{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE ViewPatterns #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE OverloadedStrings #-}
module Internal.FixWarnings
  ( fixWarning
  , fixRedundancyWarning
  , RedundancyWarn(..)
  ) where

import           Control.Applicative ((<|>))
import           Control.Monad
import           Control.Monad.IO.Class
import           Control.Monad.Trans.State
import           Data.Bifunctor (first)
import qualified Data.ByteString.Char8 as BS
import           Data.Char (isSpace)
import           Data.Maybe (isJust)
import           Data.Monoid (Alt(..))
import qualified Data.Map.Strict as M
import qualified System.Directory as Dir
import qualified Text.ParserCombinators.ReadP as P

import qualified Internal.GhcFacade as Ghc
import           Internal.Types

-- | Fixes applicable warning
fixWarning :: ModuleFile -> WarningsWithModDate -> IO WarningsWithModDate
fixWarning modFile
           warns@MkWarningsWithModDate
             { lastUpdated = modifiedAt
             , warningsMap = MonoidMap warnMap
             } = do

  lastModification <- liftIO $ Dir.getModificationTime modFile

  -- Do not attempt to edit if file has been touched since last reload
  if lastModification /= modifiedAt
  then do
    putStrLn
      $ "'" <> modFile
      <> "' has been modified since last compiled. Reload and try again."
    pure warns

  else do
    curSrcLines <- liftIO . fmap BS.lines $ BS.readFile modFile

    -- State is used to keep the contents of the source file in memory while
    -- warnings for the file are fixed.
    (pairs, newFileContents) <- (`runStateT` curSrcLines)
             . flip filterM (reverse $ M.toList warnMap) $ \case
      ((start, _), warnSet)
        | Alt (Just reWarn) -- Take the first redundancy warning parsed
            <- foldMap (Alt . parseRedundancyWarn) warnSet
        -> do
          srcLines <- get

          -- attempt to fix the warning
          let startLine = Ghc.srcLocLine start
              mNewSrcLines =
                fixRedundancyWarning startLine reWarn srcLines

          case mNewSrcLines of
            Nothing -> pure True

            Just newSrcLines -> do
              put newSrcLines
              pure False

      _ -> pure True

    when (length pairs /= length warnMap) $ do
      -- write the changes to the file
      BS.writeFile modFile $ BS.unlines newFileContents
      putStrLn $ "'" <> modFile <> "' has been edited"

    pure MkWarningsWithModDate
           { lastUpdated = lastModification
           , warningsMap = MonoidMap $ M.fromList pairs
           }

-- | Attempt to fix redundant import warning.
-- Returns 'Nothing' if incapable of fixing.
fixRedundancyWarning :: Int
                     -> RedundancyWarn
                     -> [BS.ByteString]
                     -> Maybe [BS.ByteString]
fixRedundancyWarning startLine warn srcLines = do
  -- The span for redundant errors is only ever a single line. This means we
  -- must search for the end of the import statement. If this a warning about a
  -- single import thing, the span line may not encompass the start of the
  -- import statement so we must search for that as well.

  (before, stmt : after) <- Just $ splitAt (startLine - 1) srcLines

  let isStart bs = "import" `BS.isPrefixOf` BS.dropSpace bs

  -- If the first line is not the start of the import declaration, search for
  -- it in the preceding lines.
  (before', stmt') <-
    if isStart stmt
       then Just (before, [stmt])
       else do
         (inS, st : rs) <- Just . break isStart $ stmt : reverse before
         Just (reverse rs, st : reverse inS)

  let (stmt'', after') = splitAtImportEnd $ stmt' <> after

      hasExplicitList
        -- Check the next line to see if it contains an explicit import list
        | a : _ <- after
        , BS.length (BS.takeWhile isSpace a)
            > BS.length (BS.takeWhile isSpace stmt)
        , BS.take 1 (BS.dropSpace a) == "("
          = True
        | otherwise = isJust (BS.elemIndex '(' stmt)

  case warn of
    WholeModule
      | hasExplicitList -> Just $ before <> after'
      | otherwise       -> Just $ before <> after

    IndividualThings things ->
      (<> after') . (before' <>) . BS.lines <$>
        foldM fixRedundantThing
              (BS.unlines stmt'')
              things

-- | Splits at the end of an import with an explicit list by counting the
-- number of opening and closing parens. If the main parens is closed, then
-- that marks the end of the import.
splitAtImportEnd :: [BS.ByteString] -> ([BS.ByteString], [BS.ByteString])
splitAtImportEnd ls = first reverse $ go 0 0 ([], ls) where
  go o c acc
    | o /= 0 , o == c
    = acc
  go _ _ acc@(_, []) = acc -- shouldn't happen
  go o c (stmt, r:rest) =
    let addO = length $ BS.elemIndices '(' r
        addC = length $ BS.elemIndices ')' r
     in go (o + addO) (c + addC) (r : stmt, rest)

-- | Removes a particular thing from an import list without disrupting the
-- formatting. Returns 'Nothing' if the thing doesn't exist or appears more
-- than once.
--
-- Edges cases not handled:
-- - Comments interspersed in the statement that mention the thing
-- - Semicolon layout
fixRedundantThing :: BS.ByteString -> String -> Maybe BS.ByteString
fixRedundantThing stmt thing
  -- Bail if there is more than one valid candidate
  | [(start, match)] <- filter isValidCandidate $ findCandidates stmt

