add metadata command to get/set metadata

Adds metadata log, and command.

Note that unsetting field values seems to currently be broken.
And in general this has had all of 2 minutes worth of testing.

This commit was sponsored by Julien Lefrique.

Command/MetaData.hs

@@ -0,0 +1,73 @@
+{- git-annex command
+ -
+ - Copyright 2014 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Command.MetaData where
+
+import Common.Annex
+import Command
+import Logs.MetaData
+import Types.MetaData
+
+import qualified Data.Set as S
+
+def :: [Command]
+def = [command "metadata" (paramPair paramFile (paramRepeating "FIELD[+-]=VALUE")) seek
+	SectionUtility "sets metadata of a file"]
+
+seek :: CommandSeek
+seek = withWords start
+
+start :: [String] -> CommandStart
+start (file:settings) = ifAnnexed file
+	go
+	(error $ "not an annexed file, so cannot add metadata: " ++ file)
+  where
+	go (k, _b) = do
+		showStart "metadata" file
+		next $ perform k (map parse settings)
+start _ = error "specify a file and the metadata to set"
+
+perform :: Key -> [Action] -> CommandPerform
+perform k actions = do
+	m <- getCurrentMetaData k
+	if null actions
+		then next $ cleanup m
+		else do
+			let m' = foldr apply m actions
+			addMetaData k m'
+			next $ cleanup m'
+	
+cleanup :: MetaData -> CommandCleanup
+cleanup m = do
+	showLongNote $ unlines $ concatMap showmeta $ fromMetaData $ currentMetaData m
+	return True
+  where
+	showmeta (f, vs) = map (\v -> fromMetaField f ++ "=" ++ fromMetaValue v) $ S.toList vs
+
+data Action
+	= AddMeta MetaField MetaValue
+	| DelMeta MetaField MetaValue
+	| SetMeta MetaField MetaValue
+
+parse :: String -> Action
+parse p = case lastMaybe f of
+	Just '+' -> AddMeta (mkf f') v
+	Just '-' -> DelMeta (mkf f') v
+	_ -> SetMeta (mkf f) v
+  where
+	(f, sv) = separate (== '=') p
+	f' = beginning f
+	v = toMetaValue sv
+	mkf fld = fromMaybe (badfield fld) (toMetaField fld)
+	badfield fld = error $ "Illegal metadata field name, \"" ++ fld ++ "\""
+
+apply :: Action -> MetaData -> MetaData
+apply (AddMeta f v) m = updateMetaData f v m
+apply (DelMeta f oldv) m = updateMetaData f (unsetMetaValue oldv) m
+apply (SetMeta f v) m = updateMetaData f v $
+	foldr (updateMetaData f) m $
+		map unsetMetaValue $ S.toList $ currentMetaDataValues f m