Refactor project structure and improve performance

Changed the `ProjectRepository` class to be static for easier usage.
Changed `ProjectService` constants to public properties for accessibility.
Changed `App.xaml` to consolidate theme resources into `Override.xaml`.
Changed `App.xaml.cs` to implement an `AppStateMachine` for better state management.
Changed `ConsolePage` and `HierarchyPage` to utilize the new ViewModel structure.
Changed `ProjectPage` to use the `ExplorerItem` model for asset display.
Changed `Entity` and `EntityManager` to enhance component management with a new `IComponentData` interface.
Changed the `Logger` class to introduce structured logging functionality.
Changed the system architecture to support dependency management for better organization.
Changed the `QueryEnumerable` class to allow for more flexible entity queries.
Changed the `TypeHandle` class to improve efficiency in retrieving type handles.
Changed the `World` class to support robust world management and multiple worlds.
Updated the `Test` class to demonstrate the new entity and component management system.

Ghost.Data/Repository/ProjectRepository.cs

@@ -1,19 +1,11 @@
 using Ghost.Data.Models;
-using System.Data;
+using Ghost.Data.Resources;
 using System.Data.SQLite;
 
 namespace Ghost.Data.Repository;
 
-internal class ProjectRepository : IDisposable
+internal static class ProjectRepository
 {
-    private readonly SQLiteConnection _connection;
-
-    public ProjectRepository(string sourceDirectory)
-    {
-        _connection = new SQLiteConnection(string.Format(Command.CONNECTION_STRING, sourceDirectory));
-        _connection.Open();
-    }
-
     private static class Command
     {
         public const string CONNECTION_STRING = "Data Source={0}\\projects.db;Version=3;";
@@ -24,18 +16,21 @@ internal class ProjectRepository : IDisposable
         public const string UPDATE_PROJECT_STRING = "UPDATE Projects SET Name = @Name, MetadataPath = @MetadataPath WHERE ID = @ID;";
     }
 
-    private async Task EnsureTableCreatedAsync()
+    private static async Task EnsureTableCreatedAsync(SQLiteConnection connection)
     {
-        using var createCommand = _connection.CreateCommand();
+        using var createCommand = connection.CreateCommand();
         createCommand.CommandText = Command.CREATE_PROJECT_TABLE_STRING;
         await createCommand.ExecuteNonQueryAsync();
     }
 
-    public async IAsyncEnumerable<ProjectInfo> LoadProjectsAsync()
+    public static async IAsyncEnumerable<ProjectInfo> LoadProjectsAsync()
     {
-        await EnsureTableCreatedAsync();
+        using var connection = new SQLiteConnection(string.Format(Command.CONNECTION_STRING, DataPath.s_applicationDataFolder));
+        connection.Open();
 
-        using var command = _connection.CreateCommand();
+        await EnsureTableCreatedAsync(connection);
+
+        using var command = connection.CreateCommand();
         command.CommandText = Command.SELECT_PROJECT_STRING;
 
         using var reader = command.ExecuteReader();
@@ -52,11 +47,14 @@ internal class ProjectRepository : IDisposable
         }
     }
 
-    public async Task AddProjectAsync(ProjectInfo project)
+    public static async Task AddProjectAsync(ProjectInfo project)
     {
-        await EnsureTableCreatedAsync();
+        using var connection = new SQLiteConnection(string.Format(Command.CONNECTION_STRING, DataPath.s_applicationDataFolder));
+        connection.Open();
 
-        using var command = _connection.CreateCommand();
+        await EnsureTableCreatedAsync(connection);
+
+        using var command = connection.CreateCommand();
         command.CommandText = Command.INSERT_PROJECT_STRING;
 
         command.Parameters.AddWithValue("@Name", project.Name);
@@ -65,9 +63,12 @@ internal class ProjectRepository : IDisposable
         await command.ExecuteNonQueryAsync();
     }
 
-    public async Task RemoveProjectAsync(ProjectInfo project)
+    public static async Task RemoveProjectAsync(ProjectInfo project)
     {
-        using var command = _connection.CreateCommand();
+        using var connection = new SQLiteConnection(string.Format(Command.CONNECTION_STRING, DataPath.s_applicationDataFolder));
+        connection.Open();
+
+        using var command = connection.CreateCommand();
         command.CommandText = Command.REMOVE_PROJECT_STRING;
 
         command.Parameters.AddWithValue("@ID", project.ID);
@@ -75,9 +76,12 @@ internal class ProjectRepository : IDisposable
         await command.ExecuteNonQueryAsync();
     }
 
-    public async Task UpdateProjectAsync(ProjectInfo project)
+    public static async Task UpdateProjectAsync(ProjectInfo project)
     {
-        using var command = _connection.CreateCommand();
+        using var connection = new SQLiteConnection(string.Format(Command.CONNECTION_STRING, DataPath.s_applicationDataFolder));
+        connection.Open();
+
+        using var command = connection.CreateCommand();
         command.CommandText = Command.UPDATE_PROJECT_STRING;
 
         command.Parameters.AddWithValue("@Name", project.Name);
@@ -86,14 +90,4 @@ internal class ProjectRepository : IDisposable
 
         await command.ExecuteNonQueryAsync();
     }
-
-    public void Dispose()
-    {
-        if (_connection.State == ConnectionState.Open)
-        {
-            _connection.Close();
-        }
-
-        _connection.Dispose();
-    }
 }

Ghost.Data/Services/ProjectService.cs

@@ -8,10 +8,11 @@ namespace Ghost.Data.Services;
 
 internal partial class ProjectService
 {
-    private const string _ASSETS_FOLDER = "Assets";
-    private const string _CONFIG_FOLDER = "ProjectConfig";
     private const string _TEMPLATE_CONTENT_FILE = "content.zip";
 
+    public const string ASSETS_FOLDER = "Assets";
+    public const string CONFIG_FOLDER = "ProjectConfig";
+
     public static void EnsureDefaultTemplate()
     {
         var templates = Directory.GetFiles(DataPath.s_projectTemplateFolder, "template.json", SearchOption.AllDirectories);
@@ -70,8 +71,8 @@ internal partial class ProjectService
             return Result<ProjectMetadataInfo>.Error("Project directory is invalid or does not exist.");
         }
 
