remove unused backend machinery

The only remaining vestiage of backends is different types of keys. These
are still called "backends", mostly to avoid needing to change user interface
and configuration. But everything to do with storing keys in different
backends was gone; instead different types of remotes are used.

In the refactoring, lots of code was moved out of odd corners like
Backend.File, to closer to where it's used, like Command.Drop and
Command.Fsck. Quite a lot of dead code was removed. Several data structures
became simpler, which may result in better runtime efficiency. There should
be no user-visible changes.

11 files changed, 196 insertions, 45 deletions

diff --git a/Command/Add.hs b/Command/Add.hs
index 6a1ffb5da..2831e1b35 100644
--- a/Command/Add.hs
+++ b/Command/Add.hs
@@ -42,8 +42,8 @@ start pair@(file, _) = notAnnexed file $ do
 
 perform :: BackendFile -> CommandPerform
 perform (file, backend) = do
-	stored <- Backend.storeFileKey file backend
-	case stored of
+	k <- Backend.genKey file backend
+	case k of
 		Nothing -> stop
 		Just (key, _) -> do
 			moveAnnex key file
diff --git a/Command/AddUrl.hs b/Command/AddUrl.hs
index ebf0810ba..e80fe9621 100644
--- a/Command/AddUrl.hs
+++ b/Command/AddUrl.hs
@@ -51,8 +51,8 @@ perform url file = do
 	if ok
 		then do
 			[(_, backend)] <- Backend.chooseBackends [file]
-			stored <- Backend.storeFileKey tmp backend
-			case stored of
+			k <- Backend.genKey tmp backend
+			case k of
 				Nothing -> stop
 				Just (key, _) -> do
 					moveAnnex key tmp
diff --git a/Command/Drop.hs b/Command/Drop.hs
index bd4740741..14f098349 100644
--- a/Command/Drop.hs
+++ b/Command/Drop.hs
@@ -8,12 +8,15 @@
 module Command.Drop where
 
 import Command
-import qualified Backend
+import qualified Remote
+import qualified Annex
 import LocationLog
 import Types
 import Content
 import Messages
 import Utility
+import Trust
+import Config
 
 command :: [Command]
 command = [repoCommand "drop" paramPath seek
@@ -25,19 +28,19 @@ seek = [withAttrFilesInGit "annex.numcopies" start]
 {- Indicates a file's content is not wanted anymore, and should be removed
  - if it's safe to do so. -}
 start :: CommandStartAttrFile
-start (file, attr) = isAnnexed file $ \(key, backend) -> do
-	inbackend <- Backend.hasKey key
-	if inbackend
+start (file, attr) = isAnnexed file $ \(key, _) -> do
+	present <- inAnnex key
+	if present
 		then do
 			showStart "drop" file
-			next $ perform key backend numcopies
+			next $ perform key numcopies
 		else stop
 	where
 		numcopies = readMaybe attr :: Maybe Int
 
-perform :: Key -> Backend Annex -> Maybe Int -> CommandPerform
-perform key backend numcopies = do
-	success <- Backend.removeKey backend key numcopies
+perform :: Key -> Maybe Int -> CommandPerform
+perform key numcopies = do
+	success <- dropKey key numcopies
 	if success
 		then next $ cleanup key
 		else stop
@@ -47,3 +50,44 @@ cleanup key = do
 	whenM (inAnnex key) $ removeAnnex key
 	logStatus key InfoMissing
 	return True
+
+{- 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. -}
+dropKey :: Key -> Maybe Int -> Annex Bool
+dropKey key numcopiesM = do
+	force <- Annex.getState Annex.force
+	if force || numcopiesM == Just 0
+		then return True
+		else do
+			(remotes, trusteduuids) <- Remote.keyPossibilitiesTrusted key
+			untrusteduuids <- trustGet UnTrusted
+			let tocheck = Remote.remotesWithoutUUID remotes (trusteduuids++untrusteduuids)
+			numcopies <- getNumCopies numcopiesM
+			findcopies numcopies trusteduuids tocheck []
+	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
+				let u = Remote.uuid r
+				let dup = u `elem` have
+				haskey <- Remote.hasKey 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"
+			Remote.showTriedRemotes bad
+			Remote.showLocations key have
+			hint
+			return False
+		unsafe = showNote "unsafe"
+		hint = showLongNote "(Use --force to override this check, or adjust annex.numcopies.)"
diff --git a/Command/DropUnused.hs b/Command/DropUnused.hs
index 2125abdc3..55007c1f7 100644
--- a/Command/DropUnused.hs
+++ b/Command/DropUnused.hs
@@ -21,7 +21,6 @@ import qualified Command.Drop
 import qualified Command.Move
 import qualified Remote
 import qualified Git
-import Backend
 import Types.Key
 import Utility
 
