{-# LANGUAGE BangPatterns               #-}
{-# LANGUAGE CPP                        #-}
{-# LANGUAGE DeriveDataTypeable         #-}
{-# LANGUAGE DeriveFoldable             #-}
{-# LANGUAGE DeriveFunctor              #-}
{-# LANGUAGE DeriveTraversable          #-}
{-# LANGUAGE ExistentialQuantification  #-}
{-# LANGUAGE FlexibleContexts           #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE LambdaCase                 #-}
{-# LANGUAGE OverloadedStrings          #-}
{-# LANGUAGE RankNTypes                 #-}
{-# LANGUAGE ScopedTypeVariables        #-}
{-# LANGUAGE StandaloneDeriving         #-}
{-# LANGUAGE TemplateHaskell            #-}
{-# LANGUAGE TupleSections              #-}
{-# OPTIONS_GHC -fno-warn-orphans #-}
{-# OPTIONS_HADDOCK show-extensions #-}

-- |
-- Module      :  Yi.Buffer.Misc
-- License     :  GPL-2
-- Maintainer  :  yi-devel@googlegroups.com
-- Stability   :  experimental
-- Portability :  portable
--
-- The 'Buffer' module defines monadic editing operations over one-dimensional
-- buffers, maintaining a current /point/.

module Yi.Buffer.Misc
  ( FBuffer (FBuffer, bmode)
  , BufferM (..)
  , WinMarks, MarkSet (..)
  , bkey
  , getMarks
  , runBuffer
  , runBufferFull
  , runBufferDummyWindow
  , screenTopLn
  , screenMidLn
  , screenBotLn
  , curLn
  , curCol
  , colOf
  , lineOf
  , lineCountB
  , sizeB
  , pointB
  , pointOfLineColB
  , solPointB
  , eolPointB
  , markLines
  , moveTo
  , moveToColB
  , moveToLineColB
  , lineMoveRel
  , lineUp
  , lineDown
  , newB
  , MarkValue (..)
  , Overlay
      (overlayAnnotation, overlayBegin, overlayEnd, overlayOwner, overlayStyle)
  , mkOverlay
  , gotoLn
  , gotoLnFrom
  , leftB
  , rightB
  , moveN
  , leftN
  , rightN
  , insertN
  , insertNAt
  , insertB
  , deleteN
  , nelemsB
  , writeB
  , writeN
  , newlineB
  , deleteNAt
  , readB
  , elemsB
  , undosA
  , undoB
  , redoB
  , getMarkB
  , setMarkHereB
  , setNamedMarkHereB
  , mayGetMarkB
  , getMarkValueB
  , markPointA
  , modifyMarkB
  , newMarkB
  , deleteMarkB
  , getVisibleSelection
  , setVisibleSelection
  , isUnchangedBuffer
  , setAnyMode
  , setMode
  , setMode0
  , modifyMode
  , regexRegionB
  , regexB
  , readAtB
  , getModeLine
  , getPercent
  , setInserting
  , savingPrefCol
  , forgetPreferCol
  , movingToPrefCol
  , movingToPrefVisCol
  , preferColA
  , markSavedB
  , retroactivelyAtSavePointB
  , addOverlayB
  , delOverlayB
  , delOverlaysOfOwnerB
  , getOverlaysOfOwnerB
  , isPointInsideOverlay
  , savingExcursionB
  , savingPointB
  , savingPositionB
  , pendingUpdatesA
  , highlightSelectionA
  , rectangleSelectionA
  , readOnlyA
  , insertingA
  , pointFollowsWindowA
  , revertPendingUpdatesB
  , askWindow
  , clearSyntax
  , focusSyntax
  , Mode (..)
  , modeNameA
  , modeAppliesA
  , modeHLA
  , modePrettifyA
  , modeKeymapA
  , modeIndentA
  , modeAdjustBlockA
  , modeFollowA
  , modeIndentSettingsA
  , modeToggleCommentSelectionA
  , modeGetStrokesA
  , modeOnLoadA
  , modeGotoDeclarationA
  , modeModeLineA
  , AnyMode (..)
  , IndentBehaviour (..)
  , IndentSettings (..)
  , expandTabsA
  , tabSizeA
  , shiftWidthA
  , modeAlwaysApplies
  , modeNeverApplies
  , emptyMode
  , withModeB
  , withMode0
  , onMode
  , withSyntaxB
  , withSyntaxB'
  , keymapProcessA
  , strokesRangesB
  , streamB
  , indexedStreamB
  , askMarks
  , pointAt
  , SearchExp
  , lastActiveWindowA
  , putBufferDyn
  , getBufferDyn
  , shortIdentString
  , identString
  , miniIdentString
  , identA
  , directoryContentA
  , BufferId (..)
  , file
  , lastSyncTimeA
  , replaceCharB
  , replaceCharWithBelowB
  , replaceCharWithAboveB
  , insertCharWithBelowB
  , insertCharWithAboveB
  , pointAfterCursorB
  , destinationOfMoveB
  , withEveryLineB
  , startUpdateTransactionB
  , commitUpdateTransactionB
  , applyUpdate
  , betweenB
  , decreaseFontSize
  , increaseFontSize
  , indentSettingsB
  , fontsizeVariationA
  , encodingConverterNameA
  , stickyEolA
  , queryBuffer
  ) where

import           Prelude                        hiding (foldr, mapM, notElem)

