{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE Safe          #-}

module Valida.Validator
    ( Selector
    , Validator (..)
    ) where

import Data.List.NonEmpty (NonEmpty)
import Data.Typeable      (Typeable)

import GHC.Generics (Generic)

import Valida.Validation (Validation (..))

-- | Convenience alias for functions that "select" a record field.

type Selector a b = a -> b

-- | An applicative validator. Validates a predicate on an input when run and returns the 'Validation' result.

newtype Validator e inp a = Validator { Validator e inp a -> inp -> Validation e a
runValidator :: inp -> Validation e a }
  deriving (Typeable, (forall x. Validator e inp a -> Rep (Validator e inp a) x)
-> (forall x. Rep (Validator e inp a) x -> Validator e inp a)
-> Generic (Validator e inp a)
forall x. Rep (Validator e inp a) x -> Validator e inp a
forall x. Validator e inp a -> Rep (Validator e inp a) x
forall a.
(forall x. a -> Rep a x) -> (forall x. Rep a x -> a) -> Generic a
forall e inp a x. Rep (Validator e inp a) x -> Validator e inp a
forall e inp a x. Validator e inp a -> Rep (Validator e inp a) x
$cto :: forall e inp a x. Rep (Validator e inp a) x -> Validator e inp a
$cfrom :: forall e inp a x. Validator e inp a -> Rep (Validator e inp a) x
Generic)

{- |

[@fmap@] 'fmap' maps given function over the 'Validation' result by re-using 'fmap' on it.

__Examples__

>>> runValidator (fmap (+1) (validate $ failureIf (==2) "IsTwo")) 3
Success 4
>>> runValidator (fmap (+1) (validate $ failureIf (==2) "IsTwo")) 2
Failure ("IsTwo" :| [])
-}
instance Functor (Validator e inp) where
    fmap :: (a -> b) -> Validator e inp a -> Validator e inp b
fmap a -> b
f (Validator inp -> Validation e a
v) = (inp -> Validation e b) -> Validator e inp b
forall e inp a. (inp -> Validation e a) -> Validator e inp a
Validator ((inp -> Validation e b) -> Validator e inp b)
-> (inp -> Validation e b) -> Validator e inp b
forall a b. (a -> b) -> a -> b
$ (a -> b) -> Validation e a -> Validation e b
forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap a -> b
f (Validation e a -> Validation e b)
-> (inp -> Validation e a) -> inp -> Validation e b
forall b c a. (b -> c) -> (a -> b) -> a -> c
. inp -> Validation e a
v

{- |

[@pure@] 'pure' creates a 'Validator' that always yields given value wrapped in 'Success', ignoring its input.

[@(\<*\>)@] '(<*>)' runs 2 validators to obtain the 2 'Validation' results and combines them with '(<*>)'.
This can be understood as-

    @
    (Validator ff) \<*\> (Validator v) = Validator (\\inp -> ff inp \<*\> v inp)
    @

    i.e Run __ff__ and __v__ on the input, and compose the 'Validation' results with '(<*>)'.

__Examples__

>>> runValidator (pure 5) 42
Success 5
>>> let v1 = validate (failureIf (==2) "IsTwo")
>>> let v2 = validate (failureIf even "IsEven")
>>> runValidator (const <$> v1 <*> v2) 5
Success 5
>>> runValidator (const <$> v1 <*> v2) 4
Failure ("IsEven" :| [])
>>> runValidator (const <$> v1 <*> v2) 2
Failure ("IsTwo" :| ["IsEven"])
-}
instance Semigroup e => Applicative (Validator e inp) where
    {-# SPECIALIZE instance Applicative (Validator (NonEmpty err) inp) #-}
    {-# SPECIALIZE instance Applicative (Validator () inp) #-}
    {-# SPECIALIZE instance Applicative (Validator [err] inp) #-}
    pure :: a -> Validator e inp a
pure = (inp -> Validation e a) -> Validator e inp a
forall e inp a. (inp -> Validation e a) -> Validator e inp a
Validator ((inp -> Validation e a) -> Validator e inp a)
-> (a -> inp -> Validation e a) -> a -> Validator e inp a
forall b c a. (b -> c) -> (a -> b) -> a -> c
. Validation e a -> inp -> Validation e a
forall a b. a -> b -> a
const (Validation e a -> inp -> Validation e a)
-> (a -> Validation e a) -> a -> inp -> Validation e a
forall b c a. (b -> c) -> (a -> b) -> a -> c
. a -> Validation e a
forall e a. a -> Validation e a
Success
    {-# INLINEABLE pure #-}
    Validator inp -> Validation e (a -> b)
ff <*> :: Validator e inp (a -> b) -> Validator e inp a -> Validator e inp b
<*> Validator inp -> Validation e a
v = (inp -> Validation e b) -> Validator e inp b
forall e inp a. (inp -> Validation e a) -> Validator e inp a
Validator ((inp -> Validation e b) -> Validator e inp b)
-> (inp -> Validation e b) -> Validator e inp b
forall a b. (a -> b) -> a -> b
$ \inp
x -> inp -> Validation e (a -> b)
ff inp
x Validation e (a -> b) -> Validation e a -> Validation e b
forall (f :: * -> *) a b. Applicative f => f (a -> b) -> f a -> f b
<*> inp -> Validation e a
v inp
x
    {-# INLINEABLE (<*>) #-}

{- |

[@(<>)@] '(<>)' applies input over both validator functions, and combines the 'Validation' results using '(<>)'.

__Examples__

This essentially reuses the '(<>)' impl of 'Validation'.
i.e Returns the first 'Success'. But also accumulates 'Failure's.

>>> let v1 = validate (failureIf (==2) "IsTwo")
>>> let v2 = validate (failureIf even "IsEven")
>>> runValidator (v1 <> v2) 5
Success 5
>>> runValidator (v1 <> v2) 4
Success 4
>>> runValidator (v1 <> v2) 2
Failure ("IsTwo" :| ["IsEven"])
-}
instance Semigroup e => Semigroup (Validator e inp a) where
    {-# SPECIALIZE instance Semigroup (Validator (NonEmpty err) inp a) #-}
    {-# SPECIALIZE instance Semigroup (Validator () inp a) #-}
    {-# SPECIALIZE instance Semigroup (Validator [err] inp a) #-}
    Validator inp -> Validation e a
f <> :: Validator e inp a -> Validator e inp a -> Validator e inp a
<> Validator inp -> Validation e a
g = (inp -> Validation e a) -> Validator e inp a
forall e inp a. (inp -> Validation e a) -> Validator e inp a
Validator ((inp -> Validation e a) -> Validator e inp a)
-> (inp -> Validation e a) -> Validator e inp a
forall a b. (a -> b) -> a -> b
$ inp -> Validation e a
f (inp -> Validation e a)
-> (inp -> Validation e a) -> inp -> Validation e a
forall a. Semigroup a => a -> a -> a
<> inp -> Validation e a
g
    {-# INLINEABLE (<>) #-}