Implement re-synchronization after connection loss

src/Automaton.hs

@@ -14,7 +14,7 @@ import qualified Data.Map as Map (delete, empty, member)
 import Control.Monad.Reader (ReaderT, ask)
 import Control.Monad.Trans (lift)
 import Hanafuda.KoiKoi (Step(..))
-import Hanafuda.Message (T(..), FromClient(..))
+import Hanafuda.Message (Coordinates(..), FromClient(..), T(..), orderCoordinates)
 import qualified Hanafuda.Message as Message (
     T(..), FromClient, PublicGame(..), PublicState(..)
   )
@@ -82,6 +82,22 @@ answer state (Error {error}) = do
   debug $ "Received error from server : " `append` pack error
   return state
 
+answer state@(Connected {games}) (Relay {from, message = Sync {latestKnown}})
+  | not $ Map.member from games =
+      send (Yield {onGameID = gameID latestKnown, to = from}) >> return state
+  | otherwise =
+    case orderCoordinates latestKnownHere latestKnown of
+      Just LT -> send $ Yield {onGameID = gameID latestKnown, to = from}
+      Just GT -> send $ Share {gameSave = game}
+      _ -> return ()
+    >> return state
+    where
+      game = games ! from
+      latestKnownHere = Message.coordinates $ Message.public game
+
+answer state@(Connected {games}) (Relay {from, message = Yield {}}) =
+  send (Share {gameSave = games ! from}) >> return state
+
 {-
  - Ignore
  -}