-- | App-level caching backed by Memcached
--
-- Usage:
--
-- 1. Have a Reader-like monad stack over some @App@
-- 2. Set up that @App@ with 'HasMemcachedClient'
-- 3. Give the value to cache a 'Cachable' instance
-- 4. Use 'caching'
--
-- To avoid 'Cachable', see 'cachingAs' and 'cachingAsJSON'.
--
module Freckle.App.Memcached
  ( Cachable(..)
  , caching
  , cachingAs
  , cachingAsJSON

  -- * Re-exports
  , module Freckle.App.Memcached.Client
  , module Freckle.App.Memcached.CacheKey
  , module Freckle.App.Memcached.CacheTTL
  ) where

import Freckle.App.Prelude

import Blammo.Logging
import Data.Aeson
import Data.ByteString (ByteString)
import qualified Data.ByteString.Lazy as BSL
import Data.Text.Encoding (decodeUtf8With)
import Data.Text.Encoding.Error (lenientDecode)
import Freckle.App.Memcached.CacheKey
import Freckle.App.Memcached.CacheTTL
import Freckle.App.Memcached.Client (HasMemcachedClient(..))
import qualified Freckle.App.Memcached.Client as Memcached
import UnliftIO.Exception (Exception(..), handleAny)

class Cachable a where
  toCachable :: a -> ByteString
  fromCachable :: ByteString -> Either String a

instance Cachable ByteString where
  toCachable :: ByteString -> ByteString
toCachable = forall a. a -> a
id
  fromCachable :: ByteString -> Either String ByteString
fromCachable = forall a b. b -> Either a b
Right

instance Cachable BSL.ByteString where
  toCachable :: ByteString -> ByteString
toCachable = ByteString -> ByteString
BSL.toStrict
  fromCachable :: ByteString -> Either String ByteString
fromCachable = forall a b. b -> Either a b
Right forall b c a. (b -> c) -> (a -> b) -> a -> c
. ByteString -> ByteString
BSL.fromStrict

instance Cachable Text where
  toCachable :: Text -> ByteString
toCachable = Text -> ByteString
encodeUtf8
  fromCachable :: ByteString -> Either String Text
fromCachable = forall a b. b -> Either a b
Right forall b c a. (b -> c) -> (a -> b) -> a -> c
. OnDecodeError -> ByteString -> Text
decodeUtf8With OnDecodeError
lenientDecode

data Cached a
  = CacheFound a
  | CacheNotFound
  | CacheError Text

-- | Memoize an action using Memcached and 'Cachable'
caching
  :: ( MonadUnliftIO m
     , MonadLogger m
     , MonadReader env m
     , HasMemcachedClient env
     , Cachable a
     )
  => CacheKey
  -> CacheTTL
  -> m a
  -> m a
caching :: forall (m :: * -> *) env a.
(MonadUnliftIO m, MonadLogger m, MonadReader env m,
 HasMemcachedClient env, Cachable a) =>
CacheKey -> CacheTTL -> m a -> m a
caching = forall (m :: * -> *) env a.
(MonadUnliftIO m, MonadLogger m, MonadReader env m,
 HasMemcachedClient env) =>
(ByteString -> Either String a)
-> (a -> ByteString) -> CacheKey -> CacheTTL -> m a -> m a
cachingAs forall a. Cachable a => ByteString -> Either String a
fromCachable forall a. Cachable a => a -> ByteString
toCachable

-- | Like 'caching', but with explicit conversion functions
cachingAs
  :: (MonadUnliftIO m, MonadLogger m, MonadReader env m, HasMemcachedClient env)
  => (ByteString -> Either String a)
  -> (a -> ByteString)
  -> CacheKey
  -> CacheTTL
  -> m a
  -> m a
cachingAs :: forall (m :: * -> *) env a.
(MonadUnliftIO m, MonadLogger m, MonadReader env m,
 HasMemcachedClient env) =>
(ByteString -> Either String a)
-> (a -> ByteString) -> CacheKey -> CacheTTL -> m a -> m a
cachingAs ByteString -> Either String a
from a -> ByteString
to CacheKey
key CacheTTL
ttl m a
f = do
  Cached a
result <-
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
fmap (forall b a. b -> (a -> b) -> Maybe a -> b
maybe forall a. Cached a
CacheNotFound (forall a c b. (a -> c) -> (b -> c) -> Either a b -> c
either (forall a. Text -> Cached a
CacheError forall b c a. (b -> c) -> (a -> b) -> a -> c
. String -> Text
pack) forall a. a -> Cached a
CacheFound forall b c a. (b -> c) -> (a -> b) -> a -> c
. ByteString -> Either String a
from))
    forall a b. (a -> b) -> a -> b
$ forall (m :: * -> *) a.
(MonadUnliftIO m, MonadLogger m) =>
a -> Text -> m a -> m a
handleCachingError forall a. Maybe a
Nothing Text
"getting"
    forall a b. (a -> b) -> a -> b
$ forall (m :: * -> *) env.
(MonadIO m, MonadReader env m, HasMemcachedClient env) =>
CacheKey -> m (Maybe ByteString)
Memcached.get CacheKey
key

