annex.genmetadata can be set to make git-annex automatically set metadata (year and month) when adding files

Annex/MetaData.hs

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+{- git-annex metadata
+ -
+ - Copyright 2014 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Annex.MetaData where
+
+import Common.Annex
+import qualified Annex
+import Types.MetaData
+import Logs.MetaData
+
+import qualified Data.Set as S
+import qualified Data.Map as M
+import Data.Time.Calendar
+import Data.Time.Clock
+import Data.Time.Clock.POSIX
+
+tagMetaField :: MetaField
+tagMetaField = MetaField "tag"
+
+yearMetaField :: MetaField
+yearMetaField = MetaField "year"
+
+monthMetaField :: MetaField
+monthMetaField = MetaField "month"
+
+{- Generates metadata for a file that has just been ingested into the
+ - annex. Passed the FileStatus of the content file.
+ -
+ - Does not overwrite any existing metadata values for the key.
+ -}
+genMetaData :: Key -> FileStatus -> Annex ()
+genMetaData key status = whenM (annexGenMetaData <$> Annex.getGitConfig) $ do
+	metadata <- getCurrentMetaData key
+	let metadata' = genMetaData' status metadata
+	unless (metadata' == emptyMetaData) $
+		addMetaData key metadata'
+
+genMetaData' :: FileStatus -> MetaData -> MetaData
+genMetaData' status old = MetaData $ M.fromList $ filter isnew
+	[ (yearMetaField, S.singleton $ toMetaValue $ show y)
+	, (monthMetaField, S.singleton $ toMetaValue $ show m)
+	]
+  where
+	isnew (f, _) = S.null (currentMetaDataValues f old)
+	(y, m, _d) = toGregorian $ utctDay $ 
+		posixSecondsToUTCTime $ realToFrac $
+			modificationTime status