-        var projectAssetsPath = Path.Combine(projectDirectory, _ASSETS_FOLDER);
+        var projectAssetsPath = Path.Combine(projectDirectory, ASSETS_FOLDER);
-        var projectConfigPath = Path.Combine(projectDirectory, _CONFIG_FOLDER);
+        var projectConfigPath = Path.Combine(projectDirectory, CONFIG_FOLDER);
         if (!Directory.Exists(projectAssetsPath) || !Directory.Exists(projectConfigPath))
         {
             return Result<ProjectMetadataInfo>.Error("Project folder structure is invalid.");
@@ -94,8 +95,8 @@ internal partial class ProjectService
 
     private static async ValueTask SetupRequestFolderAsync(string projectDirectory, string templateDirectory)
     {
-        var projectAssetsPath = Path.Combine(projectDirectory, _ASSETS_FOLDER);
+        var projectAssetsPath = Path.Combine(projectDirectory, ASSETS_FOLDER);
-        var projectConfigPath = Path.Combine(projectDirectory, _CONFIG_FOLDER);
+        var projectConfigPath = Path.Combine(projectDirectory, CONFIG_FOLDER);
         var templateContentPath = Path.Combine(templateDirectory, _TEMPLATE_CONTENT_FILE);
 
         Directory.CreateDirectory(projectAssetsPath);
@@ -111,13 +112,17 @@ internal partial class ProjectService
     }
 }
 
-internal partial class ProjectService : IDisposable
+internal partial class ProjectService
 {
-    private readonly ProjectRepository _repository = new(DataPath.s_applicationDataFolder);
+    public static ProjectMetadataInfo CurrentProject
+    {
+        get;
+        set;
+    }
 
     public Task AddProjectAsync(ProjectInfo project)
     {
-        return _repository.AddProjectAsync(project);
+        return ProjectRepository.AddProjectAsync(project);
     }
 
     public async Task<ProjectInfo> AddProjectAsync(string name, string path)
@@ -127,27 +132,27 @@ internal partial class ProjectService : IDisposable
             Name = name,
             MetadataPath = path,
         };
-        await _repository.AddProjectAsync(project);
+        await ProjectRepository.AddProjectAsync(project);
 
         return project;
     }
 
     public Task RemoveProjectAsync(ProjectInfo project)
     {
-        return _repository.RemoveProjectAsync(project);
+        return ProjectRepository.RemoveProjectAsync(project);
     }
 
     public Task UpdateProjectAsync(ProjectInfo project)
     {
-        return _repository.UpdateProjectAsync(project);
+        return ProjectRepository.UpdateProjectAsync(project);
     }
 
     public IAsyncEnumerable<ProjectInfo> LoadAllProjectAsync()
     {
-        return _repository.LoadProjectsAsync();
+        return ProjectRepository.LoadProjectsAsync();
     }
 
-    public async Task<Result<ProjectInfo>> CreateProjectAsync(string projectName, string projectDirectory, Version engineVersion, string templatePath)
+    public async Task<Result<ProjectMetadataInfo>> CreateProjectAsync(string projectName, string projectDirectory, Version engineVersion, string templatePath)
     {
         try
         {
@@ -161,7 +166,7 @@ internal partial class ProjectService : IDisposable
                 // Check if folder is empty
                 if (Directory.EnumerateFiles(projectPath, "*", SearchOption.AllDirectories).Any())
                 {
-                    return new(false, null, "Directory is not empty");
+                    return new(false, default, "Directory is not empty");
                 }
             }
 
@@ -171,11 +176,11 @@ internal partial class ProjectService : IDisposable
             await SetupRequestFolderAsync(projectPath, templatePath);
 
             var info = await AddProjectAsync(projectName, metadataPath);
-            return new(true, info);
+            return new(true, new(metadataPath, metadata));
         }
         catch (Exception e)
         {
-            return Result<ProjectInfo>.Error($"Failed to create project: {e.Message}");
+            return Result<ProjectMetadataInfo>.Error($"Failed to create project: {e.Message}");
         }
     }
 
@@ -189,9 +194,4 @@ internal partial class ProjectService : IDisposable
 
         return result;
     }
-
-    public void Dispose()
-    {
-        _repository.Dispose();
-    }
 }

Ghost.Editor/App.xaml

@@ -9,10 +9,8 @@
             <ResourceDictionary.MergedDictionaries>
                 <XamlControlsResources xmlns="using:Microsoft.UI.Xaml.Controls" />
                 <XamlControlsResources Source="/Controls/EditorControls.xaml" />
-                <ResourceDictionary Source="/Themes/Dark.xaml" />
+                <ResourceDictionary Source="/Themes/Override.xaml" />
-                <ResourceDictionary Source="/Themes/Light.xaml" />
             </ResourceDictionary.MergedDictionaries>
-            <!--  Other app resources here  -->
         </ResourceDictionary>
     </Application.Resources>
 </Application>

Ghost.Editor/App.xaml.cs

@@ -1,5 +1,5 @@
-using Ghost.Editor.AppStates;
+using Ghost.Editor.Helpers;
-using Ghost.Editor.Helpers;
+using Ghost.Editor.Infrastructures.AppState;
 using Ghost.Editor.Services;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
@@ -20,7 +20,7 @@ namespace Ghost.Editor
 
         internal static Window? Window
         {
-            get => (Current as App)?._window;
+            get => (Current as App)!._window;
             set
             {
                 if (Current is App app)
@@ -48,16 +48,10 @@ namespace Ghost.Editor
                 UseContentRoot(AppContext.BaseDirectory).
                 ConfigureServices((context, services) =>
                 {
-                    services.AddSingleton(sp =>
-                    {
-                        return new AppStateService(
-                            new LandingState(),
-                            new EditorState());
-                    });
-
                     HostHelper.AddLandingScope(context, services);
                     HostHelper.AddEngineScope(context, services);
 
