module Files (
      File(..)
    , absoluteLink
    , filePath
    , find
  ) where

import System.Directory (doesDirectoryExist, doesFileExist, listDirectory)
import System.FilePath ((</>))

data File = File FilePath | Dir FilePath

absoluteLink :: FilePath -> FilePath
absoluteLink ('.':path) = path
absoluteLink path = "/" </> path

filePath :: File -> IO (Either String FilePath)
filePath = filePathAux
  where
    filePathAux (File path) = ifIO doesFileExist path Right (notExist . File)
    filePathAux (Dir path) = ifIO doesDirectoryExist path Right (notExist . Dir)
    ifIO predicate value whenTrue whenFalse = do
      result <- predicate value
      return $ if result then whenTrue value else whenFalse value
    notExist (File path) = Left $ path ++ ": no such file"
    notExist (Dir path) = Left $ path ++ ": no such directory"

find :: FilePath -> IO [FilePath]
find path =
  filePath (Dir path) >>= emptyIfMissing (fmap ((path </>) <$>) . listDirectory)
  where
    emptyIfMissing = either (\_ -> return [])