1 files changed, 23 insertions, 1 deletions
diff --git a/src/Erebos/Network.hs b/src/Erebos/Network.hs
index d8e868a..32d06f2 100644
--- a/src/Erebos/Network.hs
+++ b/src/Erebos/Network.hs
@@ -24,6 +24,7 @@ module Erebos.Network (
     sendToPeerStored, sendManyToPeerStored,
     sendToPeerWith,
     runPeerService,
+    modifyServiceGlobalState,
 
     discoveryPort,
 ) where
@@ -899,7 +900,7 @@ sendToPeerWith peer fobj = do
          Left err -> throwError err
 
 
-lookupService :: forall s. Service s => Proxy s -> [SomeService] -> Maybe (SomeService, ServiceAttributes s)
+lookupService :: forall s proxy. Service s => proxy s -> [SomeService] -> Maybe (SomeService, ServiceAttributes s)
 lookupService proxy (service@(SomeService (_ :: Proxy t) attr) : rest)
     | Just (Refl :: s :~: t) <- eqT = Just (service, attr)
     | otherwise = lookupService proxy rest
@@ -954,6 +955,27 @@ runPeerServiceOn mbservice peer handler = liftIO $ do
         _ -> atomically $ do
             logd $ "unhandled service '" ++ show (toUUID svc) ++ "'"
 
+modifyServiceGlobalState
+    :: forall s a m proxy. (Service s, MonadIO m, MonadError String m)
+    => Server -> proxy s
+    -> (ServiceGlobalState s -> ( ServiceGlobalState s, a ))
+    -> m a
+modifyServiceGlobalState server proxy f = do
+    let svc = serviceID proxy
+    case lookupService proxy (serverServices server) of
+        Just ( service, _ ) -> do
+            liftIO $ atomically $ do
+                global <- takeTMVar (serverServiceStates server)
+                ( global', res ) <- case fromMaybe (someServiceEmptyGlobalState service) $ M.lookup svc global of
+                    SomeServiceGlobalState (_ :: Proxy gs) gs -> do
+                        (Refl :: s :~: gs) <- return $ fromMaybe (error "service ID mismatch in global map") eqT
+                        let ( gs', res ) = f gs
+                        return ( M.insert svc (SomeServiceGlobalState (Proxy @s) gs') global, res )
+                putTMVar (serverServiceStates server) global'
+                return res
+        Nothing -> do
+            throwError $ "unhandled service '" ++ show (toUUID svc) ++ "'"
+
 
 foreign import ccall unsafe "Network/ifaddrs.h join_multicast" cJoinMulticast :: CInt -> Ptr CSize -> IO (Ptr Word32)
 foreign import ccall unsafe "Network/ifaddrs.h local_addresses" cLocalAddresses :: Ptr CSize -> IO (Ptr InetAddress)