-- Copyright (C) 2008 JP Bernardy

module Yi.UI.Utils where
-- Utilities shared by various UIs

import Yi.Buffer
import Yi.Buffer.HighLevel
import Yi.Prelude
import Prelude (Ordering(..))
import Yi.Window
import Control.Arrow (second)

-- | return index of Sol on line @n@ above current line
indexOfSolAbove :: Int -> BufferM Point
indexOfSolAbove n = savingPointB $ do
    gotoLnFrom (negate n)
    pointB

-- | Transform (scroll) the window so that the point is visible.
moveWinTosShowPoint :: FBuffer -> Window -> FBuffer
moveWinTosShowPoint b w = result
  where (_, result) = runBuffer w b $ 
            do ln <- curLn
               let gap = min (ln-1) (height w `div` 2)
               i <- indexOfSolAbove gap
               f <- fromMark <$> askMarks
               setMarkPointB f i
               return ()

-- | Turn a sequence of (from,style,to) strokes into a sequence
--   of picture points (from,style), taking special care to
--   ensure that the points are strictly increasing and introducing
--   padding segments where neccessary.
--   Precondition: Strokes are ordered and not overlapping.
strokePicture :: [(Point,(a -> a),Point)] -> [(Point,(a -> a))]
strokePicture [] = []
strokePicture wholeList@((leftMost,_,_):_) = helper leftMost wholeList
    where helper :: Point -> [(Point,(a -> a),Point)] -> [(Point,(a -> a))]
          helper prev [] = [(prev,id)]
          helper prev ((l,f,r):xs) 
              | prev < l  = (prev, id) : (l,f) : helper r xs
              | otherwise = (l,f) : helper r xs

-- | Paint the given stroke-picture on top of an existing picture
paintStrokes :: (a -> a) -> a -> [(Point,(a -> a))] -> [(Point,a)] -> [(Point,a)]
paintStrokes f0 _  [] lx = fmap (second f0)     lx
paintStrokes _  x0 lf [] = fmap (second ($ x0)) lf
paintStrokes f0 x0 lf@((pf,f):tf) lx@((px,x):tx) =
  case pf `compare` px of
    LT -> (pf, f  x0):paintStrokes f  x0 tf lx
    EQ -> (pf, f  x ):paintStrokes f  x  tf tx
    GT -> (px, f0 x ):paintStrokes f0 x  lf tx

    

paintPicture :: a -> [[(Point,(a -> a),Point)]] -> [(Point,a)]
paintPicture a = foldr (paintStrokes id a . strokePicture) []