module Day9_1 where
import System.IO (openFile, IOMode (ReadMode), hClose, hGetContents)
import Data.Char (digitToInt)
import Data.List (sort)

-- i gave up on my original solution
-- this isn't very original and is influcenced by other people's solutions
-- i'm sorry

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

xy :: Int -> Int -> [[Int]] -> (Int, Int) -> Int
xy w h arr (x, y)
    | x < 0 || x >= w = 9
    | y < 0 || y >= h = 9
    | otherwise = arr !! y !! x 

-- left, right, up, down from current coord
neigh :: (Int, Int) -> [(Int, Int)]
neigh (x, y) = [(x - 1, y), (x + 1, y), (x, y - 1), (x, y + 1)]

basin :: Int -> Int -> [[Int]] -> [(Int, Int)] -> [(Int, Int)] -> [(Int, Int)]
basin w h ints acc [] = acc
basin w h ints acc (x:xs)
    | pos x == 9 || x `elem` acc = basin w h ints acc xs
    | otherwise = basin w h ints (x:acc) (xs ++ neigh x)
    where pos = xy w h ints

main :: IO ()
main = do
    input <- openFile "inputs/9.txt" ReadMode
    contents <- hGetContents input

    let ints = map (map digitToInt) $ lines contents

    let width = columns contents
    let height = length ints

    let coordMap = [ (x, y) | x <- [0..width-1], y <- [0..height-1] ]
    let pos = xy width height ints

    let lowest = [ coord | coord <- coordMap, and [neighbor > pos coord | neighbor <- pos <$> neigh coord] ]

    print . product . take 3 . reverse . sort $ map (length . basin width height ints [] . pure) lowest

    hClose input