add functionality to have enemies tract to player's attack

fcore/game-update.sml

@@ -18,6 +18,8 @@ struct
       val enemyTree = Enemy.generateTree enemies
       val player = Player.checkEnemyCollisions (player, enemies, enemyTree)
 
+      val enemies = PlayerAttack.attackEnemies (player, enemies, enemyTree)
+
       val enemies = Enemy.update
         (enemies, walls, wallTree, platforms, platformTree, player, graph)
 

fcore/player/player-attack.sml

@@ -0,0 +1,44 @@
+structure PlayerAttack =
+struct
+  structure AttackEnemies =
+    MakeQuadTreeFold
+      (struct
+         type env = unit
+         type state = EnemyMap.t
+
+         open EnemyType
+
+         fun onAttacked
+           (enemyID: int, enemy: EnemyType.enemy, enemyMap: EnemyMap.t) =
+           case #variant enemy of
+             PATROL_SLIME => EnemyMap.remove (enemyID, enemyMap)
+           | FOLLOW_SLIME => EnemyMap.remove (enemyID, enemyMap)
+           | STRAIGHT_BAT => EnemyMap.remove (enemyID, enemyMap)
+
+         fun fold (enemyID, (), enemyMap) =
+           case EnemyMap.get (enemyID, enemyMap) of
+             SOME enemy => onAttacked (enemyID, enemy, enemyMap)
+           | NONE => enemyMap
+       end)
+
+  fun attackEnemies (player: PlayerType.player, enemyMap, enemyTree) =
+    let
+      open PlayerType
+      val {x, y, facing, mainAttack, ...} = player
+    in
+      case mainAttack of
+        MAIN_ATTACKING {length, ...} =>
+          let
+            open EntityType
+            val height = Constants.playerSize
+            val x =
+              (case facing of
+                 FACING_RIGHT => x + Constants.playerSize
+               | FACING_LEFT => x - length)
+          in
+            AttackEnemies.foldRegion
+              (x, y, length, height, (), enemyMap, enemyTree)
+          end
+      | _ => enemyMap
+    end
+end