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+{- git-annex key/value backend data type
+ -
+ - Most things should not need this, using Types instead
+ -
+ - Copyright 2010 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module BackendClass where
+
+import Key
+
+data Backend a = Backend {
+	-- name of this backend
+	name :: String,
+	-- converts a filename to a key
+	getKey :: FilePath -> a (Maybe Key),
+	-- stores a file's contents to a key
+	storeFileKey :: FilePath -> Key -> a Bool,
+	-- retrieves a key's contents to a file
+	retrieveKeyFile :: Key -> FilePath -> a Bool,
+	-- removes a key, optionally checking that enough copies are stored
+	-- elsewhere
+	removeKey :: Key -> Maybe Int -> a Bool,
+	-- checks if a backend is storing the content of a key
+	hasKey :: Key -> a Bool,
+	-- called during fsck to check a key
+	-- (second parameter may be the filename associated with it)
+	-- (third parameter may be the number of copies that there should
+	-- be of the key)
+	fsckKey :: Key -> Maybe FilePath -> Maybe Int -> a Bool
+}
+
+instance Show (Backend a) where
+	show backend = "Backend { name =\"" ++ name backend ++ "\" }"
+
+instance Eq (Backend a) where
+	a == b = name a == name b