module Data.Graph.Inductive.Internal.Queue(
    -- * Type
    Queue(..),
    -- * Operations
    mkQueue, queuePut, queuePutList, queueGet, queueEmpty
) where

import Data.List (foldl')

data Queue a = MkQueue [a] [a]

mkQueue :: Queue a
mkQueue = MkQueue [] []

queuePut :: a -> Queue a -> Queue a
queuePut item (MkQueue ins outs) = MkQueue (item:ins) outs

queuePutList :: [a] -> Queue a -> Queue a
queuePutList xs q = foldl' (flip queuePut) q xs

queueGet :: Queue a -> (a, Queue a)
queueGet (MkQueue ins (item:rest)) = (item, MkQueue ins rest)
queueGet (MkQueue ins []) = queueGet (MkQueue [] (reverse ins))

queueEmpty :: Queue a -> Bool
queueEmpty (MkQueue ins outs) = null ins && null outs