factor out new module

Annex/View/ViewedFile.hs

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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 where
+
+import Common.Annex
+import Types.View
+import Types.MetaData
+import qualified Git
+import qualified Git.DiffTree as DiffTree
+import qualified Git.Branch
+import qualified Git.LsFiles
+import qualified Git.Ref
+import Git.UpdateIndex
+import Git.Sha
+import Git.HashObject
+import Git.Types
+import Git.FilePath
+import qualified Backend
+import Annex.Index
+import Annex.Link
+import Annex.CatFile
+import Logs.MetaData
+import Logs.View
+import Utility.Glob
+import Utility.FileMode
+import Types.Command
+import Config
+import CmdLine.Action
+
+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 file
+ - in some way. However, the branch's directory structure is not replicated
+ - in the view.
+ -
+ - So, from dir/subdir/file.foo, generate file_{dir;subdir}.foo
+ -
+ - (To avoid collisions with a filename that already contains {foo},
+ - that is doubled to {{foo}}.)
+ -}
+viewedFileFromReference :: MkViewedFile
+viewedFileFromReference f = concat
+	[ double base
+	, if null dirs then "" else "_{" ++ double (intercalate ";" dirs) ++ "}"
+	, double $ concat extensions
+	]
+  where
+	(path, basefile) = splitFileName f
+	dirs = filter (/= ".") $ map dropTrailingPathSeparator (splitPath path)
+	(base, extensions) = splitShortExtensions basefile
+
+	double = replace "{" "{{" . replace "}" "}}"
+
+viewedFileReuse :: MkViewedFile
+viewedFileReuse = takeFileName