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{-# LANGUAGE MultiParamTypeClasses, TypeFamilies, FlexibleContexts #-}

{-# LANGUAGE TemplateHaskell #-}

{-| All RPC calls are run within this monad.

It encapsulates:

* IO operations,

* failures,

* working with the daemon state.

Code that is specific either to the configuration or the lock management, should

go into their corresponding dedicated modules.

-}

{-

Copyright (C) 2014 Google Inc.

This program is free software; you can redistribute it and/or modify

it under the terms of the GNU General Public License as published by

the Free Software Foundation; either version 2 of the License, or

(at your option) any later version.

This program is distributed in the hope that it will be useful, but

WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

General Public License for more details.

You should have received a copy of the GNU General Public License

along with this program; if not, write to the Free Software

Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

02110-1301, USA.

-}

module Ganeti.WConfd.Monad

  ( DaemonHandle

  , dhConfigPath

  , dhSaveConfigWorker

  , mkDaemonHandle

  , WConfdMonadInt

  , runWConfdMonadInt

  , WConfdMonad

  , daemonHandle

  , modifyConfigState

  , readConfigState

  , modifyLockAllocation

  , modifyLockAllocation_

  , readLockAllocation

  ) where

import Control.Applicative

import Control.Monad

import Control.Monad.Base

import Control.Monad.Error

import Control.Monad.Reader

import Control.Monad.Trans.Control

import Data.IORef.Lifted

import Data.Tuple (swap)

import Ganeti.BasicTypes

import Ganeti.Errors

import Ganeti.Lens

import Ganeti.Locking.Locks

import Ganeti.Logging

import Ganeti.Utils.AsyncWorker

import Ganeti.WConfd.ConfigState

-- * Pure data types used in the monad

-- | The state of the daemon, capturing both the configuration state and the

-- locking state.

data DaemonState = DaemonState

  { dsConfigState :: ConfigState

  , dsLockAllocation :: GanetiLockAllocation

  }

$(makeCustomLenses ''DaemonState)

data DaemonHandle = DaemonHandle

  { dhDaemonState :: IORef DaemonState -- ^ The current state of the daemon

  , dhConfigPath :: FilePath           -- ^ The configuration file path

  -- all static information that doesn't change during the life-time of the

  -- daemon should go here;

  -- all IDs of threads that do asynchronous work should probably also go here

  , dhSaveConfigWorker :: AsyncWorker ()

  , dhSaveLocksWorker :: AsyncWorker ()

  }

mkDaemonHandle :: FilePath

               -> ConfigState

               -> GanetiLockAllocation

               -> (IO ConfigState -> ResultG (AsyncWorker ()))

                  -- ^ A function that creates a worker that asynchronously

                  -- saves the configuration to the master file.

               -> (IO GanetiLockAllocation -> ResultG (AsyncWorker ()))

                  -- ^ A function that creates a worker that asynchronously

                  -- saves the lock allocation state.

               -> ResultG DaemonHandle

mkDaemonHandle cpath cstat lstat saveConfigWorkerFn saveLockWorkerFn = do

  ds <- newIORef $ DaemonState cstat lstat

  saveConfigWorker <- saveConfigWorkerFn $ dsConfigState `liftM` readIORef ds

  saveLockWorker <- saveLockWorkerFn $ dsLockAllocation `liftM` readIORef ds

  return $ DaemonHandle ds cpath saveConfigWorker saveLockWorker

-- * The monad and its instances

-- | A type alias for easier referring to the actual content of the monad

-- when implementing its instances.

type WConfdMonadIntType = ReaderT DaemonHandle IO

-- | The internal part of the monad without error handling.

newtype WConfdMonadInt a = WConfdMonadInt

  { getWConfdMonadInt :: WConfdMonadIntType a }

instance Functor WConfdMonadInt where

  fmap f = WConfdMonadInt . fmap f . getWConfdMonadInt

instance Applicative WConfdMonadInt where

  pure = WConfdMonadInt . pure

  WConfdMonadInt f <*> WConfdMonadInt k = WConfdMonadInt $ f <*> k

instance Monad WConfdMonadInt where

  return = WConfdMonadInt . return

  (WConfdMonadInt k) >>= f = WConfdMonadInt $ k >>= getWConfdMonadInt . f

instance MonadIO WConfdMonadInt where

  liftIO = WConfdMonadInt . liftIO

instance MonadBase IO WConfdMonadInt where

  liftBase = WConfdMonadInt . liftBase

instance MonadBaseControl IO WConfdMonadInt where

  newtype StM WConfdMonadInt b = StMWConfdMonadInt

    { runStMWConfdMonadInt :: StM WConfdMonadIntType b }

  liftBaseWith f = WConfdMonadInt . liftBaseWith

                   $ \r -> f (liftM StMWConfdMonadInt . r . getWConfdMonadInt)

  restoreM = WConfdMonadInt . restoreM . runStMWConfdMonadInt

instance MonadLog WConfdMonadInt where

  logAt p = WConfdMonadInt . logAt p

-- | Runs the internal part of the WConfdMonad monad on a given daemon

-- handle.

runWConfdMonadInt :: WConfdMonadInt a -> DaemonHandle -> IO a

runWConfdMonadInt (WConfdMonadInt k) = runReaderT k

-- | The complete monad with error handling.

type WConfdMonad = ResultT GanetiException WConfdMonadInt

-- * Basic functions in the monad

-- | Returns the daemon handle.

daemonHandle :: WConfdMonad DaemonHandle

daemonHandle = lift . WConfdMonadInt $ ask

-- | Returns the current configuration, given a handle

readConfigState :: WConfdMonad ConfigState

readConfigState = liftM dsConfigState . readIORef . dhDaemonState

                  =<< daemonHandle

-- | Atomically modifies the configuration state in the WConfdMonad.

modifyConfigState :: (ConfigState -> (ConfigState, a)) -> WConfdMonad a

modifyConfigState f = do

  dh <- daemonHandle

  let modCS cs = let (cs', r) = f cs

                  in ((r, cs /= cs'), cs')

  let mf = traverseOf dsConfigStateL modCS

  (r, modified) <- atomicModifyIORef (dhDaemonState dh) (swap . mf)

  when modified $ do

    -- trigger the config. saving worker and wait for it

    logDebug "Triggering config write"

    liftBase . triggerAndWait . dhSaveConfigWorker $ dh

    logDebug "Config write finished"

    -- trigger the config. distribution worker asynchronously

    -- TODO

  return r

-- | Atomically modifies the lock allocation state in WConfdMonad.

modifyLockAllocation :: (GanetiLockAllocation -> (GanetiLockAllocation, a))

                     -> WConfdMonad a

modifyLockAllocation f = do

  dh <- lift . WConfdMonadInt $ ask

  r <- atomicModifyIORef (dhDaemonState dh)

                         (swap . traverseOf dsLockAllocationL (swap . f))

  logDebug "Triggering lock state write"

  liftBase . triggerAndWait . dhSaveLocksWorker $ dh

  logDebug "Lock write finished"

  return r

-- | Atomically modifies the lock allocation state in WConfdMonad, not

-- producing any result

modifyLockAllocation_ :: (GanetiLockAllocation -> GanetiLockAllocation)

                      -> WConfdMonad ()

modifyLockAllocation_ = modifyLockAllocation . (flip (,) () .)

-- | Read the lock allocation state.

readLockAllocation :: WConfdMonad GanetiLockAllocation

readLockAllocation = liftM dsLockAllocation . readIORef . dhDaemonState

                     =<< daemonHandle