import           Control.Applicative (liftA2)
import           Control.Monad (when, void, replicateM_, join)
import           Data.Monoid
import           Control.Monad.Reader
import           Control.Monad.State.Strict     hiding (get, put)
import           Data.Binary                    (Binary (..), Get)
import           Data.Char                      (ord)
import           Data.Default                   (Default (def))
import           Data.DynamicState.Serializable (getDyn, putDyn)
import           Data.Foldable                  (Foldable (foldr), forM_, notElem)
import qualified Data.Map.Strict                as M (Map, empty, insert, lookup)
import           Data.Maybe                     (fromMaybe, isNothing)
import qualified Data.Sequence                  as S
import qualified Data.Set                       as Set (Set)
import qualified Data.Text                      as T (Text, concat, justifyRight, pack, snoc, unpack)
import qualified Data.Text.Encoding             as E (decodeUtf8, encodeUtf8)
import           Data.Time                      (UTCTime (UTCTime))
import           Data.Traversable               (Traversable (mapM), forM)
import           Lens.Micro.Platform            (Lens', lens, (&), (.~), (%~), (^.), use, (.=), (%=), view)
import           Numeric                        (showHex)
import           System.FilePath                (joinPath, splitPath)
import           Yi.Buffer.Basic                (BufferRef, Point (..), Size (Size), WindowRef)
import           Yi.Buffer.Implementation
import           Yi.Buffer.Undo
import           Yi.Interact                    as I (P (End))
import           Yi.Monad                       (getsAndModify)
import           Yi.Region                      (Region, mkRegion)
import           Yi.Rope                        (YiString)
import qualified Yi.Rope                        as R
import           Yi.Syntax                      (ExtHL (ExtHL), Stroke, noHighlighter)
import           Yi.Types
import           Yi.Utils                       (SemiNum ((+~)), makeClassyWithSuffix, makeLensesWithSuffix)
import           Yi.Window                      (Window (width, wkey, actualLines), dummyWindow)


uses l f = f <$> use l

-- In addition to Buffer's text, this manages (among others):
--  * Log of updates mades
--  * Undo

makeClassyWithSuffix "A" ''Attributes

instance HasAttributes FBuffer where
    attributesA = lens attributes (\(FBuffer f1 f2 _) a -> FBuffer f1 f2 a)

-- | Gets a short identifier of a buffer. If we're given a 'MemBuffer'
-- then just wraps the buffer name like so: @*name*@. If we're given a
-- 'FileBuffer', it drops the number of path components.
--
-- >>> let memBuf = newB (BufferRef 0) (MemBuffer "foo/bar/hello") ""
-- >>> shortIdentString 2 memBuf
-- "*foo/bar/hello*"
-- >>> let fileBuf = newB (BufferRef 0) (FileBuffer "foo/bar/hello") ""
-- >>> shortIdentString 2 fileBuf
-- "hello"
shortIdentString :: Int -- ^ Number of characters to drop from FileBuffer names
                 -> FBuffer -- ^ Buffer to work with
                 -> T.Text
shortIdentString dl b = case b ^. identA of
  MemBuffer bName -> "*" <> bName <> "*"
  FileBuffer fName -> T.pack . joinPath . drop dl $ splitPath fName

-- | Gets the buffer's identifier string, emphasising the 'MemBuffer':
--
-- >>> let memBuf = newB (BufferRef 0) (MemBuffer "foo/bar/hello") ""
-- >>> identString memBuf
-- "*foo/bar/hello*"
-- >>> let fileBuf = newB (BufferRef 0) (FileBuffer "foo/bar/hello") ""
-- >>> identString fileBuf
-- "foo/bar/hello"
identString :: FBuffer -> T.Text
identString b = case b ^. identA of
  MemBuffer bName -> "*" <> bName <> "*"
  FileBuffer fName -> T.pack fName


-- TODO: proper instance + de-orphan
instance Show FBuffer where
    show b = Prelude.concat [ "Buffer #", show (bkey b)
                            , " (",  T.unpack (identString b), ")" ]


miniIdentString :: FBuffer -> T.Text
miniIdentString b = case b ^. identA of
  MemBuffer bufName -> bufName
  FileBuffer _ -> "MINIFILE:"

-- unfortunately the dynamic stuff can't be read.
instance Binary FBuffer where
    put (FBuffer binmode r attributes_) =
      let strippedRaw :: BufferImpl ()
          strippedRaw = setSyntaxBI (modeHL emptyMode) r
      in do
          put binmode
          put strippedRaw
          put attributes_
    get =
        FBuffer <$> get <*> getStripped <*> get
      where getStripped :: Get (BufferImpl ())
            getStripped = get

-- | update the syntax information (clear the dirty "flag")
clearSyntax :: FBuffer -> FBuffer
clearSyntax = modifyRawbuf updateSyntax

queryRawbuf :: (forall syntax. BufferImpl syntax -> x) -> FBuffer -> x
queryRawbuf f (FBuffer _ fb _) = f fb

modifyRawbuf :: (forall syntax. BufferImpl syntax -> BufferImpl syntax) -> FBuffer -> FBuffer
modifyRawbuf f (FBuffer f1 f2 f3) = FBuffer f1 (f f2) f3

queryAndModifyRawbuf :: (forall syntax. BufferImpl syntax -> (BufferImpl syntax,x)) ->
                     FBuffer -> (FBuffer, x)
queryAndModifyRawbuf f (FBuffer f1 f5 f3) =
    let (f5', x) = f f5
    in (FBuffer f1 f5' f3, x)

file :: FBuffer -> Maybe FilePath
file b = case b ^. identA of
  FileBuffer f -> Just f
  MemBuffer _ -> Nothing

highlightSelectionA :: Lens' FBuffer Bool
highlightSelectionA = selectionStyleA .
  lens highlightSelection (\e x -> e { highlightSelection = x })

rectangleSelectionA :: Lens' FBuffer Bool
rectangleSelectionA = selectionStyleA .
  lens rectangleSelection (\e x -> e { rectangleSelection = x })

