Mouse rotator system (#19267)

Co-authored-by: metalgearsloth <31366439+metalgearsloth@users.noreply.github.com>

Content.Shared/MouseRotator/SharedMouseRotatorSystem.cs

@@ -0,0 +1,60 @@
+using Content.Shared.Interaction;
+using Robust.Shared.Timing;
+
+namespace Content.Shared.MouseRotator;
+
+/// <summary>
+/// This handles rotating an entity based on mouse location
+/// </summary>
+/// <see cref="MouseRotatorComponent"/>
+public abstract class SharedMouseRotatorSystem : EntitySystem
+{
+    [Dependency] private readonly RotateToFaceSystem _rotate = default!;
+
+    public override void Initialize()
+    {
+        base.Initialize();
+
+        SubscribeAllEvent<RequestMouseRotatorRotationEvent>(OnRequestRotation);
+    }
+
+    public override void Update(float frameTime)
+    {
+        base.Update(frameTime);
+
+        // TODO maybe `ActiveMouseRotatorComponent` to avoid querying over more entities than we need?
+        // (if this is added to players)
+        // (but arch makes these fast anyway, so)
+        var query = EntityQueryEnumerator<MouseRotatorComponent, TransformComponent>();
+        while (query.MoveNext(out var uid, out var rotator, out var xform))
+        {
+            if (rotator.GoalRotation == null)
+                continue;
+
+            if (_rotate.TryRotateTo(
+                    uid,
+                    rotator.GoalRotation.Value,
+                    frameTime,
+                    rotator.AngleTolerance,
+                    MathHelper.DegreesToRadians(rotator.RotationSpeed),
+                    xform))
+            {
+                // Stop rotating if we finished
+                rotator.GoalRotation = null;
+                Dirty(uid, rotater);
+            }
+        }
+    }
+
+    private void OnRequestRotation(RequestMouseRotatorRotationEvent msg, EntitySessionEventArgs args)
+    {
+        if (args.SenderSession.AttachedEntity is not { } ent || !TryComp<MouseRotatorComponent>(ent, out var rotator))
+        {
+            Log.Error($"User {args.SenderSession.Name} ({args.SenderSession.UserId}) tried setting local rotation without a mouse rotator component attached!");
+            return;
+        }
+
+        rotator.GoalRotation = msg.Rotation;
+        Dirty(ent, rotator);
+    }
+}