{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE CPP #-}
module Network.QueryResponse.TCP where

#ifdef THREAD_DEBUG
import Control.Concurrent.Lifted.Instrument
#else
import Control.Concurrent.Lifted
import GHC.Conc                  (labelThread)
#endif

import Control.Arrow
import Control.Concurrent.STM
import Control.Monad
import Data.ByteString (ByteString,hPut)
import Data.Function
import Data.Hashable
import Data.Maybe
import Data.Ord
import Data.Time.Clock.POSIX
import Data.Word
import Data.String (IsString(..))
import Network.BSD
import Network.Socket
import System.Timeout
import System.IO
import System.IO.Error

import DebugTag
import DPut
import Connection.Tcp (socketFamily)
import qualified Data.MinMaxPSQ as MM
import Network.QueryResponse

data TCPSession st
    = PendingTCPSession
    | TCPSession
        { tcpHandle :: Handle
        , tcpState  :: st
        , tcpThread :: ThreadId
        }

newtype TCPAddress = TCPAddress SockAddr
 deriving (Eq,Ord,Show)

instance Hashable TCPAddress where
    hashWithSalt salt (TCPAddress x) = case x of
        SockAddrInet port addr   -> hashWithSalt salt (fromIntegral port :: Word16,addr)
        SockAddrInet6 port b c d -> hashWithSalt salt (fromIntegral port :: Word16,b,c,d)
        _                        -> 0

data TCPCache st = TCPCache
    { lru    :: TVar (MM.MinMaxPSQ' TCPAddress (Down POSIXTime) (TCPSession st))
    , tcpMax :: Int
    }

data SessionProtocol x y = SessionProtocol
    { streamGoodbye :: IO ()        -- ^ "Goodbye" protocol upon termination.
    , streamDecode  :: IO (Maybe x) -- ^ Parse inbound messages.
    , streamEncode  :: y -> IO ()   -- ^ Serialize outbound messages.
    }

data StreamHandshake addr x y = StreamHandshake
    { streamHello :: addr -> Handle -> IO (SessionProtocol x y) -- ^ "Hello" protocol upon fresh connection.
    , streamAddr  :: addr -> SockAddr
    }

killSession :: TCPSession st -> IO ()
killSession PendingTCPSession       = return ()
killSession TCPSession{tcpThread=t} = killThread t

showStat :: IsString p => TCPSession st -> p
showStat r = case r of PendingTCPSession -> "pending."
                       TCPSession {}     -> "established."

acquireConnection :: MVar (Maybe (Either a (x, addr)))
                           -> TCPCache (SessionProtocol x y)
                           -> StreamHandshake addr x y
                           -> addr
                           -> Bool
                           -> IO (Maybe (y -> IO ()))
acquireConnection mvar tcpcache stream addr bDoCon = do
    now <- getPOSIXTime
    -- dput XTCP $ "acquireConnection 0 " ++ show (streamAddr stream addr)
    entry <- atomically $ do
        c <- readTVar (lru tcpcache)
        let v = MM.lookup' (TCPAddress $ streamAddr stream addr) c
        case v of
            Nothing | bDoCon -> writeTVar (lru tcpcache)
                                $ MM.insert' (TCPAddress $ streamAddr stream addr) PendingTCPSession (Down now) c
                    | otherwise -> return ()
            Just (tm, v) -> modifyTVar' (lru tcpcache) $ MM.insert' (TCPAddress $ streamAddr stream addr) v (Down now)
        return v
    -- dput XTCP $ "acquireConnection 1 " ++ show (streamAddr stream addr, fmap (second showStat) entry)
    case entry of
        Nothing -> fmap join $ forM (guard bDoCon) $ \() -> do
            proto <- getProtocolNumber "tcp"
            mh <- catchIOError (do h <- timeout 10000000 $ do
                                       sock <- socket (socketFamily $ streamAddr stream addr) Stream proto
                                       connect sock (streamAddr stream addr) `catchIOError` (\e -> close sock)
                                       h <- socketToHandle sock ReadWriteMode
                                       hSetBuffering h NoBuffering
                                       return h
                                   return h)
                               $ \e -> return Nothing
            ret <- fmap join $ forM mh $ \h -> do
                st <- streamHello stream addr h
                dput XTCP $ "TCP Connected! " ++ show (streamAddr stream addr)
                signal <- newTVarIO False
                let showAddr a = show (streamAddr stream a)
                rthread <- forkLabeled ("tcp:"++showAddr addr) $ do
                  atomically (readTVar signal >>= check)
                  fix $ \loop -> do
                    x <- streamDecode st
                    dput XTCP $ "TCP streamDecode " ++ show (streamAddr stream addr) ++ " --> " ++ maybe "Nothing" (const "got") x
                    case x of
                        Just u -> do
                            m <- timeout (1000000) $ putMVar mvar $ Just $ Right (u, addr)
                            when (isNothing m) $ do
                                dput XTCP $ "TCP "++show (streamAddr stream addr) ++ " dropped packet."
                                tryTakeMVar mvar
                                return ()
                            loop
                        Nothing -> do
                            dput XTCP $ "TCP disconnected: " ++ show (streamAddr stream addr)
                            do atomically $ modifyTVar' (lru tcpcache)
                                       $ MM.delete (TCPAddress $ streamAddr stream addr)
                            c <- atomically $ readTVar (lru tcpcache)
                            now <- getPOSIXTime
                            forM_ (zip [1..] $ MM.toList c) $ \(i,MM.Binding (TCPAddress addr) r (Down tm)) -> do
                                dput XTCP $ unwords [show i ++ ".", "Still connected:",  show addr, show (now - tm), showStat r]
                            hClose h
                let v = TCPSession
                        { tcpHandle = h
                        , tcpState  = st
                        , tcpThread = rthread
                        }
                t <- getPOSIXTime
                retires <- atomically $ do
                    c <- readTVar (lru tcpcache)
                    let (rs,c') = MM.takeView (tcpMax tcpcache)
                                $ MM.insert' (TCPAddress $ streamAddr stream addr) v (Down t) c
                    writeTVar (lru tcpcache) c'
                    writeTVar signal True
                    return rs
                forM_ retires $ \(MM.Binding (TCPAddress k) r _) -> void $ forkLabeled ("tcp-close:"++show k) $ do
                    dput XTCP $ "TCP dropped: " ++ show k
                    killSession r
                    case r of TCPSession {tcpState=st,tcpHandle=h} -> do
                                    streamGoodbye st
                                    hClose h
                              _ -> return ()

