-- This Source Code Form is subject to the terms of the Mozilla Public
-- License, v. 2.0. If a copy of the MPL was not distributed with this
-- file, You can obtain one at http://mozilla.org/MPL/2.0/.

{-# LANGUAGE BangPatterns               #-}
{-# LANGUAGE CPP                        #-}
{-# LANGUAGE FlexibleContexts           #-}
{-# LANGUAGE FlexibleInstances          #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE MultiParamTypeClasses      #-}
{-# LANGUAGE OverloadedStrings          #-}
{-# LANGUAGE ScopedTypeVariables        #-}
{-# LANGUAGE TemplateHaskell            #-}
{-# LANGUAGE TypeFamilies               #-}
{-# LANGUAGE UndecidableInstances       #-}

module Database.CQL.IO.Client
    ( Client
    , MonadClient (..)
    , ClientState
    , DebugInfo   (..)
    , runClient
    , Database.CQL.IO.Client.init
    , shutdown
    , request
    , requestN
    , request1
    , mkRequest
    , execute
    , executeWithPrepare
    , prepare
    , retry
    , debugInfo
    , preparedQueries
    , withPrepareStrategy
    ) where

import Control.Applicative
import Control.Concurrent (threadDelay)
import Control.Concurrent.Async (async, wait)
import Control.Concurrent.STM hiding (retry)
import Control.Exception (IOException)
import Control.Lens hiding ((.=), Context)
import Control.Monad (void, when)
import Control.Monad.Base (MonadBase (..))
import Control.Monad.Catch
import Control.Monad.IO.Class
import Control.Monad.Reader (ReaderT (..), runReaderT, MonadReader, ask)
import Control.Monad.Trans.Class
import Control.Monad.Trans.Control (MonadBaseControl (..))
#if MIN_VERSION_transformers(0,4,0)
import Control.Monad.Trans.Except
#endif
import Control.Retry
import Data.Foldable (for_, foldrM)
import Data.List (find)
import Data.List.NonEmpty (NonEmpty (..))
import Data.Map.Strict (Map)
import Data.Maybe (fromMaybe, listToMaybe)
import Data.Text (Text)
import Data.Word
import Database.CQL.IO.Cluster.Discovery as Discovery
import Database.CQL.IO.Cluster.Host
import Database.CQL.IO.Cluster.Policies
import Database.CQL.IO.Connection hiding (request)
import Database.CQL.IO.Jobs (Jobs)
import Database.CQL.IO.Pool
import Database.CQL.IO.PrepQuery (PrepQuery, PreparedQueries)
import Database.CQL.IO.Protocol
import Database.CQL.IO.Settings
import Database.CQL.IO.Signal
import Database.CQL.IO.Timeouts (TimeoutManager)
import Database.CQL.IO.Types
import Database.CQL.Protocol hiding (Map)
import Network.Socket (SockAddr (..), PortNumber)
import System.Logger.Class hiding (Settings, new, settings, create)
import Prelude

import qualified Control.Monad.Reader       as Reader
import qualified Control.Monad.State.Strict as S
import qualified Control.Monad.State.Lazy   as LS
import qualified Data.List.NonEmpty         as NE
import qualified Data.Map.Strict            as Map
import qualified Database.CQL.IO.Connection as C
import qualified Database.CQL.IO.Jobs       as Jobs
import qualified Database.CQL.IO.PrepQuery  as PQ
import qualified Database.CQL.IO.Timeouts   as TM
import qualified System.Logger              as Logger

data ControlState
    = Disconnected
    | Connected
    | Reconnecting
    deriving (Eq, Ord, Show)

data Control = Control
    { _state      :: !ControlState
    , _connection :: !Connection
    }

data Context = Context
    { _settings      :: !Settings
    , _logger        :: !Logger
    , _timeouts      :: !TimeoutManager
    , _sigMonit      :: !(Signal HostEvent)
    }

