{-# LANGUAGE DeriveDataTypeable, BangPatterns #-}
-----------------------------------------------------------------------------
-- |
-- Module      :  Data.Acid.Memory.Pure
-- Copyright   :  PublicDomain
--
-- Maintainer  :  lemmih@gmail.com
-- Portability :  non-portable (uses GHC extensions)
--
-- AcidState container without a transaction log. Mostly used for testing.
--
-- This module consists of internal implementation details for
-- "Data.Acid.Memory".  You should not normally need to import it.  Call
-- 'Data.Acid.Memory.openMemoryState' and thereafter use the API from
-- "Data.Acid" instead.
--

module Data.Acid.Memory.Pure
    ( IsAcidic(..)
    , AcidState
    , Event(..)
    , EventResult
    , EventState
    , UpdateEvent
    , QueryEvent
    , Update
    , Query
    , openAcidState
    , update
    , update_
    , query
    , liftQuery
    , runUpdate
    , runQuery
    ) where

import Data.Acid.Core
import Data.Acid.Common

import Control.Monad.State
import Control.Monad.Reader

{-| Pure state value used internally. This is not the same as
  'Data.Acid.AcidState' from "Data.Acid".
-}
data AcidState st
    = AcidState { forall st. AcidState st -> MethodMap st
localMethods :: MethodMap st
                , forall st. AcidState st -> st
localState   :: st
                }

-- | Issue an Update event and wait for its result. Once this call returns, you are
--   guaranteed that the changes to the state are durable. Events may be issued in
--   parallel.
--
--   It's a run-time error to issue events that aren't supported by the AcidState.
update :: UpdateEvent event => AcidState (EventState event) -> event -> ( AcidState (EventState event)
                                                                        , EventResult event)
update :: forall event.
UpdateEvent event =>
AcidState (EventState event)
-> event -> (AcidState (EventState event), EventResult event)
update AcidState (EventState event)
acidState event
event
    = case forall s a. State s a -> s -> (a, s)
runState State (EventState event) (EventResult event)
hotMethod (forall st. AcidState st -> st
localState AcidState (EventState event)
acidState) of
        !(EventResult event
result, !EventState event
newState) -> ( AcidState (EventState event)
acidState { localState :: EventState event
localState = EventState event
newState }
                                , EventResult event
result )
    where hotMethod :: State (EventState event) (EventResult event)
hotMethod = forall method.
Method method =>
MethodMap (MethodState method)
-> method -> State (MethodState method) (MethodResult method)
lookupHotMethod (forall st. AcidState st -> MethodMap st
localMethods AcidState (EventState event)
acidState) event
event

-- | Same as 'update' but ignoring the event result.
update_ :: UpdateEvent event => AcidState (EventState event) -> event -> AcidState (EventState event)
update_ :: forall event.
UpdateEvent event =>
AcidState (EventState event)
-> event -> AcidState (EventState event)
update_ AcidState (EventState event)
acidState event
event
    = forall a b. (a, b) -> a
fst (forall event.
UpdateEvent event =>
AcidState (EventState event)
-> event -> (AcidState (EventState event), EventResult event)
update AcidState (EventState event)
acidState event
event)

-- | Issue a Query event and wait for its result.
query  :: QueryEvent event  => AcidState (EventState event) -> event -> EventResult event
query :: forall event.
QueryEvent event =>
AcidState (EventState event) -> event -> EventResult event
query AcidState (EventState event)
acidState event
event
    = case forall s a. State s a -> s -> (a, s)
runState State (EventState event) (EventResult event)
hotMethod (forall st. AcidState st -> st
localState AcidState (EventState event)
acidState) of
        !(EventResult event
result, !EventState event
_st) -> EventResult event
result
    where hotMethod :: State (EventState event) (EventResult event)
hotMethod = forall method.
Method method =>
MethodMap (MethodState method)
-> method -> State (MethodState method) (MethodResult method)
lookupHotMethod (forall st. AcidState st -> MethodMap st
localMethods AcidState (EventState event)
acidState) event
event

-- | Create an AcidState given an initial value.
openAcidState :: IsAcidic st
              => st                          -- ^ Initial state value.
              -> AcidState st
openAcidState :: forall st. IsAcidic st => st -> AcidState st
openAcidState st
initialState
    = AcidState { localMethods :: MethodMap st
localMethods = forall st. [MethodContainer st] -> MethodMap st
mkMethodMap (forall st. [Event st] -> [MethodContainer st]
eventsToMethods forall st. IsAcidic st => [Event st]
acidEvents)
                , localState :: st
localState   = st
initialState }

-- | Execute the 'Update' monad in a pure environment.
runUpdate :: Update s r -> s -> (r, s)
runUpdate :: forall s r. Update s r -> s -> (r, s)
runUpdate Update s r
update = forall s a. State s a -> s -> (a, s)
runState forall a b. (a -> b) -> a -> b
$ forall st a. Update st a -> State st a
unUpdate Update s r
update

-- | Execute the 'Query' monad in a pure environment.
runQuery :: Query s r -> s -> r
runQuery :: forall s r. Query s r -> s -> r
runQuery Query s r
query = forall r a. Reader r a -> r -> a
runReader forall a b. (a -> b) -> a -> b
$ forall st a. Query st a -> Reader st a
unQuery Query s r
query