Add fallback placement for falled link based placement spots

src/Dodge/LevelGen.hs

@@ -26,6 +26,8 @@ import Control.Monad.State
 import Control.Lens
 import qualified Data.IntSet as IS
 
+-- potential failure cases: randomising using an already set link position
+-- others?
 placeSpot :: World -> (Room , Placement) -> World
 placeSpot w (rm, plmnt@Placement{_placementSpot=PSRoomRand i}) =
     let (ps,g) = runState (_rmRandPSs rm !! i) $_randGen w
@@ -40,20 +42,24 @@ placeSpot w (rm, plmnt@Placement{}) =
 placeSpot w (rm, PlacementUsingPos p subpl) = placeSpot w (rm, subpl (shiftPoint3By shift p))
   where
     shift = _rmShift rm
--- random placements SHOULD be dealt with already (see assignPlacementSpots)
 placeSpot w (rm, RandomPlacement rplmnt) = placeSpot (w & randGen .~ g) (rm, plmnt)
   where
     (plmnt, g) = runState rplmnt (_randGen w)
 
--- ok, this is unsafe, but whatever
+-- this should be woven into placeSpot
 assignPSToLnk :: Room -> Placement -> World -> World
-assignPSToLnk rm plmnt w = placeSpot (w & randGen .~ g) (rm, updatePS (f lnk) plmnt)
+assignPSToLnk rm plmnt w = case lnks of
+    (lnk:_) -> placeSpot (w & randGen .~ g) (rm, updatePS (f lnk) plmnt)
+    [] -> case fallback of
+        Nothing -> w
+        Just plmnt' -> placeSpot w (rm,plmnt')
   where
     rps = _placementSpot plmnt
+    fallback = _psFallback rps
     test = _psLinkTest rps
-    (lnk:_,g) = runState (shuffle $ filter test $ map (invShiftLinkBy $ _rmShift rm) $ _rmLinks rm) 
+    (lnks,g) = runState (shuffle $ filter test $ map (invShiftLinkBy $ _rmShift rm) $ _rmLinks rm) 
         $ _randGen w
-    f x (PSLnk t s)
+    f x (PSLnk t s _)
         | t x = uncurry PS $ s x
     f _ ps = ps
     invShiftLinkBy :: (Point2,Float) -> (Point2,Float) -> (Point2,Float)