@@ -64,9 +63,7 @@ perform key = maybe droplocal dropremote =<< Annex.getState Annex.fromremote
 			r <- Remote.byName name
 			showNote $ "from " ++ Remote.name r ++ "..."
 			next $ Command.Move.fromCleanup r True key
-		droplocal = do
-			backend <- keyBackend key
-			Command.Drop.perform key backend (Just 0) -- force drop
+		droplocal = Command.Drop.perform key (Just 0) -- force drop
 
 performOther :: (Git.Repo -> Key -> FilePath) -> Key -> CommandPerform
 performOther filespec key = do
diff --git a/Command/FromKey.hs b/Command/FromKey.hs
index 34816d657..fb9ab0775 100644
--- a/Command/FromKey.hs
+++ b/Command/FromKey.hs
@@ -15,7 +15,6 @@ import Control.Monad (unless)
 import Command
 import qualified AnnexQueue
 import Utility
-import qualified Backend
 import Content
 import Messages
 import Types.Key
@@ -30,7 +29,7 @@ seek = [withFilesMissing start]
 start :: CommandStartString
 start file = notBareRepo $ do
 	key <- cmdlineKey
-	inbackend <- Backend.hasKey key
+	inbackend <- inAnnex key
 	unless inbackend $ error $
 		"key ("++keyName key++") is not present in backend"
 	showStart "fromkey" file
diff --git a/Command/Fsck.hs b/Command/Fsck.hs
index 988cfd28d..446d25a44 100644
--- a/Command/Fsck.hs
+++ b/Command/Fsck.hs
@@ -9,10 +9,15 @@ module Command.Fsck where
 
 import Control.Monad (when)
 import Control.Monad.State (liftIO)
+import System.Directory
+import Data.List
+import System.Posix.Files
 
 import Command
-import qualified Backend
 import qualified Annex
+import qualified Remote
+import qualified Types.Backend
+import qualified Types.Key
 import UUID
 import Types
 import Messages
@@ -20,6 +25,9 @@ import Utility
 import Content
 import LocationLog
 import Locations
+import Trust
+import DataUnits
+import Config
 
 command :: [Command]
 command = [repoCommand "fsck" (paramOptional $ paramRepeating paramPath) seek
@@ -40,7 +48,7 @@ perform key file backend numcopies = do
 	-- the location log is checked first, so that if it has bad data
 	-- that gets corrected
 	locationlogok <- verifyLocationLog key file
-	backendok <- Backend.fsckKey backend key (Just file) numcopies
+	backendok <- fsckKey backend key (Just file) numcopies
 	if locationlogok && backendok
 		then next $ return True
 		else stop
@@ -80,3 +88,68 @@ verifyLocationLog key file = do
 		fix g u s = do
 			showNote "fixing location log"
 			logChange g key u s
+
+{- Checks a key for problems. -}
+fsckKey :: Backend Annex -> Key -> Maybe FilePath -> Maybe Int -> Annex Bool
+fsckKey backend key file numcopies = do
+	size_ok <- checkKeySize key
+	copies_ok <- checkKeyNumCopies key file numcopies
+	backend_ok <-(Types.Backend.fsckKey backend) key
+	return $ size_ok && copies_ok && backend_ok
+
+{- The size of the data for a key is checked against the size encoded in
+ - the key's metadata, if available. -}
+checkKeySize :: Key -> Annex Bool
+checkKeySize key = do
+	g <- Annex.gitRepo
+	let file = gitAnnexLocation g key
+	present <- liftIO $ doesFileExist file
+	case (present, Types.Key.keySize key) of
+		(_, Nothing) -> return True
+		(False, _) -> return True
+		(True, Just size) -> do
+			stat <- liftIO $ getFileStatus file
+			let size' = fromIntegral (fileSize stat)
+			if size == size'
+				then return True
+				else do
+					dest <- moveBad key
+					warning $ "Bad file size (" ++
+						compareSizes storageUnits True size size' ++ 
+						"); moved to " ++ dest
+					return False
+
+
+checkKeyNumCopies :: Key -> Maybe FilePath -> Maybe Int -> Annex Bool
+checkKeyNumCopies key file numcopies = do
+	needed <- getNumCopies numcopies
+	locations <- keyLocations key
+	untrusted <- trustGet UnTrusted
+	let untrustedlocations = intersect untrusted locations
+	let safelocations = filter (`notElem` untrusted) locations
+	let present = length safelocations
+	if present < needed
+		then do
+			ppuuids <- Remote.prettyPrintUUIDs untrustedlocations
+			warning $ missingNote (filename file key) present needed ppuuids
+			return False
+		else return True
+	where
+		filename Nothing k = show k
+		filename (Just f) _ = f
+
+missingNote :: String -> Int -> Int -> String -> String
+missingNote file 0 _ [] = 
+		"** No known copies exist of " ++ file
+missingNote file 0 _ untrusted =
+		"Only these untrusted locations may have copies of " ++ file ++
+		"\n" ++ untrusted ++
+		"Back it up to trusted locations with git-annex copy."
+missingNote file present needed [] =
+		"Only " ++ show present ++ " of " ++ show needed ++ 
+		" trustworthy copies exist of " ++ file ++
+		"\nBack it up with git-annex copy."
+missingNote file present needed untrusted = 
+		missingNote file present needed [] ++
+		"\nThe following untrusted locations may also have copies: " ++
+		"\n" ++ untrusted
diff --git a/Command/Get.hs b/Command/Get.hs
index 50dc009fe..cc780cb6a 100644
--- a/Command/Get.hs
+++ b/Command/Get.hs
@@ -8,7 +8,6 @@
 module Command.Get where
 