    -- 1) remove the needle
    -- 2) remove enclosing parens
    -- 3) remove stuff to the right (..) etc.
    -- 4) if there's a comma to the right, remove it as well

    -- preserve the whitespace immediately after the ',' or '('
  , let start' = let (s, e) = BS.breakEnd (`elem` [',', '(']) start
                  in s <> BS.takeWhile isSpace e

        end = BS.drop thingLen match
  = do
    (start'', end') <- traverse removeAssociatedIds
                     $ removeEnclosingParens start' end
    BS.uncons end' >>= \case
      -- Don't do this if the removed thing was an associated constructor
      (',', end'')
        | Just (_, e) <- BS.unsnoc $ BS.dropWhileEnd isSpace start''
        , e `elem` [',', '('] -- Check if the target thing was not an associated constructor/method
        -> Just $ start'' <> BS.dropSpace end''
        | otherwise -> Just $ start'' <> end'
      -- If bound on the right by ')', remove the suffix containing ',' from start
      (')', _) -> Just $ BS.dropWhileEnd (== ',') startTrim <> end'
        where
          startTrim = BS.dropWhileEnd isSpace start''
      _ -> Nothing

  | otherwise = Nothing
  where
    thingBS = BS.pack thing
    thingLen = BS.length thingBS

    -- A list of substring matches where each element is a pair of the prefix
    -- with the match and remaining suffix.
    findCandidates "" = []
    findCandidates inp =
    -- first isolate the portion that is within an open parens, otherwise
    -- if the module name is the same as the target then the search will fail.
      let (beforeParen, inp') = BS.break (\c -> c == '(' || c == ',') inp
          (pre, match) = BS.breakSubstring thingBS inp'
       in (beforeParen <> pre, match) :
            ( first ((beforeParen <> pre <> thingBS) <>)
            <$> findCandidates (BS.drop thingLen match)
            )

    -- Test if a match pair is valid by checking that the match is not a
    -- substring of a different identifier
    isValidCandidate (start, match) =
      not (BS.null match)
      && isSeparator (BS.drop thingLen match)
      && isCellStart (BS.reverse start)

    isSeparator = headPred $ \c -> isSpace c || c `elem` [',', '(', ')']
    isCellStart = headPred $ \c -> isSpace c || c `elem` [',', '(']
    headPred :: (Char -> Bool) -> BS.ByteString -> Bool
    headPred p = maybe False (p . fst) . BS.uncons

    -- If dealing with an operator, there will be enclosing parens with possible
    -- whitespace surrounding the operator.
    removeEnclosingParens startBS (BS.dropSpace -> endBS)
      | Just (')', end') <- BS.uncons endBS
      , Just (start', '(') <- BS.unsnoc $ BS.dropWhileEnd isSpace startBS
      -- recurse because it could be an associated constructor that is an operator,
      -- i.e. NonEmpty((:|))
      = removeEnclosingParens start' end'
      | otherwise = (startBS, endBS)

-- | Remove list of associated constructors of a type or methods of a class
-- and any space up until the next cell terminator.
removeAssociatedIds :: BS.ByteString -> Maybe BS.ByteString
removeAssociatedIds = checkForParens
  where
    checkForParens bs =
      let bs' = BS.dropSpace bs
       in case BS.uncons bs' of
            Nothing -> Just ""
            Just (c, r)
              | c == '(' -> removeParens 1 r
            _ -> Just bs'

    -- counts the depth of nested parens to handle the case of an operator
    -- appearing in the list.
    removeParens :: Int -> BS.ByteString -> Maybe BS.ByteString
    removeParens 0 bs = Just $ BS.dropSpace bs
    removeParens !n bs =
      let bs' = BS.dropWhile (\x -> x /= '(' && x /= ')') bs
       in case BS.uncons bs' of
            Just (c, r)
              | c == '(' -> removeParens (succ n) r
              | c == ')' -> removeParens (pred n) r
            _ -> Nothing

--------------------------------------------------------------------------------
-- Parsing
--------------------------------------------------------------------------------

-- | Redundant import warnings
data RedundancyWarn
  = WholeModule
  | IndividualThings [String]
  deriving Show

parseRedundancyWarn :: Warning -> Maybe RedundancyWarn
parseRedundancyWarn warn =
  case P.readP_to_S redundancyWarnParser (showWarning warn) of
    [(w, "")] -> Just w
    _ -> Nothing

redundancyWarnParser :: P.ReadP RedundancyWarn
redundancyWarnParser = do
  _ <- P.string "The import of ‘"
   <|> P.string "The qualified import of ‘"

  inQuotes <-
    P.sepBy1 (P.munch1 $ \c -> not (isSpace c) && c `notElem` [',', '’'])
             (P.char ',' <* P.skipSpaces)

  _ <- P.char '’'

  let terms
        = IndividualThings inQuotes
         <$ ( P.skipSpaces
           *> P.string "from module ‘"
           *> P.munch1 (/= '’')
           *> P.string "’ is redundant"
            )

      wholeMod = WholeModule
              <$ (P.skipSpaces *> P.string "is redundant")

  result <- P.choice [terms, wholeMod]

  _ <- P.munch (const True)

  pure result