    {-# LANGUAGE CPP #-}
    {-# LANGUAGE TypeFamilies #-}
    {-# LANGUAGE FlexibleInstances #-}
    {-# LANGUAGE UndecidableInstances #-}
    {-# LANGUAGE MultiParamTypeClasses #-}
    {-# LANGUAGE FunctionalDependencies #-}
    {-# OPTIONS_GHC -fno-warn-warnings-deprecations #-}

    #ifndef MIN_VERSION_mtl
    #define MIN_VERSION_mtl(x,y,z) 1
    #endif

    #ifndef MIN_VERSION_profunctors
    #define MIN_VERSION_profunctors(x,y,z) 1
    #endif

    #if __GLASGOW_HASKELL__ < 708 || !(MIN_VERSION_profunctors(4,4,0))
    {-# LANGUAGE Trustworthy #-}
    #endif

    -------------------------------------------------------------------------------
    -- |
    -- Module      :  Control.Lens.Zoom
    -- Copyright   :  (C) 2012-15 Edward Kmett
    -- License     :  BSD-style (see the file LICENSE)
    -- Maintainer  :  Edward Kmett <ekmett@gmail.com>
    -- Stability   :  provisional
    -- Portability :  Rank2Types
    --
    -------------------------------------------------------------------------------
    module Control.Lens.Zoom
      ( Magnify(..)
      , Zoom(..)
      ) where

    import Control.Lens.Getter
    import Control.Lens.Internal.Zoom
    import Control.Lens.Type
    import Control.Monad
    import Control.Monad.Reader as Reader
    import Control.Monad.State as State
    import Control.Monad.Trans.State.Lazy as Lazy
    import Control.Monad.Trans.State.Strict as Strict
    import Control.Monad.Trans.Writer.Lazy as Lazy
    import Control.Monad.Trans.Writer.Strict as Strict
    import Control.Monad.Trans.RWS.Lazy as Lazy
    import Control.Monad.Trans.RWS.Strict as Strict
    import Control.Monad.Trans.Error
    import Control.Monad.Trans.Except
    import Control.Monad.Trans.List
    import Control.Monad.Trans.Identity
    import Control.Monad.Trans.Maybe
    import Data.Monoid
    import Data.Profunctor.Unsafe
    import Prelude

    -- $setup
    -- >>> import Control.Lens
    -- >>> import Control.Monad.State
    -- >>> import Data.Map as Map
    -- >>> import Debug.SimpleReflect.Expr as Expr
    -- >>> import Debug.SimpleReflect.Vars as Vars
    -- >>> let f :: Expr -> Expr; f = Vars.f
    -- >>> let g :: Expr -> Expr; g = Vars.g
    -- >>> let h :: Expr -> Expr -> Expr; h = Vars.h

    -- Chosen so that they have lower fixity than ('%='), and to match ('<~').
    infixr 2 `zoom`, `magnify`

