Get and Sort DontDestroy gameObjects

// Author: Daniele Giardini - http://www.demigiant.com
// Created: 2020/10/25

using System;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.SceneManagement;
using Object = UnityEngine.Object;

namespace Demigiant.DemiTools.DeUnityExtended
{
    public static class DeSceneUtils
    {
        #region Public Methods

        /// <summary>
        /// Returns all root DontDestroyOnLoad GameObjects, or an empty list if none was found.<para/>
        /// WARNING, expensive method with allocations (can be partially avoided by passing an existing DontDestroy GameObject):<para/>
        /// - new list creation<para/>
        /// - new GameObject creation-then-destruction (necessary to detect the DontDestroy scene, avoidable if anyDontDestroyGameObject is provided)
        /// </summary>
        /// <param name="anyDontDestroyGameObject">Providing this will avoid having to create and destroy a temporary gameObject during this process</param>
        public static List<GameObject> GetDontDestroyRootGameObjects(GameObject anyDontDestroyGameObject = null)
        {
            List<GameObject> result = new List<GameObject>();
            Scene dontDestroyScene;
            if (anyDontDestroyGameObject != null) {
                dontDestroyScene = anyDontDestroyGameObject.scene;
                dontDestroyScene.GetRootGameObjects(result);
            } else {
                const string tmpGuid = "bb179a0d-94b2-4008-ad78-f3871dc82ba6";
                GameObject tmpGO = new GameObject(tmpGuid);
                Object.DontDestroyOnLoad(tmpGO);
                dontDestroyScene = tmpGO.scene;
                Object.Destroy(tmpGO);
                dontDestroyScene.GetRootGameObjects(result);
                int tot = result.Count;
                for (int i = 0; i < tot; ++i) {
                    if (result[i].name != tmpGuid) continue;
                    result.RemoveAt(i);
                    break;
                }
            }
            return result;
        }

        /// <summary>
        /// Sorts all GameObjects in the DontDestroy scene.<para/>
        /// WARNING, expensive method with allocations (can be partially avoided by passing an existing DontDestroy GameObject):<para/>
        /// - new list creation<para/>
        /// - new GameObject creation-then-destruction (necessary to detect the DontDestroy scene, avoidable if anyDontDestroyGameObject is provided)
        /// </summary>
        /// <param name="anyDontDestroyGameObject">Providing this will avoid having to create and destroy a temporary gameObject during this process</param>
        public static void SortDontDestroyGameObjectsAlphabetically(GameObject anyDontDestroyGameObject = null)
        {
            List<GameObject> allRootDontDestroyGos = GetDontDestroyRootGameObjects(anyDontDestroyGameObject);
            allRootDontDestroyGos.Sort(SortGameObjectsByName);
            int tot = allRootDontDestroyGos.Count;
            for (int i = 0; i < tot; ++i) allRootDontDestroyGos[i].transform.SetSiblingIndex(i);
        }

        #endregion

        #region Methods

        static int SortGameObjectsByName(GameObject a, GameObject b)
        {
            return string.Compare(a.name, b.name, StringComparison.InvariantCultureIgnoreCase);
        }

        #endregion
    }
}