feat(callback): Change log callback log level to KafkaLogLevel

* Int becomes KafkaLogLevel (breaking changes)
* Add documentation for callbacks

Closes #135

Author: Julien Debon

src/Kafka/Callbacks.hs

@@ -7,18 +7,48 @@ where
 
 import Kafka.Internal.RdKafka (rdKafkaConfSetErrorCb, rdKafkaConfSetLogCb, rdKafkaConfSetStatsCb)
 import Kafka.Internal.Setup (HasKafkaConf(..), getRdKafkaConf)
-import Kafka.Types (KafkaError(..))
+import Kafka.Types (KafkaError(..), KafkaLogLevel(..))
 
+-- | Add a callback for errors.
+--
+-- ==== __Examples__
+--
+-- Basic usage:
+--
+-- > setCallback (errorCallback myErrorCallback)
+-- >
+-- > myErrorCallback :: KafkaError -> String -> IO ()
+-- > myErrorCallback kafkaError message = print $ show kafkaError <> "|" <> message
 errorCallback :: HasKafkaConf k => (KafkaError -> String -> IO ()) -> k -> IO ()
 errorCallback callback k =
   let realCb _ err = callback (KafkaResponseError err)
   in rdKafkaConfSetErrorCb (getRdKafkaConf k) realCb
 
-logCallback :: HasKafkaConf k => (Int -> String -> String -> IO ()) -> k -> IO ()
+-- | Add a callback for logs.
+--
+-- ==== __Examples__
+--
+-- Basic usage:
+--
+-- > setCallback (logCallback myLogCallback)
+-- >
+-- > myLogCallback :: KafkaLogLevel -> String -> String -> IO ()
+-- > myLogCallback level facility message = print $ show level <> "|" <> facility <> "|" <> message
+logCallback :: HasKafkaConf k => (KafkaLogLevel -> String -> String -> IO ()) -> k -> IO ()
 logCallback callback k =
-  let realCb _ = callback
+  let realCb _ = callback . toEnum
   in rdKafkaConfSetLogCb (getRdKafkaConf k) realCb
 
+-- | Add a callback for stats.
+--
+-- ==== __Examples__
+--
+-- Basic usage:
+--
+-- > setCallback (statsCallback mystatsCallback)
+-- >
+-- > mystatsCallback :: String -> IO ()
+-- > mystatsCallback stats = print $ show stats
 statsCallback :: HasKafkaConf k => (String -> IO ()) -> k -> IO ()
 statsCallback callback k =
   let realCb _ = callback