{-# LANGUAGE CPP #-}
{-# LANGUAGE Rank2Types #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE Trustworthy #-}

-----------------------------------------------------------------------------

-- |

-- Module      :  Control.Lens.Level

-- Copyright   :  (C) 2012-16 Edward Kmett

-- License     :  BSD-style (see the file LICENSE)

-- Maintainer  :  Edward Kmett <ekmett@gmail.com>

-- Stability   :  provisional

-- Portability :  Rank2Types

--

-- This module provides combinators for breadth-first searching within

-- arbitrary traversals.

----------------------------------------------------------------------------

module Control.Lens.Level
  ( Level
  , levels
  , ilevels
  ) where

import Control.Applicative
import Control.Lens.Internal.Bazaar
import Control.Lens.Internal.Context
import Control.Lens.Internal.Indexed
import Control.Lens.Internal.Level
import Control.Lens.Traversal
import Control.Lens.Type
import Data.Profunctor.Unsafe

-- $setup

-- >>> :set -XNoOverloadedStrings

-- >>> import Control.Lens

-- >>> import Data.Char


levelIns :: BazaarT (->) f a b t -> [Level () a]
levelIns = go 0 . (getConst #. bazaar (rmapConst (deepening ()))) where
  go k z = k `seq` runDeepening z k $ \ xs b ->
    xs : if b then (go $! k + 1) z else []
{-# INLINE levelIns #-}

levelOuts :: BazaarT (->) f a b t -> [Level j b] -> t
levelOuts bz = runFlows $ runBazaarT bz $ \ _ -> Flows $ \t -> case t of
  One _ a : _ -> a
  _           -> error "levelOuts: wrong shape"
{-# INLINE levelOuts #-}

-- | This provides a breadth-first 'Traversal' or 'Fold' of the individual

-- 'levels' of any other 'Traversal' or 'Fold' via iterative deepening

-- depth-first search. The levels are returned to you in a compressed format.

--

-- This can permit us to extract the 'levels' directly:

--

-- >>> ["hello","world"]^..levels (traverse.traverse)

-- [Zero,Zero,One () 'h',Two 0 (One () 'e') (One () 'w'),Two 0 (One () 'l') (One () 'o'),Two 0 (One () 'l') (One () 'r'),Two 0 (One () 'o') (One () 'l'),One () 'd']

--

-- But we can also traverse them in turn:

--

-- >>> ["hello","world"]^..levels (traverse.traverse).traverse

-- "hewlolrold"

--

-- We can use this to traverse to a fixed depth in the tree of ('<*>') used in the 'Traversal':

--

-- >>> ["hello","world"] & taking 4 (levels (traverse.traverse)).traverse %~ toUpper

-- ["HEllo","World"]

--

-- Or we can use it to traverse the first @n@ elements in found in that 'Traversal' regardless of the depth

-- at which they were found.

--

-- >>> ["hello","world"] & taking 4 (levels (traverse.traverse).traverse) %~ toUpper

-- ["HELlo","World"]

--

-- The resulting 'Traversal' of the 'levels' which is indexed by the depth of each 'Level'.

--

-- >>> ["dog","cat"]^@..levels (traverse.traverse) <. traverse

-- [(2,'d'),(3,'o'),(3,'c'),(4,'g'),(4,'a'),(5,'t')]

--

-- @

-- 'levels' :: 'Traversal' s t a b      -> 'IndexedTraversal' 'Int' s t ('Level' () a) ('Level' () b)

-- 'levels' :: 'Fold' s a               -> 'IndexedFold' 'Int' s ('Level' () a)

-- @

--

-- /Note:/ Internally this is implemented by using an illegal 'Applicative', as it extracts information

-- in an order that violates the 'Applicative' laws.

levels :: Applicative f
       => Traversing (->) f s t a b
       -> IndexedLensLike Int f s t (Level () a) (Level () b)
levels l f s = levelOuts bz <$> traversed f (levelIns bz) where
  bz = l sell s
{-# INLINE levels #-}

-- This is only a temporary work around added to deal with a bug in an unreleased version

-- of GHC 7.10. We should remove it as soon as we're able.

rmapConst :: Profunctor p => p a b -> p a (Const b x)
rmapConst p = Const #. p
{-# INLINE rmapConst #-}

ilevelIns :: BazaarT (Indexed i) f a b t -> [Level i a]
ilevelIns = go 0 . (getConst #. bazaar (Indexed $ \ i -> rmapConst (deepening i))) where
  go k z = k `seq` runDeepening z k $ \ xs b ->
    xs : if b then (go $! k + 1) z else []
{-# INLINE ilevelIns #-}

ilevelOuts :: BazaarT (Indexed i) f a b t -> [Level j b] -> t
ilevelOuts bz = runFlows $ runBazaarT bz $ Indexed $ \ _ _ -> Flows $ \t -> case t of
  One _ a : _ -> a
  _           -> error "ilevelOuts: wrong shape"
{-# INLINE ilevelOuts #-}

-- | This provides a breadth-first 'Traversal' or 'Fold' of the individual

-- levels of any other 'Traversal' or 'Fold' via iterative deepening depth-first

-- search. The levels are returned to you in a compressed format.

--

-- This is similar to 'levels', but retains the index of the original 'IndexedTraversal', so you can

-- access it when traversing the levels later on.

--

-- >>> ["dog","cat"]^@..ilevels (traversed<.>traversed).itraversed

-- [((0,0),'d'),((0,1),'o'),((1,0),'c'),((0,2),'g'),((1,1),'a'),((1,2),'t')]

--

-- The resulting 'Traversal' of the levels which is indexed by the depth of each 'Level'.

--

-- >>> ["dog","cat"]^@..ilevels (traversed<.>traversed)<.>itraversed

-- [((2,(0,0)),'d'),((3,(0,1)),'o'),((3,(1,0)),'c'),((4,(0,2)),'g'),((4,(1,1)),'a'),((5,(1,2)),'t')]

--

-- @

-- 'ilevels' :: 'IndexedTraversal' i s t a b      -> 'IndexedTraversal' 'Int' s t ('Level' i a) ('Level' i b)

-- 'ilevels' :: 'IndexedFold' i s a               -> 'IndexedFold' 'Int' s ('Level' i a)

-- @

--

-- /Note:/ Internally this is implemented by using an illegal 'Applicative', as it extracts information

-- in an order that violates the 'Applicative' laws.

ilevels :: Applicative f
        => Traversing (Indexed i) f s t a b
        -> IndexedLensLike Int f s t (Level i a) (Level j b)
ilevels l f s = ilevelOuts bz <$> traversed f (ilevelIns bz) where
  bz = l sell s
{-# INLINE ilevels #-}