{- dropping of unwanted content
 -
 - Copyright 2012-2014 Joey Hess <joey@kitenet.net>
 -
 - Licensed under the GNU GPL version 3 or higher.
 -}

module Annex.Drop where

import Common.Annex
import Logs.Trust
import Types.Remote (uuid)
import qualified Remote
import qualified Command.Drop
import Command
import Annex.Wanted
import Annex.Exception
import Config
import Annex.Content.Direct

import qualified Data.Set as S
import System.Log.Logger (debugM)

type Reason = String

{- Drop a key from local and/or remote when allowed by the preferred content
 - and numcopies settings.
 -
 - The UUIDs are ones where the content is believed to be present.
 - The Remote list can include other remotes that do not have the content;
 - only ones that match the UUIDs will be dropped from.
 - If allowed to drop fromhere, that drop will be tried first.
 -
 - A remote can be specified that is known to have the key. This can be
 - used an an optimisation when eg, a key has just been uploaded to a
 - remote.
 -
 - In direct mode, all associated files are checked, and only if all
 - of them are unwanted are they dropped.
 -
 - The runner is used to run commands, and so can be either callCommand
 - or commandAction.
 -}
handleDropsFrom :: [UUID] -> [Remote] -> Reason -> Bool -> Key -> AssociatedFile -> Maybe Remote -> CommandActionRunner -> Annex ()
handleDropsFrom _ _ _ _ _ Nothing _ _ = noop
handleDropsFrom locs rs reason fromhere key (Just afile) knownpresentremote runner = do
	fs <- ifM isDirect
		( do
			l <- associatedFilesRelative key
			if null l
				then return [afile]
				else return l
		, return [afile]
		)
	n <- getcopies fs
	if fromhere && checkcopies n Nothing
		then go fs rs =<< dropl fs n
		else go fs rs n
  where
	getcopies fs = do
		(untrusted, have) <- trustPartition UnTrusted locs
		numcopies <- maximum <$> mapM (getNumCopies <=< numCopies) fs
		return (length have, numcopies, S.fromList untrusted)

	{- Check that we have enough copies still to drop the content.
	 - When the remote being dropped from is untrusted, it was not
	 - counted as a copy, so having only numcopies suffices. Otherwise,
	 - we need more than numcopies to safely drop. -}
	checkcopies (have, numcopies, _untrusted) Nothing = have > numcopies
	checkcopies (have, numcopies, untrusted) (Just u)
		| S.member u untrusted = have >= numcopies
		| otherwise = have > numcopies
	
	decrcopies (have, numcopies, untrusted) Nothing =
		(have - 1, numcopies, untrusted)
	decrcopies v@(_have, _numcopies, untrusted) (Just u)
		| S.member u untrusted = v
		| otherwise = decrcopies v Nothing

	go _ [] _ = noop
	go fs (r:rest) n
		| uuid r `S.notMember` slocs = go fs rest n
		| checkcopies n (Just $ Remote.uuid r) =
			dropr fs r n >>= go fs rest
		| otherwise = noop

	checkdrop fs n@(have, numcopies, _untrusted) u a =
		ifM (allM (wantDrop True u . Just) fs)
			( ifM (safely $ runner $ a (Just numcopies))
				( do
					liftIO $ debugM "drop" $ unwords
						[ "dropped"
						, afile
						, "(from " ++ maybe "here" show u ++ ")"
						, "(copies now " ++ show (have - 1) ++ ")"
						, ": " ++ reason
						]
					return $ decrcopies n u
				, return n
				)
			, return n
			)

	dropl fs n = checkdrop fs n Nothing $ \numcopies ->
		Command.Drop.startLocal (Just afile) numcopies key knownpresentremote

	dropr fs r n  = checkdrop fs n (Just $ Remote.uuid r) $ \numcopies ->
		Command.Drop.startRemote (Just afile) numcopies key r

	slocs = S.fromList locs
	
	safely a = either (const False) id <$> tryAnnex a