Makes construction graphs turing complete (#3516)

* Makes construction graphs turing complete

* Improvements

Content.Server/Construction/Completions/ConditionalAction.cs

@@ -0,0 +1,33 @@
+#nullable enable
+using System.Threading.Tasks;
+using Content.Shared.Construction;
+using JetBrains.Annotations;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Serialization.Manager.Attributes;
+
+namespace Content.Server.Construction.Completions
+{
+    [UsedImplicitly]
+    [DataDefinition]
+    public class ConditionalAction : IGraphAction
+    {
+        [field: DataField("passUser")] public bool PassUser { get; } = false;
+
+        [field: DataField("condition", required:true)] public IEdgeCondition? Condition { get; } = null;
+
+        [field: DataField("action", required:true)] public IGraphAction? Action { get; } = null;
+
+        [field: DataField("else")] public IGraphAction? Else { get; } = null;
+
+        public async Task PerformAction(IEntity entity, IEntity? user)
+        {
+            if (Condition == null || Action == null)
+                return;
+
+            if (await Condition.Condition(PassUser && user != null ? user : entity))
+                await Action.PerformAction(entity, user);
+            else if (Else != null)
+                await Else.PerformAction(entity, user);
+        }
+    }
+}