module Misc where

import qualified System.Console.GetOpt as GetOpt
import System.Environment
import System.Exit

-- | exception on 'Left'
unwrap :: Show a => FilePath -> Either a b -> IO b
unwrap file = either (\x -> fail $ file <> ":" <> show x) return

getOptionsWith :: (String -> String) -> ([String] -> Maybe a)
               -> [GetOpt.OptDescr (a -> a)] -> IO a
getOptionsWith hdr mkDef descrs = do
  res <- GetOpt.getOpt GetOpt.Permute descrs <$> getArgs
  case res of
    (fs, rest, []) | Just def <- mkDef rest ->
      return $ foldl (flip ($)) def fs
    _ -> do
      prog <- getProgName
      putStrLn $ GetOpt.usageInfo (hdr prog) descrs
      exitFailure