-- | Opaque client state/environment.
data ClientState = ClientState
    { _context     :: !Context
    , _policy      :: !Policy
    , _prepQueries :: !PreparedQueries
    , _control     :: !(TVar Control)
    , _hostmap     :: !(TVar (Map Host Pool))
    , _jobs        :: !(Jobs InetAddr)
    }

makeLenses ''Control
makeLenses ''Context
makeLenses ''ClientState

-- | The Client monad.
--
-- A simple reader monad around some internal state. Prior to executing
-- this monad via 'runClient', its state must be initialised through
-- 'Database.CQL.IO.Client.init' and after finishing operation it should be
-- terminated with 'shutdown'.
--
-- Actual CQL queries are handled by invoking 'request'.
-- Additionally 'debugInfo' returns an internal cluster view.
newtype Client a = Client
    { client :: ReaderT ClientState IO a
    } deriving ( Functor
               , Applicative
               , Monad
               , MonadIO
               , MonadThrow
               , MonadMask
               , MonadCatch
               , MonadReader ClientState
               , MonadBase IO
               )

instance MonadLogger Client where
    log l m = view (context.logger) >>= \g -> Logger.log g l m

#if MIN_VERSION_monad_control(1,0,0)
instance MonadBaseControl IO Client where
    type StM Client a = StM (ReaderT ClientState IO) a
    liftBaseWith f = Client . liftBaseWith $ \run -> f (run . client)
    restoreM = Client . restoreM
#else
instance MonadBaseControl IO Client where
    newtype StM Client a = ClientStM
        { unClientStM :: StM (ReaderT ClientState IO) a }

    liftBaseWith f =
        Client . liftBaseWith $ \run -> f (fmap ClientStM . run . client)

    restoreM = Client . restoreM . unClientStM
#endif

-- | Monads in which 'Client' actions may be embedded.
class (Functor m, Applicative m, Monad m, MonadIO m, MonadCatch m) => MonadClient m
  where
    -- | Lift a computation to the 'Client' monad.
    liftClient :: Client a -> m a
    -- | Execute an action with a modified 'ClientState'.
    localState :: (ClientState -> ClientState) -> m a -> m a

instance MonadClient Client where
    liftClient = id
    localState = Reader.local

instance MonadClient m => MonadClient (ReaderT r m) where
    liftClient     = lift . liftClient
    localState f m = ReaderT (localState f . runReaderT m)

instance MonadClient m => MonadClient (S.StateT s m) where
    liftClient     = lift . liftClient
    localState f m = S.StateT (localState f . S.runStateT m)

instance MonadClient m => MonadClient (LS.StateT s m) where
    liftClient     = lift . liftClient
    localState f m = LS.StateT (localState f . LS.runStateT m)

#if MIN_VERSION_transformers(0,4,0)
instance MonadClient m => MonadClient (ExceptT e m) where
    liftClient     = lift . liftClient
    localState f m = ExceptT $ localState f (runExceptT m)
#endif

-----------------------------------------------------------------------------
-- API

-- | Execute the client monad.
runClient :: MonadIO m => ClientState -> Client a -> m a
runClient p a = liftIO $ runReaderT (client a) p

-- | Use given 'RetrySettings' during execution of some client action.
retry :: MonadClient m => RetrySettings -> m a -> m a
retry r = localState (set (context.settings.retrySettings) r)

-- | Change the default 'PrepareStrategy' for the given client action.
withPrepareStrategy :: MonadClient m => PrepareStrategy -> m a -> m a
withPrepareStrategy s = localState (set (context.settings.prepStrategy) s)

-- | Send a CQL 'Request' to the server and return a 'Response'.
--
-- This function will first ask the clients load-balancing 'Policy' for
-- some host and use its connection pool to acquire a connection for
-- request transmission.
--
-- If all available hosts are busy (i.e. their connection pools are fully
-- utilised), the function will block until a connection becomes available
-- or the maximum wait-queue length has been reached.
request :: (MonadClient m, Tuple a, Tuple b) => Request k a b -> m (Response k a b)
request a = liftClient $ do
    n <- liftIO . hostCount =<< view policy
    snd <$> mkRequest (requestN n) a

mkRequest :: (Tuple a, Tuple b)
          => (Request k a b -> ClientState -> Client (Maybe (Host, Response k a b)))
          -> Request k a b
          -> Client (Host, Response k a b)
mkRequest fn a = do
    s <- ask
    recovering (s^.context.settings.retrySettings.retryPolicy) recoverFrom $ \i -> do
        r <- if i == 0 then fn a s else fn (newRequest s) (adjust s)
        maybe (throwM HostsBusy) return r
  where
    adjust s =
        let x = s^.context.settings.retrySettings.sendTimeoutChange
            y = s^.context.settings.retrySettings.recvTimeoutChange
        in over (context.settings.connSettings.sendTimeout)     (+ x)
         . over (context.settings.connSettings.responseTimeout) (+ y)
         $ s

