Click Drag Functionality + Refactor Interaction Interfaces (#1125)

Co-authored-by: Víctor Aguilera Puerto <6766154+Zumorica@users.noreply.github.com>
Co-authored-by: ComicIronic <comicironic@gmail.com>
Co-authored-by: Pieter-Jan Briers <pieterjan.briers+git@gmail.com>

Content.Server/Interfaces/GameObjects/Components/Interaction/IInteractHand.cs

@@ -0,0 +1,54 @@
+using System;
+using JetBrains.Annotations;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Interfaces.GameObjects;
+
+namespace Content.Server.Interfaces.GameObjects.Components.Interaction
+{
+    /// <summary>
+    /// This interface gives components behavior when being clicked on by a user with an empty hand
+    /// who is in range and has unobstructed reach of the target entity (allows inside blockers).
+    /// </summary>
+    public interface IInteractHand
+    {
+        /// <summary>
+        /// Called when a player directly interacts with an empty hand when user is in range of the target entity.
+        /// </summary>
+        bool InteractHand(InteractHandEventArgs eventArgs);
+    }
+
+    public class InteractHandEventArgs : EventArgs, ITargetedInteractEventArgs
+    {
+        public IEntity User { get; set; }
+        public IEntity Target { get; set; }
+    }
+
+
+    /// <summary>
+    ///      Raised when being clicked on or "attacked" by a user with an empty hand.
+    /// </summary>
+    [PublicAPI]
+    public class AttackHandMessage : EntitySystemMessage
+    {
+        /// <summary>
+        ///     If this message has already been "handled" by a previous system.
+        /// </summary>
+        public bool Handled { get; set; }
+
+        /// <summary>
+        ///     Entity that triggered the attack.
+        /// </summary>
+        public IEntity User { get; }
+
+        /// <summary>
+        ///     Entity that was attacked.
+        /// </summary>
+        public IEntity Attacked { get; }
+
+        public AttackHandMessage(IEntity user, IEntity attacked)
+        {
+            User = user;
+            Attacked = attacked;
+        }
+    }
+}