module Buffer.Motion where

import Data.List (dropWhileEnd)
import Buffer.Class

-- TODO factor Count
-- TODO various Vim gX
data Motion
  = CharsBackward
  | CharsForward
  | ToStartOfLine
  -- | GotoFirstNonBlankChar
  | ToEndOfLine             -- XXX in Vi this can go downwards
  | ToColumn
  -- | GotoFindLeft (Char -> Bool)   -- TODO don't use functions here
  -- | GotoFindRight (Char -> Bool)  -- TODO ^ dto.
  -- | GotillFindLeft Char
  -- | GotillFindRight Char
  -- | RepeatLastFind
  -- | RepeatLastFindReverse
  | WordsForward
  | WordsBackward
  deriving (Show)


-- TODO fail if cannot splitAt properly OR if we didn't modify the buffer
gotoLeft :: Int -> Buffer -> Buffer
gotoLeft i (ls, rs) =
  let (lls, rls) = splitAt (length ls - i) ls in (lls, rls ++ rs)


-- TODO fail if cannot splitAt properly OR if we didn't modify the buffer
gotoRight :: Int -> Buffer -> Buffer
gotoRight i (ls, rs) =
  let (lrs, rrs) = splitAt i rs in (ls ++ lrs, rrs)


gotoFirstChar :: Buffer -> Buffer
gotoFirstChar (ls, rs) = ("", ls ++ rs)


gotoEndOfLine :: Buffer -> Buffer
gotoEndOfLine (ls, rs) = (ls ++ rs, "")


-- TODO fail if i <= 0 or i > length
gotoColumn :: Int -> Buffer -> Buffer
gotoColumn i (ls, rs) = splitAt (i - 1) $ ls ++ rs


wordsForward :: Int -> Buffer -> Buffer
wordsForward i (ls, rs) =
  let rs' = dropWhile (==' ') $ dropWhile (/=' ') rs
      ls' = ls ++ take (length rs - length rs') rs
      b' = (ls', rs')
  in
    if i > 1
      then wordsForward (i - 1) b'
      else b'


wordsBackward :: Int -> Buffer -> Buffer
wordsBackward i (ls, rs) =
  let ls' = dropWhileEnd (/=' ') $ dropWhileEnd (==' ') ls
      rs' = drop (length ls') ls ++ rs
      b' = (ls', rs')
  in
    if i > 1
      then wordsBackward (i - 1) b'
      else b'


move :: Motion -> Int -> Buffer -> Buffer
move CharsBackward c = gotoLeft c
move CharsForward c = gotoRight c
move ToStartOfLine _ = gotoFirstChar -- TODO use count
move ToEndOfLine _ = gotoEndOfLine -- TODO use count
move ToColumn c = gotoColumn c
move WordsForward c = wordsForward c
move WordsBackward c = wordsBackward c


select :: Motion -> Int -> Buffer -> String
select x i b =
    if nls' < nls then take (nls - nls') rs' else
    if nrs' < nrs then take (nrs - nrs') rs else
    ""
  where
    (ls, rs) = b
    (ls', rs') = move x i b
    nls = length ls
    nls' = length ls'
    nrs = length rs
    nrs' = length rs'


delete :: Motion -> Int -> Buffer -> Buffer
delete x i b =
    ( if nls' < nls then ls' else ls
    , if nrs' < nrs then rs' else rs
    )
  where
    (ls, rs) = b
    (ls', rs')= move x i b
    nls = length ls
    nls' = length ls'
    nrs = length rs
    nrs' = length rs'