Session.hs

{-|
Module      : Game.GoreAndAsh.Core.Session
Description : Definition of game session that holds current time.
Copyright   : (c) Anton Gushcha, 2015-2016
                  Oganyan Levon, 2016
License     : BSD3
Maintainer  : ncrashed@gmail.com
Stability   : experimental
Portability : POSIX

Utilities for handling time in engine arrows.
-}
module Game.GoreAndAsh.Core.Session(
    GameTime
  , GameSession
  , NominalDiffTime
  , newGameSession
  , stepGameSession
  ) where

import Control.Monad.IO.Class
import Control.Wire.Session
import Data.Time.Clock

-- | Current value of simulation time.
type GameTime = Timed NominalDiffTime ()

-- | Session that stores time in diff format
-- The only purpose is to store time while stepping simulation.
type GameSession = Session IO GameTime

-- | Creates new empty game session
newGameSession :: GameSession
newGameSession = clockSession_

-- | Generates next value of game session and outputs current simulation time
-- That simulation time should be feeded to game wire and next
-- value of session should be used at next step of simulation.
stepGameSession :: MonadIO m => GameSession -> m (GameTime, GameSession)
stepGameSession s = liftIO $ stepSession s