    newRequest s =
        case s^.context.settings.retrySettings.reducedConsistency of
            Nothing -> a
            Just  c ->
                case a of
                    RqQuery   (Query   q p) -> RqQuery (Query q p { consistency = c })
                    RqExecute (Execute q p) -> RqExecute (Execute q p { consistency = c })
                    RqBatch b               -> RqBatch b { batchConsistency = c }
                    _                       -> a

    recoverFrom =
        [ const $ Handler $ \e -> case e of
            ReadTimeout  {} -> return True
            WriteTimeout {} -> return True
            Overloaded   {} -> return True
            Unavailable  {} -> return True
            ServerError  {} -> return True
            _               -> return False
        , const $ Handler $ \(_ :: ConnectionError) -> return True
        , const $ Handler $ \(_ :: IOException)     -> return True
        , const $ Handler $ \(_ :: HostError)       -> return True
        ]

-- | Invoke 'request1' up to @n@ times with different hosts if no
-- connection is available. May return 'Nothing' if no connection
-- is available on any of the tried hosts.
requestN :: (Tuple b, Tuple a) => Word -> Request k a b -> ClientState -> Client (Maybe (Host, Response k a b))
requestN !n a s = do
    hst <- pickHost (s^.policy)
    res <- request1 hst a s
    case res of
        Just  _ -> return res
        Nothing -> if n > 0 then requestN (n - 1) a s else return Nothing
  where
    pickHost p = maybe (throwM NoHostAvailable) return =<< liftIO (select p)

-- | Get 'Response' from a single 'Host'.
-- May return 'Nothing' if no connection is available.
request1 :: (Tuple a, Tuple b) => Host -> Request k a b -> ClientState -> Client (Maybe (Host, Response k a b))
request1 h a s = do
    p <- Map.lookup h <$> readTVarIO' (s^.hostmap)
    case p of
        Just  x -> with x transaction `catches` handlers
        Nothing -> do
            err $ msg (val "no pool for host " +++ h)
            p' <- mkPool (s^.context) (h^.hostAddr)
            atomically' $ modifyTVar' (s^.hostmap) (Map.alter (maybe (Just p') Just) h)
            request1 h a s
  where
    transaction c = do
        let x = s^.context.settings.connSettings.compression
        let v = s^.context.settings.protoVersion
        r <- parse x <$> C.request c (serialise v x a)
        r `seq` return (h, r)

    handlers =
        [ Handler $ \(e :: ConnectionError) -> onConnectionError h e >> throwM e
        , Handler $ \(e :: IOException)     -> onConnectionError h e >> throwM e
        ]

-- | Execute the given request. If an 'Unprepared' error is returned, this
-- function will automatically try to re-prepare the query and re-execute
-- the original request using the same host which was used for re-preparation.
executeWithPrepare :: (Tuple b, Tuple a) => Maybe Host -> Request k a b -> Client (Response k a b)
executeWithPrepare h q = do
    f <- selectAction h
    r <- mkRequest f q
    case snd r of
        RsError _ (Unprepared _ i) -> do
            pq <- preparedQueries
            qs <- atomically' (PQ.lookupQueryString (QueryId i) pq)
            case qs of
                Nothing -> throwM $ InternalError "Unknown QueryID returned from server"
                Just  s -> do
                    (g, _) <- prepare (Just LazyPrepare) (s :: Raw QueryString)
                    executeWithPrepare (Just g) q
        RsError _ e -> throwM e
        x           -> return x
  where
    selectAction Nothing  = view policy >>= liftIO . hostCount >>= return . requestN
    selectAction (Just x) = return (request1 x)

