Menu Manager

using System.Collections;
using System.Collections.Generic;
using System.Linq;
using UnityEngine;

public class MenuManager : MonoBehaviour {
    public static MenuManager Instance;

    private GameObject _fadeImg;
    private readonly List<GameObject> _menuScreens = new List<GameObject>();
    private GameObject _lastViewedScreen;
    private GameObject _currentScreen;

    private void Awake() {
        if (Instance == null) {
            Instance = this;
        } else {
            Destroy(gameObject);
        }
    }

    private void Start() {
        _fadeImg = GameObject.Find("FadeIMG");
        AddAllScreensToList();
        DisableAllScreens();
        ShowFirstScreen();
    }

    private void AddAllScreensToList() {
        foreach (Transform child in transform) {
            _menuScreens.Add(child.gameObject);
        }
    }

    private void DisableAllScreens() {
        foreach (GameObject Screen in _menuScreens) {
            if (Screen.name == "MainMenu") {
                _currentScreen = Screen;
            }
            if ((Screen.name != "MainMenu") && (Screen.name != "FadeIMG") && (Screen.name != "FPS")) {
                Screen.SetActive(false);
            }
        }
    }

    private void ShowFirstScreen() {
        GetScreenFromList("MainMenu").SetActive(true);
        StartCoroutine(ScreenFade());
    }

    private void CheckChildScreens(GameObject child) {
        List<GameObject> childObjects = GameObject.FindGameObjectsWithTag("ViewLayer").ToList()
            .FindAll(c => c.transform.IsChildOf(_currentScreen.transform));
        childObjects.ForEach(c => c.SetActive(false));
        child.SetActive(true);
    }

    private void UpdateTexts() {
        ScoreManager.Instance.UpdateTexts();
    }

    public GameObject GetScreenFromList(string screenName) {
        foreach (GameObject Screen in _menuScreens) {
            if (Screen.name == screenName) {
                return Screen;
            }
        }
        Debug.LogFormat("The given screen: {0} could not be found", screenName);
        return null;
    }

    public void ShowScreen(GameObject screenToShow) {
        if (screenToShow.name == "MainMenu") {
            StartCoroutine(ReloadScene());
        } else if (screenToShow.transform.IsChildOf(_currentScreen.transform)) {
            CheckChildScreens(screenToShow);
            UpdateTexts();
        } else {
            StartCoroutine(SetNewScreen(screenToShow));
            UpdateTexts();
        }
    }

    public void ShowLastScreen() {
        ShowScreen(_lastViewedScreen);
    }

    public void DisablePlayServicesRelatedButtons() {
        List<GameObject> childObjects = GameObject.FindGameObjectsWithTag("PlayServicesButton").ToList()
            .FindAll(c => c.transform.IsChildOf(_currentScreen.transform));
        childObjects.ForEach(c => c.SetActive(Social.localUser.authenticated));
        childObjects[0].gameObject.transform.parent.position =
            Camera.main.ViewportToScreenPoint(new Vector3(0.33f, 0, 0));
    }

    private IEnumerator ReloadScene() {
        _fadeImg.SetActive(true);
        GetComponent<Animator>().Play("FadeIn");
        yield return new WaitForSeconds(GetComponent<Animator>().GetCurrentAnimatorStateInfo(0).length);
        SceneLoadingHelper.LoadSceneSingle("_Main");
    }

    private IEnumerator SetNewScreen(GameObject screenToShow) {
        foreach (GameObject MenuScreen in _menuScreens) {
            if ((MenuScreen != screenToShow) && MenuScreen.activeSelf && MenuScreen.GetComponent<Animator>()) {
                MenuScreen.GetComponent<Animator>().Play("LeaveScreenState");
                yield return new WaitForSeconds(MenuScreen.GetComponent<Animator>().GetCurrentAnimatorStateInfo(0)
                    .length);
            }
            if (MenuScreen.name != "FPS") {
                MenuScreen.SetActive(false);
            }
        }
        screenToShow.SetActive(true);
        if (screenToShow.GetComponent<Animator>()) {
            screenToShow.GetComponent<Animator>().Play("EnterScreenState");
        }
        _lastViewedScreen = _currentScreen;
        _currentScreen = screenToShow;
    }

    private IEnumerator ScreenFade() {
        _fadeImg.SetActive(true);
        GetComponent<Animator>().Play("FadeOut");
        yield return new WaitForSeconds(GetComponent<Animator>().GetCurrentAnimatorStateInfo(0).length);
        _fadeImg.SetActive(false);
    }
}