module Commons where

import GHC.IO.Handle (isEOF)
import Data.Array (Array, listArray, (!), Ix (inRange), bounds, array, indices, assocs)


data Tile = Plot { reachable :: Bool } | Rock deriving (Eq, Show)
type Garden = Array (Int, Int) Tile


parseLine :: String -> [Tile]
parseLine = map (\case
                  'S' -> Plot {reachable = False}
                  '.' -> Plot {reachable = False}
                  '#' -> Rock)

parseGarden :: IO [[Tile]]
parseGarden = do done <- isEOF
                 if done
                    then return []
                    else do line <- getLine
                            let gardenLine = parseLine line
                            garden <- parseGarden
                            return (gardenLine: garden)

parse :: IO Garden
parse = do garden <- parseGarden
           return $ listArray ((1, 1), (length garden, length $ head garden)) $ concat garden


move :: [(Int, Int)] -> Garden -> [((Int, Int), Tile)]
move [] _ = []
move ((y, x): t) garden = if garden ! (y, x) == Rock then ((y, x), Rock): move t garden
                          else let r1 = inRange (bounds garden) (y + 1, x) && (garden ! (y + 1, x) == Plot True)
                                   r2 = inRange (bounds garden) (y - 1, x) && (garden ! (y - 1, x) == Plot True)
                                   r3 = inRange (bounds garden) (y, x + 1) && (garden ! (y, x + 1) == Plot True)
                                   r4 = inRange (bounds garden) (y, x - 1) && (garden ! (y, x - 1) == Plot True)
                               in ((y, x), Plot {reachable = r1 || r2 || r3 || r4}): move t garden

applyMove :: Garden -> Garden
applyMove garden = array (bounds garden) $ move (indices garden) garden

applyNMove :: Int -> Garden -> Garden
applyNMove 0 garden = garden
applyNMove n garden = applyNMove (n - 1) $ applyMove garden

getReachableAfterNMove :: Int -> Garden -> [((Int, Int), Tile)]
getReachableAfterNMove n garden = let finalGarden = applyNMove n garden
                                  in filter (\ (_, t) -> t == Plot True) $ assocs finalGarden