#!/usr/bin/env runhaskell
\begin{code}
{-# OPTIONS -Wall -cpp #-}

import Data.List
import Distribution.PackageDescription
import Distribution.Simple
import Distribution.Simple.LocalBuildInfo
import Distribution.Simple.Setup
import System.Console.GetOpt

main :: IO ()
main = do
   let hooks = simpleUserHooks {
                 preConf   = generateConfigHs
            }
   defaultMainWithHooks hooks
\end{code}


\begin{code}

data CoreLinkerFlag = WithGhc FilePath | GhcFlag String
  deriving (Eq, Show)

coreLinkerOptions :: [OptDescr CoreLinkerFlag]
coreLinkerOptions = [Option [] ["with-ghc"] (ReqArg WithGhc "FILEPATH")
       ("Location of the GHC you want to use to compile files to Core.\n"
      ++ "Default is 'ghc'."),
                     Option [] ["ghc-flag"] (ReqArg GhcFlag "STRING")
       ("A flag to pass to GHC. You may supply multiple --ghc-flag options.")]

getGhc :: [CoreLinkerFlag] -> Maybe FilePath
getGhc args = case findGhc args of
  Just (WithGhc g) -> Just g
  _                -> Nothing

getFlags :: [CoreLinkerFlag] -> [String]
getFlags = foldr (\ a rest -> case a of
  (GhcFlag s) -> s:rest
  _           -> rest) []
 
findGhc :: [CoreLinkerFlag] -> Maybe CoreLinkerFlag
findGhc = find isGhc

isGhc :: CoreLinkerFlag -> Bool
isGhc (WithGhc _) = True
isGhc _           = False

generateConfigHs :: Args -> ConfigFlags -> IO HookedBuildInfo
generateConfigHs _ confFlags = do
  let userConfigArgs = configConfigureArgs confFlags
  case getOpt Permute coreLinkerOptions userConfigArgs of
    (opts,_,_) -> case (getGhc opts,getFlags opts) of
                    (Just ghc,fs) -> writeConfigHs ghc fs
                    (Nothing,fs) -> putStrLn ("Warning: no ghc command supplied."
                      ++ " Will default to 'ghc'.\nTo specify a different GHC "
                      ++ "to use to build Core files, use the flag:\n"
                      ++ "--configure-option=--with-ghc=/path/to/ghc") >>
                               (writeConfigHs "ghc" fs)
  return emptyHookedBuildInfo

writeConfigHs :: FilePath -> [String] -> IO ()
writeConfigHs ghcCmd flags = writeFile "Config.hs" 
  ("module Config where\nghcStr::FilePath\nghcStr = \"" ++ ghcCmd ++ "\"\n" ++
   showFlags ++ "\n")
  where showFlags = "ghcFlags::[String]\nghcFlags = " ++ show flags

type Hook a = PackageDescription -> LocalBuildInfo -> UserHooks -> a -> IO ()

\end{code}