ported from perforce

RobotAndDonkey.Game/Modifiers/ModifierStack.cs

@@ -0,0 +1,79 @@
+using System.Diagnostics;
+using System.Runtime.InteropServices;
+using RobotAndDonkey.Game.Execution.Results;
+using RobotAndDonkey.Game.GameState;
+using RobotAndDonkey.Game.Intents;
+
+namespace RobotAndDonkey.Game.Modifiers;
+
+public class ModifierStack
+{
+    public void Push(Entity entity)
+    {
+        m_Stack.Push((entity, entity.Modifiers));
+    }
+
+    public void Pop()
+    {
+        _ = m_Stack.Pop();
+    }
+
+    private IEnumerable<(Entity Owner, Modifier Modifier)> GetModifiers()
+    {
+        foreach (var (owner, modifiers) in m_Stack)
+        {
+            foreach (var modifier in modifiers)
+            {
+                if (modifier.DebuffSources.Count == 0)
+                    yield return (owner, modifier);
+            }
+        }
+    }
+
+    public void Execute(Guid requestId, CoreLoop coreLoop, List<Intent> intents, List<Result> results, bool force, bool verbose)
+    {
+        var newIntents = new List<Intent>();
+        var index = 0;
+        do
+        {
+            var currentIntents = intents[index..];
+            var modifiableIntents = currentIntents.Where(i => !i.Immune).ToArray();
+            foreach (var (owner, modifier) in GetModifiers())
+            {
+                if (modifier.DebuffSources.Count == 0)
+                {
+                    if (verbose)
+                        Debug.WriteLine($"Before {modifier}");
+                    modifier.Before(requestId, modifiableIntents, coreLoop, owner, newIntents, results);
+                }
+            }
+
+            foreach (var intent in currentIntents)
+            {
+                var isValid = intent.IsValid(coreLoop);
+                if (force || isValid)
+                {
+                    if (verbose)
+                        Debug.WriteLine($"Run {(isValid ? "Valid" : "Invalid")} intent: {intent}");
+                    intent.Run(requestId, coreLoop, newIntents, results);
+                }
+            }
+
+            foreach (var (owner, modifier) in GetModifiers())
+            {
+                if (modifier.DebuffSources.Count == 0)
+                {
+                    if (verbose)
+                        Debug.WriteLine($"After {modifier}");
+                    modifier.After(requestId, modifiableIntents, coreLoop, owner, newIntents, results);
+                }
+            }
+
+            index = intents.Count;
+            intents.AddRange(newIntents);
+            newIntents.Clear();
+        } while (index < intents.Count);
+    }
+
+    private readonly Stack<(Entity Owner, IReadOnlyList<Modifier> Modifiers)> m_Stack = [];
+}