module Day1 where

parseLine :: String -> (Char, Int)
parseLine (c : s) = (c, read s)

parseInput :: String -> [(Char,Int)]
parseInput input = map parseLine $ lines input

doRotations :: [(Char, Int)] -> Int -> [Int]
doRotations (('L', l) : rest) n = (n : doRotations rest ((n-l) `mod` 100))
doRotations (('R', r) : rest) n = (n : doRotations rest ((n+r) `mod` 100))
doRotations [] n = [n]

getCrossings :: [(Char, Int)] -> Int -> [Int]
getCrossings (('L', l) : rest) n = (((l-n) `div` 100) + (if n > 0 then 1 else 0) : getCrossings rest ((n-l) `mod` 100))
getCrossings (('R', r) : rest) n = (((n+r) `div` 100) : getCrossings rest ((n+r) `mod` 100))
getCrossings [] _ = []

part1 :: String -> String
part1 input =
  let rotations = parseInput input
      states = doRotations rotations 50
   in show $ length (filter (== 0) states)

part2 :: String -> String
part2 input =
  let rotations = parseInput input
      zeroCrossings = getCrossings rotations 50
    in show $ sum zeroCrossings