{-# LANGUAGE BangPatterns #-}

module HIE.Bios.Ghc.Logger (
    withLogger
  ) where

import Bag (Bag, bagToList)
import CoreMonad (liftIO)
import DynFlags (LogAction, dopt, DumpFlag(Opt_D_dump_splices))
import ErrUtils
import Exception (ghandle)
import FastString (unpackFS)
import GHC (DynFlags(..), SrcSpan(..), Severity(SevError), GhcMonad)
import qualified GHC as G
import HscTypes (SourceError, srcErrorMessages)
import Outputable (PprStyle, SDoc)

import Data.IORef (IORef, newIORef, readIORef, writeIORef, modifyIORef)
import Data.Maybe (fromMaybe)
import System.FilePath (normalise)

import HIE.Bios.Ghc.Doc (showPage, getStyle)
import HIE.Bios.Ghc.Api (withDynFlags)

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

type Builder = [String] -> [String]

newtype LogRef = LogRef (IORef Builder)

newLogRef :: IO LogRef
newLogRef = LogRef <$> newIORef id

readAndClearLogRef :: LogRef -> IO String
readAndClearLogRef (LogRef ref) = do
    b <- readIORef ref
    writeIORef ref id
    return $! unlines (b [])

appendLogRef :: DynFlags -> LogRef -> LogAction
appendLogRef df (LogRef ref) _ _ sev src style msg = do
        let !l = ppMsg src sev df style msg
        modifyIORef ref (\b -> b . (l:))

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

-- | Set the session flag (e.g. "-Wall" or "-w:") then
--   executes a body. Log messages are returned as 'String'.
--   Right is success and Left is failure.
withLogger ::
  (GhcMonad m)
  => (DynFlags -> DynFlags) -> m () -> m (Either String String)
withLogger setDF body = ghandle sourceError $ do
    logref <- liftIO newLogRef
    withDynFlags (setLogger logref . setDF) $ do
      body
      liftIO $ Right <$> readAndClearLogRef logref
  where
    setLogger logref df = df { log_action =  appendLogRef df logref }

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

-- | Converting 'SourceError' to 'String'.
sourceError ::
  (GhcMonad m)
  => SourceError -> m (Either String String)
sourceError err = do
    dflag <- G.getSessionDynFlags
    style <- getStyle dflag
    let ret = unlines . errBagToStrList dflag style . srcErrorMessages $ err
    return (Left ret)

errBagToStrList :: DynFlags -> PprStyle -> Bag ErrMsg -> [String]
errBagToStrList dflag style = map (ppErrMsg dflag style) . reverse . bagToList

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

ppErrMsg :: DynFlags -> PprStyle -> ErrMsg -> String
ppErrMsg dflag style err = ppMsg spn SevError dflag style msg -- ++ ext
   where
     spn = errMsgSpan err
     msg = pprLocErrMsg err
     -- fixme
--     ext = showPage dflag style (pprLocErrMsg $ errMsgReason err)

ppMsg :: SrcSpan -> Severity-> DynFlags -> PprStyle -> SDoc -> String
ppMsg spn sev dflag style msg = prefix ++ cts
  where
    cts  = showPage dflag style msg
    defaultPrefix
      | isDumpSplices dflag = ""
      | otherwise           = checkErrorPrefix
    prefix = fromMaybe defaultPrefix $ do
        (line,col,_,_) <- getSrcSpan spn
        file <- normalise <$> getSrcFile spn
        let severityCaption = showSeverityCaption sev
        return $ file ++ ":" ++ show line ++ ":" ++ show col ++ ":" ++ severityCaption

checkErrorPrefix :: String
checkErrorPrefix = "Dummy:0:0:Error:"

showSeverityCaption :: Severity -> String
showSeverityCaption SevWarning = "Warning: "
showSeverityCaption _          = ""

getSrcFile :: SrcSpan -> Maybe String
getSrcFile (G.RealSrcSpan spn) = Just . unpackFS . G.srcSpanFile $ spn
getSrcFile _                   = Nothing

isDumpSplices :: DynFlags -> Bool
isDumpSplices dflag = dopt Opt_D_dump_splices dflag

getSrcSpan :: SrcSpan -> Maybe (Int,Int,Int,Int)
getSrcSpan (RealSrcSpan spn) = Just ( G.srcSpanStartLine spn
                                    , G.srcSpanStartCol spn
                                    , G.srcSpanEndLine spn
                                    , G.srcSpanEndCol spn)
getSrcSpan _ = Nothing