Optics.hs

module Hedgehog.Optics
  (
    wellFormedPrism, wellFormedLens, wellFormedIso,
    prismExample,
  )
  where

import Control.Monad (Monad (return))
import Data.Either (Either (Left, Right))
import Data.Eq (Eq)
import Data.Function ((.))
import Data.Maybe (Maybe (Just))
import Hedgehog (Gen, PropertyT, annotate, forAll, (===))
import Optics.AffineFold (preview)
import Optics.AffineTraversal (matching)
import Optics.Getter (view)
import Optics.Iso (Iso')
import Optics.Lens (Lens')
import Optics.Prism (Prism')
import Optics.Review (review)
import Optics.Setter (set)
import Text.Show (Show)

{-| Checks whether a prism respects the well-formedness
    laws given in "Optics.Prism" -}
wellFormedPrism :: Monad m =>
    (Show large, Eq large) => (Show small, Eq small) =>
    Gen large -> Gen small
    -> Prism' large small -- ^ Prism signifying that the @small@ type
                          --   is a subset of the @large@ type -}
    -> PropertyT m ()
wellFormedPrism genLarge genSmall o = do
    getSetPrismLaw genLarge o
    setGetPrismLaw genSmall o

getSetPrismLaw :: Monad m =>
    (Show large, Eq large) => (Show small, Eq small) =>
    Gen large -> Prism' large small -> PropertyT m ()
getSetPrismLaw genLarge o = do
    large <- forAll genLarge
    case matching o large of
        Right small -> do
            annotate "The get-set law must hold for a Prism"
            review o small === large
        Left _ -> return ()

setGetPrismLaw :: Monad m =>
    (Show large, Eq large) => (Show small, Eq small) =>
    Gen small -> Prism' large small -> PropertyT m ()
setGetPrismLaw genSmall o = do
    small <- forAll genSmall
    annotate "The set-get law must hold for a Prism"
    matching o (review o small) === Right small

{-| Checks whether a lens respects the well-formedness
    laws given in "Optics.Lens" -}
wellFormedLens :: Monad m =>
    (Show large, Eq large) => (Show small, Eq small) =>
    Gen large -> Gen small
    -> Lens' large small -- ^ Lens signifying that the @small@ type is
                         --   a constituent part of the @large@ type
    -> PropertyT m ()
wellFormedLens genLarge genSmall o = do
    getPutLensLaw genLarge genSmall o
    putGetLensLaw genLarge o
    putPutLensLaw genLarge genSmall o

getPutLensLaw :: Monad m =>
    (Show large, Eq large) => (Show small, Eq small) =>
    Gen large -> Gen small -> Lens' large small
    -> PropertyT m ()
getPutLensLaw genLarge genSmall o = do
    large <- forAll genLarge
    small <- forAll genSmall
    annotate "The set-get law must hold for a Lens"
    view o (set o small large) === small

putGetLensLaw :: Monad m =>
    (Show large, Eq large) => (Show small, Eq small) =>
    Gen large -> Lens' large small -> PropertyT m ()
putGetLensLaw genLarge o = do
    large <- forAll genLarge
    annotate "The get-set law must hold for a Lens"
    set o (view o large) large === large

putPutLensLaw :: Monad m =>
    (Show large, Eq large) => (Show small, Eq small) =>
    Gen large -> Gen small -> Lens' large small
    -> PropertyT m ()
putPutLensLaw genLarge genSmall o = do
    large <- forAll genLarge
    small1 <- forAll genSmall
    small2 <- forAll genSmall
    annotate "The set-set law must hold for a Lens"
    set o small2 (set o small1 large) === set o small2 large

{-| Checks whether an isomorphism respects the
    well-formedness laws given in "Optics.Iso" -}
wellFormedIso :: Monad m =>
    (Show a, Eq a) => (Show b, Eq b) =>
    Gen a -> Gen b
    -> Iso' a b -- ^ Isomorphism signifying that types
                --   @a@ and @b@ are basically the same thing
    -> PropertyT m ()
wellFormedIso genA genB o = do
    setGetIsoLaw genB o
    getSetIsoLaw genA o

setGetIsoLaw :: Monad m =>
    (Show a, Eq a) => (Show b, Eq b) =>
    Gen b -> Iso' a b -> PropertyT m ()
setGetIsoLaw genB o = do
    b <- forAll genB
    annotate "The set-get law must hold for an Iso"
    (view o . review o) b === b

getSetIsoLaw :: Monad m =>
    (Show a, Eq a) => (Show b, Eq b) =>
    Gen a -> Iso' a b -> PropertyT m ()
getSetIsoLaw genA o = do
    a <- forAll genA
    annotate "The get-set law must hold for an Iso"
    (review o . view o) a === a

{-| Assert that a prism matches for a particular set of values

A 'review' of the @small@ value should produce the @large@ value, and
a 'preview' of the @large@ value should produce the @small@ value. -}
prismExample :: Monad m =>
    (Show large, Eq large) => (Show small, Eq small) =>
    Prism' large small -- ^ Prism signifying that the @small@
                       --   type is a subset of the @large@ type
    -> large
    -> small
    -> PropertyT m ()

prismExample o large small = do
    review o small === large
    preview o large === Just small