-- | Prepare the given query according to the given
-- 'PrepareStrategy', returning the resulting 'QueryId'
-- and 'Host' which was used for preparation.
prepare :: (Tuple b, Tuple a) => Maybe PrepareStrategy -> QueryString k a b -> Client (Host, QueryId k a b)
prepare (Just LazyPrepare) qs = do
    s <- ask
    n <- liftIO $ hostCount (s^.policy)
    (h, r) <- mkRequest (requestN n) (RqPrepare (Prepare qs))
    case r of
        RsResult _ (PreparedResult i _ _) -> return (h, i)
        RsError  _ e                      -> throwM e
        _                                 -> throwM UnexpectedResponse
prepare (Just EagerPrepare) qs = view policy
    >>= liftIO . current
    >>= mapM (action (RqPrepare (Prepare qs)))
    >>= first
  where
    action rq h = do
        r <- mkRequest (request1 h) rq
        case snd r of
            RsResult _ (PreparedResult i _ _) -> return (h, i)
            RsError  _ e                      -> throwM e
            _                                 -> throwM UnexpectedResponse
    first (x:_) = return x
    first []    = throwM NoHostAvailable
prepare Nothing qs = do
    ps <- view (context.settings.prepStrategy)
    prepare (Just ps) qs

-- | Execute a prepared query (transparently re-preparing if necessary).
execute :: (Tuple b, Tuple a) => PrepQuery k a b -> QueryParams a -> Client (Response k a b)
execute q p = do
    pq <- view prepQueries
    maybe (new pq) (run Nothing) =<< atomically' (PQ.lookupQueryId q pq)
  where
    run h i = executeWithPrepare h (RqExecute (Execute i p))
    new pq  = do
        (h, i) <- prepare (Just LazyPrepare) (PQ.queryString q)
        atomically' (PQ.insert q i pq)
        run (Just h) i

data DebugInfo = DebugInfo
    { policyInfo :: String     -- ^ 'Policy' string representation
    , jobInfo    :: [InetAddr] -- ^ hosts currently checked for reachability
    , hostInfo   :: [Host]     -- ^ all known hosts
    }

instance Show DebugInfo where
    show dbg = showString "running jobs: "
             . shows (jobInfo dbg)
             . showString "\nknown hosts: "
             . shows (hostInfo dbg)
             . showString "\npolicy info: "
             . shows (policyInfo dbg)
             $ ""

debugInfo :: MonadClient m => m DebugInfo
debugInfo = liftClient $ do
    hosts <- Map.keys <$> (readTVarIO' =<< view hostmap)
    pols  <- liftIO . display =<< view policy
    jbs   <- Jobs.showJobs =<< view jobs
    return $ DebugInfo pols jbs hosts

preparedQueries :: Client PreparedQueries
preparedQueries = view prepQueries

-----------------------------------------------------------------------------
-- Initialisation

-- | Initialise client state with the given 'Settings' using the provided
-- 'Logger' for all it's logging output.
init :: MonadIO m => Logger -> Settings -> m ClientState
init g s = liftIO $ do
    t <- TM.create 250
    c <- tryAll (s^.contacts) (mkConnection t)
    e <- Context s g t <$> signal
    p <- s^.policyMaker
    x <- ClientState e
            <$> pure p
            <*> PQ.new
            <*> newTVarIO (Control Connected c)
            <*> newTVarIO Map.empty
            <*> Jobs.new
    e^.sigMonit |-> onEvent p
    runClient x (initialise c)
    return x
  where
    mkConnection t h = do
        as <- C.resolve h (s^.portnumber)
        NE.fromList as `tryAll` doConnect t

    doConnect t a = do
        Logger.debug g $ msg (val "connecting to " +++ a)
        c <- C.connect (s^.connSettings) t (s^.protoVersion) g a
        Logger.info g $ msg (val "control connection: " +++ c)
        return c

initialise :: Connection -> Client ()
initialise c = do
    startup c
    env <- ask
    pol <- view policy
    ctx <- view context
    l <- local2Host (c^.address) . listToMaybe <$> query c One Discovery.local ()
    r <- discoverPeers ctx c
    (u, d) <- mkHostMap ctx pol (l:r)
    m <- view hostmap
    let h = Map.union u d
    atomically' $ writeTVar m h
    liftIO $ setup pol (Map.keys u) (Map.keys d)
    register c allEventTypes (runClient env . onCqlEvent)
    info $ msg (val "known hosts: " +++ show (Map.keys h))
    j <- view jobs
    for_ (Map.keys d) $ \down ->
        Jobs.add j (down^.hostAddr) True $ monitor ctx 1000000 60000000 down

discoverPeers :: MonadIO m => Context -> Connection -> m [Host]
discoverPeers ctx c = liftIO $ do
    let p = ctx^.settings.portnumber
    map (peer2Host p . asRecord) <$> query c One peers ()

