+testSim = simSet (initSimSpace 3 3) (ChunkData Water) 1 1
+
+physStep sim@Simulation{simW=w,simH=h} = _physStep [(x, y) | x <- [0..w-1], y <- [0..h-1]] sim sim
+-- _physStep grid acc sim@Simulation{simSpace=s,simW=w,simH=h} | trace ("" ++ show acc) False = undefined
+_physStep grid acc sim@Simulation{simSpace=s,simW=w,simH=h} =
+ if null grid then acc
+ else _physStep (tail grid) next sim
+ where x = fst $ head grid
+ y = snd $ head grid
+ valid = validDirects x y w h
+ next = case simGetChunkType sim x y of
+ Water -> updateWaterChunk x y valid acc
+ _ -> acc
+
+-- takes in list of valid chunks, as well as the sim to modify
+updateWaterChunk x y valid sim =
+ -- if the chunk below is free, fall straight down
+ if elem (0,-1) valid && fromEnum (simGetChunkType sim x (y-1)) == fromEnum Air
+ then
+ let moved = simSet sim ChunkData { chunkType=Air } x y
+ in simSet moved ChunkData { chunkType=Water } x (y-1)
+ else if elem (-1,-1) valid && fromEnum (simGetChunkType sim (x-1) (y-1)) == fromEnum Air
+ then
+ let moved = simSet sim ChunkData { chunkType=Air } x y
+ in simSet moved ChunkData { chunkType=Water } (x-1) (y-1)
+ else if elem (1,-1) valid && fromEnum (simGetChunkType sim (x+1) (y-1)) == fromEnum Air
+ then
+ let moved = simSet sim ChunkData { chunkType=Air } x y
+ in simSet moved ChunkData { chunkType=Water } (x+1) (y-1)
+ -- stay put
+ else sim
+
+-- gets chunks around a given chunk that are inside grid
+validDirects x y w h = filter
+ (\q -> 0 <= (fst q) && (fst q) < w && (snd q) <= 0 && (snd q) < h)
+ [(a-x,b-y) | a <- [x-1..x+1], b <- [y-1..y+1], not (a==x && b==y)]
+
+simToString :: Simulation -> [Char]
+simToString sim@Simulation{simW=w} =
+ let simStr = V.toList $ V.map chunkToChar $ simSpace sim
+ in insert w '\n' simStr
+
+-- from https://stackoverflow.com/questions/12659562/insert-specific-element-y-after-every-n-elements-in-a-list
+insert :: Int -> a -> [a] -> [a]
+insert n y xs = countdown n xs where
+ countdown 0 xs = y:countdown n xs
+ countdown _ [] = []
+ countdown m (x:xs) = x:countdown (m-1) xs