Actions System + UI (#2710)

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

Content.Shared/Actions/IActionBehavior.cs

@@ -0,0 +1,44 @@
+using System;
+using Content.Shared.GameObjects.Components.Mobs;
+using Robust.Shared.Interfaces.GameObjects;
+using Robust.Shared.Interfaces.Serialization;
+
+namespace Content.Shared.Actions
+{
+    /// <summary>
+    /// Currently just a marker interface delineating the different possible
+    /// types of action behaviors.
+    /// </summary>
+    public interface IActionBehavior : IExposeData { }
+
+    /// <summary>
+    /// Base class for all action event args
+    /// </summary>
+    public abstract class ActionEventArgs : EventArgs
+    {
+        /// <summary>
+        /// Entity performing the action.
+        /// </summary>
+        public readonly IEntity Performer;
+        /// <summary>
+        /// Action being performed
+        /// </summary>
+        public readonly ActionType ActionType;
+        /// <summary>
+        /// Actions component of the performer.
+        /// </summary>
+        public readonly SharedActionsComponent PerformerActions;
+
+        public ActionEventArgs(IEntity performer, ActionType actionType)
+        {
+            Performer = performer;
+            ActionType = actionType;
+            if (!Performer.TryGetComponent(out PerformerActions))
+            {
+                throw new InvalidOperationException($"performer {performer.Name} tried to perform action {actionType} " +
+                                                    $" but the performer had no actions component," +
+                                                    " which should never occur");
+            }
+        }
+    }
+}