mkHostMap :: Context -> Policy -> [Host] -> Client (Map Host Pool, Map Host Pool)
mkHostMap c p = liftIO . foldrM checkHost (Map.empty, Map.empty)
  where
    checkHost h (up, down) = do
        okay <- acceptable p h
        if okay then do
            isUp <- C.ping (h^.hostAddr)
            if isUp then do
                up' <- Map.insert h <$> mkPool c (h^.hostAddr) <*> pure up
                return (up', down)
            else do
                down' <- Map.insert h <$> mkPool c (h^.hostAddr) <*> pure down
                return (up, down')
        else
            return (up, down)

mkPool :: MonadIO m => Context -> InetAddr -> m Pool
mkPool ctx i = liftIO $ do
    let s = ctx^.settings
    let m = s^.connSettings.maxStreams
    create (connOpen s) connClose (ctx^.logger) (s^.poolSettings) m
  where
    connOpen s = do
        let g = ctx^.logger
        c <- C.connect (s^.connSettings) (ctx^.timeouts) (s^.protoVersion) g i
        Logger.debug g $ "client.connect" .= c
        connInit c `onException` connClose c
        return c

    connInit con = do
        C.startup con
        for_ (ctx^.settings.connSettings.defKeyspace) $
            C.useKeyspace con

    connClose con = do
        Logger.debug (ctx^.logger) $ "client.close" .= con
        C.close con

-----------------------------------------------------------------------------
-- Termination

-- | Terminate client state, i.e. end all running background checks and
-- shutdown all connection pools.  Once this is entered, the client
-- will eventually be shut down, though an asynchronous exception can
-- interrupt the wait for that to occur.
shutdown :: MonadIO m => ClientState -> m ()
shutdown s = liftIO $ asyncShutdown >>= wait
  where
    asyncShutdown = async $ do
        TM.destroy (s^.context.timeouts) True
        Jobs.destroy (s^.jobs)
        ignore $ C.close . view connection =<< readTVarIO (s^.control)
        mapM_ destroy . Map.elems =<< readTVarIO (s^.hostmap)

-----------------------------------------------------------------------------
-- Monitoring

monitor :: Context -> Int -> Int -> Host -> IO ()
monitor ctx initial upperBound h = do
    threadDelay initial
    Logger.info (ctx^.logger) $ msg (val "monitoring: " +++ h)
    hostCheck 0 maxN
  where
    hostCheck :: Int -> Int -> IO ()
    hostCheck n mx = do
        threadDelay (2^(min n mx) * 50000)
        isUp <- C.ping (h^.hostAddr)
        if isUp then do
            ctx^.sigMonit $$ HostUp (h^.hostAddr)
            Logger.info (ctx^.logger) $ msg (val "reachable: " +++ h)
        else do
            Logger.info (ctx^.logger) $ msg (val "unreachable: " +++ h)
            hostCheck (n + 1) mx

    maxN :: Int
    maxN = floor . logBase 2 $ (fromIntegral (upperBound `div` 50000) :: Double)

-----------------------------------------------------------------------------
-- Exception handling

onConnectionError :: Exception e => Host -> e -> Client ()
onConnectionError h exc = do
    warn $ "exception" .= show exc
    e <- ask
    c <- atomically' $ do
        ctrl <- readTVar (e^.control)
        let a = ctrl^.connection.address
        if ctrl^.state == Connected && a == h^.hostAddr then do
            writeTVar (e^.control) (set state Reconnecting ctrl)
            return $ Just (ctrl^.connection)
        else
            return Nothing
    maybe (liftIO . ignore . onEvent (e^.policy) $ HostDown (h^.hostAddr))
          (liftIO . void . async . recovering reconnectPolicy reconnectHandlers . const . continue e)
          c
    Jobs.add (e^.jobs) (h^.hostAddr) True $
        monitor (e^.context) 0 30000000 h
  where
    continue e conn = do
        Jobs.destroy (e^.jobs)
        ignore $ C.close conn
        ignore $ onEvent (e^.policy) (HostDown (h^.hostAddr))
        x <- NE.nonEmpty . map (view hostAddr) . Map.keys <$> readTVarIO (e^.hostmap)
        case x of
            Just  a -> a `tryAll` (runClient e . replaceControl) `onException` reconnect e a
            Nothing -> do
                atomically $ modifyTVar' (e^.control) (set state Disconnected)
                Logger.fatal (e^.context.logger) $ "error-handler" .= val "no host available"

