{-# LANGUAGE OverloadedStrings, DeriveGeneric, GeneralizedNewtypeDeriving #-}
{-# LANGUAGE FlexibleContexts, FlexibleInstances, ScopedTypeVariables #-}

module WebSockets (
	connectionOptions,
	runClientApp,
	clientApp,
	protocolError,
	relayFromSocket,
	relayToSocket,
	negotiateWireVersion,
	WireProtocol(..),
	Mode(..),
	ClientSends(..),
	ServerSends(..),
) where

import Types
import SessionID
import ProtocolBuffers
import PrevActivity

import Network.WebSockets hiding (Message)
import Control.Concurrent.STM
import Control.Concurrent.STM.TMChan
import Control.Concurrent.Async
import Control.Exception
import GHC.Generics (Generic)
import Data.Aeson (FromJSON, ToJSON)
import Data.ProtocolBuffers
import qualified Data.Aeson
import qualified Data.Serialize
import qualified Data.Text as T
import qualified Data.ByteString.Lazy as L
import Data.List
import Data.Monoid
import Control.Monad

-- | Enable compression.
connectionOptions :: ConnectionOptions
connectionOptions = defaultConnectionOptions
	{ connectionCompressionOptions =
		PermessageDeflateCompression defaultPermessageDeflate
	}

-- For some reason, runClient throws ConnectionClosed
-- when the server hangs up cleanly. Catch this unwanted exception.
-- See https://github.com/jaspervdj/websockets/issues/142
runClientApp :: ClientApp a -> IO (Maybe a)
runClientApp app = do
	rv <- newEmptyTMVarIO
	let go conn = do
		r <- app conn
		atomically $ putTMVar rv r
	catchJust catchconnclosed
		(runClientWith "localhost" 8081 "/" connectionOptions [] go)
		(\_ -> return ())
	atomically (tryReadTMVar rv)
  where
	catchconnclosed ConnectionClosed = Just ()
	catchconnclosed _ = Nothing

-- | Make a client that sends and receives AnyMessages over a websocket.
clientApp
	:: Mode
	-> RecentActivity
	-> (sent -> AnyMessage)
	-> (AnyMessage -> Maybe received)
	-> (TMChan sent -> TMChan received -> SessionID -> IO a)
	-> ClientApp a
clientApp mode recentactivity mksent filterreceived a conn = do
	-- Ping every 30 seconds to avoid timeouts caused by proxies etc.
	forkPingThread conn 30
	_v <- negotiateWireVersion conn
	sendBinaryData conn (SelectMode ClientSends mode)
	r <- receiveData conn
	case r of
		Ready ServerSends sid -> bracket setup cleanup (go sid)
		WireProtocolError e -> error e
		_ -> protocolError conn "Did not get expected Ready message from server"
  where
	setup = do
		schan <- newTMChanIO
		rchan <- newTMChanIO
		sthread <- async $ relayToSocket conn mksent $
			atomically (readTMChan schan)
		rthread <- async $ do
			relayFromSocket conn recentactivity (waitTillDrained rchan) $ \v -> do
				case filterreceived v of
					Nothing -> return ()
					Just r -> atomically $ writeTMChan rchan r
			-- Server sent Done, so close channels.
			atomically $ do
				closeTMChan schan
				closeTMChan rchan
		return (schan, rchan, sthread, rthread)
	cleanup (schan, _, sthread, rthread) = do
		sendBinaryData conn Done
		atomically $ closeTMChan schan
		-- Wait for any more data from the server.
		-- These often die with a ConnectionClosed.
		void $ waitCatch sthread
		cancel rthread
		void $ waitCatch rthread
	go sid (schan, rchan, _, _) = a schan rchan sid

waitTillDrained :: TMChan a -> IO ()
waitTillDrained c = atomically $ do
	e <- isEmptyTMChan c
	if e
		then return ()
		else retry

relayFromSocket :: Connection -> RecentActivity -> IO () -> (AnyMessage -> IO ()) -> IO ()
relayFromSocket conn recentactivity waitprevprocessed sender = go
  where
	go = do
		r <- receiveData conn
		case r of
			AnyMessage msg -> do
				waitprevprocessed
				msg' <- atomically $
					restorePrevActivityHash recentactivity msg
				sender msg'
				go
			Done -> return ()
			WireProtocolError e -> protocolError conn e
			_ -> protocolError conn "Protocol error"

relayToSocket :: Connection -> (received -> AnyMessage) -> IO (Maybe received) -> IO ()
relayToSocket conn mksent getter = go
  where
	go = do
		mmsg <- getter
		case mmsg of
			Nothing -> return ()
			Just msg -> do
				sendBinaryData conn $ AnyMessage $
					removePrevActivityHash $ mksent msg
				go

