{-# LANGUAGE DuplicateRecordFields #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE NamedFieldPuns #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE ScopedTypeVariables #-}

module Simplex.Messaging.Transport.Server
  ( TransportServerConfig (..),
    defaultTransportServerConfig,
    runTransportServerState,
    SocketState,
    newSocketState,
    runTransportServer,
    runTransportServerSocket,
    runTCPServer,
    runTCPServerSocket,
    startTCPServer,
    loadSupportedTLSServerParams,
    loadTLSServerParams,
    loadFingerprint,
    smpServerHandshake,
    tlsServerCredentials,
  )
where

import Control.Applicative ((<|>))
import Control.Logger.Simple
import Control.Monad
import qualified Crypto.Store.X509 as SX
import Data.Default (def)
import Data.IntMap.Strict (IntMap)
import qualified Data.IntMap.Strict as IM
import Data.List (find)
import Data.Maybe (fromJust, fromMaybe)
import qualified Data.X509 as X
import Data.X509.Validation (Fingerprint (..))
import qualified Data.X509.Validation as XV
import Foreign.C.Error
import GHC.IO.Exception (ioe_errno)
import Network.Socket
import qualified Network.TLS as T
import Simplex.Messaging.Transport
import Simplex.Messaging.Util (catchAll_, labelMyThread, tshow)
import System.Exit (exitFailure)
import System.IO.Error (tryIOError)
import System.Mem.Weak (Weak, deRefWeak)
import UnliftIO (timeout)
import UnliftIO.Concurrent
import qualified UnliftIO.Exception as E
import UnliftIO.STM

data TransportServerConfig = TransportServerConfig
  { logTLSErrors :: Bool,
    tlsSetupTimeout :: Int,
    transportTimeout :: Int,
    alpn :: Maybe [ALPN]
  }
  deriving (Eq, Show)

defaultTransportServerConfig :: TransportServerConfig
defaultTransportServerConfig =
  TransportServerConfig
    { logTLSErrors = True,
      tlsSetupTimeout = 60000000,
      transportTimeout = 40000000,
      alpn = Nothing
    }

serverTransportConfig :: TransportServerConfig -> TransportConfig
serverTransportConfig TransportServerConfig {logTLSErrors} =
  -- TransportConfig {logTLSErrors, transportTimeout = Just transportTimeout}
  TransportConfig {logTLSErrors, transportTimeout = Nothing}

-- | Run transport server (plain TCP or WebSockets) on passed TCP port and signal when server started and stopped via passed TMVar.
--
-- All accepted connections are passed to the passed function.
runTransportServer :: forall c. Transport c => TMVar Bool -> ServiceName -> T.ServerParams -> TransportServerConfig -> (c -> IO ()) -> IO ()
runTransportServer started port params cfg server = do
  ss <- atomically newSocketState
  runTransportServerState ss started port params cfg server

runTransportServerState :: forall c . Transport c => SocketState -> TMVar Bool -> ServiceName -> T.ServerParams -> TransportServerConfig -> (c -> IO ()) -> IO ()
runTransportServerState ss started port = runTransportServerSocketState ss started (startTCPServer started port) (transportName (TProxy :: TProxy c))

-- | Run a transport server with provided connection setup and handler.
runTransportServerSocket :: Transport a => TMVar Bool -> IO Socket -> String -> T.ServerParams -> TransportServerConfig -> (a -> IO ()) -> IO ()
runTransportServerSocket started getSocket threadLabel serverParams cfg server = do
  ss <- atomically newSocketState
  runTransportServerSocketState ss started getSocket threadLabel serverParams cfg server

-- | Run a transport server with provided connection setup and handler.
runTransportServerSocketState :: Transport a => SocketState -> TMVar Bool -> IO Socket -> String -> T.ServerParams -> TransportServerConfig -> (a -> IO ()) -> IO ()
runTransportServerSocketState ss started getSocket threadLabel serverParams cfg server = do
  labelMyThread $ "transport server for " <> threadLabel
  runTCPServerSocket ss started getSocket $ \conn ->
    E.bracket (setup conn >>= maybe (fail "tls setup timeout") pure) closeConnection server
  where
    tCfg = serverTransportConfig cfg
    setup conn = timeout (tlsSetupTimeout cfg) $ do
      labelMyThread $ threadLabel <> "/setup"
      tls <- connectTLS Nothing tCfg serverParams conn
      getServerConnection tCfg (fst $ tlsServerCredentials serverParams) tls

tlsServerCredentials :: T.ServerParams -> (X.CertificateChain, X.PrivKey)
tlsServerCredentials serverParams = case T.sharedCredentials $ T.serverShared serverParams of
  T.Credentials [creds] -> creds
  _ -> error "server has more than one key"

-- | Run TCP server without TLS
runTCPServer :: TMVar Bool -> ServiceName -> (Socket -> IO ()) -> IO ()
runTCPServer started port server = do
  ss <- atomically newSocketState
  runTCPServerSocket ss started (startTCPServer started port) server

