{-# LANGUAGE ExistentialQuantification #-}
{-# LANGUAGE OverloadedStrings         #-}
{-# LANGUAGE RecordWildCards           #-}
--------------------------------------------------------------------------------
-- |
-- Module : Database.EventStore.Internal.TimerService
-- Copyright : (C) 2017 Yorick Laupa
-- License : (see the file LICENSE)
--
-- Maintainer : Yorick Laupa <yo.eight@gmail.com>
-- Stability : provisional
-- Portability : non-portable
--
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module Database.EventStore.Internal.TimerService
  ( timerService ) where

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import Data.Typeable

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import Database.EventStore.Internal.Communication
import Database.EventStore.Internal.Control
import Database.EventStore.Internal.Logger
import Database.EventStore.Internal.Prelude
import Database.EventStore.Internal.Types

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data Internal =
  Internal { _stopped :: IORef Bool }

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timerService :: Hub -> IO ()
timerService mainBus = do

  internal <- Internal <$> newIORef False

  subscribe mainBus (onInit internal)
  subscribe mainBus (onShutdown internal)
  subscribe mainBus (onNew internal)

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delayed :: Typeable e
        => Internal
        -> e
        -> Duration
        -> Bool
        -> EventStore ()
delayed Internal{..} msg (Duration timespan) oneOff = () <$ fork (go timespan)
  where
    go n = do
      when (n > 0) $ do
        let waiting = min n (fromIntegral (maxBound :: Int))
        threadDelay $ fromIntegral waiting
        go (timespan - waiting)

      publish msg
      stopped <- readIORef _stopped
      unless (oneOff || stopped) $ go timespan

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onInit ::Internal -> SystemInit -> EventStore ()
onInit Internal{..} _ = publish (Initialized TimerService)

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onShutdown :: Internal -> SystemShutdown -> EventStore ()
onShutdown Internal{..} _ = do
  $logInfo "Shutting down..."
  atomicWriteIORef _stopped True
  publish (ServiceTerminated TimerService)

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onNew :: Internal -> NewTimer -> EventStore ()
onNew self (NewTimer msg duration oneOff) = delayed self msg duration oneOff