+                    services.AddSingleton<AppStateMachine>();
                     services.AddSingleton<StackedNotificationService>();
                 })
                 .Build();
@@ -92,7 +86,11 @@ namespace Ghost.Editor
 
             Host.Start();
 
-            await GetService<AppStateService>().TransitionToAsync(StateKey.Landing);
+            var stateMachine = GetService<AppStateMachine>();
+            stateMachine.RegisterState(StateKey.Landing, () => new LandingState());
+            stateMachine.RegisterState(StateKey.EngineEditor, () => new EditorState());
+
+            await stateMachine.TransitionToAsync(StateKey.Landing);
         }
 
         private void App_UnhandledException(object sender, Microsoft.UI.Xaml.UnhandledExceptionEventArgs e)

Ghost.Editor/Controls/ViewModelPage.cs

@@ -0,0 +1,38 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+using Ghost.Editor.Contracts;
+using Microsoft.UI.Xaml.Controls;
+using Microsoft.UI.Xaml.Navigation;
+
+namespace Ghost.Editor.Controls;
+
+public abstract partial class ViewModelPage<VM> : Page
+    where VM : ObservableObject
+{
+    public VM ViewModel
+    {
+        get;
+    }
+
+    protected ViewModelPage(VM viewModel)
+    {
+        ViewModel = viewModel;
+    }
+
+    protected override void OnNavigatedTo(NavigationEventArgs e)
+    {
+        base.OnNavigatedTo(e);
+        if (ViewModel is INavigationAware navigationAware)
+        {
+            navigationAware.OnNavigatedTo(e.Parameter);
+        }
+    }
+
+    protected override void OnNavigatedFrom(NavigationEventArgs e)
+    {
+        base.OnNavigatedFrom(e);
+        if (ViewModel is INavigationAware navigationAware)
+        {
+            navigationAware.OnNavigatedFrom();
+        }
+    }
+}

Ghost.Editor/Ghost.Editor.csproj

@@ -44,9 +44,8 @@
     <None Remove="Controls\EditorControls.xaml" />
     <None Remove="Controls\Internal\InspectorView.xaml" />
     <None Remove="Controls\Internal\InternalControls.xaml" />
-    <None Remove="Themes\Dark.xaml" />
-    <None Remove="Themes\Light.xaml" />
     <None Remove="View\Pages\EngineEditor\ConsolePage.xaml" />
+    <None Remove="View\Pages\EngineEditor\HierarchyPage.xaml" />
     <None Remove="View\Pages\EngineEditor\ProjectPage.xaml" />
     <None Remove="View\Pages\Landing\CreateProjectPage.xaml" />
     <None Remove="View\Pages\Landing\OpenProjectPage.xaml" />
@@ -105,7 +104,7 @@
     </Page>
   </ItemGroup>
   <ItemGroup>
-    <Folder Include="Helpers\Converters\" />
+    <Folder Include="AppStates\" />
     <Folder Include="Resources\" />
   </ItemGroup>
   <ItemGroup>
@@ -113,6 +112,11 @@
       <HintPath>..\..\Class\Misaki.HighPerformance\Misaki.HighPerformance.Unsafe\bin\Release\net9.0\Misaki.HighPerformance.Unsafe.dll</HintPath>
     </Reference>
   </ItemGroup>
+  <ItemGroup>
+    <Page Update="View\Pages\EngineEditor\HierarchyPage.xaml">
+      <Generator>MSBuild:Compile</Generator>
+    </Page>
+  </ItemGroup>
   <ItemGroup>
     <Page Update="View\Pages\EngineEditor\ProjectPage.xaml">
       <Generator>MSBuild:Compile</Generator>
@@ -124,12 +128,7 @@
     </Page>
   </ItemGroup>
   <ItemGroup>
-    <Page Update="Themes\Light.xaml">
+    <Page Update="Themes\Override.xaml">
-      <Generator>MSBuild:Compile</Generator>
-    </Page>
-  </ItemGroup>
-  <ItemGroup>
-    <Page Update="Themes\Dark.xaml">
       <Generator>MSBuild:Compile</Generator>
     </Page>
   </ItemGroup>

Ghost.Editor/Helpers/Converters/AssetPathToGlyphConverter.cs

@@ -0,0 +1,40 @@
+using Microsoft.UI.Xaml.Data;
+using System;
+using System.IO;
+
+namespace Ghost.Editor.Helpers.Converters;
+
+public partial class AssetPathToGlyphConverter : IValueConverter
+{
+    public object? Convert(object value, Type targetType, object parameter, string language)
+    {
+        if (value is not string path)
+        {
+            return null;
+        }
+
+        if (Directory.Exists(path))
+        {
+            return "\uE8B7";
+        }
+
+        var extension = Path.GetExtension(path).ToLowerInvariant();
+
+        // TODO: Use resource dictionary for icons.
+        return extension switch
+        {
+            ".fbx" or ".obj" => "\uF158",
+            ".png" or ".jpg" or ".jpeg" or ".gif" or ".bmp" => "\uE91B", // Image icon
+            ".mp3" or ".wav" or ".ogg" => "\uE767", // Audio icon
+            ".mp4" or ".avi" or ".mkv" => "\uE714", // Video icon
+            ".txt" or ".md" => "\uF000", // Text file icon
+            ".cs" or ".hlsl" => "\uE943", // Code file icon
+            _ => "\uE8A5", // Default file icon
+        };
+    }
+
+    public object ConvertBack(object value, Type targetType, object parameter, string language)
+    {
+        throw new NotImplementedException();
+    }
+}

Ghost.Editor/Helpers/HostHelpers.Page.cs

@@ -1,8 +1,11 @@
 using Ghost.Data.Services;
+using Ghost.Editor.View.Pages.EngineEditor;
 using Ghost.Editor.View.Pages.Landing;
 using Ghost.Editor.View.Windows;
-using Ghost.Editor.ViewModel.Pages.Landing;
+using Ghost.Editor.ViewModels.Pages.EngineEditor;
-using Ghost.Editor.ViewModel.Windows;
+using Ghost.Editor.ViewModels.Pages.Landing;
+using Ghost.Editor.ViewModels.Windows;
+using Ghost.Engine;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
 
