Remove IBody, IBodyPart, IMechanism and IMechanismBehavior (#4187)

* Remove IBody, IBodyPart, IMechanism and IMechanismBehavior interfaces

* Summary cleanup

Content.Shared/Body/Behavior/SharedMechanismBehavior.cs

@@ -0,0 +1,119 @@
+#nullable enable
+using Content.Shared.Body.Components;
+using Content.Shared.Body.Mechanism;
+using Content.Shared.Body.Part;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Serialization.Manager.Attributes;
+
+namespace Content.Shared.Body.Behavior
+{
+    /// <summary>
+    ///     Gives functionality to a mechanism when added to it.
+    /// </summary>
+    [ImplicitDataDefinitionForInheritors]
+    public abstract class SharedMechanismBehavior
+    {
+        public abstract SharedBodyComponent? Body { get; }
+
+        public abstract SharedBodyPartComponent? Part { get; }
+
+        public abstract SharedMechanismComponent Parent { get; }
+
+        /// <summary>
+        ///     The entity that owns <see cref="Parent"/>.
+        ///     For the entity owning the body that this mechanism may be in,
+        ///     see <see cref="Body"/>'s <see cref="SharedBodyComponent.Owner"/>.
+        /// </summary>
+        public abstract IEntity Owner { get; }
+
+        /// <summary>
+        ///     Called when this behavior is added to a mechanism, during <see cref="IComponent.Initialize"/>.
+        ///     If it is added after component initialization,
+        ///     it is called immediately.
+        /// </summary>
+        /// <param name="parent">
+        ///     The mechanism that owns this behavior.
+        /// </param>
+        public abstract void Initialize(SharedMechanismComponent parent);
+
+        /// <summary>
+        ///     Called when this behavior is added to a mechanism, during <see cref="Component.Startup"/>.
+        ///     If it is added after component startup, it is called immediately.
+        /// </summary>
+        public abstract void Startup();
+
+        /// <summary>
+        ///     Runs an update cycle on this behavior.
+        /// </summary>
+        /// <param name="frameTime">
+        ///     The amount of seconds that passed since the last update.
+        /// </param>
+        public abstract void Update(float frameTime);
+
+        /// <summary>
+        ///     Called when the containing part is attached to a body.
+        ///     For instance, attaching a head with a brain inside to a body.
+        ///     DO NOT CALL THIS DIRECTLY FROM OUTSIDE BODY SYSTEM CODE!
+        /// </summary>
+        /// <param name="body">
+        ///     The body that the containing mechanism was added to.
+        /// </param>
+        public abstract void AddedToBody(SharedBodyComponent body);
+
+        /// <summary>
+        ///     Called when the parent mechanism is added into a part that is not attached to a body.
+        ///     For instance, adding a brain to a dismembered head.
+        ///     DO NOT CALL THIS DIRECTLY FROM OUTSIDE BODY SYSTEM CODE!
+        /// </summary>
+        /// <param name="part">
+        ///     The part that the containing mechanism was added to.
+        /// </param>
+        public abstract void AddedToPart(SharedBodyPartComponent part);
+
+        /// <summary>
+        ///     Called when the parent mechanism is added to a part that is attached to a body.
+        ///     For instance, adding a brain to a head that is attached to a body.
+        ///     DO NOT CALL THIS DIRECTLY FROM OUTSIDE BODY SYSTEM CODE!
+        /// </summary>
+        /// <param name="body">
+        ///     The body that the containing mechanism was added to.
+        /// </param>
+        /// <param name="part">
+        ///     The part that the containing mechanism was added to.
+        /// </param>
+        public abstract void AddedToPartInBody(SharedBodyComponent body, SharedBodyPartComponent part);
+
+        /// <summary>
+        ///     Called when the parent part is removed from a body.
+        ///     For instance, removing a head with a brain inside from a body.
+        ///     DO NOT CALL THIS DIRECTLY FROM OUTSIDE BODY SYSTEM CODE!
+        /// </summary>
+        /// <param name="old">
+        ///     The body that the containing mechanism was removed from.
+        /// </param>
+        public abstract void RemovedFromBody(SharedBodyComponent old);
+
+        /// <summary>
+        ///     Called when the parent mechanism is removed from a part that is not attached to a body.
+        ///     For instance, removing a brain from a dismembered head.
+        ///     DO NOT CALL THIS DIRECTLY FROM OUTSIDE BODY SYSTEM CODE!
+        /// </summary>
+        /// <param name="old">
+        ///     The part that the containing mechanism was removed from.
+        /// </param>
+        public abstract void RemovedFromPart(SharedBodyPartComponent old);
+
+        /// <summary>
+        ///     Called when the parent mechanism is removed from a part that is attached to a body.
+        ///     For instance, removing a brain from a head that is attached to a body.
+        ///     DO NOT CALL THIS DIRECTLY FROM OUTSIDE BODY SYSTEM CODE!
+        /// </summary>
+        /// <param name="oldBody">
+        ///     The body that the containing mechanism was removed from.
+        /// </param>
+        /// <param name="oldPart">
+        ///     The part that the containing mechanism was removed from.
+        /// </param>
+        public abstract void RemovedFromPartInBody(SharedBodyComponent oldBody, SharedBodyPartComponent oldPart);
+    }
+}