module Check (checkSyntax) where

import Bag
import Control.Applicative
import Data.IORef
import DynFlags
import ErrUtils
import Exception
import FastString
import GHC
import GHC.Paths (libdir)
import HscTypes
import Outputable hiding (showSDoc)
import Param
import Pretty

----------------------------------------------------------------

checkSyntax :: Options -> String -> IO String
checkSyntax _ file = unlines <$> check file

----------------------------------------------------------------

-- I don't know why, but parseDynamicFlags must be used.
cmdOptions :: [Located String]
cmdOptions = map noLoc ["-Wall","-fno-warn-unused-do-bind"]

check :: String -> IO [String]
check fileName = ghandle ignore $ runGhc (Just libdir) $ do
    ref <- liftIO $ newIORef []
    initSession
    setTargetFile fileName
    loadWithLogger (refLogger ref) LoadAllTargets
    liftIO $ readIORef ref
  where
    -- I don't know why, but parseDynamicFlags must be used.
    initSession = do
        dflags <- getSessionDynFlags
        (dflags',_,_) <- parseDynamicFlags dflags cmdOptions
        setSessionDynFlags $ setFlags dflags'
    setTargetFile file = do
        target <- guessTarget file Nothing
        setTargets [target]
    ignore :: SomeException -> IO [String]
    ignore _ = return []

----------------------------------------------------------------

refLogger :: IORef [String] -> WarnErrLogger
refLogger ref Nothing = do
    warns <- map showErrMsg . reverse . bagToList <$> getWarnings
    liftIO $ writeIORef ref warns
    clearWarnings
refLogger ref (Just e) = do
    let errs = map showErrMsg . reverse . bagToList . srcErrorMessages $ e
    liftIO $ writeIORef ref errs
    clearWarnings

----------------------------------------------------------------

setFlags :: DynFlags -> DynFlags
setFlags d = d {
    importPaths = importPaths d ++ importDirs
  , packageFlags = ghcPackage : packageFlags d
  , ghcLink = NoLink
-- GHC.desugarModule does not produces the pattern warnings, why?
--  , hscTarget = HscNothing
  , hscTarget = HscInterpreted
  }

importDirs :: [String]
importDirs = ["..","../..","../../..","../../../../.."]

ghcPackage :: PackageFlag
ghcPackage = ExposePackage "ghc"

----------------------------------------------------------------

showErrMsg :: ErrMsg -> String
showErrMsg err = file ++ ":" ++ line ++ ":" ++ col ++ ":" ++ msg
   where
     spn = head (errMsgSpans err)
     file = unpackFS (srcSpanFile spn)
     line = show (srcSpanStartLine spn)
     col  = show (srcSpanStartCol spn)
     msg = showSDoc (errMsgShortDoc err)

style :: PprStyle
style = mkUserStyle neverQualify AllTheWay

showSDoc :: SDoc -> String
showSDoc d = Pretty.showDocWith OneLineMode (d style)