-- | Just stores the mode name.
instance Binary (Mode syntax) where
    put = put . E.encodeUtf8 . modeName
    get = do
      n <- E.decodeUtf8 <$> get
      return (emptyMode {modeName = n})

-- | Increases the font size in the buffer by specified number. What
-- this number actually means depends on the front-end.
increaseFontSize :: Int -> BufferM ()
increaseFontSize x = fontsizeVariationA %= \fs -> max 1 (fs + x)

-- | Decreases the font size in the buffer by specified number. What
-- this number actually means depends on the front-end.
decreaseFontSize :: Int -> BufferM ()
decreaseFontSize x = fontsizeVariationA %= \fs -> max 1 (fs - x)

-- | Given a buffer, and some information update the modeline
--
-- N.B. the contents of modelines should be specified by user, and
-- not hardcoded.
getModeLine :: [T.Text] -> BufferM T.Text
getModeLine prefix = withModeB (`modeModeLine` prefix)

defaultModeLine :: [T.Text] -> BufferM T.Text
defaultModeLine prefix = do
    col <- curCol
    pos <- pointB
    ln <- curLn
    p <- pointB
    s <- sizeB
    curChar <- readB
    ro <-use readOnlyA
    modeNm <- gets (withMode0 modeName)
    unchanged <- gets isUnchangedBuffer
    enc <- use encodingConverterNameA >>= return . \case
      Nothing -> mempty :: T.Text
      Just cn -> T.pack $ R.unCn cn
    let pct
          | pos == 0 || s == 0 = " Top"
          | pos == s = " Bot"
          | otherwise = getPercent p s
        changed = if unchanged then "-" else "*"
        readOnly' = if ro then "%" else changed
        hexxed = T.pack $ showHex (ord curChar) ""
        hexChar = "0x" <> T.justifyRight 2 '0' hexxed
        toT = T.pack . show

    nm <- gets $ shortIdentString (length prefix)
    return $ T.concat [ enc, " ", readOnly', changed, " ", nm
                      , "     ", hexChar, "  "
                      , "L", T.justifyRight 5 ' ' (toT ln)
                      , "  "
                      , "C", T.justifyRight 3 ' ' (toT col)
                      , "  ", pct , "  ", modeNm , "  ", toT $ fromPoint p
                      ]

-- | Given a point, and the file size, gives us a percent string
getPercent :: Point -> Point -> T.Text
getPercent a b = T.justifyRight 3 ' ' (T.pack $ show p) `T.snoc` '%'
    where p = ceiling (aa / bb * 100.0 :: Double) :: Int
          aa = fromIntegral a :: Double
          bb = fromIntegral b :: Double

queryBuffer :: (forall syntax. BufferImpl syntax -> x) -> BufferM x
queryBuffer x = gets (queryRawbuf x)

modifyBuffer :: (forall syntax. BufferImpl syntax -> BufferImpl syntax) -> BufferM ()
modifyBuffer x = modify' (modifyRawbuf x)

queryAndModify :: (forall syntax. BufferImpl syntax -> (BufferImpl syntax,x)) -> BufferM x
queryAndModify x = getsAndModify (queryAndModifyRawbuf x)

-- | Adds an "overlay" to the buffer
addOverlayB :: Overlay -> BufferM ()
addOverlayB ov = do
  pendingUpdatesA %= (S.|> overlayUpdate ov)
  modifyBuffer $ addOverlayBI ov

getOverlaysOfOwnerB :: R.YiString -> BufferM (Set.Set Overlay)
getOverlaysOfOwnerB owner = queryBuffer (getOverlaysOfOwnerBI owner)

-- | Remove an existing "overlay"
delOverlayB :: Overlay -> BufferM ()
delOverlayB ov = do
  pendingUpdatesA %= (S.|> overlayUpdate ov)
  modifyBuffer $ delOverlayBI ov

delOverlaysOfOwnerB :: R.YiString -> BufferM ()
delOverlaysOfOwnerB owner =
  modifyBuffer $ delOverlaysOfOwnerBI owner

isPointInsideOverlay :: Point -> Overlay -> Bool
isPointInsideOverlay point overlay =
    let Overlay _ (MarkValue start _) (MarkValue finish _) _ _ = overlay
    in start <= point && point <= finish

