module-navigation-tool/Editor/Toolbar/Utilities/ToolbarUtility.cs

using System;
using System.Collections.Generic;
using UnityEngine;
using System.Reflection;
using System.Runtime.Serialization;
using Object = UnityEngine.Object;

#if UNITY_2019_1_OR_NEWER
using UnityEngine.UIElements;
#else
using UnityEngine.Experimental.UIElements;
#endif

namespace Module.NavigationTool.Editor.Toolbar
{
    internal static class ToolbarUtility
    {
        private static readonly Assembly ASSEMBLY = typeof(UnityEditor.Editor).Assembly;
        
        #if UNITY_2021_1_OR_NEWER
        private static ScriptableObject CURRENT_TOOLBAR;
        private static VisualElement CURRENT_PARENT_LEFT;
        private static VisualElement CURRENT_PARENT_RIGHT;
        private static int CURRENT_INSTANCE_ID = -1;
        #endif
        
        #if UNITY_2021_1_OR_NEWER
        public static void OnUpdate(Action<VisualElement, VisualElement> callback)
        {
            if (CURRENT_TOOLBAR == null)
                CURRENT_TOOLBAR = GetToolbarObject();
            
            if (CURRENT_TOOLBAR != null && CURRENT_PARENT_LEFT != null && CURRENT_TOOLBAR.GetInstanceID() != CURRENT_INSTANCE_ID)
            {
                CURRENT_PARENT_LEFT.RemoveFromHierarchy();
                CURRENT_PARENT_LEFT = null;
                
                CURRENT_PARENT_RIGHT.RemoveFromHierarchy();
                CURRENT_PARENT_RIGHT = null;
                
                CURRENT_INSTANCE_ID = CURRENT_TOOLBAR.GetInstanceID();
            }

            if (CURRENT_TOOLBAR == null || CURRENT_PARENT_LEFT != null)
                return;

            CURRENT_PARENT_LEFT?.RemoveFromHierarchy();
            CURRENT_PARENT_RIGHT?.RemoveFromHierarchy();

            FieldInfo root = CURRENT_TOOLBAR.GetType().GetField("m_Root", BindingFlags.NonPublic | BindingFlags.Instance);
            object rawRoot = root?.GetValue(CURRENT_TOOLBAR);
            var mRoot = rawRoot as VisualElement;
            
            CURRENT_PARENT_LEFT = CreateParent(mRoot, "ToolbarZoneLeftAlign", true);
            CURRENT_PARENT_RIGHT = CreateParent(mRoot, "ToolbarZoneRightAlign", false);
            callback?.Invoke(CURRENT_PARENT_LEFT, CURRENT_PARENT_RIGHT);
        }

        private static VisualElement CreateParent(VisualElement root, string query, bool isLeft)
        {
            VisualElement parent = root.Q(query);
            VisualElement result;
            
            if (isLeft)
            {
                result = new VisualElement
                {
                    style = {
                        flexGrow = 1,
                        flexDirection = FlexDirection.Row
                    }
                };
                
                result.Add(new VisualElement
                {
                    style = {
                        flexGrow = 1
                    }
                });
            }
            else
            {
                result = new VisualElement
                {
                    style = {
                        flexGrow = 1,
                        flexDirection = FlexDirection.RowReverse
                    }
                };
                
                result.Add(new VisualElement
                {
                    style =
                    {
                        flexGrow = 1
                    }
                });
            }

            parent.Add(result);
            return result;
        }
        #else
        public static void AddGuiListener(Action action)
        {
            ScriptableObject so = GetToolbarObject();
            
            if (so == null)
                return;
            
            Type typeGuiView = ASSEMBLY.GetType("UnityEditor.GUIView");

            #if UNITY_2020_1_OR_NEWER
		    Type typeWindowBackend = ASSEMBLY.GetType("UnityEditor.IWindowBackend");
		    PropertyInfo piWindowBackend = typeGuiView.GetProperty("windowBackend", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
		    PropertyInfo piVisualTree = typeWindowBackend.GetProperty("visualTree", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);

            if (piWindowBackend == null)
                return;
            #else
            PropertyInfo piVisualTree = typeGuiView.GetProperty("visualTree", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);
            #endif

            if (piVisualTree == null)
                return;
            
            FieldInfo fiImguiContainer = typeof(IMGUIContainer).GetField("m_OnGUIHandler", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);

            if (fiImguiContainer == null)
                return;
            
            #if UNITY_2020_1_OR_NEWER
			object windowBackend = piWindowBackend.GetValue(so);
			var visualTree = (VisualElement)piVisualTree.GetValue(windowBackend, null);
            #else
            var visualTree = (VisualElement)piVisualTree.GetValue(so, null);
            #endif
                
            var container = (IMGUIContainer)visualTree[0];
            var handler = (Action)fiImguiContainer.GetValue(container);
            handler -= action;
            handler += action;
            fiImguiContainer.SetValue(container, handler);
        }
        #endif

        private static ScriptableObject GetToolbarObject()
        {
            Type typeToolbar = ASSEMBLY.GetType("UnityEditor.Toolbar");
            Object[] toolbars = Resources.FindObjectsOfTypeAll(typeToolbar);
            return toolbars.Length > 0 ? (ScriptableObject)toolbars[0] : null;
        }

        public static AbstractToolbarDrawer[] GetAllDrawers()
        {
            var list = new List<AbstractToolbarDrawer>(8);

            try
            {
                Assembly[] assemblies = AppDomain.CurrentDomain.GetAssemblies();
                Type iType = typeof(AbstractToolbarDrawer);

            

                for (var i = 0; i < assemblies.Length; i++)
                {
                    Assembly assembly = assemblies[i];
                    Type[] types = assembly.GetTypes();

                    for (var j = 0; j < types.Length; j++)
                    {
                        Type type = types[j];

                        if (!type.IsAbstract && iType.IsAssignableFrom(type))
                            list.Add((AbstractToolbarDrawer)FormatterServices.GetUninitializedObject(type));
                    }
                }
            }
            catch (Exception)
            {
                // Fail silently
            }

            return list.ToArray();
        }
    }
}