ported from perforce

RobotAndDonkey.Game/Modifiers/Entity.cs

@@ -0,0 +1,48 @@
+using RobotAndDonkey.Game.Intents;
+
+namespace RobotAndDonkey.Game.Modifiers;
+
+public record Entity()
+{
+    protected Entity(Entity clone)
+    {
+        m_Modifiers = [];
+        foreach (var modifier in clone.Modifiers)
+            AddModifier(modifier.DeepClone(), []);
+    }
+
+    public void InsertModifier(Modifier modifier, List<Intent> newIntents)
+    {
+        if (m_Modifiers.Any(m => m.Id == modifier.Id))
+            throw new InvalidOperationException();
+
+        m_Modifiers.Insert(0, modifier);
+        modifier.OnAdded(this, newIntents);
+    }
+
+    public void AddModifier(Modifier modifier, List<Intent> newIntents)
+    {
+        if (m_Modifiers.Any(m => m.Id == modifier.Id))
+            throw new InvalidOperationException();
+
+        m_Modifiers.Add(modifier);
+        modifier.OnAdded(this, newIntents);
+    }
+
+    public void RemoveModifier(Modifier modifier, List<Intent> newIntents)
+    {
+        if (!m_Modifiers.Remove(modifier))
+            throw new InvalidOperationException();
+
+        modifier.OnRemoved(this, newIntents);
+    }
+
+    public override string ToString()
+    {
+        return "[" + string.Join(", ", m_Modifiers) + "]";
+    }
+
+    public IReadOnlyList<Modifier> Modifiers => m_Modifiers;
+
+    private readonly List<Modifier> m_Modifiers = [];
+}