implement import --deduplicate and import --clean-duplicates

Note that --deduplicate currently checksums each file twice,
once to see if it's a known key, and once when importing it.

Perhaps this could be revisited and the extra checksum gotten rid of,
at the cost of not locking down the file when adding it.

Command/Import.hs

@@ -15,6 +15,9 @@ import qualified Annex
 import qualified Command.Add
 import qualified Option
 import Utility.CopyFile
+import Backend
+import Remote
+import Types.KeySource
 
 def :: [Command]
 def = [withOptions opts $ notBareRepo $ command "import" paramPaths seek
@@ -65,14 +68,37 @@ start mode (srcfile, destfile) =
 		)
 
 perform :: DuplicateMode -> FilePath -> FilePath -> CommandPerform
-perform mode srcfile destfile = do
-	whenM (liftIO $ doesFileExist destfile) $
-		unlessM (Annex.getState Annex.force) $
-			error $ "not overwriting existing " ++ destfile ++
-				" (use --force to override)"
-
-	liftIO $ createDirectoryIfMissing True (parentDir destfile)
-	liftIO $ if mode == Duplicate
-		then void $ copyFileExternal srcfile destfile
-		else moveFile srcfile destfile
-	Command.Add.perform destfile
+perform mode srcfile destfile =
+	case mode of
+		DeDuplicate -> ifM isdup
+			( deletedup
+			, go
+			)
+		CleanDuplicates -> ifM isdup
+			( deletedup
+			, next $ return True
+			)
+		_ -> go
+  where
+	isdup = do
+		backend <- chooseBackend destfile
+		let ks = KeySource srcfile srcfile Nothing
+		v <- genKey ks backend
+		case v of
+			Just (k, _) -> not . null <$> keyLocations k
+			_ -> return False
+	deletedup = do
+		showNote "duplicate"
+		liftIO $ removeFile srcfile
+		next $ return True
+	go = do
+		whenM (liftIO $ doesFileExist destfile) $
+			unlessM (Annex.getState Annex.force) $
+				error $ "not overwriting existing " ++ destfile ++
+					" (use --force to override)"
+	
+		liftIO $ createDirectoryIfMissing True (parentDir destfile)
+		liftIO $ if mode == Duplicate
+			then void $ copyFileExternal srcfile destfile
+			else moveFile srcfile destfile
+		Command.Add.perform destfile