@@ -12,19 +15,31 @@ internal static partial class HostHelper
 {
     public static void AddLandingScope(HostBuilderContext context, IServiceCollection services)
     {
-        services.AddSingleton<LandingWindow>();
+        services.AddTransient<LandingWindow>();
 
         services.AddTransient<CreateProjectPage>();
         services.AddTransient<CreateProjectViewModel>();
 
         services.AddTransient<OpenProjectPage>();
+        services.AddTransient<OpenProjectViewModel>();
 
         services.AddTransient<ProjectService>();
     }
 
     public static void AddEngineScope(HostBuilderContext context, IServiceCollection services)
     {
-        services.AddSingleton<EngineEditorWindow>();
+        services.AddSingleton<EngineCore>();
-        services.AddSingleton<EngineEditorViewModel>();
+
+        services.AddTransient<EngineEditorWindow>();
+        services.AddTransient<EngineEditorViewModel>();
+
+        services.AddTransient<HierarchyPage>();
+        services.AddTransient<HierarchyViewModel>();
+
+        services.AddTransient<ProjectPage>();
+        services.AddTransient<ProjectViewModel>();
+
+        services.AddTransient<ConsolePage>();
+        services.AddTransient<ConsoleViewModel>();
     }
 }

Ghost.Editor/Infrastructures/AppState/AppStateMachine.cs

@@ -1,20 +1,23 @@
-using Ghost.Editor.AppStates;
+using System;
-using Ghost.Editor.Contracts;
 using System.Collections.Generic;
-using System.Linq;
 using System.Threading.Tasks;
 
-namespace Ghost.Editor.Services;
+namespace Ghost.Editor.Infrastructures.AppState;
 
-internal class AppStateService(params IEnumerable<IAppState<StateKey>> states)
+internal class AppStateMachine
 {
-    private readonly Dictionary<StateKey, IAppState<StateKey>> _states = states.ToDictionary(s => s.StateKy, s => s);
+    private Dictionary<StateKey, Lazy<IAppState>> s_states = new();
-    private IAppState<StateKey>? _current;
+    private IAppState? s_current;
+
+    public void RegisterState(StateKey key, Func<IAppState> stateFactory)
+    {
+        s_states[key] = new(stateFactory);
+    }
 
     public async Task TransitionToAsync(StateKey stateKey, object? parameter = null)
     {
-        var previous = _current;
+        var previous = s_current;
-        var next = _states[stateKey];
+        var next = s_states[stateKey].Value;
 
         if (previous != null)
         {
@@ -30,6 +33,6 @@ internal class AppStateService(params IEnumerable<IAppState<StateKey>> states)
 
         await next.OnEnteredAsync(parameter);
 
-        _current = next;
+        s_current = next;
     }
 }

Ghost.Editor/Infrastructures/AppState/EditorState.cs

@@ -1,15 +1,15 @@
 using Ghost.Data.Models;
-using Ghost.Editor.Contracts;
+using Ghost.Data.Services;
 using Ghost.Editor.View.Windows;
+using Ghost.Engine;
 using System.Threading.Tasks;
 
-namespace Ghost.Editor.AppStates;
+namespace Ghost.Editor.Infrastructures.AppState;
 
-internal class EditorState : IAppState<StateKey>
+internal class EditorState : IAppState
 {
     private EngineEditorWindow? _window;
-
+    private EngineCore? _engineCore;
-    public StateKey StateKy => StateKey.EngineEditor;
 
     public Task OnExitingAsync()
     {
@@ -20,23 +20,31 @@ internal class EditorState : IAppState<StateKey>
         return Task.CompletedTask;
     }
 
-    public Task OnEnteringAsync(object? parameter)
+    public async Task OnEnteringAsync(object? parameter)
     {
-        if (parameter is not ProjectMetadata metadata)
+        if (parameter is not ProjectMetadataInfo metadataInfo)
         {
             throw new System.ArgumentException("Parameter must be of type ProjectMetadata.", nameof(parameter));
         }
 
+        ProjectService.CurrentProject = metadataInfo;
+
+        _engineCore = App.GetService<EngineCore>();
+        await _engineCore.StartAsync(new Engine.Models.LaunchArgument());
+
         _window = App.GetService<EngineEditorWindow>();
-        _window.ViewModel.CurrentProject = metadata;
         _window.Activate();
 
         App.Window = _window;
-        return Task.CompletedTask;
     }
 
-    public Task OnExitedAsync()
+    public async Task OnExitedAsync()
     {
+        if (_engineCore != null)
+        {
+            await _engineCore.ShutDownAsync();
+        }
+
         if (App.Window == _window)
         {
             App.Window = null;
@@ -44,7 +52,6 @@ internal class EditorState : IAppState<StateKey>
 
         _window?.Close();
         _window = null;
-        return Task.CompletedTask;
     }
 
     public Task OnEnteredAsync(object? parameter)

Ghost.Editor/Infrastructures/AppState/IAppState.cs

@@ -1,14 +1,9 @@
 using System.Threading.Tasks;
 
-namespace Ghost.Editor.Contracts;
+namespace Ghost.Editor.Infrastructures.AppState;
 
-internal interface IAppState<Key>
+internal interface IAppState
 {
-    public Key StateKy
-    {
-        get;
-    }
-
     /// <summary>
     /// Called when exiting the state.
     /// </summary>

Ghost.Editor/Infrastructures/AppState/LandingState.cs

@@ -1,15 +1,12 @@
-using Ghost.Editor.Contracts;
+using Ghost.Editor.View.Windows;
-using Ghost.Editor.View.Windows;
 using System.Threading.Tasks;
 
-namespace Ghost.Editor.AppStates;
+namespace Ghost.Editor.Infrastructures.AppState;
 
-internal class LandingState : IAppState<StateKey>
+internal class LandingState : IAppState
 {
     private LandingWindow? _window;
 