-- | Wrap socket provider in a TCP server bracket.
runTCPServerSocket :: SocketState -> TMVar Bool -> IO Socket -> (Socket -> IO ()) -> IO ()
runTCPServerSocket (accepted, gracefullyClosed, clients) started getSocket server =
  E.bracket getSocket (closeServer started clients) $ \sock ->
    forever . E.bracketOnError (safeAccept sock) (close . fst) $ \(conn, _peer) -> do
      cId <- atomically $ stateTVar accepted $ \cId -> let cId' = cId + 1 in cId `seq` (cId', cId')
      let closeConn _ = do
            atomically $ modifyTVar' clients $ IM.delete cId
            gracefulClose conn 5000 `catchAll_` pure () -- catchAll_ is needed here in case the connection was closed earlier
            atomically $ modifyTVar' gracefullyClosed (+ 1)
      tId <- mkWeakThreadId =<< server conn `forkFinally` closeConn
      atomically $ modifyTVar' clients $ IM.insert cId tId

-- | Recover from errors in `accept` whenever it is safe.
-- Some errors are safe to ignore, while blindly restaring `accept` may trigger a busy loop.
--
-- man accept says:
-- @
-- For  reliable  operation the application should detect the network errors defined for the protocol after accept() and treat them like EAGAIN by retrying.
-- In  the  case  of  TCP/IP, these are ENETDOWN, EPROTO, ENOPROTOOPT, EHOSTDOWN, ENONET, EHOSTUNREACH, EOPNOTSUPP, and ENETUNREACH.
-- @
safeAccept :: Socket -> IO (Socket, SockAddr)
safeAccept sock =
  tryIOError (accept sock) >>= \case
    Right r -> pure r
    Left e
      | retryAccept -> logWarn err >> safeAccept sock
      | otherwise -> logError err >> E.throwIO e
      where
        retryAccept = maybe False ((`elem` again) . Errno) errno
        again = [eAGAIN, eNETDOWN, ePROTO, eNOPROTOOPT, eHOSTDOWN, eNONET, eHOSTUNREACH, eOPNOTSUPP, eNETUNREACH]
        err = "socket accept error: " <> tshow e <> maybe "" ((", errno=" <>) . tshow) errno
        errno = ioe_errno e

type SocketState = (TVar Int, TVar Int, TVar (IntMap (Weak ThreadId)))

newSocketState :: STM SocketState
newSocketState = (,,) <$> newTVar 0 <*> newTVar 0 <*> newTVar mempty

closeServer :: TMVar Bool -> TVar (IntMap (Weak ThreadId)) -> Socket -> IO ()
closeServer started clients sock = do
  readTVarIO clients >>= mapM_ (deRefWeak >=> mapM_ killThread)
  close sock
  void . atomically $ tryPutTMVar started False

startTCPServer :: TMVar Bool -> ServiceName -> IO Socket
startTCPServer started port = withSocketsDo $ resolve >>= open >>= setStarted
  where
    resolve =
      let hints = defaultHints {addrFlags = [AI_PASSIVE], addrSocketType = Stream}
       in select <$> getAddrInfo (Just hints) Nothing (Just port)
    select as = fromJust $ family AF_INET6 <|> family AF_INET
      where
        family f = find ((== f) . addrFamily) as
    open addr = do
      sock <- socket (addrFamily addr) (addrSocketType addr) (addrProtocol addr)
      setSocketOption sock ReuseAddr 1
      withFdSocket sock setCloseOnExecIfNeeded
      logInfo $ "binding to " <> tshow (addrAddress addr)
      bind sock $ addrAddress addr
      listen sock 1024
      pure sock
    setStarted sock = atomically (tryPutTMVar started True) >> pure sock

loadTLSServerParams :: FilePath -> FilePath -> FilePath -> Maybe [ALPN] -> IO T.ServerParams
loadTLSServerParams = loadSupportedTLSServerParams supportedParameters

loadSupportedTLSServerParams :: T.Supported -> FilePath -> FilePath -> FilePath -> Maybe [ALPN] -> IO T.ServerParams
loadSupportedTLSServerParams serverSupported caCertificateFile certificateFile privateKeyFile alpn_ = do
  tlsServerParams <- fromCredential <$> loadServerCredential
  pure tlsServerParams {T.serverHooks = maybe def alpnHooks alpn_}
  where
    loadServerCredential :: IO T.Credential
    loadServerCredential =
      T.credentialLoadX509Chain certificateFile [caCertificateFile] privateKeyFile >>= \case
        Right credential -> pure credential
        Left _ -> putStrLn "invalid credential" >> exitFailure
    fromCredential :: T.Credential -> T.ServerParams
    fromCredential credential =
      def
        { T.serverWantClientCert = False,
          T.serverShared = def {T.sharedCredentials = T.Credentials [credential]},
          T.serverHooks = def,
          T.serverSupported = serverSupported
        }
    alpnHooks supported = def {T.onALPNClientSuggest = Just $ pure . fromMaybe "" . find (`elem` supported)}

loadFingerprint :: FilePath -> IO Fingerprint
loadFingerprint certificateFile = do
  (cert : _) <- SX.readSignedObject certificateFile
  pure $ XV.getFingerprint (cert :: X.SignedExact X.Certificate) X.HashSHA256