{- git-annex command
 -
 - Copyright 2010-2011 Joey Hess <joey@kitenet.net>
 -
 - Licensed under the GNU GPL version 3 or higher.
 -}

{-# LANGUAGE BangPatterns #-}

module Command.Unused where

import qualified Data.Set as S
import qualified Data.ByteString.Lazy.Char8 as L

import Common.Annex
import Command
import Annex.Content
import Utility.FileMode
import Utility.TempFile
import Logs.Location
import qualified Annex
import qualified Git
import qualified Git.Ref
import qualified Git.LsFiles as LsFiles
import qualified Git.LsTree as LsTree
import qualified Backend
import qualified Remote
import qualified Annex.Branch
import Annex.CatFile

def :: [Command]
def = [dontCheck fromOpt $ command "unused" paramNothing seek
	"look for unused file content"]

seek :: [CommandSeek]
seek = [withNothing start]

{- Finds unused content in the annex. -} 
start :: CommandStart
start = do
	from <- Annex.getState Annex.fromremote
	let (name, action) = case from of
		Nothing -> (".", checkUnused)
		Just "." -> (".", checkUnused)
		Just n -> (n, checkRemoteUnused n)
	showStart "unused" name
	next action

checkUnused :: CommandPerform
checkUnused = do
	(unused, stalebad, staletmp) <- unusedKeys
	_ <- list "" unusedMsg unused 0 >>=
		list "bad" staleBadMsg stalebad >>=
			list "tmp" staleTmpMsg staletmp
	next $ return True
	where
		list file msg l c = do
			let unusedlist = number c l
			unless (null l) $ showLongNote $ msg unusedlist
			writeUnusedFile file unusedlist
			return $ c + length l

checkRemoteUnused :: String -> CommandPerform
checkRemoteUnused name = do
	checkRemoteUnused' =<< Remote.byName name
	next $ return True

checkRemoteUnused' :: Remote.Remote Annex -> Annex ()
checkRemoteUnused' r = do
	showAction "checking for unused data"
	remotehas <- loggedKeysFor (Remote.uuid r)
	remoteunused <- excludeReferenced remotehas
	let list = number 0 remoteunused
	writeUnusedFile "" list
	unless (null remoteunused) $ showLongNote $ remoteUnusedMsg r list

writeUnusedFile :: FilePath -> [(Int, Key)] -> Annex ()
writeUnusedFile prefix l = do
	logfile <- fromRepo $ gitAnnexUnusedLog prefix
	liftIO $ viaTmp writeFile logfile $
		unlines $ map (\(n, k) -> show n ++ " " ++ show k) l

table :: [(Int, Key)] -> [String]
table l = "  NUMBER  KEY" : map cols l
	where
		cols (n,k) = "  " ++ pad 6 (show n) ++ "  " ++ show k
		pad n s = s ++ replicate (n - length s) ' '

number :: Int -> [a] -> [(Int, a)]
number _ [] = []
number n (x:xs) = (n+1, x) : number (n+1) xs

staleTmpMsg :: [(Int, Key)] -> String
staleTmpMsg t = unlines $ 
	["Some partially transferred data exists in temporary files:"]
	++ table t ++ [dropMsg Nothing]

staleBadMsg :: [(Int, Key)] -> String
staleBadMsg t = unlines $ 
	["Some corrupted files have been preserved by fsck, just in case:"]
	++ table t ++ [dropMsg Nothing]

unusedMsg :: [(Int, Key)] -> String
unusedMsg u = unusedMsg' u
	["Some annexed data is no longer used by any files:"]
	[dropMsg Nothing]
unusedMsg' :: [(Int, Key)] -> [String] -> [String] -> String
unusedMsg' u header trailer = unlines $
	header ++
	table u ++
	["(To see where data was previously used, try: git log --stat -S'KEY')"] ++
	trailer

remoteUnusedMsg :: Remote.Remote Annex -> [(Int, Key)] -> String
remoteUnusedMsg r u = unusedMsg' u
	["Some annexed data on " ++ name ++ " is not used by any files:"]
	[dropMsg $ Just r]
	where
		name = Remote.name r 

dropMsg :: Maybe (Remote.Remote Annex) -> String
dropMsg Nothing = dropMsg' ""
dropMsg (Just r) = dropMsg' $ " --from " ++ Remote.name r
dropMsg' :: String -> String
dropMsg' s = "\nTo remove unwanted data: git-annex dropunused" ++ s ++ " NUMBER\n"