-    public StateKey StateKy => StateKey.Landing;
-
     public Task OnExitingAsync()
     {
         if (App.Window == _window)

Ghost.Editor/Infrastructures/AppState/StateKey.cs

@@ -1,4 +1,4 @@
-namespace Ghost.Editor.AppStates;
+namespace Ghost.Editor.Infrastructures.AppState;
 
 internal enum StateKey
 {

Ghost.Editor/Infrastructures/SceneGraph/EntityNode.cs

@@ -0,0 +1,17 @@
+using Ghost.Entities;
+
+namespace Ghost.Editor.Infrastructures.SceneGraph;
+
+public partial class EntityNode : SceneGraphNode
+{
+    private readonly Entity _entity;
+
+    public Entity Entity => _entity;
+    public override NodeType Type => NodeType.Entity;
+
+    public EntityNode(Entity entity, string name)
+    {
+        _entity = entity;
+        Name = name;
+    }
+}

Ghost.Editor/Infrastructures/SceneGraph/SceneGraphHelpers.cs

@@ -0,0 +1,112 @@
+using Ghost.Engine.Components;
+using Ghost.Entities;
+
+namespace Ghost.Editor.Infrastructures.SceneGraph;
+
+internal class SceneGraphHelpers
+{
+    /// <summary>
+    /// Creates a new <see cref="EntityNode"/> entity with default components.
+    /// </summary>
+    /// <param name="world">The world context where the entity will be created.</param>
+    /// <param name="entity">The entity to be wrapped in the <see cref="EntityNode"/>.</param>
+    public static EntityNode CreateEntityNode(World world, Entity entity, string name)
+    {
+        world.EntityManager.AddComponent(entity, LocalToWorld.Identity);
+        world.EntityManager.AddComponent(entity, Hierarchy.Root);
+        return new EntityNode(entity, name);
+    }
+
+    /// <summary>
+    /// Creates a new <see cref="Entity"/> and <see cref="EntityNode"/> entity with default components.
+    /// </summary>
+    /// <param name="world">The world context where the entity will be created.</param>
+    public static EntityNode CreateEntityNode(World world, string name)
+    {
+        var entity = world.EntityManager.CreateEntity();
+        return CreateEntityNode(world, entity, name);
+    }
+
+    /// <summary>
+    /// Attaches childEntity to parentEntity in the scene graph.
+    /// </summary>
+    /// <param name="world">The world context where the entities exist.</param>
+    /// <param name="parentNode">The parent entity to which the child will be attached.</param>
+    /// <param name="childNode">The child entity to be attached.</param>
+    public static void AttachChild(SceneNode scene, EntityNode parentNode, EntityNode childNode)
+    {
+        // 1) If the child already has a parent, detach it first
+        var childHierarchy = scene.World.EntityManager.GetComponent<Hierarchy>(childNode.Entity);
+        if (childHierarchy.ValueRO.parent != Entity.Invalid)
+        {
+            DetachFromParent(scene, childNode);
+        }
+
+        // 2) Link child to new parent
+        childHierarchy.ValueRW.parent = parentNode.Entity;
+
+        // 3) Insert child at the head of parent's child list
+        var parentHierarchy = scene.World.EntityManager.GetComponent<Hierarchy>(parentNode.Entity);
+
+        childHierarchy.ValueRW.nextSibling = parentHierarchy.ValueRO.firstChild;
+        parentHierarchy.ValueRW.firstChild = childNode.Entity;
+
+        // 4) Write back
+        scene.World.EntityManager.SetComponent(parentNode.Entity, in parentHierarchy.ValueRO);
+        scene.World.EntityManager.SetComponent(childNode.Entity, in childHierarchy.ValueRO);
+
+        // 5) Update children list in parent node
+        parentNode.Children.Add(childNode);
+    }
+
+    /// <summary>
+    /// Detaches the specified entity from its parent in the scene graph.
+    /// </summary>
+    /// <param name="world">The world context where the entities exist.</param>
+    /// <param name="node">The entity to detach from its parent.</param>
+    public static void DetachFromParent(SceneNode scene, EntityNode node)
+    {
+        var hierarchy = scene.World.EntityManager.GetComponent<Hierarchy>(node.Entity);
+        var parent = hierarchy.ValueRO.parent;
+        if (parent == Entity.Invalid)
+        {
+            return; // already root
+        }
+
+        var parentHierarchy = scene.World.EntityManager.GetComponent<Hierarchy>(parent);
+
+        // If entity is the first child, simply move head
+        if (parentHierarchy.ValueRO.firstChild == node.Entity)
+        {
+            parentHierarchy.ValueRW.firstChild = hierarchy.ValueRO.nextSibling;
+        }
+        else
+        {
+            // Otherwise, find the previous sibling in the linked list
+            var prevSibling = parentHierarchy.ValueRO.firstChild;
+            while (prevSibling != Entity.Invalid)
+            {
+                var prevHierarchy = scene.World.EntityManager.GetComponent<Hierarchy>(prevSibling);
+                if (prevHierarchy.ValueRW.nextSibling == node.Entity)
+                {
+                    prevHierarchy.ValueRW.nextSibling = hierarchy.ValueRO.nextSibling;
+                    scene.World.EntityManager.SetComponent(prevSibling, in prevHierarchy.ValueRO);
+                    break;
+                }
+
+                prevSibling = prevHierarchy.ValueRO.nextSibling;
+            }
+        }
+
+        // Clear child's references
+        hierarchy.ValueRW.parent = Entity.Invalid;
+        hierarchy.ValueRW.nextSibling = Entity.Invalid;
+
+        // Write back
+        scene.World.EntityManager.SetComponent(parent, in parentHierarchy.ValueRO);
+        scene.World.EntityManager.SetComponent(node.Entity, in hierarchy.ValueRO);
+
+        // Remove from parent's children list
+        scene.EntityNodeLookup[parent].Children.Remove(node);
+    }
+}

