module Development.IDE.Types.HscEnvEq
(   HscEnvEq,
    hscEnv, newHscEnvEq,
    hscEnvWithImportPaths,
    newHscEnvEqPreserveImportPaths,
    newHscEnvEqWithImportPaths,
    envImportPaths,
    envPackageExports,
    envVisibleModuleNames,
    deps
) where


import Development.IDE.Types.Exports (ExportsMap, createExportsMap)
import Data.Unique
import Development.Shake.Classes
import Module (InstalledUnitId)
import System.Directory (canonicalizePath)
import Development.IDE.GHC.Compat
import GhcPlugins(HscEnv (hsc_dflags), PackageState (explicitPackages), InstalledPackageInfo (exposedModules), Module(..), packageConfigId, listVisibleModuleNames)
import System.FilePath
import Development.IDE.GHC.Util (lookupPackageConfig)
import Control.Monad.IO.Class
import TcRnMonad (initIfaceLoad, WhereFrom (ImportByUser))
import LoadIface (loadInterface)
import qualified Maybes
import OpenTelemetry.Eventlog (withSpan)
import Control.Monad.Extra (mapMaybeM, join, eitherM)
import Control.Concurrent.Extra (newVar, modifyVar)
import Control.Concurrent.Async (Async, async, waitCatch)
import Control.Exception (throwIO, mask, evaluate)
import Development.IDE.GHC.Error (catchSrcErrors)
import Control.DeepSeq (force)
import Data.Either (fromRight)

-- | An 'HscEnv' with equality. Two values are considered equal
--   if they are created with the same call to 'newHscEnvEq'.
data HscEnvEq = HscEnvEq
    { envUnique :: !Unique
    , hscEnv :: !HscEnv
    , deps   :: [(InstalledUnitId, DynFlags)]
               -- ^ In memory components for this HscEnv
               -- This is only used at the moment for the import dirs in
               -- the DynFlags
    , envImportPaths :: Maybe [String]
        -- ^ If Just, import dirs originally configured in this env
        --   If Nothing, the env import dirs are unaltered
    , envPackageExports :: IO ExportsMap
    , envVisibleModuleNames :: IO (Maybe [ModuleName])
        -- ^ 'listVisibleModuleNames' is a pure function,
        -- but it could panic due to a ghc bug: https://github.com/haskell/haskell-language-server/issues/1365
        -- So it's wrapped in IO here for error handling
        -- If Nothing, 'listVisibleModuleNames' panic
    }

-- | Wrap an 'HscEnv' into an 'HscEnvEq'.
newHscEnvEq :: FilePath -> HscEnv -> [(InstalledUnitId, DynFlags)] -> IO HscEnvEq
newHscEnvEq cradlePath hscEnv0 deps = do
    let relativeToCradle = (takeDirectory cradlePath </>)
        hscEnv = removeImportPaths hscEnv0

    -- Canonicalize import paths since we also canonicalize targets
    importPathsCanon <-
      mapM canonicalizePath $ relativeToCradle <$> importPaths (hsc_dflags hscEnv0)

    newHscEnvEqWithImportPaths (Just importPathsCanon) hscEnv deps

newHscEnvEqWithImportPaths :: Maybe [String] -> HscEnv -> [(InstalledUnitId, DynFlags)] -> IO HscEnvEq
newHscEnvEqWithImportPaths envImportPaths hscEnv deps = do

    let dflags = hsc_dflags hscEnv

    envUnique <- newUnique

    -- it's very important to delay the package exports computation
    envPackageExports <- onceAsync $ withSpan "Package Exports" $ \_sp -> do
        -- compute the package imports
        let pkgst   = pkgState dflags
            depends = explicitPackages pkgst
            targets =
                [ (pkg, mn)
                | d        <- depends
                , Just pkg <- [lookupPackageConfig d hscEnv]
                , (mn, _)  <- exposedModules pkg
                ]

            doOne (pkg, mn) = do
                modIface <- liftIO $ initIfaceLoad hscEnv $ loadInterface
                    ""
                    (Module (packageConfigId pkg) mn)
                    (ImportByUser False)
                return $ case modIface of
                    Maybes.Failed    _r -> Nothing
                    Maybes.Succeeded mi -> Just mi
        modIfaces <- mapMaybeM doOne targets
        return $ createExportsMap modIfaces

    -- similar to envPackageExports, evaluated lazily
    envVisibleModuleNames <- onceAsync $
      fromRight Nothing
        <$> catchSrcErrors
          dflags
          "listVisibleModuleNames"
          (evaluate . force . Just $ listVisibleModuleNames dflags)

    return HscEnvEq{..}

-- | Wrap an 'HscEnv' into an 'HscEnvEq'.
newHscEnvEqPreserveImportPaths
    :: HscEnv -> [(InstalledUnitId, DynFlags)] -> IO HscEnvEq
newHscEnvEqPreserveImportPaths = newHscEnvEqWithImportPaths Nothing

-- | Unwrap the 'HscEnv' with the original import paths.
--   Used only for locating imports
hscEnvWithImportPaths :: HscEnvEq -> HscEnv
hscEnvWithImportPaths HscEnvEq{..}
    | Just imps <- envImportPaths
    = hscEnv{hsc_dflags = (hsc_dflags hscEnv){importPaths = imps}}
    | otherwise
    = hscEnv

removeImportPaths :: HscEnv -> HscEnv
removeImportPaths hsc = hsc{hsc_dflags = (hsc_dflags hsc){importPaths = []}}

instance Show HscEnvEq where
  show HscEnvEq{envUnique} = "HscEnvEq " ++ show (hashUnique envUnique)

instance Eq HscEnvEq where
  a == b = envUnique a == envUnique b

instance NFData HscEnvEq where
  rnf (HscEnvEq a b c d _ _) =
      -- deliberately skip the package exports map and visible module names
      rnf (hashUnique a) `seq` b `seq` c `seq` rnf d

instance Hashable HscEnvEq where
  hashWithSalt s = hashWithSalt s . envUnique

-- Fake instance needed to persuade Shake to accept this type as a key.
-- No harm done as ghcide never persists these keys currently
instance Binary HscEnvEq where
  put _ = error "not really"
  get = error "not really"

-- | Given an action, produce a wrapped action that runs at most once.
--   The action is run in an async so it won't be killed by async exceptions
--   If the function raises an exception, the same exception will be reraised each time.
onceAsync :: IO a -> IO (IO a)
onceAsync act = do
    var <- newVar OncePending
    let run as = eitherM throwIO pure (waitCatch as)
    pure $ mask $ \unmask -> join $ modifyVar var $ \v -> case v of
        OnceRunning x -> pure (v, unmask $ run x)
        OncePending -> do
            x <- async (unmask act)
            pure (OnceRunning x, unmask $ run x)

data Once a = OncePending | OnceRunning (Async a)