Fix barstool rotation (#5134)

Content.Shared/Interaction/RotateToFaceSystem.cs

@@ -0,0 +1,76 @@
+using System;
+using System.Linq;
+using System.Threading.Tasks;
+using Content.Shared.ActionBlocker;
+using Content.Shared.Hands;
+using Content.Shared.Hands.Components;
+using Content.Shared.Buckle.Components;
+using Content.Shared.Rotatable;
+using Content.Shared.Inventory;
+using Content.Shared.Physics;
+using Content.Shared.Popups;
+using Content.Shared.Throwing;
+using Content.Shared.Timing;
+using Content.Shared.Verbs;
+using JetBrains.Annotations;
+using Robust.Shared.GameObjects;
+using Robust.Shared.IoC;
+using Robust.Shared.Localization;
+using Robust.Shared.Map;
+using Robust.Shared.Maths;
+using Robust.Shared.Physics;
+using Robust.Shared.Random;
+using Robust.Shared.Serialization;
+
+namespace Content.Shared.Interaction
+{
+    /// <summary>
+    /// Contains common code used to rotate a player to face a given target or direction.
+    /// This interaction in itself is useful for various roleplay purposes.
+    /// But it needs specialized code to handle chairs and such.
+    /// Doesn't really fit with SharedInteractionSystem so it's not there.
+    /// </summary>
+    [UsedImplicitly]
+    public class RotateToFaceSystem : EntitySystem
+    {
+        [Dependency] private readonly ActionBlockerSystem _actionBlockerSystem = default!;
+        public bool TryFaceCoordinates(IEntity user, Vector2 coordinates)
+        {
+            var diff = coordinates - user.Transform.MapPosition.Position;
+            if (diff.LengthSquared <= 0.01f)
+                return true;
+            var diffAngle = Angle.FromWorldVec(diff);
+            return TryFaceAngle(user, diffAngle);
+        }
+
+        public bool TryFaceAngle(IEntity user, Angle diffAngle)
+        {
+            if (_actionBlockerSystem.CanChangeDirection(user))
+            {
+                user.Transform.WorldRotation = diffAngle;
+                return true;
+            }
+            else
+            {
+                if (user.TryGetComponent(out SharedBuckleComponent? buckle) && buckle.Buckled)
+                {
+                    var suid = buckle.LastEntityBuckledTo;
+                    if (suid != null)
+                    {
+                        // We're buckled to another object. Is that object rotatable?
+                        if (EntityManager.TryGetComponent<RotatableComponent>(suid.Value!, out var rotatable) && rotatable.RotateWhileAnchored)
+                        {
+                            // Note the assumption that even if unanchored, user can only do spinnychair with an "independent wheel".
+                            // (Since the user being buckled to it holds it down with their weight.)
+                            // This is logically equivalent to RotateWhileAnchored.
+                            // Barstools and office chairs have independent wheels, while regular chairs don't.
+                            rotatable.Owner.Transform.WorldRotation = diffAngle;
+                            return true;
+                        }
+                    }
+                }
+            }
+            return false;
+        }
+    }
+}