module Buffer.Motion where

import Data.List (dropWhileEnd)
import Buffer.Class

--data Motion = Motion Int LeftRightMotion


-- TODO factor Count
-- TODO various Vim gX
data LeftRightMotion
  = GotoLeft Int
  | GotoRight Int
  | GotoFirstChar
  -- | GotoFirstNonBlankChar
  | GotoEndOfLine             -- XXX in Vi this can go downwards
  | GotoColumn Int
  | GotoFindLeft Int Char 
  | GotoFindRight Int Char
  | GotillFindLeft Int Char
  | GotillFindRight Int Char
  -- | RepeatLastFind Int
  -- | RepeatLastFindReverse Int
  deriving (Show)

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

gotoFirstChar (ls, rs) = ("", ls ++ rs)

gotoEndOfLine (ls, rs) = (ls ++ rs, "")

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

-- TODO is this definition correct?
spanEnd :: (a -> Bool) -> [a] -> ([a], [a])
spanEnd p xs = let ls = dropWhileEnd p xs in (ls, drop (length ls) xs)

-- TODO don't allow i == 0 in go{to,till}Find{Left,Right}

gotoFindLeft i c b@(ls, rs) 
  | i == 0 = b
  | i > 0 = 
    let (lls, rls) = spanEnd (/= c) ls
    in gotoFindLeft (i - 1) c (init lls, last lls : rls ++ rs)

gotoFindRight i c b@(ls, rs) 
  | i == 0 = b
  | i > 0 = 
    let (lrs, rrs) = span (/= c) rs
    in gotoFindRight (i - 1) c (ls ++ lrs ++ [head rrs], tail rrs)

-- TODO this has to fail it there aren't enought c's
gotillFindLeft i c b@(ls, rs) =
    let (lls, rls) = spanEnd (/= c) ls
    in
        if i > 1
            then gotillFindLeft (i - 1) c (init lls, last lls : rls ++ rs)
            else (lls, rls ++ rs)

--gotillFindRight i c b@(ls, rs) 
--  | i == 0 = b
--  | i > 0 = 
--    let (lrs, rrs) = span (/= c) rs
--    in gotoFindRight (i - 1) c (ls ++ lrs, rrs)

gotillFindRight i c b@(ls, rs) =
    let (lrs, rrs) = span (/= c) rs
    in
        if i > 1
            then gotillFindRight (i - 1) c (ls ++ lrs ++ [head rrs], tail rrs)
            else (ls ++ lrs, rrs)


move :: LeftRightMotion -> Buffer -> Buffer
move (GotoLeft i) = gotoLeft i
move (GotoRight i) = gotoRight i
move GotoFirstChar = gotoFirstChar
move GotoEndOfLine = gotoEndOfLine
move (GotoColumn i) = gotoColumn i
move (GotoFindLeft i c) = gotoFindLeft i c
move (GotoFindRight i c) = gotoFindRight i c
move (GotillFindLeft i c) = gotillFindLeft i c
move (GotillFindRight i c) = gotillFindRight i c