{-# LANGUAGE OverloadedStrings #-}
module Kafka.Avro.Encode
( encodeKey, encodeValue
, encodeWithSchema
, EncodeError(..)
) where

import           Control.Monad.IO.Class    (MonadIO)
import           Data.Avro                 as A (ToAvro, encode, schemaOf)
import           Data.Avro.Schema          (Schema)
import qualified Data.Binary               as B
import           Data.Bits                 (shiftL)
import           Data.ByteString.Lazy      (ByteString)
import qualified Data.ByteString.Lazy      as BL hiding (zipWith)
import           Data.Monoid
import           Kafka.Avro.SchemaRegistry

data EncodeError = EncodeRegistryError SchemaRegistryError
  deriving (Show, Eq)

-- | Encodes a provided value as a message key.
--
-- Registers the schema in SchemaRegistry with "<subject>-key" subject.
encodeKey :: (MonadIO m, ToAvro a)
          => SchemaRegistry
          -> Subject
          -> a
          -> m (Either EncodeError ByteString)
encodeKey sr (Subject subj) a =
  let keySubj = Subject (subj <> "-key")
   in encodeWithSchema sr keySubj a

-- | Encodes a provided value as a message value.
--
-- Registers the schema in SchemaRegistry with "<subject>-value" subject.
encodeValue :: (MonadIO m, ToAvro a)
            => SchemaRegistry
            -> Subject
            -> a
            -> m (Either EncodeError ByteString)
encodeValue sr (Subject subj) a =
  let valSubj = Subject (subj <> "-value")
   in encodeWithSchema sr valSubj a

-- | Encodes a provided value into Avro
-- and registers value's schema in SchemaRegistry.
encodeWithSchema :: (MonadIO m, ToAvro a)
                 => SchemaRegistry
                 -> Subject
                 -> a
                 -> m (Either EncodeError ByteString)
encodeWithSchema sr subj a = do
  mbSid <- sendSchema sr subj (schemaOf a)
  case mbSid of
    Left err  -> return . Left . EncodeRegistryError $ err
    Right sid -> return . Right $ appendSchemaId sid (encode a)


appendSchemaId :: SchemaId -> ByteString -> ByteString
appendSchemaId (SchemaId sid) bs =
  -- add a "magic byte" followed by schema id
  BL.cons (toEnum 0) (B.encode sid) <> bs