module Day3 where
import System.IO (openFile, IOMode (ReadMode), hClose, hGetContents)
import Data.List ( maximumBy, minimumBy, group, sort )
import Data.Function (on)
import Data.Char (digitToInt)

column :: String -> Int -> String
column str i = map (!! i) $ lines str

columns :: String -> Int
columns str = maximum $ map length $ lines str

mostCommon :: String -> Char
mostCommon str = head . maximumBy (compare `on` length) . group $ sort str

leastCommon :: String -> Char
leastCommon str = head . minimumBy (compare `on` length) . group $ sort str

binaryToDecimal :: Int -> Int
binaryToDecimal = foldl1 ((+) . (2 *)) . map digitToInt . show

main :: IO ()
main = do
    input <- openFile "inputs/3.txt" ReadMode
    contents <- hGetContents input

    let gamma = mostCommon . column contents <$> [0..(columns contents - 1)]
    let epsilon = leastCommon . column contents <$> [0..(columns contents - 1)]

    let energy = product (binaryToDecimal . read <$> [gamma, epsilon] :: [Int])

    print energy

    hClose input