Add utility AI (#806)

Co-authored-by: Pieter-Jan Briers <pieterjan.briers@gmail.com>
Co-authored-by: Metal Gear Sloth <metalgearsloth@gmail.com>
Co-authored-by: Pieter-Jan Briers <pieterjan.briers+git@gmail.com>

Content.Server/GameObjects/EntitySystems/AI/LoadBalancer/AiActionRequestJob.cs

@@ -0,0 +1,128 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using Content.Server.AI.Utility.Actions;
+using Content.Server.AI.Utility.ExpandableActions;
+using Content.Server.AI.WorldState.States;
+using Content.Server.AI.WorldState.States.Utility;
+using Content.Server.GameObjects.Components.Movement;
+using Content.Server.GameObjects.EntitySystems.JobQueues;
+using Content.Shared.AI;
+
+namespace Content.Server.GameObjects.EntitySystems.AI.LoadBalancer
+{
+    public class AiActionRequestJob : Job<UtilityAction>
+    {
+#if DEBUG
+        public static event Action<SharedAiDebug.UtilityAiDebugMessage> FoundAction;
+#endif
+        private readonly AiActionRequest _request;
+
+        public AiActionRequestJob(
+            double maxTime,
+            AiActionRequest request,
+            CancellationToken cancellationToken = default) : base(maxTime, cancellationToken)
+        {
+            _request = request;
+        }
+
+        protected override async Task<UtilityAction> Process()
+        {
+            if (_request.Context == null)
+            {
+                return null;
+            }
+
+            var entity = _request.Context.GetState<SelfState>().GetValue();
+
+            if (entity == null || !entity.HasComponent<AiControllerComponent>())
+            {
+                return null;
+            }
+
+            if (_request.Actions == null || _request.Context == null)
+            {
+                return null;
+            }
+
+            var consideredTaskCount = 0;
+            // Actions are pre-sorted
+            var actions = new Stack<IAiUtility>(_request.Actions);
+
+            // So essentially we go through and once we have a valid score that score becomes the cutoff;
+            // once the bonus of new tasks is below the cutoff we can stop evaluating.
+
+            // Use last action as the basis for the cutoff
+            var cutoff = _request.Context.GetState<LastUtilityScoreState>().GetValue();
+            UtilityAction foundAction = null;
+
+            // To see what I was trying to do watch these 2 videos about Infinite Axis Utility System (IAUS):
+            // Architecture Tricks: Managing Behaviors in Time, Space, and Depth
+            // Building a Better Centaur
+
+            // We'll want to cap the considered entities at some point, e.g. if 500 guns are in a stack cap it at 256 or whatever
+            while (actions.Count > 0)
+            {
+                if (consideredTaskCount > 0 && consideredTaskCount % 5 == 0)
+                {
+                    await SuspendIfOutOfTime();
+
+                    // If this happens then that means something changed when we resumed so ABORT
+                    if (actions.Count == 0 || _request.Context == null)
+                    {
+                        return null;
+                    }
+                }
+
+                var action = actions.Pop();
+                switch (action)
+                {
+                    case ExpandableUtilityAction expandableUtilityAction:
+                        foreach (var expanded in expandableUtilityAction.GetActions(_request.Context))
+                        {
+                            actions.Push(expanded);
+                        }
+                        break;
+                    case UtilityAction utilityAction:
+                        consideredTaskCount++;
+                        var bonus = (float) utilityAction.Bonus;
+
+                        if (bonus < cutoff)
+                        {
+                            // We know none of the other actions can beat this as they're pre-sorted
+                            actions.Clear();
+                            break;
+                        }
+
+                        var score = utilityAction.GetScore(_request.Context, cutoff);
+                        if (score > cutoff)
+                        {
+                            foundAction = utilityAction;
+                            cutoff = score;
+                        }
+                        break;
+                    default:
+                        throw new ArgumentOutOfRangeException();
+                }
+            }
+
+            _request.Context.GetState<LastUtilityScoreState>().SetValue(cutoff);
+#if DEBUG
+            if (foundAction != null)
+            {
+                FoundAction?.Invoke(new SharedAiDebug.UtilityAiDebugMessage(
+                    _request.Context.GetState<SelfState>().GetValue().Uid,
+                    DebugTime,
+                    cutoff,
+                    foundAction.GetType().Name,
+                    consideredTaskCount));
+            }
+
+#endif
+            _request.Context.ResetPlanning();
+
+            return foundAction;
+        }
+    }
+}