-- | Execute a @BufferM@ value on a given buffer and window.  The new state of
-- the buffer is returned alongside the result of the computation.
runBuffer :: Window -> FBuffer -> BufferM a -> (a, FBuffer)
runBuffer w b f =
    let (a, _, b') = runBufferFull w b f
    in (a, b')

getMarks :: Window -> BufferM (Maybe WinMarks)
getMarks = gets . getMarksRaw

getMarksRaw :: Window -> FBuffer -> Maybe WinMarks
getMarksRaw w b = M.lookup (wkey w) (b ^. winMarksA)

runBufferFull :: Window -> FBuffer -> BufferM a -> (a, S.Seq Update, FBuffer)
runBufferFull w b f =
    let (a, b') = runState (runReaderT (fromBufferM f') w) b
        updates = b' ^. updateStreamA
        -- We're done running BufferM, don't store updates in editor
        -- state.
        !newSt = b' & updateStreamA .~ mempty
        f' = do
            ms <- getMarks w
            when (isNothing ms) $ do
                -- this window has no marks for this buffer yet; have to create them.
                newMarkValues <- if wkey (b ^. lastActiveWindowA) == def
                    then return
                        -- no previous window, create some marks from scratch.
                         MarkSet { insMark = MarkValue 0 Forward,
                                   selMark = MarkValue 0 Backward, -- sel
                                   fromMark = MarkValue 0 Backward } -- from
                    else do
                        Just mrks  <- uses winMarksA (M.lookup $ wkey (b ^. lastActiveWindowA))
                        forM mrks getMarkValueB
                newMrks <- forM newMarkValues newMarkB
                winMarksA %= M.insert (wkey w) newMrks
            lastActiveWindowA .= w
            f
    in (a, updates, pendingUpdatesA %~ (S.>< fmap TextUpdate updates) $ newSt)

getMarkValueRaw :: Mark -> FBuffer -> MarkValue
getMarkValueRaw m = fromMaybe (MarkValue 0 Forward) . queryRawbuf (getMarkValueBI m)

getMarkValueB :: Mark -> BufferM MarkValue
getMarkValueB = gets . getMarkValueRaw

newMarkB :: MarkValue -> BufferM Mark
newMarkB v = queryAndModify $ newMarkBI v

deleteMarkB :: Mark -> BufferM ()
deleteMarkB m = modifyBuffer $ deleteMarkValueBI m

-- | Execute a @BufferM@ value on a given buffer, using a dummy window.  The new state of
-- the buffer is discarded.
runBufferDummyWindow :: FBuffer -> BufferM a -> a
runBufferDummyWindow b = fst . runBuffer (dummyWindow $ bkey b) b


-- | Mark the current point in the undo list as a saved state.
markSavedB :: UTCTime -> BufferM ()
markSavedB t = do undosA %= setSavedFilePointU
                  lastSyncTimeA .= t

bkey :: FBuffer -> BufferRef
bkey = view bkey__A

isUnchangedBuffer :: FBuffer -> Bool
isUnchangedBuffer = isAtSavedFilePointU . view undosA

startUpdateTransactionB :: BufferM ()
startUpdateTransactionB = do
  transactionPresent <- use updateTransactionInFlightA
  if transactionPresent
  then error "Already started update transaction"
  else do
    undosA %= addChangeU InteractivePoint
    updateTransactionInFlightA .= True

commitUpdateTransactionB :: BufferM ()
commitUpdateTransactionB = do
  transactionPresent <- use updateTransactionInFlightA
  if not transactionPresent
  then error "Not in update transaction"
  else do
    updateTransactionInFlightA .= False
    transacAccum <- use updateTransactionAccumA
    updateTransactionAccumA .= mempty

    undosA %= (appEndo . foldr (<>) mempty) (Endo . addChangeU . AtomicChange <$> transacAccum)
    undosA %= addChangeU InteractivePoint


undoRedo :: (forall syntax. Mark -> URList -> BufferImpl syntax
             -> (BufferImpl syntax, (URList, S.Seq Update)))
         -> BufferM ()
undoRedo f = do
  isTransacPresent <- use updateTransactionInFlightA
  if isTransacPresent
  then error "Can't undo while undo transaction is in progress"
  else do
      m <- getInsMark
      ur <- use undosA
      (ur', updates) <- queryAndModify (f m ur)
      undosA .= ur'
      updateStreamA %= (<> updates)

undoB :: BufferM ()
undoB = undoRedo undoU

redoB :: BufferM ()
redoB = undoRedo redoU

-- | Undo all updates that happened since last save,
-- perform a given action and redo all updates again.
-- Given action must not modify undo history.
retroactivelyAtSavePointB :: BufferM a -> BufferM a
retroactivelyAtSavePointB action = do
    (undoDepth, result) <- go 0
    replicateM_ undoDepth redoB
    return result
    where
        go step = do
            atSavedPoint <- gets isUnchangedBuffer
            if atSavedPoint
            then (step,) <$> action
            else undoB >> go (step + 1)


-- | Analogous to const, but returns a function that takes two parameters,
-- rather than one.
const2 :: t -> t1 -> t2 -> t
const2 x _ _ = x

-- | Mode applies function that always returns True.
modeAlwaysApplies :: a -> b -> Bool
modeAlwaysApplies = const2 True

-- | Mode applies function that always returns False.
modeNeverApplies :: a -> b -> Bool
modeNeverApplies = const2 False

emptyMode :: Mode syntax
emptyMode = Mode
  {
   modeName = "empty",
   modeApplies = modeNeverApplies,
   modeHL = ExtHL noHighlighter,
   modePrettify = const $ return (),
   modeKeymap = id,
   modeIndent = \_ _ -> return (),
   modeAdjustBlock = \_ _ -> return (),
   modeFollow = const emptyAction,
   modeIndentSettings = IndentSettings
   { expandTabs = True
   , tabSize = 8
   , shiftWidth = 4
   },
   modeToggleCommentSelection = Nothing,
   modeGetStrokes = \_ _ _ _ -> [],
   modeOnLoad = return (),
   modeGotoDeclaration = return (),
   modeModeLine = defaultModeLine
  }

