Update radio prefix parsing (#13777)

Content.Shared/Radio/EntitySystems/SharedHeadsetSystem.cs

@@ -0,0 +1,38 @@
+using Content.Shared.Inventory;
+using Content.Shared.Inventory.Events;
+using Content.Shared.Radio.Components;
+
+namespace Content.Shared.Radio.EntitySystems;
+
+public abstract class SharedHeadsetSystem : EntitySystem
+{
+    public override void Initialize()
+    {
+        base.Initialize();
+        SubscribeLocalEvent<HeadsetComponent, InventoryRelayedEvent<GetDefaultRadioChannelEvent>>(OnGetDefault);
+        SubscribeLocalEvent<HeadsetComponent, GotEquippedEvent>(OnGotEquipped);
+        SubscribeLocalEvent<HeadsetComponent, GotUnequippedEvent>(OnGotUnequipped);
+    }
+
+    private void OnGetDefault(EntityUid uid, HeadsetComponent component, InventoryRelayedEvent<GetDefaultRadioChannelEvent> args)
+    {
+        if (!component.Enabled || !component.IsEquipped)
+        {
+            // don't provide default channels from pocket slots.
+            return;
+        }
+
+        if (TryComp(uid, out EncryptionKeyHolderComponent? keyHolder))
+            args.Args.Channel ??= keyHolder.DefaultChannel; 
+    }
+
+    protected virtual void OnGotEquipped(EntityUid uid, HeadsetComponent component, GotEquippedEvent args)
+    {
+        component.IsEquipped = args.SlotFlags.HasFlag(component.RequiredSlot);
+    }
+
+    protected virtual void OnGotUnequipped(EntityUid uid, HeadsetComponent component, GotUnequippedEvent args)
+    {
+        component.IsEquipped = false;
+    }
+}