backup savegames in case of computer hardware malfunction

The backups are removed at game over, so permadeath still enforced.

src/Action.hs

@@ -11,6 +11,7 @@ import Display2 hiding (display)
 import Message
 import State
 import Level
+import qualified Save
 
 newtype Action a = Action
   { runAction ::
@@ -53,7 +54,7 @@ handlerToIO :: Session -> State -> Message -> Action () -> IO ()
 handlerToIO session state msg h =
   runAction h
     session
-    (shutdown session)         -- get out of the game
+    (Save.rmBkp (sconfig state) >> shutdown session)  -- get out of the game
     (perception_ state)        -- cached perception
     (\ _ _ x -> return x)      -- final continuation returns result
     (ioError $ userError "unhandled abort")

src/Actions.hs

@@ -25,9 +25,9 @@ import Message
 import Monster
 import Perception
 import Random
-import qualified Save as S
 import State
 import qualified Config
+import qualified Save
 
 displayHistory :: Action ()
 displayHistory =
@@ -52,7 +52,7 @@ saveGame =
       then do
         -- Save the game state
         st <- get
-        liftIO $ S.saveGame st
+        liftIO $ Save.saveGame st
         ln <- gets (lname . slevel)
         let total = calculateTotal st
             status = H.Camping ln
@@ -400,6 +400,9 @@ lvlchange vdir =
                   updatePlayerBody (\ p -> p { mloc = nloc })
                   -- Change the level of the player recorded in cursor.
                   modify (updateCursor (\ c -> c { creturnLn = nln }))
+                  -- Create a backup of the savegame.
+                  state <- get
+                  liftIO $ Save.saveGame state >> Save.mvBkp (sconfig state)
       _ -> -- no stairs
         if targeting
         then do

src/Config.hs

@@ -44,7 +44,7 @@ defaultCP :: CP
 defaultCP = toCP defCF
 
 -- | Path to the user configuration file.
-file :: IO String
+file :: IO FilePath
 file =
   do
     appData <- getAppUserDataDirectory "LambdaHack"

src/Save.hs

@@ -9,7 +9,7 @@ import State
 import qualified Config
 
 -- | Name of the save game.
-file :: Config.CP -> IO String
+file :: Config.CP -> IO FilePath
 file config = Config.getFile config "files" "saveGame"
 
 -- | We save a simple serialized version of the current level and
@@ -18,7 +18,7 @@ saveGame :: State -> IO ()
 saveGame state =
   do
     f <- file (sconfig state)
-    encodeCompressedFile f (state,False)
+    encodeCompressedFile f (state, False)
 
 -- | Restore a saved game. Returns either the current level and
 -- game state, or a string containing an error message if restoring
@@ -27,10 +27,26 @@ restoreGame :: Config.CP -> IO (Either State String)
 restoreGame config =
   E.catch (do
              f <- file config
-             r <- strictDecodeCompressedFile f
-             removeFile f
-             case r of
-               (x,z) -> (z :: Bool) `seq` return $ Left x)
+             (x, z) <- strictDecodeCompressedFile f
+             mvBkp config
+             (z :: Bool) `seq` return $ Left x)
           (\ e -> case e :: IOException of
-                    _ -> return (Right $ "Restore failed: " ++
-                                 (unwords . lines) (show e)))
+                    _ -> return (Right $
+                                   "Restore failed: "
+                                   ++ (unwords . lines) (show e)))
+
+-- | Move the savegame file to a backup slot.
+mvBkp :: Config.CP -> IO ()
+mvBkp config =
+  do
+    f <- file config
+    renameFile f (f ++ ".bkp")
+
+-- | Remove the backup of the savegame. Should be called before any
+-- non-error exit from the game.
+rmBkp :: Config.CP -> IO ()
+rmBkp config =
+  do
+    f <- file config
+    E.catch (removeFile (f ++ ".bkp"))
+      (\ e -> case e :: IOException of _ -> return ())