{-# LANGUAGE CPP #-}
{-# LANGUAGE NamedFieldPuns #-}
{-# LANGUAGE ViewPatterns #-}

module HsInspect.Runner (runGhcAndJamMasterShe, ghcflags_flags) where

#if MIN_VERSION_GLASGOW_HASKELL(9,3,0,0)
import qualified GHC.Driver.Env.Types as GHC
import qualified GHC.Unit.Env as GHC
#endif

#if MIN_VERSION_GLASGOW_HASKELL(9,0,0,0)
import qualified GHC.Driver.Session as GHC
import qualified GHC.Data.EnumSet as GHC
#else
import qualified DynFlags as GHC
import qualified EnumSet as GHC
#endif
import qualified GHC as GHC

import Control.Monad
import Control.Monad.IO.Class
import Control.Monad.Trans.Except (ExceptT(..))
import Data.List (find, isPrefixOf)
import qualified Data.List as L
import Data.Maybe (catMaybes)
import qualified Data.Text as T
import HsInspect.Context
import HsInspect.Util (homeSources)
import HsInspect.Workarounds (parseModuleName')
import System.Directory (getCurrentDirectory, setCurrentDirectory)
import System.Environment (setEnv)

-- expects the PWD to be the same as the .cabal file and the PATH to be what the
-- build tool sees.
runGhcAndJamMasterShe :: [String] -> Bool -> GHC.Ghc a -> IO a
runGhcAndJamMasterShe (filterFlags -> flags) setTargets work =
  let libdir = (drop 2) <$> find ("-B" `isPrefixOf`) flags
      flags' = filter (not . ("-B" `isPrefixOf`)) flags
   in GHC.runGhc libdir $ do
  dflags <- GHC.getSessionDynFlags
  (GHC.updOptLevel 0 -> dflags', (GHC.unLoc <$>) -> _ghcargs, _) <-
    liftIO $ GHC.parseDynamicFlagsCmdLine dflags (GHC.noLoc <$> flags')
  void $ GHC.setSessionDynFlags dflags'
         {
#if MIN_VERSION_GLASGOW_HASKELL(9,5,0,0)
           GHC.backend = GHC.interpreterBackend
#elif MIN_VERSION_GLASGOW_HASKELL(9,1,0,0)
           GHC.backend = GHC.Interpreter
#else
           GHC.hscTarget = GHC.HscInterpreted -- HscNothing compiles home modules, dunno why
#endif
         , GHC.ghcLink   = GHC.LinkInMemory   -- required by HscInterpreted
         , GHC.ghcMode   = GHC.MkDepend       -- prefer .hi to .hs for dependencies
         , GHC.warningFlags = GHC.empty
         , GHC.fatalWarningFlags = GHC.empty
         }

  when setTargets $ do
    -- The caller may have provided a list of home modules, but we do not trust
    -- them because the ghcflags plugin does not keep the flags up to date for
    -- incremental compiles.
#if MIN_VERSION_GLASGOW_HASKELL(9,3,0,0)
    sess <- GHC.getSession
    let unitid = GHC.ue_current_unit $ GHC.hsc_unit_env sess
        mkTarget m = GHC.Target (GHC.TargetModule m) True unitid Nothing
#else
    let mkTarget m = GHC.Target (GHC.TargetModule m) True Nothing
#endif
    homeModules <- inferHomeModules
    GHC.setTargets $ mkTarget <$> homeModules

  work

-- gets the flags (and sets the environment) from the output of the ghcflags plugin
ghcflags_flags :: Maybe FilePath -> ExceptT String IO [String]
ghcflags_flags mf = do
  from <- liftIO $ maybe getCurrentDirectory pure mf
  Context{package_dir, ghcflags, ghcpath} <- findContext from
  liftIO $ do
    setCurrentDirectory package_dir
    setEnv "PATH" (T.unpack ghcpath)
  pure $ T.unpack <$> ghcflags

inferHomeModules :: GHC.GhcMonad m => m [GHC.ModuleName]
inferHomeModules = do
  files <- homeSources
  mmns <- traverse parseModuleName' files
  let main' = GHC.mkModuleName "Main"
  pure . L.nub . filter (main' /=) $ catMaybes mmns
  -- stack often has duplicates

-- removes the "+RTS ... -RTS" sections
filterFlags :: [String] -> [String]
filterFlags args = case span ("+RTS" /=) args of
  (front, []) -> front
  (front, _ : middle) -> case span ("-RTS" /=) middle of
    (_, []) -> front -- bad input?
    (_, _ : back) -> front <> back