Add post-checks for do_after (#1940)

* Add post-checks for do_after

So you can do InRangeUnobstructed or whatever at the end.

Individual components should do their own check upfront to avoid the state ever being sent. I added a pre-made function for people to do InRangeUnobstructed.

* Woops imports

Co-authored-by: Metal Gear Sloth <metalgearsloth@gmail.com>

Content.Server/GameObjects/EntitySystems/DoAfter/DoAfter.cs

@@ -1,7 +1,6 @@
 #nullable enable
 using System;
 using System.Threading.Tasks;
-using Content.Server.GameObjects.Components.Damage;
 using Content.Server.GameObjects.Components.GUI;
 using Content.Server.GameObjects.Components.Items.Storage;
 using Content.Server.GameObjects.Components.Mobs;
@@ -86,7 +85,16 @@ namespace Content.Server.GameObjects.EntitySystems.DoAfter
 
             if (IsFinished())
             {
-                Tcs.SetResult(DoAfterStatus.Finished);
+                // Do the final checks here
+                if (!TryPostCheck())
+                {
+                    Tcs.SetResult(DoAfterStatus.Cancelled);
+                }
+                else
+                {
+                    Tcs.SetResult(DoAfterStatus.Finished);
+                }
+                
                 return;
             }
 
@@ -98,6 +106,11 @@ namespace Content.Server.GameObjects.EntitySystems.DoAfter
 
         private bool IsCancelled()
         {
+            if (EventArgs.User.Deleted || EventArgs.Target?.Deleted == true)
+            {
+                return true;
+            }
+            
             //https://github.com/tgstation/tgstation/blob/1aa293ea337283a0191140a878eeba319221e5df/code/__HELPERS/mobs.dm
             if (EventArgs.CancelToken.IsCancellationRequested)
             {
@@ -157,10 +170,15 @@ namespace Content.Server.GameObjects.EntitySystems.DoAfter
                     }
                 }
             }
-
+            
             return false;
         }
 
+        private bool TryPostCheck()
+        {
+            return EventArgs.PostCheck?.Invoke() != false;
+        }
+
         private bool IsFinished()
         {
             if (Elapsed <= EventArgs.Delay)

Content.Server/GameObjects/EntitySystems/DoAfter/DoAfterEventArgs.cs

@@ -1,6 +1,9 @@
 #nullable enable
 using System;
 using System.Threading;
+using Content.Shared.GameObjects.EntitySystems;
+using Content.Shared.Physics;
+using Robust.Shared.GameObjects.Systems;
 using Robust.Shared.Interfaces.GameObjects;
 
 // ReSharper disable UnassignedReadonlyField
@@ -9,6 +12,18 @@ namespace Content.Server.GameObjects.EntitySystems.DoAfter
 {
     public sealed class DoAfterEventArgs
     {
+        // Premade checks
+        public Func<bool> GetInRangeUnobstructed(int collisionMask = (int) CollisionGroup.MobMask)
+        {
+            if (Target == null)
+            {
+                throw new InvalidOperationException("Can't supply a null target to DoAfterEventArgs.GetInRangeUnobstructed");
+            }
+            var interactionSystem = EntitySystem.Get<SharedInteractionSystem>();
+            Func<IEntity, bool> ignored = entity => entity == User || entity == Target;
+            return () => interactionSystem.InRangeUnobstructed(User.Transform.MapPosition, Target.Transform.MapPosition, collisionMask: collisionMask, predicate: ignored);
+        }
+        
         /// <summary>
         ///     The entity invoking do_after
         /// </summary>
@@ -49,6 +64,14 @@ namespace Content.Server.GameObjects.EntitySystems.DoAfter
         public bool BreakOnDamage { get; set; }
         public bool BreakOnStun { get; set; }
 
+        /// <summary>
+        ///     Requires a function call once at the end (like InRangeUnobstructed).
+        /// </summary>
+        /// <remarks>
+        ///     Anything that needs a pre-check should do it itself so no DoAfterState is ever sent to the client.
+        /// </remarks>
+        public Func<bool>? PostCheck { get; set; } = null;
+        
         /// <summary>
         ///     Additional conditions that need to be met. Return false to cancel.
         /// </summary>