-- | Create buffer named @nm@ with contents @s@
newB :: BufferRef -> BufferId -> YiString -> FBuffer
newB unique nm s =
 FBuffer { bmode  = emptyMode
         , rawbuf = newBI s
         , attributes =
 Attributes { ident  = nm
            , bkey__ = unique
            , undos  = emptyU
            , preferCol = Nothing
            , preferVisCol = Nothing
            , stickyEol = False
            , bufferDynamic = mempty
            , pendingUpdates = mempty
            , selectionStyle = SelectionStyle False False
            , keymapProcess = I.End
            , winMarks = M.empty
            , lastActiveWindow = dummyWindow unique
            , lastSyncTime = epoch
            , readOnly = False
            , directoryContent = False
            , inserting = True
            , pointFollowsWindow = mempty
            , updateTransactionInFlight = False
            , updateTransactionAccum = mempty
            , fontsizeVariation = 0
            , encodingConverterName = Nothing
            , updateStream = mempty
            } }

epoch :: UTCTime
epoch = UTCTime (toEnum 0) (toEnum 0)

-- | Point of eof
sizeB :: BufferM Point
sizeB = queryBuffer sizeBI

-- | Extract the current point
pointB :: BufferM Point
pointB = use . markPointA =<< getInsMark

nelemsB :: Int -> Point -> BufferM YiString
nelemsB n i = R.take n <$> streamB Forward i

streamB :: Direction -> Point -> BufferM YiString
streamB dir i = queryBuffer $ getStream dir i

indexedStreamB :: Direction -> Point -> BufferM [(Point,Char)]
indexedStreamB dir i = queryBuffer $ getIndexedStream dir i

strokesRangesB :: Maybe SearchExp -> Region -> BufferM [[Stroke]]
strokesRangesB regex r = do
  p <- pointB
  getStrokes <- withSyntaxB modeGetStrokes
  queryBuffer $ strokesRangesBI getStrokes regex r p

------------------------------------------------------------------------
-- Point based operations

-- | Move point in buffer to the given index
moveTo :: Point -> BufferM ()
moveTo x = do
  forgetPreferCol
  maxP <- sizeB
  let p = case () of
        _ | x < 0 -> Point 0
          | x > maxP -> maxP
          | otherwise -> x
  (.= p) . markPointA =<< getInsMark

------------------------------------------------------------------------

setInserting :: Bool -> BufferM ()
setInserting = (insertingA .=)

checkRO :: BufferM Bool
checkRO = do
  ro <- use readOnlyA
  when ro (fail "Read Only Buffer")
  return ro

applyUpdate :: Update -> BufferM ()
applyUpdate update = do
  runp <- liftA2 (&&) (not <$> checkRO) (queryBuffer (isValidUpdate update))
  when runp $ do
    forgetPreferCol
    modifyBuffer (applyUpdateI update)
    isTransacPresent <- use updateTransactionInFlightA
    if isTransacPresent
    then updateTransactionAccumA %= (reverseUpdateI update S.<|)
    else undosA %= addChangeU (AtomicChange $ reverseUpdateI update)

    updateStreamA %= (S.|> update)


-- | Revert all the pending updates; don't touch the point.
revertPendingUpdatesB :: BufferM ()
revertPendingUpdatesB = do
  updates <- use pendingUpdatesA
  modifyBuffer $ \stx ->
    let applyTextUpdate (TextUpdate u) bi = applyUpdateI (reverseUpdateI u) bi
        applyTextUpdate _ bi = bi
    in foldr applyTextUpdate stx updates

-- | Write an element into the buffer at the current point.
writeB :: Char -> BufferM ()
writeB c = do
  deleteN 1
  insertB c

-- | Write the list into the buffer at current point.
writeN :: YiString -> BufferM ()
writeN cs = do
  off <- pointB
  deleteNAt Forward (R.length cs) off
  insertNAt cs off

-- | Insert newline at current point.
newlineB :: BufferM ()
newlineB = insertB '\n'

------------------------------------------------------------------------

-- | Insert given 'YiString' at specified point, extending size of the
-- buffer.
insertNAt :: YiString -> Point -> BufferM ()
insertNAt rope pnt = applyUpdate (Insert pnt Forward rope)

-- | Insert the 'YiString' at current point, extending size of buffer
insertN :: YiString -> BufferM ()
insertN cs = pointB >>= insertNAt cs

-- | Insert the char at current point, extending size of buffer
--
-- Implementation note: This just 'insertB's a 'R.singleton'. This
-- seems sub-optimal because we should be able to do much better
-- without spewing chunks of size 1 everywhere. This approach is
-- necessary however so an 'Update' can be recorded. A possible
-- improvement for space would be to have ‘yi-rope’ package optimise
-- for appends with length 1.
insertB :: Char -> BufferM ()
insertB = insertN . R.singleton

------------------------------------------------------------------------

-- | @deleteNAt n p@ deletes @n@ characters forwards from position @p@
deleteNAt :: Direction -> Int -> Point -> BufferM ()
deleteNAt _ 0 _ = return ()
deleteNAt dir n pos = do
  els <- R.take n <$> streamB Forward pos
  applyUpdate $ Delete pos dir els


