rename files in git lost-found directory

rename-lost-files.hs

-- rename Project Euler files in git lost-found directory

-- get the file type and the problem number from the initial comments
-- in each file

import System.Directory
import Text.Regex.Posix
import Control.Monad (forM_)

lostFilesDir = ".git/lost-found/other"

fileType s =
  let firstToken = fst $ head $ lex s
  in case firstToken of
    ";"  -> "clj"
    "--" -> "hs"
    "#"  -> "pl"
    _    -> "??"

problemId s = snd $ head $ filter (\(a, b) -> a `elem` ["Problem", "problem"]) $ zip ws $ tail ws
              where ws = words s

headerLine contents =
  case filter (isHeaderLine) $ lines contents of
       (x:_) -> Just x
       []    -> Nothing
  where isHeaderLine = (=~ "[pP]roblem [0-9]+")

findFileName line =
  let ft = fileType line
  in ft ++ "/" ++ problemId line ++ "." ++ ft

main = do
  files <- getDirectoryContents lostFilesDir
  forM_ (filter (\file -> not $ file `elem` [".", ".."]) files)
    (\file -> do
        let path = lostFilesDir ++ "/" ++ file
        contents <- readFile $ path
        case headerLine contents of
          Just hl -> print $ path ++ " -> " ++ findFileName hl
          _       -> print $ file ++ ": No program???"
          )