{-# LANGUAGE Rank2Types #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE MultiParamTypeClasses #-}
-----------------------------------------------------------------------------
-- |
-- Module      :  Control.Lens.Action
-- Copyright   :  (C) 2012-13 Edward Kmett
-- License     :  BSD-style (see the file LICENSE)
-- Maintainer  :  Edward Kmett <ekmett@gmail.com>
-- Stability   :  experimental
-- Portability :  non-portable
--
----------------------------------------------------------------------------
module Control.Lens.Action
  (
  -- * Composable Actions
    Action
  , act
  , acts
  , perform
  , performs
  , liftAct
  , (^!)
  , (^!!)
  , (^!?)

  -- * Indexed Actions
  , IndexedAction
  , iact
  , iperform
  , iperforms
  , (^@!)
  , (^@!!)
  , (^@!?)

  -- * Folds with Effects
  , MonadicFold
  , IndexedMonadicFold

  -- * Implementation Details
  , Acting
  , IndexedActing
  , Effective
  ) where

import Control.Comonad
import Control.Lens.Internal.Action
import Control.Lens.Internal.Fold
import Control.Lens.Internal.Indexed
import Control.Lens.Type
import Control.Monad (liftM)
import Control.Monad.Trans.Class
import Data.Profunctor
import Data.Profunctor.Rep
import Data.Profunctor.Unsafe

-- $setup
-- >>> :m + Control.Lens

infixr 8 ^!, ^!!, ^@!, ^@!!, ^!?, ^@!?

-- | Used to evaluate an 'Action'.
type Acting m r s t a b = LensLike (Effect m r) s t a b

-- | Perform an 'Action'.
--
-- @
-- 'perform' ≡ 'flip' ('^!')
-- @
perform :: Monad m => Acting m a s t a b -> s -> m a
perform l = getEffect #. l (Effect #. return)
{-# INLINE perform #-}

-- | Perform an 'Action' and modify the result.
--
-- @
-- 'performs' :: 'Monad' m => 'Acting' m e s t a b -> (a -> e) -> s -> m e
-- @
performs :: (Profunctor p, Monad m) => Over p (Effect m e) s t a b -> p a e -> s -> m e
performs l f = getEffect #. l (rmap (Effect #. return) f)
{-# INLINE performs #-}

-- | Perform an 'Action'.
--
-- >>> ["hello","world"]^!folded.act putStrLn
-- hello
-- world
(^!) :: Monad m => s -> Acting m a s t a b -> m a
a ^! l = getEffect (l (Effect #. return) a)
{-# INLINE (^!) #-}

-- | Perform a 'MonadicFold' and collect all of the results in a list.
(^!!) :: Monad m => s -> Acting m [a] s t a b -> m [a]
a ^!! l = getEffect (l (Effect #. return . return) a)
{-# INLINE (^!!) #-}

-- | Perform a 'MonadicFold' and collect the leftmost result.
--
-- /Note:/ this still causes all effects for all elements.
(^!?) :: Monad m => s -> Acting m (Leftmost a) s t a b -> m (Maybe a)
a ^!?  l = liftM getLeftmost .# getEffect $ l (Effect #. return . LLeaf) a
{-# INLINE (^!?) #-}

-- | Construct an 'Action' from a monadic side-effect.
--
-- >>> ["hello","world"]^!folded.act (\x -> [x,x ++ "!"])
-- ["helloworld","helloworld!","hello!world","hello!world!"]
--
-- @
-- 'act' :: 'Monad' m => (s -> m a) -> 'Action' m s a
-- 'act' sma afb a = 'effective' (sma a '>>=' 'ineffective' '.' afb)
-- @
act :: Monad m => (s -> m a) -> IndexPreservingAction m s a
act sma pafb = cotabulate $ \ws -> effective $ do
   a <- sma (extract ws)
   ineffective (corep pafb (a <$ ws))
{-# INLINE act #-}

-- | A self-running 'Action', analogous to 'Control.Monad.join'.
--
-- @
-- 'acts' ≡ 'act' 'id'
-- @
--
-- >>> (1,"hello")^!_2.acts.to succ
-- "ifmmp"
acts :: Action m (m a) a
acts = act id
{-# INLINE acts #-}

-- | Apply a 'Monad' transformer to an 'Action'.
liftAct :: (MonadTrans trans, Monad m) => Acting m a s t a b -> Action (trans m) s a
liftAct l = act (lift . perform l)
{-# INLINE liftAct #-}

-----------------------------------------------------------------------------
-- Indexed Actions
----------------------------------------------------------------------------

-- | Used to evaluate an 'IndexedAction'.
type IndexedActing i m r s t a b = Over (Indexed i) (Effect m r) s t a b

-- | Perform an 'IndexedAction'.
--
-- @
-- 'iperform' ≡ 'flip' ('^@!')
-- @
iperform :: Monad m => IndexedActing i m (i, a) s t a b -> s -> m (i, a)
iperform l = getEffect #. l (Indexed $ \i a -> Effect (return (i, a)))
{-# INLINE iperform #-}

-- | Perform an 'IndexedAction' and modify the result.
iperforms :: Monad m => IndexedActing i m e s t a b -> (i -> a -> e) -> s -> m e
iperforms l = performs l .# Indexed
{-# INLINE iperforms #-}

-- | Perform an 'IndexedAction'.
(^@!) :: Monad m => s -> IndexedActing i m (i, a) s t a b -> m (i, a)
s ^@! l = getEffect (l (Indexed $ \i a -> Effect (return (i, a))) s)
{-# INLINE (^@!) #-}

-- | Obtain a list of all of the results of an 'IndexedMonadicFold'.
(^@!!) :: Monad m => s -> IndexedActing i m [(i, a)] s t a b -> m [(i, a)]
s ^@!! l = getEffect (l (Indexed $ \i a -> Effect (return [(i, a)])) s)
{-# INLINE (^@!!) #-}

-- | Perform an 'IndexedMonadicFold' and collect the 'Leftmost' result.
--
-- /Note:/ this still causes all effects for all elements.
(^@!?) :: Monad m => s -> IndexedActing i m (Leftmost (i, a)) s t a b -> m (Maybe (i, a))
a ^@!?  l = liftM getLeftmost .# getEffect $ l (Indexed $ \i -> Effect #. return . LLeaf . (,) i) a
{-# INLINE (^@!?) #-}

-- | Construct an 'IndexedAction' from a monadic side-effect.
iact :: Monad m => (s -> m (i, a)) -> IndexedAction i m s a
iact smia iafb s = effective $ do
  (i, a) <- smia s
  ineffective (indexed iafb i a)
{-# INLINE iact #-}