{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE ViewPatterns #-}

module HSE.All(
    CppFlags(..), ParseFlags(..), defaultParseFlags,
    parseFlagsAddFixities, parseFlagsSetLanguage,
    ParseError(..), ModuleEx(..),
    parseModuleEx, ghcComments,
    parseExpGhcWithMode, parseImportDeclGhcWithMode, parseDeclGhcWithMode,
    ) where

import Util
import Data.Char
import Data.List.Extra
import Timing
import Language.Preprocessor.Cpphs
import qualified Data.Map as Map
import System.IO.Extra
import Fixity
import Extension
import FastString

import GHC.Hs
import SrcLoc
import ErrUtils
import Outputable
import Lexer hiding (context)
import GHC.LanguageExtensions.Type
import ApiAnnotation
import DynFlags hiding (extensions)
import Bag

import Language.Haskell.GhclibParserEx.GHC.Parser
import Language.Haskell.GhclibParserEx.Fixity
import GHC.Util

-- | What C pre processor should be used.
data CppFlags
    = NoCpp -- ^ No pre processing is done.
    | CppSimple -- ^ Lines prefixed with @#@ are stripped.
    | Cpphs CpphsOptions -- ^ The @cpphs@ library is used.

-- | Created with 'defaultParseFlags', used by 'parseModuleEx'.
data ParseFlags = ParseFlags
    {cppFlags :: CppFlags -- ^ How the file is preprocessed (defaults to 'NoCpp').
    ,baseLanguage :: Maybe Language -- ^ Base language (e.g. Haskell98, Haskell2010), defaults to 'Nothing'.
    ,extensions :: [Extension] -- ^ List of extensions enabled for parsing, defaults to many non-conflicting extensions.
    ,fixities :: [FixityInfo] -- ^ List of fixities to be aware of, defaults to those defined in @base@.
    }

-- | Default value for 'ParseFlags'.
defaultParseFlags :: ParseFlags
defaultParseFlags = ParseFlags NoCpp Nothing defaultExtensions defaultFixities

-- | Given some fixities, add them to the existing fixities in 'ParseFlags'.
parseFlagsAddFixities :: [FixityInfo] -> ParseFlags -> ParseFlags
parseFlagsAddFixities fx x = x{fixities = fx ++ fixities x}

parseFlagsSetLanguage :: (Maybe Language, [Extension]) -> ParseFlags -> ParseFlags
parseFlagsSetLanguage (l, es) x = x{baseLanguage = l, extensions = es}


runCpp :: CppFlags -> FilePath -> String -> IO String
runCpp NoCpp _ x = pure x
runCpp CppSimple _ x = pure $ unlines [if "#" `isPrefixOf` trimStart x then "" else x | x <- lines x]
runCpp (Cpphs o) file x = dropLine <$> runCpphs o file x
    where
        -- LINE pragmas always inserted when locations=True
        dropLine (line1 -> (a,b)) | "{-# LINE " `isPrefixOf` a = b
        dropLine x = x

---------------------------------------------------------------------
-- PARSING

-- | A parse error.
data ParseError = ParseError
    { parseErrorLocation :: SrcSpan -- ^ Location of the error.
    , parseErrorMessage :: String  -- ^ Message about the cause of the error.
    , parseErrorContents :: String -- ^ Snippet of several lines (typically 5) including a @>@ character pointing at the faulty line.
    }

-- | Result of 'parseModuleEx', representing a parsed module.
data ModuleEx = ModuleEx {
    ghcModule :: Located (HsModule GhcPs)
  , ghcAnnotations :: ApiAnns
}

-- | Extract a list of all of a parsed module's comments.
ghcComments :: ModuleEx -> [Located AnnotationComment]
ghcComments m = concat (Map.elems $ snd (ghcAnnotations m))


-- | The error handler invoked when GHC parsing has failed.
ghcFailOpParseModuleEx :: String
                       -> FilePath
                       -> String
                       -> (SrcSpan, ErrUtils.MsgDoc)
                       -> IO (Either ParseError ModuleEx)
ghcFailOpParseModuleEx ppstr file str (loc, err) = do
   let pe = case loc of
            RealSrcSpan r -> context (srcSpanStartLine r) ppstr
            _ -> ""
       msg = Outputable.showSDoc baseDynFlags err
   pure $ Left $ ParseError loc msg pe

-- GHC extensions to enable/disable given HSE parse flags.
ghcExtensionsFromParseFlags :: ParseFlags -> ([Extension], [Extension])
ghcExtensionsFromParseFlags ParseFlags{extensions=exts}= (exts, [])

