content: {-# LANGUAGE Rank2Types, CPP #-}
  {-# LANGUAGE NoPolyKinds #-}
  
  {-| Provides all lens-related functions.
  
  -}
  
  {-
  
  Copyright (C) 2014 Google Inc.
  All rights reserved.
  
  Redistribution and use in source and binary forms, with or without
  modification, are permitted provided that the following conditions are
  met:
  
  1. Redistributions of source code must retain the above copyright notice,
  this list of conditions and the following disclaimer.
  
  2. Redistributions in binary form must reproduce the above copyright
  notice, this list of conditions and the following disclaimer in the
  documentation and/or other materials provided with the distribution.
  
  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
  IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
  TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
  CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
  LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
  -}
  
  module Ganeti.Lens
    ( module Control.Lens
    , lensWith
    , makeCustomLenses
    , makeCustomLenses'
    , traverseOf2
    , mapMOf2
    , atSet
    ) where
  
  import Control.Applicative (WrappedMonad(..))
  import Control.Lens
  import Control.Monad
  import Data.Functor.Compose (Compose(..))
  import qualified Data.Set as S
  import Language.Haskell.TH
  
  -- | Creates an optimized lens where the setter also gets the original value
  -- from the getter.
  lensWith :: (s -> a) -> (s -> a -> b -> t) -> Lens s t a b
  lensWith sa sbt f s = uncurry (sbt s) <$> (\a -> fmap ((,) a) (f a)) (sa s)
  
  lensFieldName :: String -> String
  lensFieldName = (++ "L")
  
  -- | Internal helper method for constructing partial set of lenses.
  makeCustomLensesFiltered :: (String -> Bool) -> Name -> Q [Dec]
  makeCustomLensesFiltered f = makeLensesWith customRules
    where
      customRules :: LensRules
      customRules = set lensField nameFun lensRules
  #if MIN_VERSION_lens(4,5,0)
      nameFun :: Name -> [Name] -> Name -> [DefName]
      nameFun _ _ = liftM (TopName . mkName) . nameFilter . nameBase
  #elif MIN_VERSION_lens(4,4,0)
      nameFun :: [Name] -> Name -> [DefName]
      nameFun _ = liftM (TopName . mkName) . nameFilter . nameBase
  #else
      nameFun :: String -> Maybe String
      nameFun = nameFilter
  #endif
      nameFilter :: (MonadPlus m) => String -> m String
      nameFilter = liftM lensFieldName . mfilter f . return
  
  -- | Create lenses for all fields of a given data type.
  makeCustomLenses :: Name -> Q [Dec]
  makeCustomLenses = makeCustomLensesFiltered (const True)
  
  -- | Create lenses for some fields of a given data type.
  makeCustomLenses' :: Name -> [Name] -> Q [Dec]
  makeCustomLenses' name lst = makeCustomLensesFiltered f name
    where
      allowed = S.fromList . map nameBase $ lst
      f = flip S.member allowed
  
  -- | Traverses over a composition of two functors.
  -- Most often the @g@ functor is @(,) r@ and 'traverseOf2' is used to
  -- traverse an effectful computation that also returns an additional output
  -- value.
  traverseOf2 :: LensLike (Compose f g) s t a b
              -> (a -> f (g b)) -> s -> f (g t)
  traverseOf2 k f = getCompose . traverseOf k (Compose . f)
  
  -- | Traverses over a composition of a monad and a functor.
  -- See 'traverseOf2'.
  mapMOf2 :: LensLike (Compose (WrappedMonad m) g) s t a b
          -> (a -> m (g b)) -> s -> m (g t)
  mapMOf2 k f = unwrapMonad . traverseOf2 k (WrapMonad . f)
  
  -- | A helper lens over sets.
  -- While a similar lens exists in the package (as @Lens' Set (Maybe ())@),
  -- it's available only in most recent versions.
  -- And using @Bool@ instead of @Maybe ()@ is more convenient.
  atSet :: (Ord a) => a -> Lens' (S.Set a) Bool
  atSet k = lensWith (S.member k) f
    where
      f s True False = S.delete k s
      f s False True = S.insert k s
      f s _ _        = s
  