    -- | This class allows us to use 'zoom' in, changing the 'State' supplied by
    -- many different 'Control.Monad.Monad' transformers, potentially quite
    -- deep in a 'Monad' transformer stack.
    class (Zoomed m ~ Zoomed n, MonadState s m, MonadState t n) => Zoom m n s t | m -> s, n -> t, m t -> n, n s -> m where
      -- | Run a monadic action in a larger 'State' than it was defined in,
      -- using a 'Lens'' or 'Control.Lens.Traversal.Traversal''.
      --
      -- This is commonly used to lift actions in a simpler 'State'
      -- 'Monad' into a 'State' 'Monad' with a larger 'State' type.
      --
      -- When applied to a 'Control.Lens.Traversal.Traversal'' over
      -- multiple values, the actions for each target are executed sequentially
      -- and the results are aggregated.
      --
      -- This can be used to edit pretty much any 'Monad' transformer stack with a 'State' in it!
      --
      -- >>> flip State.evalState (a,b) $ zoom _1 $ use id
      -- a
      --
      -- >>> flip State.execState (a,b) $ zoom _1 $ id .= c
      -- (c,b)
      --
      -- >>> flip State.execState [(a,b),(c,d)] $ zoom traverse $ _2 %= f
      -- [(a,f b),(c,f d)]
      --
      -- >>> flip State.runState [(a,b),(c,d)] $ zoom traverse $ _2 <%= f
      -- (f b <> f d <> mempty,[(a,f b),(c,f d)])
      --
      -- >>> flip State.evalState (a,b) $ zoom both (use id)
      -- a <> b
      --
      -- @
      -- 'zoom' :: 'Monad' m             => 'Lens'' s t      -> 'StateT' t m a -> 'StateT' s m a
      -- 'zoom' :: ('Monad' m, 'Monoid' c) => 'Control.Lens.Traversal.Traversal'' s t -> 'StateT' t m c -> 'StateT' s m c
      -- 'zoom' :: ('Monad' m, 'Monoid' w)             => 'Lens'' s t      -> 'RWST' r w t m c -> 'RWST' r w s m c
      -- 'zoom' :: ('Monad' m, 'Monoid' w, 'Monoid' c) => 'Control.Lens.Traversal.Traversal'' s t -> 'RWST' r w t m c -> 'RWST' r w s m c
      -- 'zoom' :: ('Monad' m, 'Monoid' w, 'Error' e)  => 'Lens'' s t      -> 'ErrorT' e ('RWST' r w t m) c -> 'ErrorT' e ('RWST' r w s m) c
      -- 'zoom' :: ('Monad' m, 'Monoid' w, 'Monoid' c, 'Error' e) => 'Control.Lens.Traversal.Traversal'' s t -> 'ErrorT' e ('RWST' r w t m) c -> 'ErrorT' e ('RWST' r w s m) c
      -- ...
      -- @
      zoom :: LensLike' (Zoomed m c) t s -> m c -> n c

    instance Monad z => Zoom (Strict.StateT s z) (Strict.StateT t z) s t where
      zoom l (Strict.StateT m) = Strict.StateT $ unfocusing #. l (Focusing #. m)
      {-# INLINE zoom #-}

    instance Monad z => Zoom (Lazy.StateT s z) (Lazy.StateT t z) s t where
      zoom l (Lazy.StateT m) = Lazy.StateT $ unfocusing #. l (Focusing #. m)
      {-# INLINE zoom #-}

    instance Zoom m n s t => Zoom (ReaderT e m) (ReaderT e n) s t where
      zoom l (ReaderT m) = ReaderT (zoom l . m)
      {-# INLINE zoom #-}

    instance Zoom m n s t => Zoom (IdentityT m) (IdentityT n) s t where
      zoom l (IdentityT m) = IdentityT (zoom l m)
      {-# INLINE zoom #-}

    instance (Monoid w, Monad z) => Zoom (Strict.RWST r w s z) (Strict.RWST r w t z) s t where
      zoom l (Strict.RWST m) = Strict.RWST $ \r -> unfocusingWith #. l (FocusingWith #. m r)
      {-# INLINE zoom #-}

    instance (Monoid w, Monad z) => Zoom (Lazy.RWST r w s z) (Lazy.RWST r w t z) s t where
      zoom l (Lazy.RWST m) = Lazy.RWST $ \r -> unfocusingWith #. l (FocusingWith #. m r)
      {-# INLINE zoom #-}

    instance (Monoid w, Zoom m n s t) => Zoom (Strict.WriterT w m) (Strict.WriterT w n) s t where
      zoom l = Strict.WriterT . zoom (\afb -> unfocusingPlus #. l (FocusingPlus #. afb)) . Strict.runWriterT
      {-# INLINE zoom #-}

    instance (Monoid w, Zoom m n s t) => Zoom (Lazy.WriterT w m) (Lazy.WriterT w n) s t where
      zoom l = Lazy.WriterT . zoom (\afb -> unfocusingPlus #. l (FocusingPlus #. afb)) . Lazy.runWriterT
      {-# INLINE zoom #-}

    instance Zoom m n s t => Zoom (ListT m) (ListT n) s t where
      zoom l = ListT . zoom (\afb -> unfocusingOn . l (FocusingOn . afb)) . runListT
      {-# INLINE zoom #-}