-- GHC fixities given HSE parse flags.
ghcFixitiesFromParseFlags :: ParseFlags -> [(String, Fixity)]
ghcFixitiesFromParseFlags = map toFixity . fixities

-- These next two functions get called frorm 'Config/Yaml.hs' for user
-- defined hint rules.

parseModeToFlags :: ParseFlags -> DynFlags
parseModeToFlags parseMode =
    flip lang_set (baseLanguage parseMode) $ foldl' xopt_unset (foldl' xopt_set baseDynFlags enable) disable
  where
    (enable, disable) = ghcExtensionsFromParseFlags parseMode

parseExpGhcWithMode :: ParseFlags -> String -> ParseResult (LHsExpr GhcPs)
parseExpGhcWithMode parseMode s =
  let fixities = ghcFixitiesFromParseFlags parseMode
  in case parseExpression s $ parseModeToFlags parseMode of
    POk pst a -> POk pst $ applyFixities fixities a
    f@PFailed{} -> f

parseImportDeclGhcWithMode :: ParseFlags -> String -> ParseResult (LImportDecl GhcPs)
parseImportDeclGhcWithMode parseMode s =
  parseImport s $ parseModeToFlags parseMode

parseDeclGhcWithMode :: ParseFlags -> String -> ParseResult (LHsDecl GhcPs)
parseDeclGhcWithMode parseMode s =
  let fixities = ghcFixitiesFromParseFlags parseMode
  in case parseDeclaration s $ parseModeToFlags parseMode of
    POk pst a -> POk pst $ applyFixities fixities a
    f@PFailed{} -> f

-- | Parse a Haskell module. Applies the C pre processor, and uses
-- best-guess fixity resolution if there are ambiguities.  The
-- filename @-@ is treated as @stdin@. Requires some flags (often
-- 'defaultParseFlags'), the filename, and optionally the contents of
-- that file.
parseModuleEx :: ParseFlags -> FilePath -> Maybe String -> IO (Either ParseError ModuleEx)
parseModuleEx flags file str = timedIO "Parse" file $ do
        str <- case str of
            Just x -> pure x
            Nothing | file == "-" -> getContentsUTF8
                    | otherwise -> readFileUTF8' file
        str <- pure $ dropPrefix "\65279" str -- remove the BOM if it exists, see #130
        ppstr <- runCpp (cppFlags flags) file str
        let enableDisableExts = ghcExtensionsFromParseFlags flags
            fixities = ghcFixitiesFromParseFlags flags
        dynFlags <- parsePragmasIntoDynFlags baseDynFlags enableDisableExts file ppstr
        case dynFlags of
          Right ghcFlags -> do
            ghcFlags <- pure $ lang_set ghcFlags $ baseLanguage flags
            case fileToModule file ppstr ghcFlags of
                POk s a -> do
                    let errs = bagToList . snd $ getMessages s ghcFlags
                    if not $ null errs then
                      handleParseFailure ghcFlags ppstr file str errs
                    else do
                      let anns =
                            ( Map.fromListWith (++) $ annotations s
                            , Map.fromList ((noSrcSpan, comment_q s) : annotations_comments s)
                            )
                      pure $ Right (ModuleEx (applyFixities fixities a) anns)
                PFailed s ->
                    handleParseFailure ghcFlags ppstr file str $  bagToList . snd $ getMessages s ghcFlags
          Left msg -> do
            -- Parsing GHC flags from dynamic pragmas in the source
            -- has failed. When this happens, it's reported by
            -- exception. It's impossible or at least fiddly getting a
            -- location so we skip that for now. Synthesize a parse
            -- error.
            let loc = mkSrcLoc (mkFastString file) (1 :: Int) (1 :: Int)
            pure $ Left (ParseError (mkSrcSpan loc loc) msg ppstr)
        where
          handleParseFailure ghcFlags ppstr file str errs =
              let errMsg = head errs
                  loc = errMsgSpan errMsg
                  doc = formatErrDoc ghcFlags (errMsgDoc errMsg)
              in ghcFailOpParseModuleEx ppstr file str (loc, doc)


-- | Given a line number, and some source code, put bird ticks around the appropriate bit.
context :: Int -> String -> String
context lineNo src =
    unlines $ dropWhileEnd (all isSpace) $ dropWhile (all isSpace) $
    zipWith (++) ticks $ take 5 $ drop (lineNo - 3) $ lines src ++ ["","","","",""]
    where ticks = drop (3 - lineNo) ["  ","  ","> ","  ","  "]