  case Cached a
result of
    CacheFound a
a -> forall (f :: * -> *) a. Applicative f => a -> f a
pure a
a
    Cached a
CacheNotFound -> m a
store
    CacheError Text
e -> do
      forall (m :: * -> *). MonadLogger m => Text -> Text -> m ()
logCachingError Text
"deserializing" Text
e
      m a
store
 where
  store :: m a
store = do
    a
a <- m a
f
    a
a forall (f :: * -> *) a b. Functor f => a -> f b -> f a
<$ forall (m :: * -> *) a.
(MonadUnliftIO m, MonadLogger m) =>
a -> Text -> m a -> m a
handleCachingError () Text
"setting" (forall (m :: * -> *) env.
(MonadIO m, MonadReader env m, HasMemcachedClient env) =>
CacheKey -> ByteString -> CacheTTL -> m ()
Memcached.set CacheKey
key (a -> ByteString
to a
a) CacheTTL
ttl)

-- | Like 'caching', but de/serializing the value as JSON
cachingAsJSON
  :: ( MonadUnliftIO m
     , MonadLogger m
     , MonadReader env m
     , HasMemcachedClient env
     , FromJSON a
     , ToJSON a
     )
  => CacheKey
  -> CacheTTL
  -> m a
  -> m a
cachingAsJSON :: forall (m :: * -> *) env a.
(MonadUnliftIO m, MonadLogger m, MonadReader env m,
 HasMemcachedClient env, FromJSON a, ToJSON a) =>
CacheKey -> CacheTTL -> m a -> m a
cachingAsJSON = forall (m :: * -> *) env a.
(MonadUnliftIO m, MonadLogger m, MonadReader env m,
 HasMemcachedClient env) =>
(ByteString -> Either String a)
-> (a -> ByteString) -> CacheKey -> CacheTTL -> m a -> m a
cachingAs forall a. FromJSON a => ByteString -> Either String a
eitherDecodeStrict forall a. ToJSON a => a -> ByteString
encodeStrict

handleCachingError
  :: (MonadUnliftIO m, MonadLogger m) => a -> Text -> m a -> m a
handleCachingError :: forall (m :: * -> *) a.
(MonadUnliftIO m, MonadLogger m) =>
a -> Text -> m a -> m a
handleCachingError a
value Text
action = forall (m :: * -> *) a.
MonadUnliftIO m =>
(SomeException -> m a) -> m a -> m a
handleAny forall a b. (a -> b) -> a -> b
$ \SomeException
ex -> do
  forall (m :: * -> *). MonadLogger m => Text -> Text -> m ()
logCachingError Text
action forall a b. (a -> b) -> a -> b
$ String -> Text
pack forall a b. (a -> b) -> a -> b
$ forall e. Exception e => e -> String
displayException SomeException
ex
  forall (f :: * -> *) a. Applicative f => a -> f a
pure a
value

logCachingError :: MonadLogger m => Text -> Text -> m ()
logCachingError :: forall (m :: * -> *). MonadLogger m => Text -> Text -> m ()
logCachingError Text
action Text
message =
  forall (m :: * -> *).
(HasCallStack, MonadLogger m) =>
Text -> Message -> m ()
logErrorNS Text
"caching"
    forall a b. (a -> b) -> a -> b
$ Text
"Error "
    forall a. Semigroup a => a -> a -> a
<> Text
action
    Text -> [SeriesElem] -> Message
:# [Key
"action" forall kv v. (KeyValue kv, ToJSON v) => Key -> v -> kv
.= Text
action, Key
"message" forall kv v. (KeyValue kv, ToJSON v) => Key -> v -> kv
.= Text
message]

encodeStrict :: ToJSON a => a -> ByteString
encodeStrict :: forall a. ToJSON a => a -> ByteString
encodeStrict = ByteString -> ByteString
BSL.toStrict forall b c a. (b -> c) -> (a -> b) -> a -> c
. forall a. ToJSON a => a -> ByteString
encode