import Common
import Data.List (elemIndex)
import Data.Maybe (fromJust)

wrap :: Int -> Int -> Int
wrap length index
  | index == 0 = length - 1
  | index == length - 1 = 0
  | index >= length = wrap length $ index - length
  | index < 0 = wrap length $ index + length
  | otherwise = index

coordinates = [1000, 2000, 3000]

decrypt :: [Int] -> Int
decrypt a = sum $ map test coordinates
  where
    test n = mixed !! (zeroIndex + n)
    zeroIndex = fromJust $ elemIndex 0 mixed
    mixed = cycle $ foldl mix a a

    len = length a

    mix :: [Int] -> Int -> [Int]
    mix list x = newList
      where
        newList = listStart ++ x : listEnd
        (listStart, listEnd) = splitAt newIndex list'
        newIndex = wrap (len - 1) $ oldIndex + x
        list' = filter (/= x) list
        oldIndex = fromJust $ elemIndex x list

main = interact $
  show
  . decrypt
  . map read . lines