Show if items can be placed in a slot when hovering (#1480)

Co-authored-by: Pieter-Jan Briers <pieterjan.briers@gmail.com>

Content.Server/GameObjects/Components/GUI/InventoryComponent.cs

@@ -36,6 +36,8 @@ namespace Content.Server.GameObjects
         [ViewVariables]
         private readonly Dictionary<Slots, ContainerSlot> SlotContainers = new Dictionary<Slots, ContainerSlot>();
 
+        private KeyValuePair<Slots, (EntityUid entity, bool fits)>? HoverEntity;
+
         public override void Initialize()
         {
             base.Initialize();
@@ -93,6 +95,11 @@ namespace Content.Server.GameObjects
         }
         public T GetSlotItem<T>(Slots slot) where T : ItemComponent
         {
+            if (!SlotContainers.ContainsKey(slot))
+            {
+                return null;
+            }
+
             var containedEntity = SlotContainers[slot].ContainedEntity;
             if (containedEntity?.Deleted == true)
             {
@@ -358,6 +365,20 @@ namespace Content.Server.GameObjects
                     }
                     break;
                 }
+                case ClientInventoryUpdate.Hover:
+                {
+                    var hands = Owner.GetComponent<HandsComponent>();
+                    var activeHand = hands.GetActiveHand;
+                    if (activeHand != null && GetSlotItem(msg.Inventoryslot) == null)
+                    {
+                        var canEquip = CanEquip(msg.Inventoryslot, activeHand, out var reason);
+                        HoverEntity = new KeyValuePair<Slots, (EntityUid entity, bool fits)>(msg.Inventoryslot, (activeHand.Owner.Uid, canEquip));
+
+                        Dirty();
+                    }
+
+                    break;
+                }
             }
         }
 
@@ -417,7 +438,11 @@ namespace Content.Server.GameObjects
                     list.Add(new KeyValuePair<Slots, EntityUid>(slot, container.ContainedEntity.Uid));
                 }
             }
-            return new InventoryComponentState(list);
+
+            var hover = HoverEntity;
+            HoverEntity = null;
+
+            return new InventoryComponentState(list, hover);
         }
 
         void IExAct.OnExplosion(ExplosionEventArgs eventArgs)