NPC refactor (#10122)

Co-authored-by: metalgearsloth <metalgearsloth@gmail.com>

Content.Client/NPC/HTN/HTNSystem.cs

@@ -0,0 +1,54 @@
+using Content.Shared.NPC;
+using Robust.Client.Graphics;
+using Robust.Client.ResourceManagement;
+
+namespace Content.Client.NPC.HTN;
+
+public sealed class HTNSystem : EntitySystem
+{
+    /*
+     * Mainly handles clientside debugging for HTN NPCs.
+     */
+    public bool EnableOverlay
+    {
+        get => _enableOverlay;
+        set
+        {
+            var overlayManager = IoCManager.Resolve<IOverlayManager>();
+            _enableOverlay = value;
+
+            if (_enableOverlay)
+            {
+                overlayManager.AddOverlay(new HTNOverlay(EntityManager, IoCManager.Resolve<IResourceCache>()));
+                RaiseNetworkEvent(new RequestHTNMessage()
+                {
+                    Enabled = true,
+                });
+            }
+            else
+            {
+                overlayManager.RemoveOverlay<HTNOverlay>();
+                RaiseNetworkEvent(new RequestHTNMessage()
+                {
+                    Enabled = false,
+                });
+            }
+        }
+    }
+
+    private bool _enableOverlay;
+
+    public override void Initialize()
+    {
+        base.Initialize();
+        SubscribeNetworkEvent<HTNMessage>(OnHTNMessage);
+    }
+
+    private void OnHTNMessage(HTNMessage ev)
+    {
+        if (!TryComp<HTNComponent>(ev.Uid, out var htn))
+            return;
+
+        htn.DebugText = ev.Text;
+    }
+}