Pager.hs

{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE RankNTypes        #-}

-- |
-- Module      : Network.AWS.Pager
-- Copyright   : (c) 2013-2017 Brendan Hay
-- License     : Mozilla Public License, v. 2.0.
-- Maintainer  : Brendan Hay <brendan.g.hay+amazonka@gmail.com>
-- Stability   : provisional
-- Portability : non-portable (GHC extensions)
--
module Network.AWS.Pager
    ( AWSPager     (..)
    , AWSTruncated (..)
    , stop
    , choice
    ) where

import           Control.Applicative
import           Data.HashMap.Strict   (HashMap)
import qualified Data.HashMap.Strict   as Map
import           Data.List.NonEmpty    (NonEmpty)
import           Data.Maybe            (isJust, fromMaybe)
import           Data.Text             (Text)
import           Network.AWS.Data.Text (ToText (..))
import           Network.AWS.Lens      (Getter, to)
import           Network.AWS.Types

-- | Specify how an 'AWSRequest' and it's associated 'Rs' response can
-- generate a subsequent request, if available.
class AWSRequest a => AWSPager a where
    page :: a -> Rs a -> Maybe a

-- | Generalise IsTruncated and other optional/required
-- response pagination fields.
class AWSTruncated a where
    truncated :: a -> Bool

instance AWSTruncated Bool where
    truncated = id

instance AWSTruncated [a] where
    truncated = not . null

instance AWSTruncated (HashMap k v) where
    truncated = not . Map.null

instance {-# OVERLAPPABLE #-} AWSTruncated (Maybe a) where
    truncated = isJust

instance {-# OVERLAPS #-} AWSTruncated (Maybe Bool) where
    truncated = fromMaybe False

stop :: AWSTruncated a => a -> Bool
stop = not . truncated

choice :: (Alternative f, ToText a, ToText b)
       => (s -> f a)
       -> (s -> f b)
       -> Getter s (f Text)
choice f g = to $ \x -> (toText <$> f x) <|> (toText <$> g x)