{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE NondecreasingIndentation #-}
{-# LANGUAGE CPP #-}
{-# LANGUAGE BangPatterns #-}

-- | Find type/location information.

module GhciFind
  (findType,FindType(..),findLoc,findNameUses,findCompletions)
  where

#if __GLASGOW_HASKELL__ >= 800
import Module
#endif
import           Control.Exception
import           Data.List
import           Data.Map (Map)
import qualified Data.Map as M
import           Data.Maybe
import           DynFlags
import           FastString
import           GHC
import           GhcMonad
import           GhciInfo (showppr)
import           GhciTypes
import           Name
import           SrcLoc
import           System.Directory
import           Var

-- | Find completions for the sample, context given by the location.
findCompletions :: (GhcMonad m)
                => Map ModuleName ModInfo
                -> FilePath
                -> String
                -> Int
                -> Int
                -> Int
                -> Int
                -> m (Either String [String])
findCompletions infos fp sample sl sc el ec =
  do mname <- guessModule infos fp
     case mname of
       Nothing ->
         return (Left "Couldn't guess that module name. Does it exist?")
       Just name ->
         case M.lookup name infos of
           Nothing ->
             return (Left ("No module info for the current file! Try loading it?"))
           Just moduleInf ->
             do df <- getDynFlags
                let toplevelNames =
                      fromMaybe [] (modInfoTopLevelScope (modinfoInfo moduleInf))
                    filteredToplevels =
                      filter (isPrefixOf sample)
                             (map (showppr df) toplevelNames)
                localNames <- findLocalizedCompletions (modinfoSpans moduleInf) sample sl sc el ec
                return (Right (take 30 (nub (localNames ++ filteredToplevels))))

-- | Find completions within the local scope of a definition of a
-- module.
findLocalizedCompletions
  :: GhcMonad m
  => [SpanInfo]
  -> String
  -> Int
  -> Int
  -> Int
  -> Int
  -> m [String]
findLocalizedCompletions spans' prefix _sl _sc _el _ec =
  do df <- getDynFlags
     return (mapMaybe (complete df) spans')
  where complete
          :: DynFlags -> SpanInfo -> Maybe String
        complete df si =
          do var <- spaninfoVar si
             let str = showppr df var
             if isPrefixOf prefix str
                then Just str
                else Nothing

-- | Find any uses of the given identifier in the codebase.
findNameUses :: (GhcMonad m)
             => Map ModuleName ModInfo
             -> FilePath
             -> String
             -> Int
             -> Int
             -> Int
             -> Int
             -> m (Either String [SrcSpan])
findNameUses infos fp string sl sc el ec =
  do mname <- guessModule infos fp
     case mname of
       Nothing ->
         return (Left "Couldn't guess that module name. Does it exist?")
       Just name ->
         case M.lookup name infos of
           Nothing ->
             return (Left ("No module info for the current file! Try loading it?"))
           Just info ->
             do mname' <- findName infos info string sl sc el ec
                case mname' of
                  Left e -> return (Left e)
                  Right name' ->
                    case getSrcSpan name' of
                      UnhelpfulSpan{} ->
                        do d <- getSessionDynFlags
                           return (Left ("Found a name, but no location information. The module is: " ++
                                         maybe "<unknown>"
                                               (showppr d . moduleName)
                                               (nameModule_maybe name')))
                      span' ->
                        return (Right (stripSurrounding
                                         (span' :
                                          map makeSrcSpan
                                              (filter (fromMaybe False .
                                                       fmap (reliableNameEquality name') .
                                                       fmap getName .
                                                       spaninfoVar)
                                                      (modinfoSpans info)))))
  where makeSrcSpan (SpanInfo sl' sc' el' ec' _ _) =
          RealSrcSpan
            (mkRealSrcSpan
               (mkRealSrcLoc (mkFastString fp)
                             sl'
                             (1 + sc'))
               (mkRealSrcLoc (mkFastString fp)
                             el'
                             (1 + ec')))

-- | Reliable equality for two names. This tests based on the start
-- line and start column and module.
--
-- We don't use standard equality. The unique can differ. Even the end
-- column can differ.
reliableNameEquality :: Name -> Name -> Bool
reliableNameEquality name1 name2 = nameSrcLoc name1 == nameSrcLoc name2

