{-# LANGUAGE DerivingVia, StandaloneDeriving #-}

{-# LANGUAGE DerivingVia, GeneralizedNewtypeDeriving, StandaloneDeriving #-}

  getFront

  getFront,
  quota,
  nestedFold

import Data.Semigroup(Max(..), Min(..))

import Data.Semigroup(Arg(..), Max(..), Min(..))

  -- | Where the items are equal by all used criteria

  -- | Where no item is preferred by any used criterion

instance Debatable a => Debatable (Arg a b) where
  weigh (Arg a _) (Arg b _) = weigh a b

newtype Front a = Front [a] deriving (Show)

newtype Front a = Front [a] deriving (Foldable, Show)

instance Foldable Strata where
  foldMap f (Strata l) = foldMap (foldMap f) l

-- | Drop fronts after those accounting for the first n items.
quota :: Int -> Strata a -> Strata a
quota _ (Strata []) = Strata []
quota n (Strata (a:r))
  | n > 0 = let
    Strata r' = quota (n - length (getFront a)) (Strata r)
    in Strata (a : r')
  | otherwise = Strata []
-- | 'foldMap' each front separately with one function, then 'foldMap' the
-- results.
nestedFold :: (Monoid m, Monoid n) => (a -> m) -> (m -> n) -> Strata a -> n
nestedFold f g (Strata l) = foldMap (g . foldMap f) l