{-# LANGUAGE CPP #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE Rank2Types #-}
{-# LANGUAGE KindSignatures #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE UndecidableInstances #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE MultiParamTypeClasses #-}
#ifdef TRUSTWORTHY
{-# LANGUAGE Trustworthy #-}
#endif
#if __GLASGOW_HASKELL__ >= 707
{-# LANGUAGE RoleAnnotations #-}
#endif
-----------------------------------------------------------------------------
-- |
-- Module      :  Control.Lens.Internal.Magma
-- Copyright   :  (C) 2012-2015 Edward Kmett
-- License     :  BSD-style (see the file LICENSE)
-- Maintainer  :  Edward Kmett <ekmett@gmail.com>
-- Stability   :  experimental
-- Portability :  non-portable
--
----------------------------------------------------------------------------
module Control.Lens.Internal.Magma
  (
  -- * Magma
    Magma(..)
  , runMagma
  -- * Molten
  , Molten(..)
  -- * Mafic
  , Mafic(..)
  , runMafic
  -- * TakingWhile
  , TakingWhile(..)
  , runTakingWhile
  ) where

import Control.Applicative
import Control.Category
import Control.Comonad
import Control.Lens.Internal.Bazaar
import Control.Lens.Internal.Context
import Control.Lens.Internal.Indexed
import Data.Foldable
import Data.Functor.Apply
import Data.Functor.Contravariant
import Data.Monoid
import Data.Profunctor.Rep
import Data.Profunctor.Unsafe
import Data.Traversable
import Prelude hiding ((.),id)

------------------------------------------------------------------------------
-- Magma
------------------------------------------------------------------------------

-- | This provides a way to peek at the internal structure of a
-- 'Control.Lens.Traversal.Traversal' or 'Control.Lens.Traversal.IndexedTraversal'
data Magma i t b a where
  MagmaAp   :: Magma i (x -> y) b a -> Magma i x b a -> Magma i y b a
  MagmaPure :: x -> Magma i x b a
  MagmaFmap :: (x -> y) -> Magma i x b a -> Magma i y b a
  Magma :: i -> a -> Magma i b b a

#if __GLASGOW_HASKELL__ >= 707
-- note the 3rd argument infers as phantom, but that would be unsound
type role Magma representational nominal nominal nominal
#endif

instance Functor (Magma i t b) where
  fmap f (MagmaAp x y)    = MagmaAp (fmap f x) (fmap f y)
  fmap _ (MagmaPure x)    = MagmaPure x
  fmap f (MagmaFmap xy x) = MagmaFmap xy (fmap f x)
  fmap f (Magma i a)  = Magma i (f a)

instance Foldable (Magma i t b) where
  foldMap f (MagmaAp x y)   = foldMap f x `mappend` foldMap f y
  foldMap _ MagmaPure{}     = mempty
  foldMap f (MagmaFmap _ x) = foldMap f x
  foldMap f (Magma _ a) = f a

instance Traversable (Magma i t b) where
  traverse f (MagmaAp x y)    = MagmaAp <$> traverse f x <*> traverse f y
  traverse _ (MagmaPure x)    = pure (MagmaPure x)
  traverse f (MagmaFmap xy x) = MagmaFmap xy <$> traverse f x
  traverse f (Magma i a)  = Magma i <$> f a

instance (Show i, Show a) => Show (Magma i t b a) where
  showsPrec d (MagmaAp x y) = showParen (d > 4) $
    showsPrec 4 x . showString " <*> " . showsPrec 5 y
  showsPrec d (MagmaPure _) = showParen (d > 10) $
    showString "pure .."
  showsPrec d (MagmaFmap _ x) = showParen (d > 4) $
    showString ".. <$> " . showsPrec 5 x
  showsPrec d (Magma i a) = showParen (d > 10) $
    showString "Magma " . showsPrec 11 i . showChar ' ' . showsPrec 11 a

