getState Annex.forcebackend
			case f of
				Just name | not (null name) ->
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					return [lookupname name]
				_ -> do
					l' <- gen . annexBackends <$> Annex.getGitConfig
					Annex.changeState $ \s -> s { Annex.backends = l' }
					return l'
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  where
	gen [] = list
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	gen ns = map lookupname ns
	lookupname = lookupBackendVariety . parseKeyVariety
{- Generates a key for a file, trying each backend in turn until one
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 - accepts it. -}
genKey :: KeySource -> Maybe Backend -> Annex (Maybe (Key, Backend))
	bs <- orderedList
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	let bs' = maybe bs (: bs) trybackend
genKey' :: [Backend] -> KeySource -> Annex (Maybe (Key, Backend))
genKey' [] _ = return Nothing
genKey' (b:bs) source = do
	r <- B.getKey b source
	case r of
		Just k -> return $ Just (makesane k, b)
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  where
	-- keyNames should not contain newline characters.
	makesane k = k { keyName = map fixbadchar (keyName k) }
	fixbadchar c
		| c == '\n' = '_'
		| otherwise = c
getBackend :: FilePath -> Key -> Annex (Maybe Backend)
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getBackend file k = case maybeLookupBackendVariety (keyVariety k) of
	Just backend -> return $ Just backend
	Nothing -> do
		warning $ "skipping " ++ file ++ " (unknown backend " ++ formatKeyVariety (keyVariety k) ++ ")"
		return Nothing
{- Looks up the backend that should be used for a file.
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 - That can be configured on a per-file basis in the gitattributes file. -}
chooseBackend :: FilePath -> Annex (Maybe Backend)
chooseBackend f = Annex.getState Annex.forcebackend >>= go
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  where
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	go Nothing =  maybeLookupBackendVariety . parseKeyVariety
		<$> checkAttr "annex.backend" f
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	go (Just _) = Just . Prelude.head <$> orderedList
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{- Looks up a backend by variety. May fail if unsupported or disabled. -}
lookupBackendVariety :: KeyVariety -> Backend
lookupBackendVariety v = fromMaybe unknown $ maybeLookupBackendVariety v
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  where
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	unknown = error $ "unknown backend " ++ formatKeyVariety v
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maybeLookupBackendVariety :: KeyVariety -> Maybe Backend
maybeLookupBackendVariety v = M.lookup v varietyMap
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varietyMap :: M.Map KeyVariety Backend
varietyMap = M.fromList $ zip (map B.backendVariety list) list
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isStableKey :: Key -> Bool
isStableKey k = maybe False (`B.isStableKey` k) 
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	(maybeLookupBackendVariety (keyVariety k))