Fruitomation/Assets/Scripts/Game/SceneController.cs

using PashaBibko.Pacore.Attributes;
using UnityEngine.SceneManagement;
using System.Collections;
using UnityEngine;
using System;
using Debug = UnityEngine.Debug;

namespace Fruitomation.Game
{
    [CreateInstanceOnStart] public class SceneController : MonoBehaviour
    {
        private SceneControllerTransition Transition;
        private static SceneController Instance;

        private void Awake()
        {
            if (Instance is not null)
            {
                Debug.LogError($"Multiple instances of [{nameof(SceneController)}] cannot exist.");
                return;
            }

            Instance = this;
            
            Canvas canvas = gameObject.AddComponent<Canvas>();
            canvas.renderMode = RenderMode.ScreenSpaceOverlay;
            
            GameObject overlayGo = new("Overlay");
            overlayGo.transform.SetParent(canvas.transform);
            
            Transition = overlayGo.AddComponent<SceneControllerTransition>();
            Transition.OnCreation(canvas);
        }

        private IEnumerator StartLoadInternal(string scene)
        {
            AsyncOperation operation = SceneManager.LoadSceneAsync(scene);
            if (operation == null)
            {
                string error = $"Unknown scene [{scene}]";
                throw new ArgumentException(error);
            }
            
            operation.allowSceneActivation = false;
            operation.completed += _ => StartCoroutine(EndLoadInternal());

            Transition.GoingUp = false;
            Time.timeScale = 0;
            float lerp = 0f;

            while (lerp < 1f)
            {
                lerp += Time.unscaledDeltaTime;
                Transition.LerpValue = Mathf.Clamp01(lerp);
                
                yield return null; // Waits for next frame
            }

            operation.allowSceneActivation = true;
        }

        private IEnumerator EndLoadInternal()
        {
            float lerp = 0f;
            
            while (lerp < 1f)
            {
                lerp += Time.unscaledDeltaTime;
                Transition.LerpValue = Mathf.Clamp01(lerp);
                
                yield return null; // Waits for next frame
            }

            Time.timeScale = 1f;
        }

        public static void StartLoadOf(string scene) => Instance.StartCoroutine(Instance.StartLoadInternal(scene));
    }
}