Game over / Restart / Pause

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using TMPro;
using UnityEngine.UI;
using UnityEngine.SceneManagement;

public class GameManager : MonoBehaviour
{
//pausescreen is a UI panel
    [SerializeField] GameObject pauseScreen;
    private bool paused;
    //deactivate the gameobjects in the inspector
    public TextMeshProUGUI gameOverText;
    //remember to assign the on click event in the inspector. Drag in the game manager and choose the restart function.
    public Button restartButton;
    public bool isGameActive;

    private void Start()
    {
        isGameActive = true;
    }
    // Update is called once per frame
    void Update()
    {
        if(Input.GetKeyDown(KeyCode.P))
        {
            PauseGame();
        }
    }

    void PauseGame()
    {
        if (!paused)
        {
            paused = true;
            pauseScreen.SetActive(true);
            Time.timeScale = 0;
        }
        else
        {
            paused = false;
            pauseScreen.SetActive(false);
            Time.timeScale = 1;
        }
    }

    public void UpdateLives(int livesToChange)
    {
        lives += livesToChange;
        livesText.text = "Lives: " + lives;
        if (lives <= 0)
        {
           GameOver();
        }
    }

    public void GameOver()
    {
        gameOverText.gameObject.SetActive(true);
        isGameActive = false;
        restartButton.gameObject.SetActive(true);
    }

    public void RestartGame()
    {
        SceneManager.LoadScene(SceneManager.GetActiveScene().name);
    }

 public void ReturnToMainMenu()
    {
        SceneManager.LoadScene(0);
    }
}