    reconnect e a = do
        Logger.info (e^.context.logger) $ msg (val "reconnecting control ...")
        a `tryAll` (runClient e . replaceControl)

    reconnectPolicy = capDelay 5000000 (exponentialBackoff 5000)

    reconnectHandlers =
        [ const (Handler $ \(_ :: IOException)     -> return True)
        , const (Handler $ \(_ :: ConnectionError) -> return True)
        , const (Handler $ \(_ :: HostError)       -> return True)
        ]

replaceControl :: InetAddr -> Client ()
replaceControl a = do
    ctx <- view context
    ctl <- view control
    let s = ctx^.settings
    c <- C.connect (s^.connSettings) (ctx^.timeouts) (s^.protoVersion) (ctx^.logger) a
    initialise c
    atomically' $ writeTVar ctl (Control Connected c)
    info $ msg (val "new control connection: " +++ c)

onCqlEvent :: Event -> Client ()
onCqlEvent x = do
    info $ "client.event" .= show x
    pol <- view policy
    prt <- view (context.settings.portnumber)
    case x of
        StatusEvent Down sa -> do
            liftIO $ onEvent pol $ HostDown (InetAddr $ mapPort prt sa)
        TopologyEvent RemovedNode sa -> do
            let a = InetAddr $ mapPort prt sa
            hmap <- view hostmap
            atomically' $
                modifyTVar' hmap (Map.filterWithKey (\h _ -> h^.hostAddr /= a))
            liftIO $ onEvent pol $ HostGone a
        StatusEvent Up sa -> do
            s <- ask
            startMonitor s $ (InetAddr $ mapPort prt sa)
        TopologyEvent NewNode sa -> do
            s <- ask
            let ctx  = s^.context
            let hmap = s^.hostmap
            ctrl <- readTVarIO' (s^.control)
            let a = InetAddr $ mapPort prt sa
            let c = ctrl^.connection
            h    <- fromMaybe (Host a "" "") . find ((a == ) . view hostAddr) <$> discoverPeers' ctx c
            okay <- liftIO $ acceptable pol h
            when okay $ do
                p <- mkPool ctx (h^.hostAddr)
                atomically' $ modifyTVar' hmap (Map.alter (maybe (Just p) Just) h)
                liftIO $ onEvent pol (HostNew h)
                Jobs.add (s^.jobs) a False $ runClient s (prepareAllQueries h)
        SchemaEvent _ -> return ()
  where
    mapPort i (SockAddrInet _ a)      = SockAddrInet i a
    mapPort i (SockAddrInet6 _ f a b) = SockAddrInet6 i f a b
    mapPort _ unix                    = unix

    discoverPeers' ctx c = discoverPeers ctx c `catchAll` (const $ return [])

    startMonitor s a = do
        hmp <- readTVarIO' (s^.hostmap)
        case find ((a ==) . view hostAddr) (Map.keys hmp) of
            Just h -> Jobs.add (s^.jobs) a False $ do
                monitor (s^.context) 3000000 60000000 h
                runClient s (prepareAllQueries h)
            Nothing -> return ()

prepareAllQueries :: Host -> Client ()
prepareAllQueries h = do
    pq <- view prepQueries
    qs <- atomically' $ PQ.queryStrings pq
    for_ qs $ \q ->
        let qry = QueryString q :: Raw QueryString in
        mkRequest (request1 h) (RqPrepare (Prepare qry))

-----------------------------------------------------------------------------
-- Utilities

peer2Host :: PortNumber -> Peer -> Host
peer2Host i p = Host (ip2inet i (peerRPC p)) (peerDC p) (peerRack p)

local2Host :: InetAddr -> Maybe (Text, Text) -> Host
local2Host i (Just (dc, rk)) = Host i dc rk
local2Host i Nothing         = Host i "" ""

allEventTypes :: [EventType]
allEventTypes = [TopologyChangeEvent, StatusChangeEvent, SchemaChangeEvent]

tryAll :: NonEmpty a -> (a -> IO b) -> IO b
tryAll (a :| []) f = f a
tryAll (a :| aa) f = f a `catchAll` (const $ tryAll (NE.fromList aa) f)

atomically' :: STM a -> Client a
atomically' = liftIO . atomically

readTVarIO' :: TVar a -> Client a
readTVarIO' = liftIO . readTVarIO