-- | Framing protocol used over a websocket connection.
--
-- This is an asynchronous protocol; both client and server can send
-- messages at the same time.
--
-- Messages that only one can send are tagged with ClientSends or
-- ServerSends.
data WireProtocol
	= Version [WireVersion]
	| SelectMode ClientSends Mode
	| Ready ServerSends SessionID
	| AnyMessage AnyMessage
	| Done
	| WireProtocolError String

data ServerSends = ServerSends
data ClientSends = ClientSends

instance WebSocketsData WireProtocol where
	toLazyByteString (Version v) = "V" <> Data.Aeson.encode v
	toLazyByteString (SelectMode _ m) = "M" <> Data.Aeson.encode m
	toLazyByteString (Ready _ sid) = "R" <> Data.Aeson.encode sid
	toLazyByteString (AnyMessage msg) = "L" <>
		let pmsg = toProtocolBuffer msg :: AnyMessageP
		in Data.Serialize.runPutLazy (encodeMessage pmsg)
	toLazyByteString Done = "D"
	toLazyByteString (WireProtocolError s) = "E" <> Data.Aeson.encode s
	fromLazyByteString b = case L.splitAt 1 b of
		("V", v) -> maybe (WireProtocolError "invalid JSON in Version")
			Version
			(Data.Aeson.decode v)
		("M", m) -> maybe (WireProtocolError "invalid JSON in Mode")
			(SelectMode ClientSends)
			(Data.Aeson.decode m)
		("R", sid) -> maybe (WireProtocolError "invalid JSON in SessionID")
			(Ready ServerSends)
			(Data.Aeson.decode sid)
		("L", l) -> case Data.Serialize.runGetLazy decodeMessage l of
			Left err -> WireProtocolError $ "Protocol buffers decode error: " ++ err
			Right (pmsg :: AnyMessageP) -> AnyMessage (fromProtocolBuffer pmsg)
		("D", "") -> Done
		("E", s) -> maybe (WireProtocolError "invalid JSON in WireProtocolError")
			WireProtocolError
			(Data.Aeson.decode s)
		_ -> WireProtocolError "received unknown websocket message"
	fromDataMessage = fromLazyByteString . fromDataMessage

protocolError :: Connection -> String -> IO a
protocolError conn err = do
	sendBinaryData conn (WireProtocolError err)
	sendClose conn Done
	error err

newtype WireVersion = WireVersion T.Text
	deriving (Show, Eq, Generic, Ord)

instance FromJSON WireVersion
instance ToJSON WireVersion

supportedWireVersions :: [WireVersion]
supportedWireVersions = [WireVersion "1"]

-- | Send supportedWireVersions and at the same time receive it from
-- the remote side. The highest version present in both lists will be used.
negotiateWireVersion :: Connection -> IO WireVersion
negotiateWireVersion conn = do
	(_, resp) <- concurrently
		(sendBinaryData conn $ Version supportedWireVersions)
		(receiveData conn)
	case resp of
		Version remoteversions -> case reverse (intersect (sort supportedWireVersions) (sort remoteversions)) of
			(v:_) -> return v
			[] -> protocolError conn $
				"Unable to negotiate protocol Version. I support: " ++ show supportedWireVersions ++ " They support: " ++ show remoteversions
		_ -> protocolError conn "Protocol error, did not receive Version"

-- | Modes of operation that can be requested for a websocket connection.
data Mode
	= InitMode T.Text -- ^ Text is unused, but reserved for expansion
	| ConnectMode T.Text -- ^ Text specifies the SessionID to connect to
	deriving (Show, Eq, Generic)

instance FromJSON Mode
instance ToJSON Mode where