{-# LANGUAGE PackageImports #-}
{-# LANGUAGE AllowAmbiguousTypes       #-}
{-# LANGUAGE DataKinds                 #-}
{-# LANGUAGE FlexibleContexts          #-}
{-# LANGUAGE FlexibleInstances         #-}
{-# LANGUAGE MultiParamTypeClasses     #-}
{-# LANGUAGE NoMonomorphismRestriction #-}
{-# LANGUAGE PolyKinds                 #-}
{-# LANGUAGE Rank2Types                #-}
{-# LANGUAGE ScopedTypeVariables       #-}
{-# LANGUAGE TypeApplications          #-}
{-# LANGUAGE TypeFamilies              #-}
{-# LANGUAGE TypeOperators             #-}
{-# LANGUAGE UndecidableInstances      #-}

-----------------------------------------------------------------------------
-- |
-- Module      :  Data.Generics.Product.Subtype
-- Copyright   :  (C) 2020 Csongor Kiss
-- License     :  BSD3
-- Maintainer  :  Csongor Kiss <kiss.csongor.kiss@gmail.com>
-- Stability   :  experimental
-- Portability :  non-portable
--
-- Structural subtype relationships between product types.
--
-----------------------------------------------------------------------------

module Data.Generics.Product.Subtype
  ( -- *Lenses
    --
    -- $setup
    Subtype (..)
  ) where


import "this" Data.Generics.Internal.VL.Lens as VL

import "generic-lens-core" Data.Generics.Internal.Void
import qualified "generic-lens-core" Data.Generics.Product.Internal.Subtype as Core

import GHC.Generics (Generic (to, from) )

-- $setup
-- == /Running example:/
--
-- >>> :set -XTypeApplications
-- >>> :set -XDataKinds
-- >>> :set -XDeriveGeneric
-- >>> :set -XDuplicateRecordFields
-- >>> import GHC.Generics
-- >>> :m +Data.Generics.Internal.VL.Lens
-- >>> :{
-- data Human = Human
--   { name    :: String
--   , age     :: Int
--   , address :: String
--   }
--   deriving (Generic, Show)
-- data Animal = Animal
--   { name    :: String
--   , age     :: Int
--   }
--   deriving (Generic, Show)
-- human :: Human
-- human = Human "Tunyasz" 50 "London"
-- :}

-- |Structural subtype relationship
--
-- @sub@ is a (structural) `subtype' of @sup@, if its fields are a subset of
-- those of @sup@.
--
class Subtype sup sub where
  -- |Structural subtype lens. Given a subtype relationship @sub :< sup@,
  --  we can focus on the @sub@ structure of @sup@.
  --
  -- >>> human ^. super @Animal
  -- Animal {name = "Tunyasz", age = 50}
  --
  -- >>> set (super @Animal) (Animal "dog" 10) human
  -- Human {name = "dog", age = 10, address = "London"}
  super  :: VL.Lens sub sub sup sup
  super
    = forall s a b t. (s -> a) -> (s -> b -> t) -> Lens s t a b
VL.lens forall sup sub. Subtype sup sub => sub -> sup
upcast (forall a b c. (a -> b -> c) -> b -> a -> c
flip forall sup sub. Subtype sup sub => sup -> sub -> sub
smash)
  {-# INLINE super #-}

  -- |Cast the more specific subtype to the more general supertype
  --
  -- >>> upcast human :: Animal
  -- Animal {name = "Tunyasz", age = 50}
  --
  -- >>> upcast (upcast human :: Animal) :: Human
  -- ...
  -- ... The type 'Animal' is not a subtype of 'Human'.
  -- ... The following fields are missing from 'Animal':
  -- ... address
  -- ...
  upcast :: sub -> sup
  upcast sub
s = sub
s forall s a. s -> ((a -> Const a a) -> s -> Const a s) -> a
^. forall sup sub. Subtype sup sub => Lens sub sub sup sup
super @sup
  {-# INLINE upcast #-}

  -- |Plug a smaller structure into a larger one
  --
  -- >>> smash (Animal "dog" 10) human
  -- Human {name = "dog", age = 10, address = "London"}
  smash  :: sup -> sub -> sub
  smash = forall s t a b. Lens s t a b -> b -> s -> t
VL.set (forall sup sub. Subtype sup sub => Lens sub sub sup sup
super @sup)
  {-# INLINE smash #-}

  {-# MINIMAL super | smash, upcast #-}

instance Core.Context a b => Subtype b a where
    smash :: b -> a -> a
smash b
p a
b = forall a x. Generic a => Rep a x -> a
to forall a b. (a -> b) -> a -> b
$ forall {k} (sub :: k -> *) (sup :: k -> *) (p :: k).
GSmash sub sup =>
sup p -> sub p -> sub p
Core.gsmash (forall a x. Generic a => a -> Rep a x
from b
p) (forall a x. Generic a => a -> Rep a x
from a
b)
    upcast :: a -> b
upcast    = forall a x. Generic a => Rep a x -> a
to forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall (sub :: * -> *) (sup :: * -> *) p.
GUpcast sub sup =>
sub p -> sup p
Core.gupcast forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall a x. Generic a => a -> Rep a x
from

instance {-# OVERLAPPING #-} Subtype a a where
  super :: Lens a a a a
super = forall a. a -> a
id

-- | Uncluttering type signatures (see 'Void')
--
-- >>> :t +d super
-- super
--   :: (Subtype sup sub, Functor f) => (sup -> f sup) -> sub -> f sub
instance {-# OVERLAPPING #-} Subtype a Void where
  super :: Lens Void Void a a
super = forall a. HasCallStack => a
undefined

-- | Uncluttering type signatures (see 'Void')
--
-- >>> :t +d super @Int
-- super @Int
--   :: (Subtype Int sub, Functor f) => (Int -> f Int) -> sub -> f sub
instance {-# OVERLAPPING #-} Subtype Void a where
  super :: Lens a a Void Void
super = forall a. HasCallStack => a
undefined