------------------------------------------------------------------------
-- Line based editing

-- | Return the current line number
curLn :: BufferM Int
curLn = do
    p <- pointB
    queryBuffer (lineAt p)


-- | Top line of the screen
screenTopLn :: BufferM Int
screenTopLn = do
    p <- use . markPointA =<< fromMark <$> askMarks
    queryBuffer (lineAt p)


-- | Middle line of the screen
screenMidLn :: BufferM Int
screenMidLn = (+) <$> screenTopLn <*> (div <$> screenLines <*> pure 2)


-- | Bottom line of the screen
screenBotLn :: BufferM Int
screenBotLn = (+) <$> screenTopLn <*> screenLines


-- | Amount of lines in the screen
screenLines :: BufferM Int
screenLines = pred <$> askWindow actualLines


-- | Return line numbers of marks
markLines :: BufferM (MarkSet Int)
markLines = mapM getLn =<< askMarks
        where getLn m = use (markPointA m) >>= lineOf


-- | Go to line number @n@. @n@ is indexed from 1. Returns the
-- actual line we went to (which may be not be the requested line,
-- if it was out of range)
gotoLn :: Int -> BufferM Int
gotoLn x = do
  moveTo 0
  succ <$> gotoLnFrom (x - 1)

---------------------------------------------------------------------

setMode0 :: forall syntax. Mode syntax -> FBuffer -> FBuffer
setMode0 m (FBuffer _ rb at) = FBuffer m (setSyntaxBI (modeHL m) rb) at

modifyMode0 :: (forall syntax. Mode syntax -> Mode syntax) -> FBuffer -> FBuffer
modifyMode0 f (FBuffer m rb f3) = FBuffer m' (setSyntaxBI (modeHL m') rb) f3
  where m' = f m

-- | Set the mode
setAnyMode :: AnyMode -> BufferM ()
setAnyMode (AnyMode m) = setMode m

setMode :: Mode syntax -> BufferM ()
setMode m = do
  modify (setMode0 m)
  -- reset the keymap process so we use the one of the new mode.
  keymapProcessA .= I.End
  modeOnLoad m

-- | Modify the mode
modifyMode :: (forall syntax. Mode syntax -> Mode syntax) -> BufferM ()
modifyMode f = do
  modify (modifyMode0 f)
  -- reset the keymap process so we use the one of the new mode.
  keymapProcessA .= I.End

onMode :: (forall syntax. Mode syntax -> Mode syntax) -> AnyMode -> AnyMode
onMode f (AnyMode m) = AnyMode (f m)

withMode0 :: (forall syntax. Mode syntax -> a) -> FBuffer -> a
withMode0 f FBuffer {bmode = m} = f m

withModeB :: (forall syntax. Mode syntax -> BufferM a) -> BufferM a
withModeB x = join (gets (withMode0 x))

withSyntax0 :: (forall syntax. Mode syntax -> syntax -> a) -> WindowRef -> FBuffer -> a
withSyntax0 f wk (FBuffer bm rb _attrs) = f bm (getAst wk rb)


withSyntaxB :: (forall syntax. Mode syntax -> syntax -> a) -> BufferM a
withSyntaxB f = withSyntax0 f <$> askWindow wkey <*> use id


focusSyntax ::  M.Map WindowRef Region -> FBuffer -> FBuffer
focusSyntax r = modifyRawbuf (focusAst r)

withSyntaxB' :: (forall syntax. Mode syntax -> syntax -> BufferM a) -> BufferM a
withSyntaxB' x = join (withSyntaxB x)

-- | Return indices of strings in buffer matched by regex in the
-- given region.
regexRegionB :: SearchExp -> Region -> BufferM [Region]
regexRegionB regex region = queryBuffer $ regexRegionBI regex region

-- | Return indices of next string in buffer matched by regex in the
-- given direction
regexB :: Direction -> SearchExp -> BufferM [Region]
regexB dir rx = do
  p <- pointB
  s <- sizeB
  regexRegionB rx (mkRegion p (case dir of Forward -> s; Backward -> 0))

---------------------------------------------------------------------

modifyMarkRaw :: Mark -> (MarkValue -> MarkValue) -> FBuffer -> FBuffer
modifyMarkRaw m f = modifyRawbuf $ modifyMarkBI m f

modifyMarkB :: Mark -> (MarkValue -> MarkValue) -> BufferM ()
modifyMarkB = (modify .) . modifyMarkRaw

setMarkHereB :: BufferM Mark
setMarkHereB = getMarkB Nothing

setNamedMarkHereB :: String -> BufferM ()
setNamedMarkHereB name = do
    p <- pointB
    getMarkB (Just name) >>= (.= p) . markPointA

-- | Highlight the selection
setVisibleSelection :: Bool -> BufferM ()
setVisibleSelection = (highlightSelectionA .=)

-- | Whether the selection is highlighted
getVisibleSelection :: BufferM Bool
getVisibleSelection = use highlightSelectionA

getInsMark :: BufferM Mark
getInsMark = insMark <$> askMarks

askMarks :: BufferM WinMarks
askMarks = do
  Just !ms <- getMarks =<< ask
  return ms

getMarkB :: Maybe String -> BufferM Mark
getMarkB m = do
  p <- pointB
  queryAndModify (getMarkDefaultPosBI m p)

mayGetMarkB :: String -> BufferM (Maybe Mark)
mayGetMarkB m = queryBuffer (getMarkBI m)