-- | Strip out spans which surrounding other spans in a parent->child
-- fashion. Those are useless.
stripSurrounding :: [SrcSpan] -> [SrcSpan]
stripSurrounding xs =
  mapMaybe (\x -> if any (\y -> overlaps x y && x /= y) xs
                     then Nothing
                     else Just x)
           xs

-- | Does x overlap y in x `overlaps` y?
overlaps :: SrcSpan -> SrcSpan -> Bool
overlaps y x =
  case (x,y) of
    (RealSrcSpan x',RealSrcSpan y') ->
      realSrcSpanStart y' <= realSrcSpanStart x' &&
      realSrcSpanEnd y' >= realSrcSpanEnd x'
    _ -> False

-- | Try to find the location of the given identifier at the given
-- position in the module.
findLoc :: (GhcMonad m)
        => Map ModuleName ModInfo
        -> FilePath
        -> String
        -> Int
        -> Int
        -> Int
        -> Int
        -> m (Either String SrcSpan)
findLoc infos fp string sl sc el ec =
  do mname <- guessModule infos fp
     case mname of
       Nothing ->
         return (Left "Couldn't guess that module name. Does it exist?")
       Just name ->
         case M.lookup name infos of
           Nothing ->
             return (Left ("No module info for the current file! Try loading it?"))
           Just info ->
             do mname' <- findName infos info string sl sc el ec
                d <- getSessionDynFlags
                case mname' of
                  Left reason ->
                    return (Left reason)
                  Right name' ->
                    case getSrcSpan name' of
                      UnhelpfulSpan{} ->
                        return (Left ("Found a name, but no location information. The module is: " ++
                                      maybe "<unknown>"
                                            (showppr d . moduleName)
                                            (nameModule_maybe name')))
                      span' ->
                        return (Right span')

-- | Try to resolve the name located at the given position, or
-- otherwise resolve based on the current module's scope.
findName :: GhcMonad m
         => Map ModuleName ModInfo
         -> ModInfo
         -> String
         -> Int
         -> Int
         -> Int
         -> Int
         -> m (Either String Name)
findName infos mi string sl sc el ec =
  case resolveName (modinfoSpans mi)
                   sl
                   sc
                   el
                   ec of
    Nothing -> tryExternalModuleResolution
    Just name ->
      case getSrcSpan name of
        UnhelpfulSpan{} -> tryExternalModuleResolution
        _ -> return (Right (getName name))
  where tryExternalModuleResolution =
          case find (matchName string)
                    (fromMaybe [] (modInfoTopLevelScope (modinfoInfo mi))) of
            Nothing ->
              return (Left "Couldn't resolve to any modules.")
            Just imported -> resolveNameFromModule infos imported
        matchName :: String -> Name -> Bool
        matchName str name =
          str ==
          occNameString (getOccName name)

-- | Try to resolve the name from another (loaded) module's exports.
resolveNameFromModule :: GhcMonad m
                      => Map ModuleName ModInfo
                      -> Name
                      -> m (Either String Name)
resolveNameFromModule infos name =
  do d <- getSessionDynFlags
     case nameModule_maybe name of
       Nothing ->
         return (Left ("No module for " ++
                       showppr d name))
       Just modL ->
         do case M.lookup (moduleName modL) infos of
              Nothing ->
#if __GLASGOW_HASKELL__ >= 800
                do (return (Left (unitIdString (moduleUnitId modL) ++ ":" ++
#elif __GLASGOW_HASKELL__ >= 709
                do (return (Left (showppr d (modulePackageKey modL) ++ ":" ++
#else
                do (return (Left (showppr d (modulePackageId modL) ++ ":" ++
#endif
                                  showppr d modL)))
              Just info ->
                case find (matchName name)
                          (modInfoExports (modinfoInfo info)) of
                  Just name' ->
                    return (Right name')
                  Nothing ->
                    return (Left "No matching export in any local modules.")
  where matchName :: Name -> Name -> Bool
        matchName x y =
          occNameString (getOccName x) ==
          occNameString (getOccName y)

