Health.cs

using System;
using UnityEngine;

public class Health : MonoBehaviour
{
    [SerializeField] private int startingHealth = 100;

    private int currentHealth;

    public event Action<float> OnHPPctChanged = delegate { };

    private void Start()
    {
        currentHealth = startingHealth;
    }

    public float CurrentHpPct
    {
        get { return (float) currentHealth / (float) startingHealth; }
    }

    public void TakeDamage(int amount)
    {
        if (amount <= 0)
            throw new ArgumentOutOfRangeException("Invalid Damage amount specified: " + amount);

        currentHealth -= amount;

        OnHPPctChanged(CurrentHpPct);
    }
}