```{-# LANGUAGE TypeSynonymInstances, TypeOperators, FlexibleInstances,
StandaloneDeriving, DeriveFunctor, DeriveFoldable, DeriveTraversable  #-}

module Data.Xournal.Select where

import Control.Applicative hiding (empty)
import Control.Compose
import Data.Foldable
import Data.Traversable
import Data.Monoid
import Data.Sequence
import Data.Xournal.Generic

import Prelude hiding (zipWith, length, splitAt)

newtype SeqZipper a = SZ { unSZ :: (a, (Seq a,Seq a)) }

deriving instance Functor SeqZipper
deriving instance Foldable SeqZipper

instance Applicative SeqZipper where
pure = singletonSZ
SZ (f,(f1s,f2s)) <*> SZ (x,(y1s,y2s)) = SZ (f x, (zipWith id f1s y1s, zipWith id f2s y2s))

deriving instance Traversable SeqZipper

singletonSZ :: a -> SeqZipper a
singletonSZ x = SZ (x, (empty,empty))

lengthSZ :: SeqZipper a -> Int
lengthSZ (SZ (x, (x1s,x2s))) = length x1s + length x2s + 1

currIndex :: SeqZipper a -> Int
currIndex (SZ (x, (x1s,x2s))) = length x1s

appendGoLast :: SeqZipper a -> a -> SeqZipper a
appendGoLast (SZ (y,(y1s,y2s))) x = SZ (x, ((y1s |> y) >< y2s, empty))

chopFirst :: SeqZipper a -> Maybe (SeqZipper a)
chopFirst (SZ (y,(y1s,y2s))) =
case viewl y1s of
EmptyL -> case viewl y2s of
EmptyL -> Nothing
z :< zs -> Just (SZ (z,(empty,zs)))
z :< zs -> Just (SZ (y,(zs,y2s)))

moveLeft :: SeqZipper a -> Maybe (SeqZipper a)
moveLeft (SZ (x,(x1s,x2s))) =
case viewr x1s of
EmptyR -> Nothing
zs :> z -> Just (SZ (z,(zs,x<|x2s)))

moveRight :: SeqZipper a -> Maybe (SeqZipper a)
moveRight (SZ (x,(x1s,x2s))) =
case viewl x2s of
EmptyL -> Nothing
z :< zs -> Just (SZ (z,(x1s|>x,zs)))

moveTo :: Int -> SeqZipper a -> Maybe (SeqZipper a)
moveTo n orig@(SZ (x,(x1s,x2s))) =
let n_x1s = length x1s
n_x2s = length x2s
result | n < 0 || n > n_x1s + n_x2s = Nothing
| n == n_x1s = Just orig
| n < n_x1s = let (x1s1, x1s2) = splitAt n x1s
el :< rm = viewl x1s2
in Just (SZ (el, (x1s1,(rm |> x) >< x2s)))
| n > n_x1s = let (x2s1,x2s2) = splitAt (n-n_x1s-1) x2s
el :< rm = viewl x2s2
in Just (SZ (el, ((x1s |> x) >< x2s1, rm)))
in result

goFirst :: SeqZipper a -> SeqZipper a
goFirst orig@(SZ (x,(x1s,x2s))) =
case viewl x1s of
EmptyL -> orig
z :< zs -> SZ (z,(empty, zs `mappend` (x <| x2s)))

goLast :: SeqZipper a -> SeqZipper a
goLast orig@(SZ (x,(x1s,x2s))) =
case viewr x2s of
EmptyR -> orig
zs :> z -> SZ (z,((x1s |> x) `mappend` zs , empty))

current :: SeqZipper a -> a
current (SZ (x,(_,_))) = x

prev :: SeqZipper a -> Maybe a
prev = fmap current . moveLeft

next :: SeqZipper a -> Maybe a
next = fmap current . moveRight

replace :: a -> SeqZipper a -> SeqZipper a
replace y (SZ (x,zs)) = SZ (y,zs)

deleteCurrent :: SeqZipper a -> Maybe (SeqZipper a)
deleteCurrent orig@(SZ (_,(xs,ys))) =
case viewl ys of
EmptyL -> case viewr xs of
EmptyR -> Nothing
zs :> z -> Just (SZ (z,(zs,ys)))
z :< zs -> Just (SZ (z,(xs,zs)))

data ZipperSelect a = NoSelect { allelems :: [a] }
| Select { zipper :: (Maybe :. SeqZipper) a }

deriving instance Functor ZipperSelect

selectFirst :: ZipperSelect a -> ZipperSelect a
selectFirst (NoSelect []) = NoSelect []
selectFirst (NoSelect lst@(x:xs))  = Select . gFromList \$ lst
selectFirst (Select (O Nothing)) = NoSelect []
selectFirst (Select (O msz)) = Select . O \$ return . goFirst =<<  msz

instance GListable (Maybe :. SeqZipper) where
gFromList [] = O Nothing
gFromList (x:xs) = O (Just (SZ (x, (empty,fromList xs))))
gToList (O Nothing) = []
gToList (O (Just (SZ (x,(xs,ys))))) = toList xs ++ (x : toList ys)

instance GListable ZipperSelect where
gFromList xs = NoSelect xs
gToList (NoSelect xs) = xs
gToList (Select xs) = gToList xs

deriving instance Foldable ZipperSelect

deriving instance Traversable ZipperSelect

---

-- data HeteroSeqZipper a b = HSZ { unHSZ :: (b, (Seq a, Seq a)) }

```