module Main (main) where
import Control.Monad (when)
import Data.List (group, sort)
import System.Exit (die)

exampleExpectedOutput = 8
exampleExpectedOutput2 = 19208

parseInput :: String -> IO [Int]
parseInput filename = do
  input <- readFile filename
  return $ map read $ lines input

compute :: [Int] -> Int
compute jolts = product $ map (([1, 1, 2, 4, 7, 13, 24] !!) . length) $ filter ((==) 1 . head) $  group $ zipWith (-) s (0 : s) --snd . head $ foldl compute' [(0, 1)] $ sort jolts
  where
    s = sort jolts
    --compute' (prev, n) x =
    --compute' (x:xs) = (length $ takeWhile (\i -> i <= x + 3) xs) * compute' xs

main :: IO ()
main = do
  example <- parseInput "example"
  let s = sort example
  print s
  print $ zipWith (-) s (0 : s)
  print $ group $ zipWith (-) s (0 : s)
  print $ filter ((==) 1 . head) $ group $ zipWith (-) s (0 : s)
  print $ map length $ filter ((==) 1 . head) $ group $ zipWith (-) s (0 : s)
  let exampleOutput = compute example
  when  (exampleOutput /= exampleExpectedOutput)  (die $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
  example2 <- parseInput "example2"
  let exampleOutput2 = compute example2
  when  (exampleOutput2 /= exampleExpectedOutput2)  (die $ "example2 failed: got " ++ show exampleOutput2 ++ " instead of " ++ show exampleExpectedOutput2)
  input <- parseInput "input"
  print $ compute input