-- 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 GeneralizedNewtypeDeriving #-}
{-# LANGUAGE OverloadedStrings          #-}
{-# LANGUAGE ScopedTypeVariables        #-}
{-# LANGUAGE TemplateHaskell            #-}

module Database.CQL.IO.Client
    ( Client
    , MonadClient (..)
    , ClientState
    , DebugInfo   (..)
    , runClient
    , Database.CQL.IO.Client.init
    , shutdown
    , request
    , command
    , retry
    , debugInfo
    ) where

import Control.Applicative
import Control.Concurrent (threadDelay)
import Control.Concurrent.Async (async)
import Control.Concurrent.STM hiding (retry)
import Control.Exception (IOException)
import Control.Lens hiding ((.=), Context)
import Control.Monad (unless, void, when)
import Control.Monad.Catch
import Control.Monad.IO.Class
import Control.Monad.Reader (ReaderT, runReaderT, MonadReader, ask)
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.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 qualified Control.Monad.Reader       as Reader
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.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
    , _control  :: TVar Control
    , _failures :: TVar Word64
    , _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' oder 'command'.
-- 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
               )

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

-- | 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

-----------------------------------------------------------------------------
-- 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)

-- | 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
    s <- ask
    n <- liftIO $ hostCount (s^.policy)
    recovering (s^.context.settings.retrySettings.retryPolicy) recoverFrom $ \i ->
        if i == 0 then
            getResponse a s n
        else let s' = adjust s in
            getResponse (newRequest s) s' n
  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 })
                    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
        ]

getResponse :: (Tuple a, Tuple b) => Request k a b -> ClientState -> Word -> Client (Response k a b)
getResponse a s n = do
    h <- pickHost (s^.policy)
    p <- Map.lookup h <$> readTVarIO' (s^.hostmap)
    case p of
        Just  x -> action x `catches` handlers h
        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)
            getResponse a s n
  where
    action p = do
        res <- tryWith p go
        case res of
            Just  r -> return r
            Nothing ->
                if n > 0 then
                    getResponse a s (n - 1)
                else case s^.context.settings.maxWaitQueue of
                    Nothing -> with p transaction
                    Just  q -> again q p

    go h = do
        atomically $ modifyTVar' (s^.failures) $ \x -> if x > 0 then x - 1 else 0
        transaction h

    again q p = do
        k <- atomically' $ do
            k <- readTVar (s^.failures)
            unless (k == q) $
                writeTVar (s^.failures) (k + 1)
            return k
        unless (k < q) $
            throwM HostsBusy
        with p go

    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 r

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

    pickHost p = maybe (throwM NoHostAvailable) return =<< liftIO (select p)

-- | Like 'request' but not returning any result.
command :: MonadClient m => Request k () () -> m ()
command = void . request

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

-----------------------------------------------------------------------------
-- 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
            <*> newTVarIO (Control Connected c)
            <*> newTVarIO 0
            <*> newTVarIO Map.empty
            <*> Jobs.new
    e^.sigMonit |-> onEvent p
    runClient x (initialise c)
    return x
  where
    mkConnection t h = do
        a <- C.resolve h (s^.portnumber)
        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) $ 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.
shutdown :: MonadIO m => ClientState -> m ()
shutdown s = liftIO $ 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) $
        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 ->
            startMonitor $ (InetAddr $ mapPort prt sa)
        TopologyEvent NewNode sa -> do
            ctx  <- view context
            hmap <- view hostmap
            ctrl <- readTVarIO' =<< view 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
        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 a = do
        hmp <- readTVarIO' =<< view hostmap
        case find ((a ==) . view hostAddr) (Map.keys hmp) of
            Just h  -> do
                ctx <- view context
                jbs <- view jobs
                Jobs.add jbs a $ monitor ctx 3000000 60000000 h
            Nothing -> return ()

-----------------------------------------------------------------------------
-- 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