{-# LANGUAGE ScopedTypeVariables, RecordWildCards #-}

module Language.Haskell.GhcMod.GHCApi (
    withGHC
  , withGHC'
  , initializeFlagsWithCradle
  , setTargetFiles
  , addTargetFiles
  , getDynamicFlags
  , getSystemLibDir
  , withDynFlags
  ) where

import Language.Haskell.GhcMod.CabalApi
import Language.Haskell.GhcMod.ErrMsg
import Language.Haskell.GhcMod.GHCChoice
import Language.Haskell.GhcMod.GhcPkg

import Control.Applicative ((<$>))
import Control.Monad (forM, void, unless)
import CoreMonad (liftIO)
import Data.Maybe (isJust, fromJust)
import Distribution.PackageDescription (PackageDescription)
import Exception (ghandle, SomeException(..))
import GHC (Ghc, GhcMonad, DynFlags(..), GhcLink(..), HscTarget(..), LoadHowMuch(..))
import qualified GHC as G
import qualified Language.Haskell.GhcMod.Gap as Gap
import Language.Haskell.GhcMod.Types
import System.Exit (exitSuccess)
import System.IO (hPutStr, hPrint, stderr)
import System.Process (readProcess)

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

-- | Obtaining the directory for system libraries.
getSystemLibDir :: IO (Maybe FilePath)
getSystemLibDir = do
    res <- readProcess "ghc" ["--print-libdir"] []
    return $ case res of
        ""   -> Nothing
        dirn -> Just (init dirn)

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

-- | Converting the 'Ghc' monad to the 'IO' monad.
withGHC :: FilePath  -- ^ A target file displayed in an error message.
        -> Ghc a -- ^ 'Ghc' actions created by the Ghc utilities.
        -> IO a
withGHC file body = ghandle ignore $ withGHC' body
  where
    ignore :: SomeException -> IO a
    ignore e = do
        hPutStr stderr $ file ++ ":0:0:Error:"
        hPrint stderr e
        exitSuccess

withGHC' :: Ghc a -> IO a
withGHC' body = do
    mlibdir <- getSystemLibDir
    G.runGhc mlibdir $ do
        dflags <- G.getSessionDynFlags
        G.defaultCleanupHandler dflags body

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

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

data Build = CabalPkg | SingleFile deriving Eq

-- | Initialize the 'DynFlags' relating to the compilation of a single
-- file or GHC session according to the 'Cradle' and 'Options'
-- provided.
initializeFlagsWithCradle :: GhcMonad m
        => Options
        -> Cradle
        -> [GHCOption]
        -> Bool
        -> m (LogReader, Maybe PackageDescription)
initializeFlagsWithCradle opt cradle ghcopts logging
  | cabal     = withCabal |||> withSandbox
  | otherwise = withSandbox
  where
    mCradleFile = cradleCabalFile cradle
    cabal = isJust mCradleFile
    withCabal = do
        pkgDesc <- liftIO $ parseCabalFile $ fromJust mCradleFile
        compOpts <- liftIO $ getCompilerOptions ghcopts cradle pkgDesc
        logger <- initSession CabalPkg opt compOpts logging
        return (logger, Just pkgDesc)
    withSandbox = do
        logger <- initSession SingleFile opt compOpts logging
        return (logger, Nothing)
      where
        pkgOpts = ghcDbStackOpts $ cradlePkgDbStack cradle
        compOpts
          | null pkgOpts = CompilerOptions ghcopts importDirs []
          | otherwise    = CompilerOptions (ghcopts ++ pkgOpts) [wdir,rdir] []
        wdir = cradleCurrentDir cradle
        rdir = cradleRootDir    cradle

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

initSession :: GhcMonad m
            => Build
            -> Options
            -> CompilerOptions
            -> Bool
            -> m LogReader
initSession build opt compOpts logging = do
    df <- initDynFlags build opt compOpts
    (df', lg) <- liftIO $ setLogger logging df opt
    _ <- G.setSessionDynFlags df'
    return lg

initDynFlags :: GhcMonad m => Build -> Options -> CompilerOptions -> m DynFlags
initDynFlags build Options {..} CompilerOptions {..} = do
    df <- G.getSessionDynFlags
    _ <- G.setSessionDynFlags =<< (addCmdOpts ghcOptions
      $ setLinkerOptions
      $ setIncludeDirs includeDirs
      $ setSplice expandSplice
      $ setBuildEnv build
      $ Gap.addPackageFlags depPackages df)
    G.getSessionDynFlags


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

-- we don't want to generate object code so we compile to bytecode
-- (HscInterpreted) which implies LinkInMemory
-- HscInterpreted
setLinkerOptions :: DynFlags -> DynFlags
setLinkerOptions df = df {
    ghcLink   = LinkInMemory
  , hscTarget = HscInterpreted
  }

setIncludeDirs :: [IncludeDir] -> DynFlags -> DynFlags
setIncludeDirs idirs df = df { importPaths = idirs }

setBuildEnv :: Build -> DynFlags -> DynFlags
setBuildEnv build = setHideAllPackages build . setCabalPackage build

-- | Set option in 'DynFlags' to Expand template haskell if first argument is
-- True
setSplice :: Bool -> DynFlags -> DynFlags
setSplice False = id
setSplice True  = Gap.setDumpSplices

-- At the moment with this option set ghc only prints different error messages,
-- suggesting the user to add a hidden package to the build-depends in his cabal
-- file for example
setCabalPackage :: Build -> DynFlags -> DynFlags
setCabalPackage CabalPkg df = Gap.setCabalPkg df
setCabalPackage _ df = df

-- | Enable hiding of all package not explicitly exposed (like Cabal does)
setHideAllPackages :: Build -> DynFlags -> DynFlags
setHideAllPackages CabalPkg df = Gap.setHideAllPackages df
setHideAllPackages _ df = df

-- | Parse command line ghc options and add them to the 'DynFlags' passed
addCmdOpts :: GhcMonad m => [GHCOption] -> DynFlags -> m DynFlags
addCmdOpts cmdOpts df =
    tfst <$> G.parseDynamicFlags df (map G.noLoc cmdOpts)
  where
    tfst (a,_,_) = a

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

-- | Set the files and load
setTargetFiles :: (GhcMonad m) => [FilePath] -> m ()
setTargetFiles files = do
    targets <- forM files $ \file -> G.guessTarget file Nothing
    unless (null targets) $ do
        G.setTargets targets
        void $ G.load LoadAllTargets

-- | Adding the files to the targets.
addTargetFiles :: (GhcMonad m) => [FilePath] -> m ()
addTargetFiles files = do
    targets <- forM files $ \file -> G.guessTarget file Nothing
    unless (null targets) $ mapM_ G.addTarget targets

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

-- | Return the 'DynFlags' currently in use in the GHC session.
getDynamicFlags :: IO DynFlags
getDynamicFlags = do
    mlibdir <- getSystemLibDir
    G.runGhc mlibdir G.getSessionDynFlags

withDynFlags :: (DynFlags -> DynFlags) -> Ghc a -> Ghc a
withDynFlags setFlag body = G.gbracket setup teardown (\_ -> body)
  where
    setup = do
        dflag <- G.getSessionDynFlags
        void $ G.setSessionDynFlags (setFlag dflag)
        return dflag
    teardown = void . G.setSessionDynFlags