Ghost.Editor/Infrastructures/SceneGraph/SceneGraphNode.cs

@@ -0,0 +1,32 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+using System.Collections.ObjectModel;
+
+namespace Ghost.Editor.Infrastructures.SceneGraph;
+
+public abstract partial class SceneGraphNode : ObservableObject
+{
+    public enum NodeType
+    {
+        Scene,
+        Entity,
+    }
+
+    public abstract NodeType Type
+    {
+        get;
+    }
+
+    [ObservableProperty]
+    public partial string Name
+    {
+        get;
+        set;
+    }
+
+    // Will the new collection allocated if ui bind to this property?
+    private ObservableCollection<EntityNode>? _children;
+    public ObservableCollection<EntityNode> Children
+    {
+        get => _children ??= new();
+    }
+}

Ghost.Editor/Infrastructures/SceneGraph/SceneNode.cs

@@ -0,0 +1,58 @@
+using Ghost.Engine.Components;
+using Ghost.Entities;
+using System.Collections.Generic;
+
+namespace Ghost.Editor.Infrastructures.SceneGraph;
+
+public partial class SceneNode : SceneGraphNode
+{
+    private readonly World _world;
+    private Dictionary<Entity, EntityNode> _entityNodeLookup = new();
+
+    public World World => _world;
+    public Dictionary<Entity, EntityNode> EntityNodeLookup => _entityNodeLookup;
+
+    public override NodeType Type => NodeType.Scene;
+
+    public SceneNode(World world, string name)
+    {
+        _world = world;
+        Name = name;
+    }
+
+    private EntityNode BuildNodeRecursive(Entity entity, World world)
+    {
+        // TODO: Node serialization.
+        var node = new EntityNode(entity, "New Entity");
+        _entityNodeLookup[entity] = node;
+
+        var hc = world.EntityManager.GetComponent<Hierarchy>(entity);
+        var child = hc.ValueRO.firstChild;
+
+        while (child != Entity.Invalid)
+        {
+            node.Children.Add(BuildNodeRecursive(child, world));
+            var childHC = world.EntityManager.GetComponent<Hierarchy>(child);
+            child = childHC.ValueRO.nextSibling;
+        }
+
+        return node;
+    }
+
+    private void BuildGraph()
+    {
+        foreach (var (entity, hierarchy) in _world.Query<Hierarchy>())
+        {
+            if (hierarchy.ValueRO.parent == Entity.Invalid)
+            {
+                var node = BuildNodeRecursive(entity, _world);
+                Children.Add(node);
+            }
+        }
+    }
+
+    public void Load()
+    {
+        BuildGraph();
+    }
+}

Ghost.Editor/Models/AssetItem.cs

@@ -0,0 +1,19 @@
+namespace Ghost.Editor.Models;
+
+internal struct AssetItem()
+{
+    public string AssetPath
+    {
+        get; set;
+    } = string.Empty;
+
+    public string AssetName
+    {
+        get; set;
+    } = string.Empty;
+
+    public string IconGlyph
+    {
+        get; set;
+    } = string.Empty;
+}

Ghost.Editor/Models/ExplorerItem.cs

@@ -0,0 +1,27 @@
+using System.Collections.ObjectModel;
+
+namespace Ghost.Editor.Models;
+
+internal class ExplorerItem(string name, string path, bool isDirectory)
+{
+    public string Name
+    {
+        get;
+    } = name;
+
+    public string Path
+    {
+        get;
+    } = path;
+
+    public bool IsDirectory
+    {
+        get;
+    } = isDirectory;
+
+    public ObservableCollection<ExplorerItem>? Children
+    {
+        get;
+        set;
+    }
+}

