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

module Command.Unused where

import Control.Monad (filterM, unless, forM_, when)
import Control.Monad.State (liftIO)
import qualified Data.Set as S
import Data.Maybe
import System.FilePath
import System.Directory

import Command
import Types
import Content
import Messages
import Locations
import Utility
import LocationLog
import qualified Annex
import qualified GitRepo as Git
import qualified Backend
import qualified Remote

command :: [Command]
command = [repoCommand "unused" paramNothing seek
	"look for unused file content"]

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

{- Finds unused content in the annex. -} 
start :: CommandStartNothing
start = notBareRepo $ do
	showStart "unused" ""
	next perform

perform :: CommandPerform
perform = do
	maybe checkUnused checkRemoteUnused =<< Annex.getState Annex.fromremote
	next $ return True

checkUnused :: Annex ()
checkUnused = do
	(unused, stalebad, staletmp) <- unusedKeys
	n  <- list "" unusedMsg unused 0
	n' <- list "bad" staleBadMsg stalebad n
	_  <- list "tmp" staleTmpMsg staletmp n'
	return ()
	where
		list file msg l c = do
			let unusedlist = number c l
			when (not $ null l) $ showLongNote $ msg unusedlist
			writeUnusedFile file unusedlist
			return $ length l

checkRemoteUnused :: String -> Annex ()
checkRemoteUnused name = checkRemoteUnused' =<< Remote.byName name

checkRemoteUnused' :: Remote.Remote Annex -> Annex ()
checkRemoteUnused' r = do
	g <- Annex.gitRepo
	showNote $ "checking for unused data on " ++ Remote.name r ++ "..."
	referenced <- getKeysReferenced
	logged <- liftIO $ loggedKeys g
	remotehas <- filterM isthere logged
	let remoteunused = remotehas `exclude` referenced
	let list = number 0 remoteunused
	writeUnusedFile "" list
	unless (null remoteunused) $ do
		showLongNote $ remoteUnusedMsg r list
		showLongNote $ "\n"
	where
		isthere k = do
			g <- Annex.gitRepo
			us <- liftIO $ keyLocations g k
			return $ uuid `elem` us
		uuid = Remote.uuid r

writeUnusedFile :: FilePath -> [(Int, Key)] -> Annex ()
writeUnusedFile prefix l = do
	g <- Annex.gitRepo
	liftIO $ safeWriteFile (gitAnnexUnusedLog prefix g) $
		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 in the repository:"]
	[dropMsg Nothing]

remoteUnusedMsg :: Remote.Remote Annex -> [(Int, Key)] -> String
remoteUnusedMsg r u = unusedMsg' u
	["Some annexed data on " ++ name ++ 
	 " is not used by any files in this repository."]
	[dropMsg $ Just r,
	 "Please be cautious -- are you sure that the remote repository",
	 "does not use this data?"]
	where
		name = Remote.name r 

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

dropMsg :: Maybe (Remote.Remote Annex) -> String
dropMsg Nothing = dropMsg' ""
dropMsg (Just r) = dropMsg' $ " --from " ++ Remote.name r
dropMsg' :: String -> String
dropMsg' s = "(To 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
			showNote "checking for unused data..."
			present <- getKeysPresent
			referenced <- getKeysReferenced
			let unused = present `exclude` referenced
			staletmp <- staleKeysPrune gitAnnexTmpDir present
			stalebad <- staleKeysPrune gitAnnexBadDir present
			return (unused, stalebad, staletmp)

{- 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
	g <- Annex.gitRepo
	files <- liftIO $ Git.inRepo g [Git.workTree g]
	keypairs <- mapM Backend.lookupFile files
	return $ map fst $ catMaybes keypairs

{- 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 dup = contents `exclude` stale

	g <- Annex.gitRepo
	let dir = dirspec g
	liftIO $ forM_ dup $ \t -> removeFile $ dir </> keyFile t

	return stale

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