Add monster energy indicator

Assets/Battle/EnergyPool.cs

@@ -0,0 +1,41 @@
+using System.Collections;
+using System.Collections.Generic;
+using UnityEngine;
+
+public class EnergyPool
+{
+    private int maxEnergy;
+    private int energy;
+
+    public delegate void EnergyChangedAction();
+    public event EnergyChangedAction OnEnergyChanged;
+
+    public void Replenish() {
+        this.energy = this.maxEnergy;
+        TriggerOnEnergyChanged();
+    }
+
+    public void DropOneEmotion() {
+        this.maxEnergy++;
+        this.energy++;
+        TriggerOnEnergyChanged();
+    }
+
+    public bool CanPayForCard(BaseCard card) {
+        return this.energy >= card.GetCost();
+    }
+
+    public void PayForCard(BaseCard card) {
+        this.energy -= card.GetCost();
+        TriggerOnEnergyChanged();
+    }
+
+    private void TriggerOnEnergyChanged() {
+        if (this.OnEnergyChanged != null) {
+            OnEnergyChanged();
+        }
+    }
+
+    public int MaxEnergy {get => this.maxEnergy; set => this.maxEnergy = value;}
+    public int Energy {get => this.energy;}
+}