Actions System + UI (#2710)

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

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

@@ -0,0 +1,63 @@
+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 removed from a hand slot,
+    ///     even if it is going into another hand slot (which would also fire <see cref="IEquippedHand"/>).
+    ///     This includes moving the entity from a hand slot into a non-hand slot (which would also fire <see cref="IEquipped"/>).
+    /// </summary>
+    public interface IUnequippedHand
+    {
+        void UnequippedHand(UnequippedHandEventArgs eventArgs);
+    }
+
+    public class UnequippedHandEventArgs : UserEventArgs
+    {
+        public UnequippedHandEventArgs(IEntity user, SharedHand hand) : base(user)
+        {
+            Hand = hand;
+        }
+
+        public SharedHand Hand { get; }
+    }
+
+    /// <summary>
+    ///     Raised when removing the entity from an inventory slot.
+    /// </summary>
+    [PublicAPI]
+    public class UnequippedHandMessage : 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 unequipped.
+        /// </summary>
+        public IEntity Unequipped { get; }
+
+        /// <summary>
+        ///     Hand the item is removed from.
+        /// </summary>
+        public SharedHand Hand { get; }
+
+        public UnequippedHandMessage(IEntity user, IEntity unequipped, SharedHand hand)
+        {
+            User = user;
+            Unequipped = unequipped;
+            Hand = hand;
+        }
+    }
+}