{- dropping of unwanted content
 -
 - Copyright 2012-2021 Joey Hess <id@joeyh.name>
 -
 - Licensed under the GNU AGPL version 3 or higher.
 -}

{-# LANGUAGE OverloadedStrings #-}

module Annex.Drop where

import Annex.Common
import qualified Annex
import Logs.Trust
import Annex.NumCopies
import Types.Remote (uuid, appendonly, config, remotetype, thirdPartyPopulated)
import qualified Remote
import qualified Command.Drop
import Command
import Annex.Wanted
import Annex.Content
import Annex.SpecialRemote.Config
import qualified Database.Keys
import Git.FilePath

import qualified Data.Set as S

type Reason = String

{- Drop a key from local and/or remote when allowed by the preferred content
 - and numcopies settings.
 -
 - Skips trying to drop from remotes that are appendonly, since those drops
 - would presumably fail. Also skips dropping from exporttree/importtree remotes,
 - which don't allow dropping individual keys, and from thirdPartyPopulated
 - remotes.
 -
 - 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 done last. This is done
 - because local drops do not need any LockedCopy evidence, and so dropping
 - from local last allows the content to be removed from more remotes.
 -
 - A VerifiedCopy can be provided as an optimisation when eg, a key
 - has just been uploaded to a remote.
 -
 - The runner is used to run CommandStart sequentially, it's typically 
 - callCommandAction.
 -}
handleDropsFrom :: [UUID] -> [Remote] -> Reason -> Bool -> Key -> AssociatedFile -> SeekInput -> [VerifiedCopy] -> (CommandStart -> CommandCleanup) -> Annex ()
handleDropsFrom locs rs reason fromhere key afile si preverified runner = do
	g <- Annex.gitRepo
	l <- map (`fromTopFilePath` g)
		<$> Database.Keys.getAssociatedFiles key
	let fs = case afile of
		AssociatedFile (Just f) -> nub (f : l)
		AssociatedFile Nothing -> l
	n <- getcopies fs
	void $ if fromhere && checkcopies n Nothing
		then go fs rs n >>= dropl fs
		else go fs rs n
  where
	getcopies fs = do
		(untrusted, have) <- trustPartition UnTrusted locs
		(numcopies, mincopies) <- if null fs
			then (,) <$> getNumCopies <*> getMinCopies
			else do
				l <- mapM getFileNumMinCopies fs
				return (maximum $ map fst l, maximum $ map snd l)
		return (length have, numcopies, mincopies, 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.
	 -
	 - This is not the final check that it's safe to drop, but it
	 - avoids doing extra work to do that check later in cases where it
	 - will surely fail.
	 -}
	checkcopies (have, numcopies, mincopies, _untrusted) Nothing =
		NumCopies have > numcopies && MinCopies have > mincopies
	checkcopies (have, numcopies, mincopies, untrusted) (Just u)
		| S.member u untrusted = NumCopies have >= numcopies && MinCopies have >= mincopies
		| otherwise = NumCopies have > numcopies && MinCopies have > mincopies
	
	decrcopies (have, numcopies, mincopies, untrusted) Nothing =
		(have - 1, numcopies, mincopies, untrusted)
	decrcopies v@(_have, _numcopies, _mincopies, untrusted) (Just u)
		| S.member u untrusted = v
		| otherwise = decrcopies v Nothing

	go _ [] n = pure n
	go fs (r:rest) n
		| uuid r `S.notMember` slocs = go fs rest n
		| appendonly r = go fs rest n
		| exportTree (config r) = go fs rest n
		| importTree (config r) = go fs rest n
		| thirdPartyPopulated (remotetype r) = go fs rest n
		| checkcopies n (Just $ Remote.uuid r) =
			dropr fs r n >>= go fs rest
		| otherwise = pure n

	checkdrop fs n u a
		| null fs = check $ -- no associated files; unused content
			wantDrop True u (Just key) (AssociatedFile Nothing)
		| otherwise = check $
			allM (wantDrop True u (Just key) . AssociatedFile . Just) fs
		where
			check c = ifM c
				( dodrop n u a
				, return n
				)

	dodrop n@(have, numcopies, mincopies, _untrusted) u a = 
		ifM (safely $ runner $ a numcopies mincopies)
			( do
				fastDebug "Annex.Drop" $ unwords
					[ "dropped"
					, case afile of
						AssociatedFile Nothing -> serializeKey key
						AssociatedFile (Just af) -> fromRawFilePath af
					, "(from " ++ maybe "here" show u ++ ")"
					, "(copies now " ++ show (have - 1) ++ ")"
					, ": " ++ reason
					]
				return $ decrcopies n u
			, return n
			)

	dropl fs n = checkdrop fs n Nothing $ \numcopies mincopies ->
		stopUnless (inAnnex key) $
			Command.Drop.startLocal afile ai si numcopies mincopies key preverified

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

	ai = mkActionItem (key, afile)

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