module-navigation-tool/Editor/Toolbar/MainToolbarElements/MainToolbarScenePickerElement.cs

#if UNITY_6000_3_OR_NEWER
using System;
using System.Collections.Generic;
using System.Text;
using UnityEditor;
using UnityEditor.SceneManagement;
using UnityEditor.Toolbars;
using UnityEngine;
using UnityEngine.SceneManagement;
using UnityEngine.Scripting;

namespace Module.NavigationTool.Editor.Toolbar
{
    internal static class MainToolbarScenePickerElement
    {
        private static readonly ScenePickerList SceneList = new();

        [Preserve]
        [MainToolbarElement("Toolbar/Scene", ussName = "", defaultDockIndex = 100, defaultDockPosition = MainToolbarDockPosition.Middle, menuPriority = 1500)]
        public static IEnumerable<MainToolbarElement> Draw()
        {
            return new List<MainToolbarElement>(3)
            {
                CreateDropdownSceneList(),
                CreateToggleSceneLoad(),
                CreateButtonAddNewScene()
            };
        }
        
        private static MainToolbarDropdown CreateDropdownSceneList()
        {
            SceneList.Refresh();
            var content = new MainToolbarContent(GetSceneLabel());
            return new MainToolbarDropdown(content, rect =>
            {
                var menu = new GenericMenu();
                    
                for (var i = 0; i < SceneList.labels.Length; i++)
                {
                    var sceneIndex = i;
                    menu.AddItem(SceneList.labels[i], SceneList.selected.Contains(i), () => SelectScene(sceneIndex));
                }
                
                menu.DropDown(rect);
            });
        }

        private static MainToolbarToggle CreateToggleSceneLoad()
        {
            var isScenePickerSetAsAdditive = ToolbarScenePickerSettings.IsScenePickerSetAsAdditive;
            var content = isScenePickerSetAsAdditive
                ? new MainToolbarContent("A", "Additive scene loading (toogle to Single)")
                : new MainToolbarContent("S", "Single scene loading (toggle to Additive)");

            return new MainToolbarToggle(content, isScenePickerSetAsAdditive, result =>
            {
                ToolbarScenePickerSettings.IsScenePickerSetAsAdditive = result;
                MainToolbar.Refresh("Toolbar/Scene");
            });
        }

        private static MainToolbarButton CreateButtonAddNewScene()
        {
            var icon = EditorGUIUtility.IconContent("d_CreateAddNew").image as Texture2D;
            var content = new MainToolbarContent(icon, "Create a new scene");
            return new MainToolbarButton(content, () =>
            {
                try
                {
                    var selection = EditorUtility.DisplayDialogComplex("Create new scene", "How do you want to add the scene?", "Single", "Additive", "Cancel");

                    if (selection == 2)
                        return;

                    var scene = EditorSceneManager.NewScene(NewSceneSetup.EmptyScene, selection == 0 ? NewSceneMode.Single : NewSceneMode.Additive);

                    if (EditorUtility.DisplayDialog("Create new scene", "Save scene to disk?", "Yes", "No"))
                        EditorSceneManager.SaveScene(scene);
                }
                catch (Exception e)
                {
                    EditorUtility.DisplayDialog("Failed to add scene", e.Message, "Ok");
                }
            });
        }
        
        private static void SelectScene(int index)
        {
            try
            {
                if (!EditorSceneManager.SaveCurrentModifiedScenesIfUserWantsTo())
                    return;

                var scenes = SceneList.scenes[index];
                var isScenePickerSetAsAdditive = ToolbarScenePickerSettings.IsScenePickerSetAsAdditive;

                for (var i = 0; i < scenes.paths.Count; i++)
                {
                    var path = scenes.paths[i];
                    var scene = SceneManager.GetSceneByPath(path);

                    if (scenes.isGroup)
                    {
                        if (isScenePickerSetAsAdditive || i != 0)
                        {
                            EditorSceneManager.OpenScene(path, OpenSceneMode.Additive);
                            var sceneIndex = SceneList.IndexOfPath(path, false);

                            if (sceneIndex != -1)
                                SceneList.selected.Add(sceneIndex);
                        }
                        else
                        {
                            EditorSceneManager.OpenScene(path, OpenSceneMode.Single);
                            var sceneIndex = SceneList.IndexOfPath(path, false);

                            SceneList.selected.Clear();

                            if (sceneIndex != -1)
                                SceneList.selected.Add(index);
                        }
                    }
                    else
                    {
                        if (scene.isLoaded)
                        {
                            if (SceneManager.sceneCount == 1)
                                return;

                            EditorSceneManager.CloseScene(scene, true);
                            SceneList.selected.Remove(index);
                        }
                        else if (isScenePickerSetAsAdditive)
                        {
                            EditorSceneManager.OpenScene(path, OpenSceneMode.Additive);
                            SceneList.selected.Add(index);
                        }
                        else
                        {
                            EditorSceneManager.OpenScene(path, OpenSceneMode.Single);
                            SceneList.selected.Clear();
                            SceneList.selected.Add(index);
                        }
                    }
                }

                GetSceneLabel();
            }
            catch (Exception e)
            {
                Debug.LogException(e);
            }
            finally
            {
                MainToolbar.Refresh("Toolbar/Scene");
            }
        }

        private static string GetSceneLabel()
        {
            var builder = new StringBuilder();

            if (SceneList.selected.Count != 0)
            {
                for (var i = 0; i < SceneList.selected.Count; i++)
                {
                    if (i > 0)
                        builder.Append(", ");

                    builder.Append(SceneList.scenes[SceneList.selected[i]].shortname);
                }
            }
            else
            {
                builder.Append("Unsaved scene(s)");
            }
            
            return builder.ToString();
        }

        public static void Refresh()
        {
            MainToolbar.Refresh("Toolbar/Scene");
        }
    }
}
#endif