StandardOutput.hs

-- | Stdout logging back-end.
module Log.Backend.StandardOutput
  ( withSimpleStdOutLogger
  , withStdOutLogger
  , withJsonStdOutLogger
  ) where

import Data.Aeson
import Prelude
import System.IO
import qualified Data.Text.IO as T
import qualified Data.ByteString.Lazy.Char8 as BSL

import Log.Data
import Log.Internal.Logger
import Log.Logger

-- | Create a simple, synchronous logger that prints messages to standard output
-- and flushes 'stdout' on each call to 'loggerWriteMessage' for the duration of
-- the given action.
withSimpleStdOutLogger :: (Logger -> IO r) -> IO r
withSimpleStdOutLogger = withLogger $ Logger
  { loggerWriteMessage = \msg -> do
      T.putStrLn $ showLogMessage Nothing msg
      hFlush stdout
  , loggerWaitForWrite = return ()
  , loggerShutdown     = return ()
  }

-- | Create a logger that prints messages to standard output for the duration of
-- the given action.
withStdOutLogger :: (Logger -> IO r) -> IO r
withStdOutLogger act = do
  logger <- mkLogger "stdout" $ \msg -> do
    T.putStrLn $ showLogMessage Nothing msg
    hFlush stdout
  withLogger logger act

-- | Create a logger that prints messages in the JSON format to standard output
-- for the duration of the given action.
withJsonStdOutLogger :: (Logger -> IO r) -> IO r
withJsonStdOutLogger act = do
  logger <- mkLogger "stdout-json" $ \msg -> do
    BSL.putStrLn $ encode msg
    hFlush stdout
  withLogger logger act