Ghost.Editor/Models/GameObject.cs

@@ -1,269 +0,0 @@
-using CommunityToolkit.Mvvm.ComponentModel;
-using Ghost.Entities;
-using Ghost.Entities.Helpers;
-using System;
-using System.Collections.Generic;
-using System.Collections.ObjectModel;
-
-namespace Ghost.Editor.Models;
-
-public partial class GameObject : ObservableObject
-{
-    [ObservableProperty]
-    public partial bool IsActive
-    {
-        get;
-        set;
-    }
-
-    [ObservableProperty]
-    public partial bool IsActiveHierarchy
-    {
-        get;
-        set;
-    }
-
-    public Entity Entity
-    {
-        get;
-    }
-
-    public Scene Scene
-    {
-        get;
-        internal set;
-    }
-
-    public GameObject? Parent
-    {
-        get;
-        internal set;
-    }
-
-    public string Name
-    {
-        get;
-        set;
-    }
-
-    [ObservableProperty]
-    public partial ObservableCollection<IComponentData>? Components
-    {
-        get;
-        private set;
-    }
-
-    [ObservableProperty]
-    public partial IEnumerable<ScriptComponent>? ScriptComponents
-    {
-        get;
-        private set;
-    }
-
-    [ObservableProperty]
-    public partial ObservableCollection<GameObject>? Children
-    {
-        get;
-        private set;
-    }
-
-    public GameObject(Scene scene, string name)
-    {
-        Entity = scene.World.EntityManager.CreateEntity();
-        Scene = scene;
-        Name = name;
-        IsActive = true;
-    }
-
-    partial void OnIsActiveChanged(bool value)
-    {
-        IsActiveHierarchy = value && (Parent?.IsActiveHierarchy ?? true);
-        HandleActiveStateChanged();
-
-        if (Children != null)
-        {
-            foreach (var child in Children)
-            {
-                child.IsActiveHierarchy = value && IsActiveHierarchy;
-            }
-        }
-    }
-
-    partial void OnIsActiveHierarchyChanged(bool value)
-    {
-        HandleActiveStateChanged();
-    }
-
-    private void HandleActiveStateChanged()
-    {
-        if (IsActive && IsActiveHierarchy)
-        {
-            OnEnable();
-        }
-        else
-        {
-            OnDisable();
-        }
-    }
-
-    internal void OnEnable()
-    {
-        if (ScriptComponents != null)
-        {
-            foreach (var script in ScriptComponents)
-            {
-                if (!script.Enable)
-                {
-                    continue;
-                }
-                script.OnEnable();
-            }
-        }
-    }
-
-    internal void OnDisable()
-    {
-        if (ScriptComponents != null)
-        {
-            foreach (var script in ScriptComponents)
-            {
-                if (!script.Enable)
-                {
-                    continue;
-                }
-                script.OnDisable();
-            }
-        }
-    }
-
-    public void AddChild(GameObject child)
-    {
-        if (child.Scene != Scene)
-        {
-            throw new InvalidOperationException("Child GameObject must belong to the same Scene.");
-        }
-
-        Children ??= new();
-        Children.Add(child);
-        child.Parent = this;
-    }
-
-    public bool RemoveChild(GameObject child)
-    {
-        if (Children is null)
-        {
-            return false;
-        }
-
-        if (!Children.Remove(child))
-        {
-            return false;
-        }
-
-        child.Parent = null;
-        return true;
-    }
-
-    public void Destroy()
-    {
-        if (ScriptComponents != null)
-        {
-            foreach (var component in ScriptComponents)
-            {
-                if (!component.Enable)
-                {
-                    continue;
-                }
-                component.OnDestroy();
-            }
-        }
-
-        if (Children != null)
-        {
-            foreach (var child in Children)
-            {
-                child.Destroy();
-            }
-
-            Children.Clear();
-        }
-
-        Parent?.Children?.Remove(this);
-        Entity.Destroy();
-    }
-}
-
-public partial class GameObject
-{
-    // TODO: Implement a more efficient synchronization mechanism for components
-    internal void SyncComponents()
-    {
-        foreach (var (typeHandle, mask) in Scene.World.ComponentStorage.ComponentEntityMasks)
-        {
-            if (!mask.IsSet(Entity.ID))
-            {
-                continue;
-            }
-
-            var pool = Scene.World.ComponentStorage.ComponentPools[typeHandle];
-        }
-    }
-
-    internal void SyncScripts()
-    {
-        var scriptsPool = Scene.World.ComponentStorage.ScriptComponentPool.ScriptComponents;
-        if (scriptsPool == null)
-        {
-            return;
-        }
-
-        scriptsPool.TryGetValue(Entity, out var scripts);
-        ScriptComponents = scripts;
-    }
-
-    public void AddComponent<T>(T component)
-        where T : struct, IComponentData
-    {
-        Entity.AddComponent<T>(component);
-        SyncComponents();
-    }
-
-    public bool RemoveComponent<T>()
-        where T : struct, IComponentData
-    {
-        var result = Entity.RemoveComponent<T>();
-        SyncComponents();
-
-        return result;
-    }
-
-    public void AddScript<T>()
-        where T : ScriptComponent, new()
-    {
-        Entity.AddScript<T>();
-        SyncScripts();
-    }
-
-    public void AddScript(Type type)
-    {
-        Entity.AddScript(type);
-        SyncScripts();
-    }
-
-    public bool RemoveScript<T>()
-        where T : ScriptComponent
-    {
-        var result = Scene.World.EntityManager.RemoveScript<T>(Entity);
-        SyncScripts();
-
-        return result;
-    }
-
-    public bool RemoveScriptAt(int index)
-    {
-        var result = Scene.World.EntityManager.RemoveScriptAt(Entity, index);
-        SyncScripts();
-
-        return result;
-    }
-}

Ghost.Editor/Models/Scene.cs

@@ -1,36 +0,0 @@
-using Ghost.Entities;
-using System.Collections.Generic;
-
-namespace Ghost.Editor.Models;
-
-public class Scene
-{
-    private readonly HashSet<GameObject> _rootObjects = new();
-    private readonly World _world = World.Create();
-
-    public IEnumerable<GameObject> RootObjects => _rootObjects;
-    public World World => _world;
-
-    internal Scene()
-    {
-    }
-
-    internal void Load()
-    {
-        foreach (var gameObject in _rootObjects)
-        {
-            gameObject.OnEnable();
-        }
-    }
-
-    internal void Unload()
-    {
-        foreach (var gameObject in _rootObjects)
-        {
-            gameObject.OnDisable();
-            gameObject.Destroy();
-        }
-
-        _rootObjects.Clear();
-    }
-}

Ghost.Editor/Themes/Dark.xaml

@@ -1,8 +0,0 @@
-<?xml version="1.0" encoding="utf-8" ?>
-<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
-    <ResourceDictionary.ThemeDictionaries>
-        <ResourceDictionary x:Key="Dark">
-            <StaticResource x:Key="TabViewItemHeaderBackgroundSelected" ResourceKey="ControlFillColorSecondaryBrush" />
-        </ResourceDictionary>
-    </ResourceDictionary.ThemeDictionaries>
-</ResourceDictionary>

Ghost.Editor/Themes/Light.xaml

@@ -1,8 +0,0 @@
-<?xml version="1.0" encoding="utf-8" ?>
-<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
-    <ResourceDictionary.ThemeDictionaries>
-        <ResourceDictionary x:Key="Light">
-            <StaticResource x:Key="TabViewItemHeaderBackgroundSelected" ResourceKey="ControlFillColorSecondaryBrush" />
-        </ResourceDictionary>
-    </ResourceDictionary.ThemeDictionaries>
-</ResourceDictionary>

Ghost.Editor/Themes/Override.xaml

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ResourceDictionary
+    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    xmlns:controls="using:Microsoft.UI.Xaml.Controls">
+    <ResourceDictionary.ThemeDictionaries>
+        <ResourceDictionary x:Key="Dark">
+            <StaticResource x:Key="TabViewItemHeaderBackgroundSelected" ResourceKey="ControlFillColorSecondaryBrush" />
+        </ResourceDictionary>
+        <ResourceDictionary x:Key="Light">
+            <StaticResource x:Key="TabViewItemHeaderBackgroundSelected" ResourceKey="ControlFillColorSecondaryBrush" />
+        </ResourceDictionary>
+    </ResourceDictionary.ThemeDictionaries>
+</ResourceDictionary>

