-----------------------------------------------------------------------------
-- |
-- Module      :  Data.Atomics
-- Copyright   :  (c) 2020-2021 EMQ Technologies Co., Ltd.
-- License     :  BSD-style (see the LICENSE file)
--
-- Maintainer  :  Feng Lee, feng@emqx.io
--                Yang M, yangm@emqx.io
-- Stability   :  experimental
-- Portability :  portable
--
-- The Atomics module.
--
-----------------------------------------------------------------------------
module Data.Atomics where

import Control.Monad (IO)
import Data.Ref (Reference)
import Data.Unit (Unit)
import Foreign (ffiIO1, ffiIO2, ffiIO3, ffiIO4)

type AtomicsRef = Reference

type AtomicsInfo =
  { size   :: Integer
    -- ^ The number of atomics in the array.
  , max    :: Integer
    -- ^ The highest possible value an atomic in this array can hold.
  , min    :: Integer
    -- ^ The lowest possible value an atomic in this array can hold.
  , memory :: Integer
    -- ^ Approximate memory consumption for the array in bytes.
  }

-- | Create a new atomic array of Arity atomics.
foreign import new :: Integer -> Boolean -> IO AtomicsRef

-- | Set atomic to Value.
put :: AtomicsRef -> Integer -> Integer -> IO ()
put = ffiIO3 :atomics :put

-- | Read atomic value.
get :: AtomicsRef -> Integer -> IO Integer
get = ffiIO2 :atomics :get

-- | Add Incr to atomic.
add :: AtomicsRef -> Integer -> Integer -> IO ()
add = ffiIO3 :atomics :add

-- | Atomic addition and return of the result.
addGet :: AtomicsRef -> Integer -> Integer -> IO Integer
addGet = ffiIO3 :atomics :add_get

-- | Subtract Decr from atomic.
sub :: AtomicsRef -> Integer -> Integer -> IO ()
sub = ffiIO3 :atomics :sub

-- | Atomic subtraction and return of the result.
subGet :: AtomicsRef -> Integer -> Integer -> IO Integer
subGet = ffiIO3 :atomics :sub_get

-- | Atomically replaces the value of the atomic with Desired and
-- returns the value it held previously.
exchange :: AtomicsRef -> Integer -> Integer -> IO Integer
exchange = ffiIO3 :atomics :exchange

-- | Atomically compares the atomic with Expected, and if those are equal,
-- set atomic to Desired. Returns ok if Desired was written. Returns the
-- actual atomic value if not equal to Expected.
compareExchange :: AtomicsRef -> Integer -> Integer -> Integer -> IO Integer
compareExchange = ffiIO4 :atomics :compare_exchange

-- | Return information about an atomic array.
info :: AtomicsRef -> IO AtomicsInfo
info = ffiIO1 :atomics :info