 import Command
-import qualified Backend
 import qualified Annex
 import qualified Remote
 import Types
@@ -24,7 +23,7 @@ seek :: [CommandSeek]
 seek = [withFilesInGit start]
 
 start :: CommandStartString
-start file = isAnnexed file $ \(key, backend) -> do
+start file = isAnnexed file $ \(key, _) -> do
 	inannex <- inAnnex key
 	if inannex
 		then stop
@@ -32,14 +31,52 @@ start file = isAnnexed file $ \(key, backend) -> do
 			showStart "get" file
 			from <- Annex.getState Annex.fromremote
 			case from of
-				Nothing -> next $ perform key backend
+				Nothing -> next $ perform key
 				Just name -> do
 					src <- Remote.byName name
 					next $ Command.Move.fromPerform src False key
 
-perform :: Key -> Backend Annex -> CommandPerform
-perform key backend = do
-	ok <- getViaTmp key (Backend.retrieveKeyFile backend key)
+perform :: Key -> CommandPerform
+perform key = do
+	ok <- getViaTmp key (getKeyFile key)
 	if ok
 		then next $ return True -- no cleanup needed
 		else stop
+
+{- Try to find a copy of the file in one of the remotes,
+ - and copy it to here. -}
+getKeyFile :: Key -> FilePath -> Annex Bool
+getKeyFile key file = do
+	remotes <- Remote.keyPossibilities key
+	if null remotes
+		then do
+			showNote "not available"
+			Remote.showLocations key []
+			return False
+		else trycopy remotes remotes
+	where
+		trycopy full [] = do
+			Remote.showTriedRemotes full
+			Remote.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.
+		probablyPresent r =
+			if Remote.hasKeyCheap r
+				then do
+					res <- Remote.hasKey r key
+					case res of
+						Right b -> return b
+						Left _ -> return False
+				else return True
+		docopy r continue = do
+			showNote $ "from " ++ Remote.name r ++ "..."
+			copied <- Remote.retrieveKeyFile r key file
+			if copied
+				then return True
+				else continue
diff --git a/Command/Migrate.hs b/Command/Migrate.hs
index 09ff6df7d..495bf9fb6 100644
--- a/Command/Migrate.hs
+++ b/Command/Migrate.hs
@@ -15,6 +15,7 @@ import System.FilePath
 import Command
 import qualified Annex
 import qualified Backend
+import qualified Types.Key
 import Locations
 import Types
 import Content
@@ -32,18 +33,20 @@ start :: CommandStartBackendFile
 start (file, b) = isAnnexed file $ \(key, oldbackend) -> do
 	exists <- inAnnex key
 	newbackend <- choosebackend b
-	upgradable <- Backend.upgradableKey oldbackend key
-	if (newbackend /= oldbackend || upgradable) && exists
+	if (newbackend /= oldbackend || upgradableKey key) && exists
 		then do
 			showStart "migrate" file
 			next $ perform file key newbackend
 		else stop
 	where
-		choosebackend Nothing = do
-			backends <- Backend.list
-			return $ head backends
+		choosebackend Nothing = return . head =<< Backend.orderedList
 		choosebackend (Just backend) = return backend
 