-- | Move point by the given number of characters.
-- A negative offset moves backwards a positive one forward.
moveN :: Int -> BufferM ()
moveN n = do
    s <- sizeB
    moveTo =<< min s . max 0 . (+~ Size n) <$> pointB

-- | Move point -1
leftB :: BufferM ()
leftB = leftN 1

-- | Move cursor -n
leftN :: Int -> BufferM ()
leftN n = moveN (-n)

-- | Move cursor +1
rightB :: BufferM ()
rightB = rightN 1

-- | Move cursor +n
rightN :: Int -> BufferM ()
rightN = moveN

-- ---------------------------------------------------------------------
-- Line based movement and friends

-- | Move point down by @n@ lines. @n@ can be negative.
-- Returns the actual difference in lines which we moved which
-- may be negative if the requested line difference is negative.
lineMoveRel :: Int -> BufferM Int
lineMoveRel = movingToPrefCol . gotoLnFrom

movingToPrefCol :: BufferM a -> BufferM a
movingToPrefCol f = do
  prefCol <- use preferColA
  targetCol <- maybe curCol return prefCol
  r <- f
  moveToColB targetCol
  preferColA .= Just targetCol
  return r

-- | Moves to a visual column within the current line as shown
-- on the editor (ie, moving within the current width of a
-- single visual line)
movingToPrefVisCol :: BufferM a -> BufferM a
movingToPrefVisCol f = do
  prefCol <- use preferVisColA
  targetCol <- maybe curVisCol return prefCol
  r <- f
  moveToVisColB targetCol
  preferVisColA .= Just targetCol
  return r

moveToColB :: Int -> BufferM ()
moveToColB targetCol = do
  solPnt <- solPointB =<< pointB
  chrs <- R.toString <$> nelemsB targetCol solPnt
  is <- indentSettingsB
  let cols = scanl (colMove is) 0 chrs    -- columns corresponding to the char
      toSkip = takeWhile (\(char,col) -> char /= '\n' && col < targetCol) (zip chrs cols)
  moveTo $ solPnt +~ fromIntegral (length toSkip)

moveToVisColB :: Int -> BufferM ()
moveToVisColB targetCol = do
  col <- curCol
  wid <- width <$> use lastActiveWindowA
  let jumps = col `div` wid
  moveToColB $ jumps * wid + targetCol

moveToLineColB :: Int -> Int -> BufferM ()
moveToLineColB line col = gotoLn line >> moveToColB col

pointOfLineColB :: Int -> Int -> BufferM Point
pointOfLineColB line col = savingPointB $ moveToLineColB line col >> pointB

forgetPreferCol :: BufferM ()
forgetPreferCol = do
  preferColA .= Nothing
  preferVisColA .= Nothing
  !st <- gets id
  return $! (st `seq` ())

savingPrefCol :: BufferM a -> BufferM a
savingPrefCol f = do
  pc <- use preferColA
  pv <- use preferVisColA
  result <- f
  preferColA .= pc
  preferVisColA .= pv
  return result

-- | Move point up one line
lineUp :: BufferM ()
lineUp = void (lineMoveRel (-1))

-- | Move point down one line
lineDown :: BufferM ()
lineDown = void (lineMoveRel 1)

-- | Return the contents of the buffer.
elemsB :: BufferM YiString
elemsB = queryBuffer mem

-- | Returns the contents of the buffer between the two points.
--
-- If the @startPoint >= endPoint@, empty string is returned. If the
-- points are out of bounds, as much of the content as possible is
-- taken: you're not guaranteed to get @endPoint - startPoint@
-- characters.
betweenB :: Point -- ^ Point to start at
         -> Point -- ^ Point to stop at
         -> BufferM YiString
betweenB (Point s) (Point e) =
  if s >= e
  then return (mempty :: YiString)
  else snd . R.splitAt s . fst . R.splitAt e <$> elemsB

-- | Read the character at the current point
readB :: BufferM Char
readB = pointB >>= readAtB

-- | Read the character at the given index
-- This is an unsafe operation: character NUL is returned when out of bounds
readAtB :: Point -> BufferM Char
readAtB i = R.head <$> nelemsB 1 i >>= return . \case
  Nothing -> '\0'
  Just c  -> c

replaceCharB :: Char -> BufferM ()
replaceCharB c = do
    writeB c
    leftB

replaceCharWithBelowB :: BufferM ()
replaceCharWithBelowB = replaceCharWithVerticalOffset 1

replaceCharWithAboveB :: BufferM ()
replaceCharWithAboveB = replaceCharWithVerticalOffset (-1)

insertCharWithBelowB :: BufferM ()
insertCharWithBelowB = maybe (return ()) insertB =<< maybeCharBelowB

insertCharWithAboveB :: BufferM ()
insertCharWithAboveB = maybe (return ()) insertB =<< maybeCharAboveB

replaceCharWithVerticalOffset :: Int -> BufferM ()
replaceCharWithVerticalOffset offset =
    maybe (return ()) replaceCharB =<< maybeCharWithVerticalOffset offset

maybeCharBelowB :: BufferM (Maybe Char)
maybeCharBelowB = maybeCharWithVerticalOffset 1

maybeCharAboveB :: BufferM (Maybe Char)
maybeCharAboveB = maybeCharWithVerticalOffset (-1)

maybeCharWithVerticalOffset :: Int -> BufferM (Maybe Char)
maybeCharWithVerticalOffset offset = savingPointB $ do
    l0 <- curLn
    c0 <- curCol
    void $ lineMoveRel offset
    l1 <- curLn
    c1 <- curCol
    curChar <- readB
    return $ if c0 == c1
                && l0 + offset == l1
                && curChar `notElem` ("\n\0" :: String)
             then Just curChar
             else Nothing

