module Main where

import Utils
import Data.List (sortOn)
import Data.Map (Map, (!))
import qualified Data.Map as Map
import Data.Maybe

dirs = [ (-1,-1), (0,-1), (1,-1)
       , (-1, 0),         (1, 0)
       , (-1, 1), (0, 1), (1, 1)
       ]

adjs1 m pt = howMany (== '#') $ mapMaybe ((`Map.lookup` m) . add pt) dirs

inGrid (x, y) w h = x < w && x >= 0 && y < h && y >= 0
adjs2 grid pt w h = howMany ((== '#') . head)
                        $ filter (not . null)
                        $ map (dropWhile (== '.')
                                . map (grid !)
                                . takeWhile (inside (0, 0) (w-1, h-1))
                                . map ($ pt)
                                . repeatF
                                . add)
                     dirs

rule1 w h m pt@(x, y) = if as == 0 then '#' else 'L'
    where as = adjs2 m pt w h

rule2 w h m pt@(x, y) = if as >= 5 then 'L' else '#'
    where as = adjs2 m pt w h

doStep w h m = Map.mapWithKey fn m
    where fn k 'L' = rule1 w h m k
          fn k '#' = rule2 w h m k
          fn k '.' = '.'

stepWhile prev w h
  | prev == next = next
  | otherwise = stepWhile next w h
  where next = doStep w h prev

main :: IO ()
main = do
    n <- readFile "input/11"
    let (grid, width, height) = makeGrid n
    let solve1 = stepWhile grid width height
    print $ howMany ((== '#') . snd) $ Map.toList solve1