+{- Checks if a key is upgradable to a newer representation. -}
+{- Ideally, all keys have file size metadata. Old keys may not. -}
+upgradableKey :: Key -> Bool
+upgradableKey key = Types.Key.keySize key == Nothing
+
 perform :: FilePath -> Key -> Backend Annex -> CommandPerform
 perform file oldkey newbackend = do
 	g <- Annex.gitRepo
@@ -55,9 +58,9 @@ perform file oldkey newbackend = do
 	let src = gitAnnexLocation g oldkey
 	let tmpfile = gitAnnexTmpDir g </> takeFileName file
 	liftIO $ createLink src tmpfile
-	stored <- Backend.storeFileKey tmpfile $ Just newbackend
+	k <- Backend.genKey tmpfile $ Just newbackend
 	liftIO $ cleantmp tmpfile
-	case stored of
+	case k of
 		Nothing -> stop
 		Just (newkey, _) -> do
 			ok <- getViaTmpUnchecked newkey $ \t -> do
diff --git a/Command/Status.hs b/Command/Status.hs
index 53589030b..2448f65a4 100644
--- a/Command/Status.hs
+++ b/Command/Status.hs
@@ -25,6 +25,7 @@ import DataUnits
 import Content
 import Types.Key
 import Locations
+import Backend
 
 -- a named computation that produces a statistic
 type Stat = StatState (Maybe (String, StatState String))
@@ -95,9 +96,8 @@ showStat s = calc =<< s
 		calc Nothing = return ()
 
 supported_backends :: Stat
-supported_backends = stat "supported backends" $
-	lift (Annex.getState Annex.supportedBackends) >>=
-		return . unwords . (map B.name)
+supported_backends = stat "supported backends" $ 
+	return $ unwords $ map B.name Backend.list
 
 supported_remote_types :: Stat
 supported_remote_types = stat "supported remote types" $
diff --git a/Command/Unannex.hs b/Command/Unannex.hs
index f0c1b27c6..f22503ee0 100644
--- a/Command/Unannex.hs
+++ b/Command/Unannex.hs
@@ -13,10 +13,10 @@ import System.Directory
 import System.Posix.Files
 
 import Command
+import qualified Command.Drop
 import qualified Annex
 import qualified AnnexQueue
 import Utility
-import qualified Backend
 import LocationLog
 import Types
 import Content
@@ -33,7 +33,7 @@ seek = [withFilesInGit start]
 
 {- The unannex subcommand undoes an add. -}
 start :: CommandStartString
-start file = isAnnexed file $ \(key, backend) -> do
+start file = isAnnexed file $ \(key, _) -> do
 	ishere <- inAnnex key
 	if ishere
 		then do
@@ -46,13 +46,12 @@ start file = isAnnexed file $ \(key, backend) -> do
 				Annex.changeState $ \s -> s { Annex.force = True }
 
 			showStart "unannex" file
-			next $ perform file key backend
+			next $ perform file key
 		else stop
 
-perform :: FilePath -> Key -> Backend Annex -> CommandPerform
-perform file key backend = do
-	-- force backend to always remove
-	ok <- Backend.removeKey backend key (Just 0)
+perform :: FilePath -> Key -> CommandPerform
+perform file key = do
+	ok <- Command.Drop.dropKey key (Just 0) -- always remove
 	if ok
 		then next $ cleanup file key
 		else stop
diff --git a/Command/Unlock.hs b/Command/Unlock.hs
index ca8b62502..8a897c365 100644
--- a/Command/Unlock.hs
+++ b/Command/Unlock.hs
@@ -12,7 +12,6 @@ import System.Directory hiding (copyFile)
 
 import Command
 import qualified Annex
-import qualified Backend
 import Types
 import Messages
 import Locations
@@ -38,7 +37,7 @@ start file = isAnnexed file $ \(key, _) -> do
 
 perform :: FilePath -> Key -> CommandPerform
 perform dest key = do
-	unlessM (Backend.hasKey key) $ error "content not present"
+	unlessM (inAnnex key) $ error "content not present"
 	
 	checkDiskSpace key