module Waterdeep.Util 
   ( mrepeat
   , deleteAt
   , on
   , nubOn
   , sortOn
   , countOf
   ) where

import Lens.Family2
import Data.List
import Data.Monoid

mrepeat :: (Monoid m) => Int -> m -> m
mrepeat n m = mconcat $ replicate n m

deleteAt :: Int -> [a] -> [a]
deleteAt n l = (take n l) ++ (drop (n + 1) l)

on :: (b -> b -> c) -> (a -> b) -> (a -> a -> c)
(f `on` g) a b = (g a) `f` (g b)

nubOn :: Eq b => (a -> b) -> [a] -> [a]
nubOn f = nubBy ((==) `on` f)

sortOn :: Ord b => (a -> b) -> [a] -> [a]
sortOn f = sortBy (compare `on` f)

countOf :: Num r => FoldLike (Sum r) a a' b b' -> (b -> Bool) -> a -> r
countOf l f = getSum . views l (\b -> if f b then Sum 1 else Sum 0)