{- git-annex pseudo-backend
 -
 - This backend does not really do any independant data storage,
 - it relies on the file contents in .git/annex/ in this repo,
 - and other accessible repos.
 -
 - This is an abstract backend; name, getKey and fsckKey have to be implemented
 - to complete it.
 -
 - Copyright 2010 Joey Hess <joey@kitenet.net>
 -
 - Licensed under the GNU GPL version 3 or higher.
 -}

module Backend.File (backend, checkKey) where

import Control.Monad.State
import System.Directory

import TypeInternals
import LocationLog
import Locations
import qualified Remotes
import qualified GitRepo as Git
import Core
import qualified Annex
import UUID
import Messages

backend :: Backend
backend = Backend {
	name = mustProvide,
	getKey = mustProvide,
	storeFileKey = dummyStore,
	retrieveKeyFile = copyKeyFile,
	removeKey = checkRemoveKey,
	hasKey = inAnnex,
	fsckKey = mustProvide
}

mustProvide :: a
mustProvide = error "must provide this field"

{- Storing a key is a no-op. -}
dummyStore :: FilePath -> Key -> Annex Bool
dummyStore _ _ = return True

{- Try to find a copy of the file in one of the remotes,
 - and copy it over to this one. -}
copyKeyFile :: Key -> FilePath -> Annex Bool
copyKeyFile key file = do
	(trusted, untrusted, _) <- Remotes.keyPossibilities key
	let remotes = trusted ++ untrusted
	if null remotes
		then do
			showNote "not available"
			showLocations key []
			return False
		else trycopy remotes remotes
	where
		trycopy full [] = do
			showTriedRemotes full
			showLocations key []
			return False
		trycopy full (r:rs) = do
			probablythere <- probablyPresent r
			if probablythere
				then docopy r (trycopy full rs)
				else trycopy full rs
		-- This check is to avoid an ugly message if a remote is a
		-- drive that is not mounted. Avoid checking inAnnex for ssh
		-- remotes because that is unnecessarily slow, and the
		-- locationlog should be trusted. (If the ssh remote is down
		-- or really lacks the file, it's ok to show an ugly message
		-- before going on to the next remote.)
		probablyPresent r =
			if not $ Git.repoIsUrl r
				then liftIO $ doesFileExist $ annexLocation r key
				else return True
		docopy r continue = do
			showNote $ "copying from " ++ Git.repoDescribe r ++ "..."
			copied <- Remotes.copyFromRemote r key file
			if copied
				then return True
				else continue

{- Checks remotes to verify that enough copies of a key exist to allow
 - for a key to be safely removed (with no data loss), and fails with an
 - error if not. -}
checkRemoveKey :: Key -> Maybe Int -> Annex Bool
checkRemoveKey key numcopiesM = do
	force <- Annex.flagIsSet "force"
	if force || numcopiesM == Just 0
		then return True
		else do
			(_, untrusted, have) <- Remotes.keyPossibilities key
			numcopies <- getNumCopies numcopiesM
			findcopies numcopies have untrusted []
	where
		findcopies need have [] bad
			| length have >= need = return True
			| otherwise = notEnoughCopies need have bad
		findcopies need have (r:rs) bad
			| length have >= need = return True
			| otherwise = do
				u <- getUUID r
				let dup = elem u have
				haskey <- Remotes.inAnnex r key
				case (dup, haskey) of
					(False, Right True)	-> findcopies need (u:have) rs bad
					(False, Left _)		-> findcopies need have rs (r:bad)
					_			-> findcopies need have rs bad
		notEnoughCopies need have bad = do
			unsafe
			showLongNote $
				"Could only verify the existence of " ++
				show (length have) ++ " out of " ++ show need ++ 
				" necessary copies"
			showTriedRemotes bad
			showLocations key have
			hint
			return False
		unsafe = showNote "unsafe"
		hint = showLongNote "(Use --force to override this check, or adjust annex.numcopies.)"

showLocations :: Key -> [UUID] -> Annex ()
showLocations key exclude = do
	g <- Annex.gitRepo
	u <- getUUID g
	uuids <- liftIO $ keyLocations g key
	let uuidsf = filter (\l -> l /= u && (not $ elem l exclude)) uuids
	ppuuids <- prettyPrintUUIDs uuidsf
	if null uuidsf
		then showLongNote $ "No other repository is known to contain the file."
		else showLongNote $ "Try making some of these repositories available:\n" ++ ppuuids

showTriedRemotes :: [Git.Repo] -> Annex ()
showTriedRemotes [] = return ()	
showTriedRemotes remotes =
	showLongNote $ "Unable to access these remotes: " ++
		Remotes.list remotes

getNumCopies :: Maybe Int -> Annex Int
getNumCopies (Just n) = return n
getNumCopies Nothing = do
	g <- Annex.gitRepo
	return $ read $ Git.configGet g config "1"
	where
		config = "annex.numcopies"

{- This is used to check that numcopies is satisfied for the key on fsck.
 - This trusts the location log, and so checks all keys, even those with
 - data not present in the current annex.
 -
 - The passed action is first run to allow backends deriving this one
 - to do their own checks.
 -}
checkKey :: (Key -> Annex Bool) -> Key -> Maybe Int -> Annex Bool
checkKey a key numcopies = do
	a_ok <- a key
	copies_ok <- checkKeyNumCopies key numcopies
	return $ a_ok && copies_ok

checkKeyNumCopies :: Key -> Maybe Int -> Annex Bool
checkKeyNumCopies key numcopies = do
	needed <- getNumCopies numcopies
	g <- Annex.gitRepo
	locations <- liftIO $ keyLocations g key
	let present = length locations
	if present < needed
		then do
			warning $ note present needed
			return False
		else return True
	where
		note 0 _ = "** No known copies of "++show key++" exist!"
		note present needed = 
			"Only " ++ show present ++ " of " ++ show needed ++ 
			" copies of "++show key++" exist. " ++
			"Back it up with git-annex copy."