module EndOfExe where

import qualified System.Directory as D (findExecutable)
import Data.Maybe (isJust)
import System.IO.Unsafe (unsafePerformIO)

-- | Function that is used instead of 'System.Info.os' to check whether the executable ends in .exe. The function returns @IO Nothing@ if there is neither @ys@ nor @(ys ++ ".exe")@ names for executables in the 
-- variable @PATH@
endOfExecutable :: String -> IO (Maybe String)
endOfExecutable ys = do
                       xs <- D.findExecutable ys
                       if isJust xs 
                         then return $ fmap (ys ++) (Just "")
                         else do
                                zs <- D.findExecutable (ys ++ ".exe")
                                if isJust zs
                                  then return $ fmap (ys ++) (Just ".exe")
                                  else error ("Please, install the executable " ++ ys ++ " into the directory in the PATH variable!")
                                  
-- | Function that is used to concat the 'endOfExecutable' to the name of the program. You can use showE \"nameOfExecutable\" e. g. inside the 'System.Process.callCommand' as the name of the executable
showE :: String -> Maybe String
showE xs | null xs = error "No executable specified!"
         | otherwise = let r = unsafePerformIO . endOfExecutable $ xs in 
            if isJust r
              then r
              else Nothing