-- | Delete @n@ characters forward from the current point
deleteN :: Int -> BufferM ()
deleteN n = pointB >>= deleteNAt Forward n

------------------------------------------------------------------------

-- | Gives the 'IndentSettings' for the current buffer.
indentSettingsB :: BufferM IndentSettings
indentSettingsB = withModeB $ return . modeIndentSettings

-- | Current column.
-- Note that this is different from offset or number of chars from sol.
-- (This takes into account tabs, unicode chars, etc.)
curCol :: BufferM Int
curCol = colOf =<< pointB

-- | Current column, visually.
curVisCol :: BufferM Int
curVisCol = rem <$> curCol <*> (width <$> use lastActiveWindowA)

colOf :: Point -> BufferM Int
colOf p = do
  is <- indentSettingsB
  R.foldl' (colMove is) 0 <$> queryBuffer (charsFromSolBI p)

lineOf :: Point -> BufferM Int
lineOf p = queryBuffer $ lineAt p

lineCountB :: BufferM Int
lineCountB = lineOf =<< sizeB

-- | Decides which column we should be on after the given character.
colMove :: IndentSettings -> Int -> Char -> Int
colMove is col '\t' | tabSize is > 1 = col + tabSize is
colMove _  col _    = col + 1

-- | Returns start of line point for a given point @p@
solPointB :: Point -> BufferM Point
solPointB p = queryBuffer $ solPoint' p

-- | Returns end of line for given point.
eolPointB :: Point -> BufferM Point
eolPointB p = queryBuffer $ eolPoint' p

-- | Go to line indexed from current point
-- Returns the actual moved difference which of course
-- may be negative if the requested difference was negative.
gotoLnFrom :: Int -> BufferM Int
gotoLnFrom x = do
    l <- curLn
    p' <- queryBuffer $ solPoint (l + x)
    moveTo p'
    l' <- curLn
    return (l' - l)

-- | Access to a value into the extensible state, keyed by its type.
--   This allows you to retrieve inside a 'BufferM' monad, ie:
--
-- > value <- getBufferDyn
getBufferDyn :: forall m a. (Default a, YiVariable a, MonadState FBuffer m, Functor m) => m a
getBufferDyn = fromMaybe (def :: a) <$> getDyn (use bufferDynamicA) (bufferDynamicA .=)

-- | Access to a value into the extensible state, keyed by its type.
--   This allows you to save inside a 'BufferM' monad, ie:
--
-- > putBufferDyn updatedvalue
putBufferDyn :: (YiVariable a, MonadState FBuffer m, Functor m) => a -> m ()
putBufferDyn = putDyn (use bufferDynamicA) (bufferDynamicA .=)

-- | perform a @BufferM a@, and return to the current point. (by using a mark)
savingExcursionB :: BufferM a -> BufferM a
savingExcursionB f = do
    m <- getMarkB Nothing
    res <- f
    moveTo =<< use (markPointA m)
    return res

markPointA :: Mark -> Lens' FBuffer Point
markPointA mark = lens getter setter where
  getter b = markPoint $ getMarkValueRaw mark b
  setter b pos = modifyMarkRaw mark (\v -> v {markPoint = pos}) b

-- | Perform an @BufferM a@, and return to the current point.
savingPointB :: BufferM a -> BufferM a
savingPointB f = savingPrefCol $ do
  p <- pointB
  res <- f
  moveTo p
  return res

-- | Perform an @BufferM a@, and return to the current line and column
-- number. The difference between this and 'savingPointB' is that here
-- we attempt to return to the specific line and column number, rather
-- than a specific number of characters from the beginning of the
-- buffer.
--
-- In case the column is further away than EOL, the point is left at
-- EOL: 'moveToLineColB' is used internally.
savingPositionB :: BufferM a -> BufferM a
savingPositionB f = savingPrefCol $ do
  (c, l) <- (,) <$> curCol <*> curLn
  res <- f
  moveToLineColB l c
  return res

pointAt :: BufferM a -> BufferM Point
pointAt f = savingPointB (f *> pointB)

pointAfterCursorB :: Point -> BufferM Point
pointAfterCursorB p = pointAt $ do
  moveTo p
  rightB

-- | What would be the point after doing the given action?
-- The argument must not modify the buffer.
destinationOfMoveB :: BufferM a -> BufferM Point
destinationOfMoveB f = savingPointB (f >> pointB)

-------------
-- Window

askWindow :: (Window -> a) -> BufferM a
askWindow = asks

withEveryLineB :: BufferM () -> BufferM ()
withEveryLineB action = savingPointB $ do
  lineCount <- lineCountB
  forM_ [1 .. lineCount] $ \l -> do
    void $ gotoLn l
    action

makeLensesWithSuffix "A" ''IndentSettings
makeLensesWithSuffix "A" ''Mode
