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+{- git-annex repository differences
+ -
+ - Copyright 2015 Joey Hess <id@joeyh.name>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Annex.Difference (
+	module Types.Difference,
+	setDifferences,
+) where
+
+import Common.Annex
+import Types.Difference
+import Logs.Difference
+import Config
+import Annex.UUID
+import Logs.UUID
+import Annex.Version
+import qualified Annex
+
+import qualified Data.Map as M
+
+-- Differences are only allowed to be tweaked when initializing a
+-- repository for the first time, and then only if there is not another
+-- known uuid. If the repository was cloned from elsewhere, it inherits
+-- the existing settings.
+--
+-- Must be called before setVersion, so it can check if this is the first
+-- time the repository is being initialized.
+setDifferences :: Annex ()
+setDifferences = do
+	u <- getUUID
+	otherds <- either error return 
+		=<< sanityCheckDifferences . allDifferences
+			<$> recordedDifferences
+	ds <- mappend otherds . annexDifferences <$> Annex.getGitConfig
+	when (ds /= mempty) $ do
+		ds'@(Differences l) <- ifM (isJust <$> getVersion)
+			( do
+				oldds <- recordedDifferencesFor u
+				when (ds /= oldds) $
+					warning $ "Cannot change tunable parameters in already initialized repository."
+				return oldds
+			, if otherds == mempty
+				then ifM (not . null . filter (/= u) . M.keys <$> uuidMap)
+					( do
+						warning "Cannot change tunable parameters in a clone of an existing repository."
+						return mempty
+					, return ds
+					)
+				else if otherds /= ds
+					then do
+						warning "The specified tunable parameters differ from values being used in other clones of this repository."
+						return otherds
+					else return ds
+			)
+		forM_ l $ \d ->
+			setConfig (ConfigKey $ differenceConfigKey d) (differenceConfigVal d)
+		recordDifferences ds' u