-- | Run a 'Magma' where all the individual leaves have been converted to the
-- expected type
runMagma :: Magma i t a a -> t
runMagma (MagmaAp l r)   = runMagma l (runMagma r)
runMagma (MagmaFmap f r) = f (runMagma r)
runMagma (MagmaPure x)   = x
runMagma (Magma _ a) = a

------------------------------------------------------------------------------
-- Molten
------------------------------------------------------------------------------

-- | This is a a non-reassociating initially encoded version of 'Bazaar'.
newtype Molten i a b t = Molten { runMolten :: Magma i t b a }

instance Functor (Molten i a b) where
  fmap f (Molten xs) = Molten (MagmaFmap f xs)
  {-# INLINE fmap #-}

instance Apply (Molten i a b) where
  (<.>) = (<*>)
  {-# INLINE (<.>) #-}

instance Applicative (Molten i a b) where
  pure  = Molten #. MagmaPure
  {-# INLINE pure #-}
  Molten xs <*> Molten ys = Molten (MagmaAp xs ys)
  {-# INLINE (<*>) #-}

instance Sellable (Indexed i) (Molten i) where
  sell = Indexed (\i -> Molten #. Magma i)
  {-# INLINE sell #-}

instance Bizarre (Indexed i) (Molten i) where
  bazaar f (Molten (MagmaAp x y))   = bazaar f (Molten x) <*> bazaar f (Molten y)
  bazaar f (Molten (MagmaFmap g x)) = g <$> bazaar f (Molten x)
  bazaar _ (Molten (MagmaPure x))   = pure x
  bazaar f (Molten (Magma i a)) = indexed f i a

instance IndexedFunctor (Molten i) where
  ifmap f (Molten xs) = Molten (MagmaFmap f xs)
  {-# INLINE ifmap #-}

instance IndexedComonad (Molten i) where
  iextract (Molten (MagmaAp x y))   = iextract (Molten x) (iextract (Molten y))
  iextract (Molten (MagmaFmap f y)) = f (iextract (Molten y))
  iextract (Molten (MagmaPure x))   = x
  iextract (Molten (Magma _ a)) = a

  iduplicate (Molten (Magma i a)) = Molten #. Magma i <$> Molten (Magma i a)
  iduplicate (Molten (MagmaPure x))   = pure (pure x)
  iduplicate (Molten (MagmaFmap f y)) = iextend (fmap f) (Molten y)
  iduplicate (Molten (MagmaAp x y))   = iextend (<*>) (Molten x) <*> iduplicate (Molten y)

  iextend k (Molten (Magma i a)) = (k .# Molten) . Magma i <$> Molten (Magma i a)
  iextend k (Molten (MagmaPure x))   = pure (k (pure x))
  iextend k (Molten (MagmaFmap f y)) = iextend (k . fmap f) (Molten y)
  iextend k (Molten (MagmaAp x y))   = iextend (\x' y' -> k $ x' <*> y') (Molten x) <*> iduplicate (Molten y)

instance a ~ b => Comonad (Molten i a b) where
  extract   = iextract
  {-# INLINE extract #-}
  extend    = iextend
  {-# INLINE extend #-}
  duplicate = iduplicate
  {-# INLINE duplicate #-}

------------------------------------------------------------------------------
-- Mafic
------------------------------------------------------------------------------

-- | This is used to generate an indexed magma from an unindexed source
--
-- By constructing it this way we avoid infinite reassociations in sums where possible.
data Mafic a b t = Mafic Int (Int -> Magma Int t b a)

