ported from perforce

RobotAndDonkey.Game/Modifiers/GravityModifier.cs

@@ -0,0 +1,34 @@
+using System;
+using System.Collections.Generic;
+using RobotAndDonkey.Game.Data;
+using RobotAndDonkey.Game.Execution.Results;
+using RobotAndDonkey.Game.GameState;
+using RobotAndDonkey.Game.Intents;
+
+namespace RobotAndDonkey.Game.Modifiers;
+
+public record GravityModifier(EModifierDuration Duration) : Modifier(EModifierKind.Robot, EModifierId.Gravity, Duration)
+{
+    protected override GravityModifier CreateInstance() => new(Duration);
+
+    public override void OnAdded(Entity owner, List<Intent> newIntents)
+    {
+        newIntents.Add(new ModifyCurrency(new(0, -Balancing.Instance.GravityMaxCarryPenalty, 0, 0, 0, 0)));
+    }
+
+    public override void Before(Guid requestId, ReadOnlySpan<Intent> intents, CoreLoop coreLoop, Entity owner, List<Intent> newIntents, List<Result> results)
+    {
+        foreach (var intent in intents)
+        {
+            if (intent is Move)
+                intent.EnergyCost += Balancing.Instance.GravityExtraMoveCost;
+        }
+    }
+
+    public override void OnRemoved(Entity owner, List<Intent> newIntents)
+    {
+        newIntents.Add(new ModifyCurrency(new(0, Balancing.Instance.GravityMaxCarryPenalty, 0, 0, 0, 0)));
+    }
+
+    public override string ToolTip => $"Gravity: −{Balancing.Instance.GravityMaxCarryPenalty} Max Carry; Move costs +{Balancing.Instance.GravityExtraMoveCost} energy (temporary).";
+}