module Run
  ( runAndReadStdout
  , tmpfile
  ) where

import Directory (removeFile)
import System (system,ExitCode(..))

#ifdef __HBC__
import UnsafePerformIO
#ifdef __HASKELL98__
import GetPid
getProcessID = getPid
#else
getProcessID = return 3154      -- arbitrary number
#endif
#endif
#ifdef __NHC__
import IOExtras (unsafePerformIO)
foreign import "getpid" getProcessID :: IO Int
#endif
#ifdef __GLASGOW_HASKELL__
import IOExts (unsafePerformIO)
import Posix (getProcessID)
#endif

-- Generate a temporary filename unique to this process.
tmpfile :: String -> String
tmpfile root = unsafePerformIO $ do p <- getProcessID
                                    return ("/tmp/"++root++"."++show p)

-- Run a shell command and collect its output.
runAndReadStdout :: String -> IO String
runAndReadStdout cmd = do
    let output = tmpfile "hmakeconfig"
    err <- system (cmd++" >"++output)
    case err of
        ExitFailure _ -> ioError (userError ("Command ("++cmd++") failed"))
        _ -> return ()
    s <- readFile output
    removeFile output   -- file will not be removed until readFile closes it
    return (safeinit s) -- strip trailing newline added by shell
  where
    safeinit []     = []
    safeinit ['\n'] = []
    safeinit [x]    = [x]
    safeinit (x:xs) = x : safeinit xs