-- | Generate a 'Magma' using from a prefix sum.
runMafic :: Mafic a b t -> Magma Int t b a
runMafic (Mafic _ k) = k 0

instance Functor (Mafic a b) where
  fmap f (Mafic w k) = Mafic w (MagmaFmap f . k)
  {-# INLINE fmap #-}

instance Apply (Mafic a b) where
  Mafic wf mf <.> ~(Mafic wa ma) = Mafic (wf + wa) $ \o -> MagmaAp (mf o) (ma (o + wf))
  {-# INLINE (<.>) #-}

instance Applicative (Mafic a b) where
  pure a = Mafic 0 $ \_ -> MagmaPure a
  {-# INLINE pure #-}
  Mafic wf mf <*> ~(Mafic wa ma) = Mafic (wf + wa) $ \o -> MagmaAp (mf o) (ma (o + wf))
  {-# INLINE (<*>) #-}

instance Sellable (->) Mafic where
  sell a = Mafic 1 $ \ i -> Magma i a
  {-# INLINE sell #-}

instance Bizarre (Indexed Int) Mafic where
  bazaar (pafb :: Indexed Int a (f b)) (Mafic _ k) = go (k 0) where
    go :: Applicative f => Magma Int t b a -> f t
    go (MagmaAp x y)   = go x <*> go y
    go (MagmaFmap f x) = f <$> go x
    go (MagmaPure x)   = pure x
    go (Magma i a) = indexed pafb (i :: Int) a
  {-# INLINE bazaar #-}

instance IndexedFunctor Mafic where
  ifmap f (Mafic w k) = Mafic w (MagmaFmap f . k)
  {-# INLINE ifmap #-}

------------------------------------------------------------------------------
-- TakingWhile
------------------------------------------------------------------------------

-- | This is used to generate an indexed magma from an unindexed source
--
-- By constructing it this way we avoid infinite reassociations where possible.
--
-- In @'TakingWhile' p g a b t@, @g@ has a @nominal@ role to avoid exposing an illegal _|_ via 'Contravariant',
-- while the remaining arguments are degraded to a @nominal@ role by the invariants of 'Magma'
data TakingWhile p (g :: * -> *) a b t = TakingWhile Bool t (Bool -> Magma () t b (Corep p a))
#if __GLASGOW_HASKELL__ >= 707
type role TakingWhile nominal nominal nominal nominal nominal
#endif

-- | Generate a 'Magma' with leaves only while the predicate holds from left to right.
runTakingWhile :: TakingWhile p f a b t -> Magma () t b (Corep p a)
runTakingWhile (TakingWhile _ _ k) = k True

instance Functor (TakingWhile p f a b) where
  fmap f (TakingWhile w t k) = let ft = f t in TakingWhile w ft $ \b -> if b then MagmaFmap f (k b) else MagmaPure ft
  {-# INLINE fmap #-}

instance Apply (TakingWhile p f a b) where
  TakingWhile wf tf mf <.> ~(TakingWhile wa ta ma) = TakingWhile (wf && wa) (tf ta) $ \o ->
    if o then MagmaAp (mf True) (ma wf) else MagmaPure (tf ta)
  {-# INLINE (<.>) #-}

instance Applicative (TakingWhile p f a b) where
  pure a = TakingWhile True a $ \_ -> MagmaPure a
  {-# INLINE pure #-}
  TakingWhile wf tf mf <*> ~(TakingWhile wa ta ma) = TakingWhile (wf && wa) (tf ta) $ \o ->
    if o then MagmaAp (mf True) (ma wf) else MagmaPure (tf ta)
  {-# INLINE (<*>) #-}

instance Corepresentable p => Bizarre p (TakingWhile p g) where
  bazaar (pafb :: p a (f b)) ~(TakingWhile _ _ k) = go (k True) where
    go :: Applicative f => Magma () t b (Corep p a) -> f t
    go (MagmaAp x y)  = go x <*> go y
    go (MagmaFmap f x)  = f <$> go x
    go (MagmaPure x)    = pure x
    go (Magma _ wa) = corep pafb wa
  {-# INLINE bazaar #-}

-- This constraint is unused intentionally, it protects TakingWhile
instance Contravariant f => Contravariant (TakingWhile p f a b) where
  contramap _ = (<$) (error "contramap: TakingWhile")
  {-# INLINE contramap #-}

instance IndexedFunctor (TakingWhile p f) where
  ifmap = fmap
  {-# INLINE ifmap #-}
