Inventory slot enumerator rejig (#21788)

Content.Server/Zombies/ZombieSystem.cs

@@ -40,6 +40,16 @@ namespace Content.Server.Zombies
         [Dependency] private readonly MobStateSystem _mobState = default!;
         [Dependency] private readonly SharedPopupSystem _popup = default!;
 
+        public const SlotFlags ProtectiveSlots =
+            SlotFlags.FEET |
+            SlotFlags.HEAD |
+            SlotFlags.EYES |
+            SlotFlags.GLOVES |
+            SlotFlags.MASK |
+            SlotFlags.NECK |
+            SlotFlags.INNERCLOTHING |
+            SlotFlags.OUTERCLOTHING;
+
         public override void Initialize()
         {
             base.Initialize();
@@ -164,33 +174,27 @@ namespace Content.Server.Zombies
 
         private float GetZombieInfectionChance(EntityUid uid, ZombieComponent component)
         {
-            var baseChance = component.MaxZombieInfectionChance;
+            var max = component.MaxZombieInfectionChance;
 
-            if (!TryComp<InventoryComponent>(uid, out var inventoryComponent))
-                return baseChance;
-
-            var enumerator =
-                new InventorySystem.ContainerSlotEnumerator(uid, inventoryComponent.TemplateId, _protoManager, _inv,
-                    SlotFlags.FEET |
-                    SlotFlags.HEAD |
-                    SlotFlags.EYES |
-                    SlotFlags.GLOVES |
-                    SlotFlags.MASK |
-                    SlotFlags.NECK |
-                    SlotFlags.INNERCLOTHING |
-                    SlotFlags.OUTERCLOTHING);
+            if (!_inventory.TryGetContainerSlotEnumerator(uid, out var enumerator, ProtectiveSlots))
+                return max;
 
             var items = 0f;
             var total = 0f;
             while (enumerator.MoveNext(out var con))
             {
                 total++;
-
                 if (con.ContainedEntity != null)
                     items++;
             }
 
-            var max = component.MaxZombieInfectionChance;
+            if (total == 0)
+                return max;
+
+            // Everyone knows that when it comes to zombies, socks & sandals provide just as much protection as an
+            // armored vest. Maybe these should be weighted per-item. I.e. some kind of coverage/protection component.
+            // Or at the very least different weights per slot.
+
             var min = component.MinZombieInfectionChance;
             //gets a value between the max and min based on how many items the entity is wearing
             var chance = (max-min) * ((total - items)/total) + min;