{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE LambdaCase                 #-}
{-# LANGUAGE OverloadedStrings          #-}
{-# LANGUAGE RankNTypes                 #-}
{-# LANGUAGE TemplateHaskell            #-}

module Hasura.Logging
  ( LoggerSettings(..)
  , defaultLoggerSettings
  , EngineLog(..)
  , EngineLogType
  , ToEngineLog(..)
  , debugT
  , debugBS
  , debugLBS
  , Logger
  , LogLevel(..)
  , mkLogger
  , LoggerCtx(..)
  , mkLoggerCtx
  , cleanLoggerCtx
  ) where

import           Hasura.Prelude

import qualified Control.AutoUpdate    as Auto
import qualified Data.Aeson            as J
import qualified Data.Aeson.Casing     as J
import qualified Data.Aeson.TH         as J
import qualified Data.ByteString       as B
import qualified Data.ByteString.Lazy  as BL
import qualified Data.TByteString      as TBS
import qualified Data.Text             as T
import qualified Data.Time.Clock       as Time
import qualified Data.Time.Format      as Format
import qualified Data.Time.LocalTime   as Time
import qualified System.Log.FastLogger as FL

newtype FormattedTime
  = FormattedTime { _unFormattedTime :: Text }
  deriving (Show, Eq, J.ToJSON)

newtype EngineLogType
  = EngineLogType { _unEngineLogType :: Text }
  deriving (Show, Eq, J.ToJSON, J.FromJSON, IsString)

data LogLevel
  = LevelDebug
  | LevelInfo
  | LevelWarn
  | LevelError
  | LevelOther Text
  deriving (Show, Eq, Ord)

instance J.ToJSON LogLevel where
  toJSON = J.toJSON . \case
    LevelDebug   -> "debug"
    LevelInfo    -> "info"
    LevelWarn    -> "warn"
    LevelError   -> "error"
    LevelOther t -> t

data EngineLog
  = EngineLog
  { _elTimestamp :: !FormattedTime
  , _elLevel     :: !LogLevel
  , _elType      :: !EngineLogType
  , _elDetail    :: !J.Value
  } deriving (Show, Eq)
$(J.deriveToJSON (J.aesonDrop 3 J.snakeCase) ''EngineLog)


newtype UnstructuredLog
  = UnstructuredLog { _unUnstructuredLog :: TBS.TByteString }
  deriving (Show, Eq)

debugT :: Text -> UnstructuredLog
debugT = UnstructuredLog . TBS.fromText

debugBS :: B.ByteString -> UnstructuredLog
debugBS = UnstructuredLog . TBS.fromBS

debugLBS :: BL.ByteString -> UnstructuredLog
debugLBS = UnstructuredLog . TBS.fromLBS

instance ToEngineLog UnstructuredLog where
  toEngineLog (UnstructuredLog t) =
    (LevelDebug, "unstructured", J.toJSON t)

class ToEngineLog a where
  toEngineLog :: a -> (LogLevel, EngineLogType, J.Value)

data LoggerCtx
  = LoggerCtx
  { _lcLoggerSet  :: !FL.LoggerSet
  , _lcLogLevel   :: !LogLevel
  , _lcTimeGetter :: !(IO FormattedTime)
  }

data LoggerSettings
  = LoggerSettings
  -- should current time be cached (refreshed every sec)
  { _lsCachedTimestamp :: !Bool
  , _lsTimeZone        :: !(Maybe Time.TimeZone)
  , _lsLevel           :: !LogLevel
  } deriving (Show, Eq)

defaultLoggerSettings :: Bool -> LoggerSettings
defaultLoggerSettings isCached =
  LoggerSettings isCached Nothing LevelInfo

getFormattedTime :: Maybe Time.TimeZone -> IO FormattedTime
getFormattedTime tzM = do
  tz <- maybe Time.getCurrentTimeZone return tzM
  t  <- Time.getCurrentTime
  let zt = Time.utcToZonedTime tz t
  return $ FormattedTime $ T.pack $ formatTime zt
  where
    formatTime = Format.formatTime Format.defaultTimeLocale format
    format = "%FT%H:%M:%S%3Q%z"
    -- format = Format.iso8601DateFormat (Just "%H:%M:%S")

mkLoggerCtx :: LoggerSettings -> IO LoggerCtx
mkLoggerCtx (LoggerSettings cacheTime tzM logLevel) = do
  loggerSet <- FL.newStdoutLoggerSet FL.defaultBufSize
  timeGetter <- bool (return $ getFormattedTime tzM) cachedTimeGetter cacheTime
  return $ LoggerCtx loggerSet logLevel timeGetter
  where
    cachedTimeGetter =
      Auto.mkAutoUpdate Auto.defaultUpdateSettings {
        Auto.updateAction = getFormattedTime tzM
      }

cleanLoggerCtx :: LoggerCtx -> IO ()
cleanLoggerCtx =
  FL.rmLoggerSet . _lcLoggerSet

type Logger = forall a. (ToEngineLog a) => a -> IO ()

mkLogger :: LoggerCtx -> Logger
mkLogger (LoggerCtx loggerSet serverLogLevel timeGetter) l = do
  localTime <- timeGetter
  let (logLevel, logTy, logDet) = toEngineLog l
  when (logLevel >= serverLogLevel) $
    FL.pushLogStrLn loggerSet $ FL.toLogStr $
    J.encode $ EngineLog localTime logLevel logTy logDet