GameManager.cs

using UnityEngine;
using UnityEngine.UI;

public class GameManager : MonoBehaviour
{
	public const int INITIAL_LIFE = 100;
	private const string SCORE_TXT = "SCORE: ";
	private const string LIFE_TXT = "LIFE: ";

	//UI
	[SerializeField] private Text scoreText;
	[SerializeField] private Text lifeText;
	[SerializeField] private Image gameOverOverlay;

	//Audio
	[SerializeField] private AudioClip attackSfx;
	[SerializeField] private AudioClip enemyDeathSfx;
	[SerializeField] private AudioClip playerDeathSfx;

	//Entities
	[SerializeField] private Player player;
	[SerializeField] private AudioSource audioSource;

	private void Start()
	{		
		InitializeUI();

		player.gameObject.SetActive(true);
	}

	private void InitializeUI()
	{
		gameOverOverlay.gameObject.SetActive(false);

		if (scoreText != null)
		{
			scoreText.text = SCORE_TXT + "0";
			scoreText.gameObject.SetActive(true);
		}

		if (lifeText != null)
		{
			lifeText.text = LIFE_TXT + INITIAL_LIFE.ToString();
			lifeText.gameObject.SetActive(true);
		}
	}

	private void DisableTextUI()
	{
		if (scoreText != null)
		{
			scoreText.gameObject.SetActive(false);
		}

		if (lifeText != null)
		{
			lifeText.gameObject.SetActive(false);
		}
	}

	public void UpdateScore(int score)
	{
		if(scoreText != null)
		{
			scoreText.text = SCORE_TXT + score.ToString();
		}
	}

	public void UpdateLife(int life)
	{
		if(lifeText != null)
		{
			lifeText.text = LIFE_TXT + life.ToString();
		}
	}
	
	public void PlayerAttacksEnemy(Enemy enemy)
	{
		if (player != null && enemy != null)
		{
			enemy.ReceiveDamage(player.Attack);
			PlayAttackSfx();

			if (enemy.IsDead)
			{
				player.AddScore(enemy.TotalPoints);
				player.AddToTotalEnemiesKilled();
			}
		}
	}

	public void EnemyAttacksPlayer(Enemy enemy)
	{
		if(enemy != null && player != null)
		{
			player.ReceiveDamage(enemy.Attack);
			PlayAttackSfx();

			if (player.IsDead)
			{
				PlayPlayerDeathSfx();
				gameOverOverlay.gameObject.SetActive(true);
				DisableTextUI();
				player.gameObject.SetActive(false);				
			}

			UpdateLife(player.Life);
		}
	}

	public void PlayAttackSfx()
	{
		if(audioSource != null && attackSfx != null)
		{
			audioSource.clip = attackSfx;
			audioSource.Play();
		}
	}

	public void PlayEnemyDeathSfx()
	{
		if (audioSource != null && enemyDeathSfx!= null)
		{
			audioSource.clip = enemyDeathSfx;
			audioSource.Play();
		}
	}

	public void PlayPlayerDeathSfx()
	{
		if (audioSource != null && playerDeathSfx != null)
		{
			audioSource.clip = playerDeathSfx;
			audioSource.Play();
		}
	}
}