    instance Zoom m n s t => Zoom (MaybeT m) (MaybeT n) s t where
      zoom l = MaybeT . liftM getMay . zoom (\afb -> unfocusingMay #. l (FocusingMay #. afb)) . liftM May . runMaybeT
      {-# INLINE zoom #-}

    instance (Error e, Zoom m n s t) => Zoom (ErrorT e m) (ErrorT e n) s t where
      zoom l = ErrorT . liftM getErr . zoom (\afb -> unfocusingErr #. l (FocusingErr #. afb)) . liftM Err . runErrorT
      {-# INLINE zoom #-}

    instance Zoom m n s t => Zoom (ExceptT e m) (ExceptT e n) s t where
      zoom l = ExceptT . liftM getErr . zoom (\afb -> unfocusingErr #. l (FocusingErr #. afb)) . liftM Err . runExceptT
      {-# INLINE zoom #-}

    -- TODO: instance Zoom m m a a => Zoom (ContT r m) (ContT r m) a a where

    -- | This class allows us to use 'magnify' part of the environment, changing the environment supplied by
    -- many different 'Monad' transformers. Unlike 'zoom' this can change the environment of a deeply nested 'Monad' transformer.
    --
    -- Also, unlike 'zoom', this can be used with any valid 'Getter', but cannot be used with a 'Traversal' or 'Fold'.
    class (Magnified m ~ Magnified n, MonadReader b m, MonadReader a n) => Magnify m n b a | m -> b, n -> a, m a -> n, n b -> m where
      -- | Run a monadic action in a larger environment than it was defined in, using a 'Getter'.
      --
      -- This acts like 'Control.Monad.Reader.Class.local', but can in many cases change the type of the environment as well.
      --
      -- This is commonly used to lift actions in a simpler 'Reader' 'Monad' into a 'Monad' with a larger environment type.
      --
      -- This can be used to edit pretty much any 'Monad' transformer stack with an environment in it:
      --
      -- >>> (1,2) & magnify _2 (+1)
      -- 3
      --
      -- >>> flip Reader.runReader (1,2) $ magnify _1 Reader.ask
      -- 1
      --
      -- >>> flip Reader.runReader (1,2,[10..20]) $ magnify (_3._tail) Reader.ask
      -- [11,12,13,14,15,16,17,18,19,20]
      --
      -- @
      -- 'magnify' :: 'Getter' s a -> (a -> r) -> s -> r
      -- 'magnify' :: 'Monoid' r => 'Fold' s a   -> (a -> r) -> s -> r
      -- @
      --
      -- @
      -- 'magnify' :: 'Monoid' w                 => 'Getter' s t -> 'RWS' t w st c -> 'RWS' s w st c
      -- 'magnify' :: ('Monoid' w, 'Monoid' c) => 'Fold' s a   -> 'RWS' a w st c -> 'RWS' s w st c
      -- ...
      -- @
      magnify :: LensLike' (Magnified m c) a b -> m c -> n c

    instance Monad m => Magnify (ReaderT b m) (ReaderT a m) b a where
      magnify l (ReaderT m) = ReaderT $ getEffect #. l (Effect #. m)
      {-# INLINE magnify #-}

    -- | @
    -- 'magnify' = 'views'
    -- @
    instance Magnify ((->) b) ((->) a) b a where
      magnify = views
      {-# INLINE magnify #-}

    instance (Monad m, Monoid w) => Magnify (Strict.RWST b w s m) (Strict.RWST a w s m) b a where
      magnify l (Strict.RWST m) = Strict.RWST $ getEffectRWS #. l (EffectRWS #. m)
      {-# INLINE magnify #-}

    instance (Monad m, Monoid w) => Magnify (Lazy.RWST b w s m) (Lazy.RWST a w s m) b a where
      magnify l (Lazy.RWST m) = Lazy.RWST $ getEffectRWS #. l (EffectRWS #. m)
      {-# INLINE magnify #-}

    instance Magnify m n b a => Magnify (IdentityT m) (IdentityT n) b a where
      magnify l (IdentityT m) = IdentityT (magnify l m)
      {-# INLINE magnify #-}