Actions System + UI (#2710)

Co-authored-by: Vera Aguilera Puerto <6766154+Zumorica@users.noreply.github.com>

Content.Shared/Interfaces/GameObjects/Components/Interaction/IEquippedHand.cs

@@ -0,0 +1,64 @@
+using System;
+using Content.Shared.GameObjects.Components.Inventory;
+using Content.Shared.GameObjects.Components.Items;
+using JetBrains.Annotations;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Interfaces.GameObjects;
+
+namespace Content.Shared.Interfaces.GameObjects.Components
+{
+    /// <summary>
+    ///     This interface gives components behavior when their entity is put in a hand inventory slot,
+    ///     even if it came from another hand slot (which would also fire <see cref="IUnequippedHand"/>).
+    ///     This includes moving the entity from a non-hand slot into a hand slot
+    ///     (which would also fire <see cref="IUnequipped"/>).
+    /// </summary>
+    public interface IEquippedHand
+    {
+        void EquippedHand(EquippedHandEventArgs eventArgs);
+    }
+
+    public class EquippedHandEventArgs : UserEventArgs
+    {
+        public EquippedHandEventArgs(IEntity user, SharedHand hand) : base(user)
+        {
+            Hand = hand;
+        }
+
+        public SharedHand Hand { get; }
+    }
+
+    /// <summary>
+    ///     Raised when putting the entity into a hand slot
+    /// </summary>
+    [PublicAPI]
+    public class EquippedHandMessage : EntitySystemMessage
+    {
+        /// <summary>
+        ///     If this message has already been "handled" by a previous system.
+        /// </summary>
+        public bool Handled { get; set; }
+
+        /// <summary>
+        ///     Entity that equipped the item.
+        /// </summary>
+        public IEntity User { get; }
+
+        /// <summary>
+        ///     Item that was equipped.
+        /// </summary>
+        public IEntity Equipped { get; }
+
+        /// <summary>
+        ///     Hand the item is going into.
+        /// </summary>
+        public SharedHand Hand { get; }
+
+        public EquippedHandMessage(IEntity user, IEntity equipped, SharedHand hand)
+        {
+            User = user;
+            Equipped = equipped;
+            Hand = hand;
+        }
+    }
+}