```{-# LANGUAGE StandaloneDeriving, DeriveDataTypeable, ScopedTypeVariables, ExistentialQuantification, GeneralizedNewtypeDeriving, MultiParamTypeClasses, TemplateHaskell #-}
-- Copyright 2008 JP Bernardy
-- | Basic types useful everywhere we play with buffers.
module Yi.Buffer.Basic where
import Prelude (reverse)
import Data.Binary
import Yi.Prelude
import qualified Data.Rope as R
import Data.DeriveTH
import Data.Ix

-- | Direction of movement inside a buffer
data Direction = Backward
| Forward
deriving (Eq,Ord,Typeable,Show,Bounded,Enum)

\$(derive makeBinary ''Direction)

reverseDir :: Direction -> Direction
reverseDir Forward = Backward
reverseDir Backward = Forward

-- | reverse if Backward
mayReverse :: Direction -> [a] -> [a]
mayReverse Forward = id
mayReverse Backward = reverse

-- | 'direction' is in the same style of 'maybe' or 'either' functions,
-- It takes one argument per direction (backward, then forward) and a
-- direction to select the output.
directionElim :: Direction -> a -> a -> a
directionElim Backward b _ = b
directionElim Forward  _ f = f

-- | A mark in a buffer
newtype Mark = Mark {markId::Int} deriving (Eq, Ord, Show, Typeable, Binary)

-- | Reference to a buffer.
newtype BufferRef = BufferRef Int
deriving (Eq, Ord, Typeable, Binary)
deriving instance Num BufferRef

instance Show BufferRef where
show (BufferRef r) = "B#" ++ show r

-- | A point in a buffer
newtype Point = Point {fromPoint :: Int}           -- offset in the buffer (#codepoints, NOT bytes)
deriving (Eq, Ord, Enum, Bounded, Typeable, Binary, Ix)

deriving instance Num Point
deriving instance Real Point
deriving instance Integral Point
instance Show Point where
show (Point p) = show p

-- | Size of a buffer region
newtype Size = Size {fromSize :: Int}             -- size in bytes (#bytes, NOT codepoints)
deriving (Show, Eq, Ord, Num, Enum, Real, Integral, Binary)

instance SemiNum Point Size where
Point p +~ Size s = Point (p + s)
Point p -~ Size s = Point (p - s)
Point p ~- Point q = Size (abs (p - q))

fromString :: String -> Rope
fromString = R.fromString

-- | Window references
newtype WindowRef = WindowRef { unWindowRef :: Int }
deriving(Eq, Ord, Enum, Show, Typeable, Binary)

instance Initializable WindowRef where initial = WindowRef (-1)

```