Gunify pneumatic cannon (#13296)

Content.Shared/PneumaticCannon/SharedPneumaticCannonSystem.cs

@@ -0,0 +1,32 @@
+using Content.Shared.Popups;
+using Content.Shared.Weapons.Ranged.Systems;
+using Robust.Shared.Containers;
+using Robust.Shared.Serialization;
+
+namespace Content.Shared.PneumaticCannon;
+
+public abstract class SharedPneumaticCannonSystem : EntitySystem
+{
+    [Dependency] protected readonly SharedContainerSystem Container = default!;
+    [Dependency] protected readonly SharedPopupSystem Popup = default!;
+
+
+    public override void Initialize()
+    {
+        base.Initialize();
+
+        SubscribeLocalEvent<PneumaticCannonComponent, AttemptShootEvent>(OnAttemptShoot);
+    }
+
+    private void OnAttemptShoot(EntityUid uid, PneumaticCannonComponent component, ref AttemptShootEvent args)
+    {
+        // we don't have atmos on shared, so just predict by the existence of a slot item
+        // server will handle auto ejecting/not adding the slot item if it doesnt have enough gas,
+        // so this won't mispredict
+        if (!Container.TryGetContainer(uid, PneumaticCannonComponent.TankSlotId, out var container) ||
+            container is not ContainerSlot slot || slot.ContainedEntity is null)
+        {
+            args.Cancelled = true;
+        }
+    }
+}