{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE FlexibleContexts  #-}

module Database.Persist.Audit.MongoDB.Util where

import           Data.ByteString          (ByteString)
import           Data.Text.Encoding       (decodeUtf8',encodeUtf8)

import           Database.MongoDB as DB
import           Database.Persist.MongoDB (keyToText,readMayMongoKey)
import           Database.Persist


-- | Used for creating instances of ToAudit when the original model database is Mongo
--   and the audit model database is SQL.
-- ==== __Example__
-- User
--     ident Text
--     password Text Maybe
--     UniqueUser ident
-- UserAudit
--     ident Text
--     password Text Maybe
--     originalId ByteString
--     auditAction AuditAction
--     editedBy Text
--     editedOn UTCTime
--  instance ToAudit User where
--    type AuditResult User = UserAudit
--    toAudit v k auditAction editedBy editedOn = UserAudit (userIdent v)
--      (userPassword v)
--      (mongoKeyToByteString k) auditAction editedBy editedOn

mongoKeyToByteString :: (ToBackendKey DB.MongoContext record) => Key record -> ByteString
mongoKeyToByteString = encodeUtf8 . keyToText . toBackendKey

-- | Used for when Mongo stored in SQL needs to be converted to a Key to query the original
--   MongoDB.
byteStringToMongoKey :: (ToBackendKey DB.MongoContext record) => ByteString -> Maybe (Key record)
byteStringToMongoKey bs = case decodeUtf8' bs of
                            Left _ -> Nothing
                            Right text -> fromBackendKey <$> readMayMongoKey text

-- | To handle SQL keys to and from MongoDB, use 'toSqlKey' and 'fromSqlKey' from Database.Persist.Sql