initial implementation of bat's update function (todo: make bat oscillate up and down while it also moves in x axis, and also code bat's collisions with player, adding to falling list if necessary, or being filtered by player's attack)

fcore/constants.sml

@@ -30,6 +30,7 @@ struct
   val enemySize = 35
   val enemySizeReal: Real32.real = 35.0
   val moveEnemyBy = 3
+  val batRestLimit = 155
 
   val moveProjectileBy = 11
 end

fcore/enemy/enemy-behaviour.sml

@@ -499,6 +499,55 @@ struct
         end
     end
 
+  fun updateStraightBat
+    (player, enemy, walls, wallTree, projectileTree, enemyList, fallingList) =
+    let
+      val {x, y, batRest, ...} = enemy
+      val size = Constants.enemySize
+    in
+      if QuadTree.hasCollisionAt (x, y, size, size, ~1, wallTree) then
+        (* has collision with wall *)
+        let
+          val enemy =
+            if batRest >= Constants.batRestLimit then
+              (* make enemy move in opposite direction *)
+              case #xAxis enemy of
+                MOVE_RIGHT =>
+                  EnemyPatch.withPatches
+                    ( enemy
+                    , [ EnemyPatch.W_X_AXIS MOVE_LEFT
+                      , EnemyPatch.W_X (x - (Constants.moveEnemyBy * 9))
+                      ]
+                    )
+              | MOVE_LEFT =>
+                  EnemyPatch.withPatches
+                    ( enemy
+                    , [ EnemyPatch.W_X_AXIS MOVE_RIGHT
+                      , EnemyPatch.W_X (x + (Constants.moveEnemyBy * 9))
+                      ]
+                    )
+              | _ => enemy
+            else
+              (* keep resting until we hit rest limit *)
+              EnemyPatch.withPatch (enemy, EnemyPatch.W_BAT_REST (batRest + 1))
+        in
+          (enemy :: enemyList, fallingList)
+        end
+      else
+        (* no collision, so continue moving in direction *)
+        let
+          val patches =
+            case #xAxis enemy of
+              MOVE_RIGHT => [EnemyPatch.W_X (x + Constants.moveEnemyBy)]
+            | MOVE_LEFT => [EnemyPatch.W_X (x - Constants.moveEnemyBy)]
+            | STAY_STILL => []
+          val patches = EnemyPatch.W_BAT_REST 0 :: patches
+          val enemy = EnemyPatch.withPatches (enemy, patches)
+        in
+          (enemy :: enemyList, fallingList)
+        end
+    end
+
   fun updateEnemyState
     ( enemy
     , projectiles
@@ -541,5 +590,15 @@ struct
             , enemyList
             , fallingList
             )
+      | STRAIGHT_BAT =>
+          updateStraightBat
+            ( player
+            , enemy
+            , walls
+            , wallTree
+            , projectileTree
+            , enemyList
+            , fallingList
+            )
     end
 end

fcore/enemy/enemy-patch.sml

@@ -8,6 +8,7 @@ sig
   | W_Y_AXIS of GameType.y_axis
   | W_PLAT_ID of int
   | W_NEXT_PLAT_ID of int
+  | W_BAT_REST of int
 
   val withPatch: GameType.enemy * enemy_patch -> GameType.enemy
 
@@ -24,6 +25,7 @@ struct
   | W_Y_AXIS of GameType.y_axis
   | W_PLAT_ID of int
   | W_NEXT_PLAT_ID of int
+  | W_BAT_REST of int
 
   fun mkEnemy
     (id, health, x, y, xAxis, yAxis, variant, platID, nextPlatID, batRest) =
@@ -136,6 +138,19 @@ struct
             , nextPlatID
             , batRest
             )
+      | W_BAT_REST batRest =>
+          mkEnemy
+            ( id
+            , health
+            , x
+            , y
+            , xAxis
+            , yAxis
+            , variant
+            , platID
+            , nextPlatID
+            , batRest
+            )
     end
 
   fun withPatches (enemy, lst) =

fcore/game-type.sml

@@ -217,9 +217,9 @@ struct
         , x = 751
         , y = 555
         , health = 1
-        , xAxis = STAY_STILL
+        , xAxis = MOVE_RIGHT
         , yAxis = FALLING
-        , variant = EnemyVariants.FOLLOW_SLIME
+        , variant = EnemyVariants.STRAIGHT_BAT
         , platID = ~1
         , nextPlatID = ~1
         , batRest = 0