module Utils where

import System.Random
import Text.Read

shuffle :: StdGen -> [a] -> [a]
shuffle g xs = shuffle' (randoms g) xs

shuffle' :: [Int] -> [a] -> [a]
shuffle' _      [] = []
shuffle' (i:is) xs = let (firsts, rest) = splitAt (1 + i `mod` length xs) xs
                     in (last firsts) : shuffle' is (init firsts ++ rest)

chunksOf :: Int -> [a] -> [[a]]
chunksOf n [] = []
chunksOf n xs = take n xs : chunksOf n (drop n xs)

query :: Read a => String -> IO a
query s = do
    putStrLn s
    l <- fmap readMaybe getLine
    case l of
        Just x -> return x
        Nothing -> query s

remove :: (a -> Bool) -> [a] -> (a, [a])
remove pred xs = foldr f (undefined, []) xs
    where f c (old, cs) = if pred c then (c, cs) else (old, c : cs)

filterMap :: (a -> Bool) -> (a -> b) -> [a] -> [b]
filterMap pred f as = foldr g [] as
    where g a bs = if pred a then f a : bs else bs