                return $ Just $ streamEncode st
            when (isNothing ret) $ do
                atomically $ modifyTVar' (lru tcpcache) $ MM.delete (TCPAddress $ streamAddr stream addr)
            return ret
        Just (tm, PendingTCPSession)
            | not bDoCon -> return Nothing
            | otherwise  -> fmap join $ timeout 10000000 $ atomically $ do
                c <- readTVar (lru tcpcache)
                let v = MM.lookup' (TCPAddress $ streamAddr stream addr) c
                case v of
                    Just (_,TCPSession{tcpState=st}) -> return $ Just $ streamEncode st
                    Nothing                          -> return Nothing
                    _                                -> retry
        Just (tm, v@TCPSession {tcpState=st}) -> return $ Just $ streamEncode st

closeAll :: TCPCache (SessionProtocol x y) -> StreamHandshake addr x y -> IO ()
closeAll tcpcache stream = do
    dput XTCP "TCP.closeAll called."
    cache <- atomically $ swapTVar (lru tcpcache) MM.empty
    forM_ (MM.toList cache) $ \(MM.Binding (TCPAddress addr) r tm) -> do
        killSession r
        case r of TCPSession{tcpState=st,tcpHandle=h} -> streamGoodbye st >> hClose h
                  _                                   -> return ()

-- Use a cache of TCP client connections for sending (and receiving) packets.
-- The boolean value prepended to the message allows the sender to specify
-- whether or not a new connection will be initiated if neccessary.  If 'False'
-- is passed, then the packet will be sent only if there already exists a
-- connection.
tcpTransport :: Int -- ^ maximum number of TCP links to maintain.
                -> StreamHandshake addr x y
                -> IO (TCPCache (SessionProtocol x y), TransportA err addr x (Bool,y))
tcpTransport maxcon stream = do
    msgvar <- newEmptyMVar
    tcpcache <- atomically $ (`TCPCache` maxcon) <$> newTVar (MM.empty)
    return $ (,) tcpcache Transport
        { awaitMessage   = \f -> takeMVar msgvar >>= \x -> f x `catchIOError` (\e -> dput XTCP ("TCP transport stopped. " ++ show e) >> f Nothing)
        , sendMessage    = \addr (bDoCon,y) -> do
                                void . forkLabeled "tcp-send" $ do
                                    msock <- acquireConnection msgvar tcpcache stream addr bDoCon
                                    mapM_ ($ y) msock
                                  `catchIOError` \e -> dput XTCP $ "TCP-send: " ++ show e
        , closeTransport = closeAll tcpcache stream >> putMVar msgvar Nothing
        }