module Commons where

import GHC.IO.Handle (isEOF)
import Data.Array (Array, listArray, bounds, (!), (//))


data Tile = Empty | Round | Square deriving (Eq, Show)
type Platform = Array (Int, Int) Tile


parseLine :: String -> [Tile]
parseLine [] = []
parseLine ('O': t) = Round: parseLine t
parseLine ('#': t) = Square: parseLine t
parseLine ('.': t) = Empty: parseLine t

parsePlatform :: IO [[Tile]]
parsePlatform = do done <- isEOF
                   if done
                      then return []
                      else do line <- getLine
                              let platformLine = parseLine line
                              platform <- parsePlatform
                              return (platformLine: platform)

parse :: IO Platform
parse = do platform <- parsePlatform
           return (listArray ((1, 1), (length platform, length $ head platform)) $ concat platform)


tilt :: (Int, Int) -> [(Int, Int)] -> Platform -> Platform
tilt _ [] platform = platform
tilt (yI, xI) ((y, x): t) platform
  | let (y2, x2) = (y + yI, x + xI)
    in y2 > 0 && y2 <= fst (snd $ bounds platform) && x2 > 0 && x2 <= snd (snd $ bounds platform)
       && platform ! (y2, x2) == Empty = tilt (yI, xI) ((y + yI, x + xI): t) $ platform // [((y, x), Empty)]
  | otherwise                          = tilt (yI, xI) t $ platform // [((y, x), Round)]