module Mesh where

import Data.Map (Map)
import qualified Data.Map as Map

import Control.Applicative

import Control.Monad
import Control.Monad.Trans
import Control.Monad.Trans.Maybe

import Control.Monad.State

data Mesh a = Mesh (Map Int (Cell a)) deriving (Eq,Show)

data Cell a = Cell a [Int] | Border a Int deriving (Eq,Show)

mesh = Mesh $ Map.fromList [(0,(Cell 'a' [1,2,3])),(1,(Border 'b' 0)),(2,(Border 'c' 0)),(3,(Border 'd' 0))]

cell (Mesh buf) id = Map.lookup id buf

neighbour mesh _   (Border _ _) = Nothing
neighbour mesh idx (Cell _ ids) = join $ (cell mesh) <$> safeIndex idx ids
    where safeIndex idx ids
            | idx < 0 = Nothing
            | idx < length ids = Just $ ids!!idx
            | otherwise = Nothing

owner mesh (Cell _ _)    = Nothing
owner mesh (Border _ id) = cell mesh id

type MMesh a b = MaybeT (State (Mesh a)) b

getMesh = get :: MMesh a (Mesh a)

cellM id = getMesh >>= (MaybeT . return) <$> (\m -> cell m id)

neighbourM idx cell = getMesh >>= (MaybeT . return) <$> (\m -> neighbour m idx cell)

ownerM cell = getMesh >>= (MaybeT . return) <$> (\m -> owner m cell)