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|
{- git-annex general metadata storage log
-
- A line of the log will look like "timestamp field [+-]value [...]"
-
- Note that unset values are preserved. Consider this case:
-
- We have:
-
- 100 foo +x
- 200 foo -x
-
- An unmerged remote has:
-
- 150 foo +x
-
- After union merge, because the foo -x was preserved, we know that
- after the other remote redundantly set foo +x, it was unset,
- and so foo currently has no value.
-
-
- Copyright 2014 Joey Hess <joey@kitenet.net>
-
- Licensed under the GNU GPL version 3 or higher.
-}
{-# OPTIONS_GHC -fno-warn-orphans #-}
{-# LANGUAGE CPP #-}
module Logs.MetaData (
getCurrentMetaData,
getMetaData,
addMetaData,
addMetaData',
currentMetaData,
) where
import Common.Annex
import Types.MetaData
import qualified Annex.Branch
import Logs
import Logs.SingleValue
import qualified Data.Set as S
import Data.Time.Clock.POSIX
instance SingleValueSerializable MetaData where
serialize = Types.MetaData.serialize
deserialize = Types.MetaData.deserialize
getMetaData :: Key -> Annex (Log MetaData)
getMetaData = readLog . metaDataLogFile
{- Go through the log from oldest to newest, and combine it all
- into a single MetaData representing the current state. -}
getCurrentMetaData :: Key -> Annex MetaData
getCurrentMetaData = currentMetaData . collect <$$> getMetaData
where
collect = foldl' unionMetaData newMetaData . map value . S.toAscList
{- Adds in some metadata, which can override existing values, or unset
- them, but otherwise leaves any existing metadata as-is. -}
addMetaData :: Key -> MetaData -> Annex ()
addMetaData k metadata = addMetaData' k metadata =<< liftIO getPOSIXTime
{- Reusing the same timestamp when making changes to the metadata
- of multiple keys is a nice optimisation. The same metadata lines
- will tend to be generated across the different log files, and so
- git will be able to pack the data more efficiently. -}
addMetaData' :: Key -> MetaData -> POSIXTime -> Annex ()
addMetaData' k metadata now = Annex.Branch.change (metaDataLogFile k) $
showLog . simplifyLog
. S.insert (LogEntry now metadata)
. parseLog
{- Simplify a log, removing historical values that are no longer
- needed.
-
- This is not as simple as just making a single log line with the newest
- state of all metadata. Consider this case:
-
- We have:
-
- 100 foo +x bar +y
- 200 foo -x
-
- An unmerged remote has:
-
- 150 bar -y baz +w
-
- If what we have were simplified to "200 foo -x bar +y" then when the line
- from the remote became available, it would be older than the simplified
- line, and its change to bar would not take effect. That is wrong.
-
- Instead, simplify it to:
-
- 100 bar +y
- 200 foo -x
-
- (Note that this ends up with the same number of lines as the
- unsimplified version, so there's really no point in updating
- the log to this version. Doing so would only add data to git,
- with little benefit.)
-
- Now merging with the remote yields:
-
- 100 bar +y
- 150 bar -y baz +w
- 200 foo -x
-
- Simplifying again:
-
- 150 bar +z baz +w
- 200 foo -x
-}
simplifyLog :: Log MetaData -> Log MetaData
simplifyLog s = case sl of
(newest:rest) ->
let sl' = go [newest] (value newest) rest
in if length sl' < length sl
then S.fromList sl'
else s
_ -> s
where
#if MIN_VERSION_containers(0,5,0)
sl = S.toDescList s
#else
sl = reverse (S.toAscList s)
#endif
go c _ [] = c
go c newer (l:ls)
| unique == newMetaData = go c newer ls
| otherwise = go (l { value = unique } : c)
(unionMetaData unique newer) ls
where
older = value l
unique = older `differenceMetaData` newer
|
