Main.hs

import Debug.Trace
import qualified Lib.Inputs
import System.IO

main :: IO ()
main = do
  handle <- openFile "input.txt" ReadMode
  contents <- hGetContents handle
  let linesList = lines contents
  let res = fn1 linesList linesList 0
  print res

fn1 :: [String] -> [String] -> Int -> Int
fn1 _ [] _ = 0
fn1 all (x:xs) row =
  parseLine all x (Position row 0) False (Position row 0) + fn1 all xs (row + 1)

data Position =
  Position Int Int
  deriving (Show)

isDigit :: Char -> Bool
isDigit x = x >= '0' && x <= '9'

getLineFromRow :: [String] -> Int -> String
getLineFromRow all row
  | row < 0 = []
  | row >= length all = []
  | otherwise = all !! row

parseLine :: [String] -> String -> Position -> Bool -> Position -> Int
parseLine _ [] _ False _ = 0
parseLine all [] (Position row col) True p =
  check all p (Position row $ col - 1)
parseLine all (x:xs) (Position row col) False p
  | isDigit x =
    parseLine all xs (Position row $ col + 1) True (Position row col)
  | otherwise = parseLine all xs (Position row $ col + 1) False p
parseLine all (x:xs) (Position row col) True p
  | isDigit x = parseLine all xs (Position row $ col + 1) True p
  | otherwise =
    check all p (Position row $ col - 1)
      + parseLine all xs (Position row $ col + 1) False (Position 0 0)

check :: [String] -> Position -> Position -> Int
check all (Position fromRow fromCol) (Position toRow toCol) =
  if found
    then number
    else 0
  where
    number = parseNumber all (Position fromRow fromCol) (Position toRow toCol)
    found =
      (containsSign (getLineFromRow all fromRow) (fromCol - 1))
        || (containsSign (getLineFromRow all fromRow) (toCol + 1))
        || (containsSignRange
              (getLineFromRow all (fromRow - 1))
              (fromCol - 1)
              (toCol + 1))
        || (containsSignRange
              (getLineFromRow all (fromRow + 1))
              (fromCol - 1)
              (toCol + 1))

containsSignRange :: String -> Int -> Int -> Bool
containsSignRange line col toCol
  | col > toCol = False
  | otherwise =
    if containsSign line col
      then True
      else containsSignRange line (col + 1) (toCol)

containsSign :: String -> Int -> Bool
containsSign [] _ = False
containsSign line col =
  if not inside
    then False
    else let v = line !! col
          in v /= '.'
  where
    inside = col >= 0 && col < length line

parseNumber :: [String] -> Position -> Position -> Int
parseNumber all from to = foldl (\acc a -> acc * 10 + a) 0 numbers
  where
    numbers = parseNumber' all from to

parseNumber' :: [String] -> Position -> Position -> [Int]
parseNumber' all (Position row col) (Position toRow toCol)
  | col > toCol = []
  | otherwise =
    fromEnum (all !! row !! col) - fromEnum '0'
      : parseNumber' all (Position row $ col + 1) (Position toRow toCol)