module Hcompta.Lib.NonEmpty where

import           Data.Function ((.))
import qualified Data.List
import           Data.List.NonEmpty (NonEmpty(..))
import           Data.Maybe (Maybe(..))
import           Data.Monoid (Monoid(..))

-- | Return the given 'NonEmpty' without its last section if any.
parent :: NonEmpty x -> Maybe (NonEmpty x)
parent (_:|[]) = Nothing
parent (x:|xs) = Just (x:|Data.List.init xs)

-- | Return all the ancestors (i.e. prefixes)
-- of the given 'NonEmpty' (including itself).
ancestors_or_self :: NonEmpty x -> [NonEmpty x]
ancestors_or_self (y:|ys) = go y [] ys []
	where
		go :: x -> [x] -> [x] -> [NonEmpty x] -> [NonEmpty x]
		go x0 s []     = (:) (x0:|s)
		go x0 s (x:xs) = go x0 (s `mappend` [x]) xs . (:) (x0:|s)