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+{- filenames (not paths) used in views
+ -
+ - Copyright 2014 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Annex.View.ViewedFile (
+	ViewedFile,
+	MkViewedFile,
+	viewedFileFromReference,
+	viewedFileReuse,
+	dirFromViewedFile,
+	prop_viewedFile_roundtrips,
+) where
+
+import Common.Annex
+
+type FileName = String
+type ViewedFile = FileName
+
+type MkViewedFile = FilePath -> ViewedFile
+
+{- Converts a filepath used in a reference branch to the
+ - filename that will be used in the view.
+ -
+ - No two filepaths from the same branch should yeild the same result,
+ - so all directory structure needs to be included in the output filename
+ - in some way.
+ -
+ - So, from dir/subdir/file.foo, generate file_%dir%subdir%.foo
+ -}
+viewedFileFromReference :: MkViewedFile
+viewedFileFromReference f = concat
+	[ escape base
+	, if null dirs then "" else "_%" ++ intercalate "%" (map escape dirs) ++ "%"
+	, escape $ concat extensions
+	]
+  where
+	(path, basefile) = splitFileName f
+	dirs = filter (/= ".") $ map dropTrailingPathSeparator (splitPath path)
+	(base, extensions) = splitShortExtensions basefile
+
+	{- To avoid collisions with filenames or directories that contain
+	 - '%', and to allow the original directories to be extracted
+	 - from the ViewedFile, '%' is escaped to '\%' (and '\' to '\\').
+	 -}
+	escape :: String -> String
+	escape = replace "%" "\\%" . replace "\\" "\\\\"
+
+{- For use when operating already within a view, so whatever filepath
+ - is present in the work tree is already a ViewedFile. -}
+viewedFileReuse :: MkViewedFile
+viewedFileReuse = takeFileName
+
+{- Extracts from a ViewedFile the directory where the file is located on
+ - in the reference branch. -}
+dirFromViewedFile :: ViewedFile -> FilePath
+dirFromViewedFile = joinPath . drop 1 . sep [] ""
+  where
+  	sep l _ [] = reverse l
+	sep l curr (c:cs)
+		| c == '%' = sep (reverse curr:l) "" cs
+		| c == '\\' = case cs of
+			(c':cs') -> sep l (c':curr) cs'
+			[] -> sep l curr cs
+		| otherwise = sep l (c:curr) cs
+
+prop_viewedFile_roundtrips :: FilePath -> Bool
+prop_viewedFile_roundtrips f
+	| isAbsolute f = True -- Only relative paths are encoded.
+	| any (isPathSeparator) (end f) = True -- Filenames wanted, not directories.
+	| otherwise = dir == dirFromViewedFile (viewedFileFromReference f)
+  where
+	dir = joinPath $ beginning $ splitDirectories f