{-|
Module      : PostgresWebsockets.Config
Description : Manages PostgresWebsockets configuration options.

This module provides a helper function to read the command line
arguments using  the AppConfig type to store
them.  It also can be used to define other middleware configuration that
may be delegated to some sort of external configuration.
-}
module PostgresWebsockets.Config 
        ( prettyVersion
        , loadConfig
        , warpSettings
        , AppConfig (..)
        ) where

import           Env
import           Data.Text                   (intercalate, pack, replace, strip, stripPrefix)
import           Data.Version                (versionBranch)
import           Paths_postgres_websockets   (version)
import           Protolude hiding            (intercalate, (<>), optional, replace)
import           Data.String (IsString(..))
import           Network.Wai.Handler.Warp
import qualified Data.ByteString                      as BS
import qualified Data.ByteString.Base64               as B64

-- | Config file settings for the server
data AppConfig = AppConfig {
    configDatabase          :: Text
  , configPath              :: Maybe Text
  , configHost              :: Text
  , configPort              :: Int
  , configListenChannel     :: Text
  , configMetaChannel       :: Maybe Text
  , configJwtSecret         :: ByteString
  , configJwtSecretIsBase64 :: Bool
  , configPool              :: Int
  , configRetries           :: Int
  }

-- | User friendly version number
prettyVersion :: Text
prettyVersion = intercalate "." $ map show $ versionBranch version

-- | Load all postgres-websockets config from Environment variables. This can be used to use just the middleware or to feed into warpSettings
loadConfig :: IO AppConfig
loadConfig = readOptions >>= loadSecretFile >>= loadDatabaseURIFile

-- | Given a shutdown handler and an AppConfig builds a Warp Settings to start a stand-alone server
warpSettings :: (IO () -> IO ()) -> AppConfig -> Settings
warpSettings waitForShutdown AppConfig{..} =
      setHost (fromString $ toS configHost)
                  . setPort configPort
                  . setServerName (toS $ "postgres-websockets/" <> prettyVersion)
                  . setTimeout 3600
                  . setInstallShutdownHandler waitForShutdown
                  . setGracefulShutdownTimeout (Just 5)
                  $ defaultSettings


-- private

-- | Function to read and parse options from the environment
readOptions :: IO AppConfig
readOptions =
    Env.parse (header "You need to configure some environment variables to start the service.") $
      AppConfig <$> var (str <=< nonempty) "PGWS_DB_URI"  (help "String to connect to PostgreSQL")
                <*> optional (var str "PGWS_ROOT_PATH" (help "Root path to serve static files, unset to disable."))
                <*> var str "PGWS_HOST" (def "*4" <> helpDef show <> help "Address the server will listen for websocket connections")
                <*> var auto "PGWS_PORT" (def 3000 <> helpDef show <> help "Port the server will listen for websocket connections")
                <*> var str "PGWS_LISTEN_CHANNEL" (def "postgres-websockets-listener" <> helpDef show <> help "Master channel used in the database to send or read messages in any notification channel")
                <*> optional (var str "PGWS_META_CHANNEL" (help "Websockets channel used to send events about the server state changes."))
                <*> var str "PGWS_JWT_SECRET" (help "Secret used to sign JWT tokens used to open communications channels")
                <*> var auto "PGWS_JWT_SECRET_BASE64" (def False <> helpDef show <> help "Indicate whether the JWT secret should be decoded from a base64 encoded string")
                <*> var auto "PGWS_POOL_SIZE" (def 10 <> helpDef show <> help "How many connection to the database should be used by the connection pool")
                <*> var auto "PGWS_RETRIES" (def 5 <> helpDef show <> help "How many times it should try to connect to the database on startup before exiting with an error")

loadDatabaseURIFile :: AppConfig -> IO AppConfig
loadDatabaseURIFile conf@AppConfig{..} =
  case stripPrefix "@" configDatabase of
    Nothing       -> pure conf
    Just filename -> setDatabase . strip <$> readFile (toS filename)
  where
    setDatabase uri = conf {configDatabase = uri}

loadSecretFile :: AppConfig -> IO AppConfig
loadSecretFile conf = extractAndTransform secret
  where
    secret   = decodeUtf8 $ configJwtSecret conf
    isB64     = configJwtSecretIsBase64 conf

    extractAndTransform :: Text -> IO AppConfig
    extractAndTransform s =
      fmap setSecret $ transformString isB64 =<<
        case stripPrefix "@" s of
          Nothing       -> return . encodeUtf8 $ s
          Just filename -> chomp <$> BS.readFile (toS filename)
      where
        chomp bs = fromMaybe bs (BS.stripSuffix "\n" bs)

    -- Turns the Base64url encoded JWT into Base64
    transformString :: Bool -> ByteString -> IO ByteString
    transformString False t = return t
    transformString True t =
      case B64.decode $ encodeUtf8 $ strip $ replaceUrlChars $ decodeUtf8 t of
        Left errMsg -> panic $ pack errMsg
        Right bs    -> return bs

    setSecret bs = conf {configJwtSecret = bs}

    -- replace: Replace every occurrence of one substring with another
    replaceUrlChars =
      replace "_" "/" . replace "-" "+" . replace "." "="