-- | Try to resolve the type display from the given span.
resolveName :: [SpanInfo] -> Int -> Int -> Int -> Int -> Maybe Var
resolveName spans' sl sc el ec =
  listToMaybe (mapMaybe spaninfoVar (filter inside (reverse spans')))
  where inside (SpanInfo sl' sc' el' ec' _ _) =
          ((sl' == sl && sc' >= sc) || (sl' > sl)) &&
          ((el' == el && ec' <= ec) || (el' < el))

data FindType
  = FindTypeFail String
  | FindType ModInfo
             Type
  | FindTyThing ModInfo
                TyThing

-- | Try to find the type of the given span.
findType :: GhcMonad m
         => Map ModuleName ModInfo
         -> FilePath
         -> String
         -> Int
         -> Int
         -> Int
         -> Int
         -> m FindType
findType infos fp string sl sc el ec =
  do mname <- guessModule infos fp
     case mname of
       Nothing ->
         return (FindTypeFail "Couldn't guess that module name. Does it exist?")
       Just modName ->
         case M.lookup modName infos of
           Nothing ->
             return (FindTypeFail "Couldn't guess the module name. Is this module loaded?")
           Just minfo ->
             do names <- lookupNamesInContext string
                let !mspaninfo =
                      resolveSpanInfo (modinfoSpans minfo)
                                      sl
                                      sc
                                      el
                                      ec
                case mspaninfo of
                  Just si
                    | Just ty <- spaninfoType si ->
                      case fmap Var.varName (spaninfoVar si) of
                        Nothing -> return (FindType minfo ty)
                        Just name ->
                          case find (reliableNameEquality name) names of
                            Just nameWithBetterType ->
                              do result <- getInfo True nameWithBetterType
                                 case result of
                                   Just (thing,_,_,_) ->
                                     return (FindTyThing minfo thing)
                                   Nothing -> return (FindType minfo ty)
                            Nothing -> return (FindType minfo ty)
                  _ ->
                    fmap (FindType minfo)
                         (exprType string)

-- | Try to resolve the type display from the given span.
resolveSpanInfo :: [SpanInfo] -> Int -> Int -> Int -> Int -> Maybe SpanInfo
resolveSpanInfo spanList spanSL spanSC spanEL spanEC =
  listToMaybe
    (sortBy (flip compareSpanInfoStart)
            (filter (contains spanSL spanSC spanEL spanEC) spanList))

-- | Compare the start of two span infos.
compareSpanInfoStart :: SpanInfo -> SpanInfo -> Ordering
compareSpanInfoStart this that =
  case compare (spaninfoStartLine this) (spaninfoStartLine that) of
    EQ -> compare (spaninfoStartCol this) (spaninfoStartCol that)
    c -> c

-- | Does the 'SpanInfo' contain the location given by the Ints?
contains :: Int -> Int -> Int -> Int -> SpanInfo -> Bool
contains spanSL spanSC spanEL spanEC (SpanInfo ancestorSL ancestorSC ancestorEL ancestorEC _ _) =
  ((ancestorSL == spanSL && spanSC >= ancestorSC) || (ancestorSL < spanSL)) &&
  ((ancestorEL == spanEL && spanEC <= ancestorEC) || (ancestorEL > spanEL))

-- | Guess a module name from a file path.
guessModule :: GhcMonad m
            => Map ModuleName ModInfo -> FilePath -> m (Maybe ModuleName)
guessModule infos fp =
  do target <- guessTarget fp Nothing
     case targetId target of
       TargetModule mn -> return (Just mn)
       TargetFile fp' _ ->
         case find ((Just fp' ==) .
                    ml_hs_file . ms_location . modinfoSummary . snd)
                   (M.toList infos) of
           Just (mn,_) -> return (Just mn)
           Nothing ->
             do fp'' <- liftIO (makeRelativeToCurrentDirectory fp')
                target' <- guessTarget fp'' Nothing
                case targetId target' of
                  TargetModule mn ->
                    return (Just mn)
                  _ ->
                    case find ((Just fp'' ==) .
                               ml_hs_file . ms_location . modinfoSummary . snd)
                              (M.toList infos) of
                      Just (mn,_) ->
                        return (Just mn)
                      Nothing -> return Nothing

-- | Lookup the name of something in the current context.
lookupNamesInContext :: GhcMonad m => String -> m [Name]
lookupNamesInContext string =
  gcatch (GHC.parseName string)
         (\(_ :: SomeException) -> return [])