{- Finds keys whose content is present, but that do not seem to be used
 - by any files in the git repo, or that are only present as bad or tmp
 - files. -}
unusedKeys :: Annex ([Key], [Key], [Key])
unusedKeys = do
	fast <- Annex.getState Annex.fast
	if fast
		then do
			showNote "fast mode enabled; only finding stale files"
			tmp <- staleKeys gitAnnexTmpDir
			bad <- staleKeys gitAnnexBadDir
			return ([], bad, tmp)
		else do
			showAction "checking for unused data"
			present <- getKeysPresent
			unused <- excludeReferenced present
			staletmp <- staleKeysPrune gitAnnexTmpDir present
			stalebad <- staleKeysPrune gitAnnexBadDir present
			return (unused, stalebad, staletmp)

{- Finds keys in the list that are not referenced in the git repository. -}
excludeReferenced :: [Key] -> Annex [Key]
excludeReferenced [] = return [] -- optimisation
excludeReferenced l = do
	c <- inRepo $ Git.pipeRead [Param "show-ref"]
	removewith (getKeysReferenced : map getKeysReferencedInGit (refs c))
		(S.fromList l)
	where
		-- Skip the git-annex branches, and get all other unique refs.
		refs = map (Git.Ref .  last) .
			nubBy cmpheads .
			filter ourbranches .
			map words . lines . L.unpack
		cmpheads a b = head a == head b
		ourbranchend = '/' : show Annex.Branch.name
		ourbranches ws = not $ ourbranchend `isSuffixOf` last ws
		removewith [] s = return $ S.toList s
		removewith (a:as) s
			| s == S.empty = return [] -- optimisation
			| otherwise = do
				referenced <- a
				let !s' = s `S.difference` S.fromList referenced
				removewith as s'

{- Finds items in the first, smaller list, that are not
 - present in the second, larger list.
 - 
 - Constructing a single set, of the list that tends to be
 - smaller, appears more efficient in both memory and CPU
 - than constructing and taking the S.difference of two sets. -}
exclude :: Ord a => [a] -> [a] -> [a]
exclude [] _ = [] -- optimisation
exclude smaller larger = S.toList $ remove larger $ S.fromList smaller
	where
		remove a b = foldl (flip S.delete) b a

{- List of keys referenced by symlinks in the git repo. -}
getKeysReferenced :: Annex [Key]
getKeysReferenced = do
	top <- fromRepo Git.workTree
	files <- inRepo $ LsFiles.inRepo [top]
	keypairs <- mapM Backend.lookupFile files
	return $ map fst $ catMaybes keypairs

{- List of keys referenced by symlinks in a git ref. -}
getKeysReferencedInGit :: Git.Ref -> Annex [Key]
getKeysReferencedInGit ref = do
	showAction $ "checking " ++ Git.Ref.describe ref
	findkeys [] =<< inRepo (LsTree.lsTree ref)
	where
		findkeys c [] = return c
		findkeys c (l:ls)
			| isSymLink (LsTree.mode l) = do
				content <- catFile ref $ LsTree.file l
				case fileKey (takeFileName $ L.unpack content) of
					Nothing -> findkeys c ls
					Just k -> findkeys (k:c) ls
			| otherwise = findkeys c ls

{- Looks in the specified directory for bad/tmp keys, and returns a list
 - of those that might still have value, or might be stale and removable. 
 - 
 - When a list of presently available keys is provided, stale keys
 - that no longer have value are deleted.
 -}
staleKeysPrune :: (Git.Repo -> FilePath) -> [Key] -> Annex [Key]
staleKeysPrune dirspec present = do
	contents <- staleKeys dirspec
	
	let stale = contents `exclude` present
	let dups = contents `exclude` stale

	dir <- fromRepo dirspec
	liftIO $ forM_ dups $ \t -> removeFile $ dir </> keyFile t

	return stale

staleKeys :: (Git.Repo -> FilePath) -> Annex [Key]
staleKeys dirspec = do
	dir <- fromRepo dirspec
	exists <- liftIO $ doesDirectoryExist dir
	if not exists
		then return []
		else do
			contents <- liftIO $ getDirectoryContents dir
			files <- liftIO $ filterM doesFileExist $
				map (dir </>) contents
			return $ mapMaybe (fileKey . takeFileName) files