module Main where

import Debug.Trace (trace)
import System.Environment (getArgs)

main :: IO ()
main = do
  input <- readFile . head =<< getArgs
  print $ part1 input
  print $ part2 input

part1 :: String -> Int
part1 = length . filter (== 0) . scanl rotate 50 . map parse . lines

rotate :: Integer -> Either Integer Integer -> Integer
rotate pos (Left rot) = (pos - rot) `mod` 100
rotate pos (Right rot) = (pos + rot) `mod` 100

parse :: String -> Either Integer Integer
parse ('L' : rest) = Left (read rest :: Integer)
parse ('R' : rest) = Right (read rest :: Integer)
parse s = error $ unwords [s, "is not on the form 'L$NUM' or 'R$NUM''"]

test_input = "L68\nL30\nR48\nL5\nR60\nL55\nL1\nL99\nR14\nL82"

part2 :: String -> Integer
part2 = snd . head . reverse . scanl rotate2 (50, 0) . map parse . lines

rotate2 :: (Integer, Integer) -> Either Integer Integer -> (Integer, Integer)
rotate2 (pos, zeros) rot =
  let pos' = rotate pos rot
      newZeros = go pos rot
   in trace ("The dial is rotated " ++ show rot ++ " to point at " ++ show pos' ++ if newZeros > 0 then "; during this rotation it points to 0 " ++ (counting newZeros) else ".") (pos', zeros + newZeros)
  where
    counting :: Integer -> String
    counting 1 = "once"
    counting 2 = "twice"
    counting n = show n ++ " times"

go :: Integer -> Either Integer Integer -> Integer
go p (Left r)
  | p == r = 1
  | r > 100 = 1 + go p (Left (r - 100))
  | p /= 0 && p - r < 0 = 1 + go 0 (Left (r - p))
  | otherwise = 0
go p (Right r) = (p + r) `div` 100

between :: Integer -> (Integer, Integer) -> Bool
between x (mn, mx) = x < mx && x > mn