Ghost.Editor/View/Pages/EngineEditor/ConsolePage.xaml

@@ -21,19 +21,19 @@
             BorderThickness="0,0,0,1">
             <CommandBar Background="{ThemeResource CardBackgroundFillColorSecondaryBrush}" DefaultLabelPosition="Collapsed">
                 <CommandBar.PrimaryCommands>
-                    <AppBarButton Content="Clear" />
+                    <AppBarButton Command="{x:Bind ViewModel.ClearLogsCommand}" Content="Clear" />
                     <AppBarSeparator />
-                    <AppBarToggleButton Width="45">
+                    <AppBarToggleButton Width="45" IsChecked="{x:Bind ViewModel.ShowInfo, Mode=TwoWay}">
                         <AppBarToggleButton.Icon>
                             <FontIcon Glyph="&#xF167;" />
                         </AppBarToggleButton.Icon>
                     </AppBarToggleButton>
-                    <AppBarToggleButton Width="45">
+                    <AppBarToggleButton Width="45" IsChecked="{x:Bind ViewModel.ShowWarning, Mode=TwoWay}">
                         <AppBarToggleButton.Icon>
                             <FontIcon Glyph="&#xE814;" />
                         </AppBarToggleButton.Icon>
                     </AppBarToggleButton>
-                    <AppBarToggleButton Width="45">
+                    <AppBarToggleButton Width="45" IsChecked="{x:Bind ViewModel.ShowError, Mode=TwoWay}">
                         <AppBarToggleButton.Icon>
                             <FontIcon Glyph="&#xEB90;" />
                         </AppBarToggleButton.Icon>
@@ -42,7 +42,10 @@
 
                 <CommandBar.SecondaryCommands>
                     <AppBarToggleButton BorderThickness="0" Label="Clear On Play" />
-                    <AppBarToggleButton BorderThickness="0" Label="Show Stack Trace" />
+                    <AppBarToggleButton
+                        BorderThickness="0"
+                        IsChecked="{x:Bind ViewModel.ShowStackTrace, Mode=TwoWay}"
+                        Label="Show Stack Trace" />
                 </CommandBar.SecondaryCommands>
             </CommandBar>
         </Grid>
@@ -54,7 +57,11 @@
                 <RowDefinition Height="100" />
             </Grid.RowDefinitions>
 
-            <ListView Grid.Row="0" />
+            <ListView
+                x:Name="LogListView"
+                Grid.Row="0"
+                ItemsSource="{x:Bind ViewModel.Logs, Mode=OneWay}"
+                SelectedItem="{x:Bind ViewModel.SelectedLog, Mode=TwoWay}" />
             <Grid
                 Grid.Row="1"
                 Padding="4"
@@ -64,7 +71,7 @@
                     <TextBlock
                         IsTextSelectionEnabled="True"
                         Style="{StaticResource CaptionTextBlockStyle}"
-                        Text="Test Log"
+                        Text="{x:Bind ViewModel.SelectedLog.ToStringWithStackTrace(), Mode=OneWay}"
                         TextWrapping="Wrap" />
                 </ScrollViewer>
             </Grid>

Ghost.Editor/View/Pages/EngineEditor/ConsolePage.xaml.cs

@@ -1,11 +1,19 @@
+using Ghost.Editor.ViewModels.Pages.EngineEditor;
 using Microsoft.UI.Xaml.Controls;
 
 namespace Ghost.Editor.View.Pages.EngineEditor;
 
-public sealed partial class ConsolePage : Page
+internal sealed partial class ConsolePage : Page
 {
+    public ConsoleViewModel ViewModel
+    {
+        get;
+    }
+
     public ConsolePage()
     {
+        ViewModel = App.GetService<ConsoleViewModel>();
+
         InitializeComponent();
     }
 }

Ghost.Editor/View/Pages/EngineEditor/HierarchyPage.xaml

@@ -0,0 +1,43 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<Page
+    x:Class="Ghost.Editor.View.Pages.EngineEditor.HierarchyPage"
+    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+    xmlns:local="using:Ghost.Editor.View.Pages.EngineEditor"
+    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+    xmlns:sg="using:Ghost.Editor.Infrastructures.SceneGraph"
+    mc:Ignorable="d">
+
+    <Page.Resources>
+        <DataTemplate x:Key="SceneTemplate" x:DataType="sg:SceneGraphNode">
+            <TreeViewItem
+                AutomationProperties.Name="{x:Bind Name}"
+                Background="{ThemeResource CardBackgroundFillColorSecondaryBrush}"
+                IsExpanded="True"
+                ItemsSource="{x:Bind Children}">
+                <StackPanel Orientation="Horizontal">
+                    <FontIcon FontSize="14" Glyph="&#xF159;" />
+                    <TextBlock Margin="10,0" Text="{x:Bind Name}" />
+                </StackPanel>
+            </TreeViewItem>
+        </DataTemplate>
+
+        <DataTemplate x:Key="EntityTemplate" x:DataType="sg:SceneGraphNode">
+            <TreeViewItem AutomationProperties.Name="{x:Bind Name}" ItemsSource="{x:Bind Children}">
+                <StackPanel Orientation="Horizontal">
+                    <FontIcon FontSize="14" Glyph="&#xF158;" />
+                    <TextBlock Margin="10,0" Text="{x:Bind Name}" />
+                </StackPanel>
+            </TreeViewItem>
+        </DataTemplate>
+    </Page.Resources>
+
+    <Grid Background="{ThemeResource LayerFillColorDefaultBrush}">
+        <TreeView ItemsSource="{x:Bind ViewModel.SceneList}">
+            <TreeView.ItemTemplateSelector>
+                <local:HierarchyTemplateSector EntityTemplate="{StaticResource EntityTemplate}" SceneTemplate="{StaticResource SceneTemplate}" />
+            </TreeView.ItemTemplateSelector>
+        </TreeView>
+    </Grid>
+</Page>

Ghost.Editor/View/Pages/EngineEditor/HierarchyPage.xaml.cs

@@ -0,0 +1,57 @@
+using Ghost.Editor.Infrastructures.SceneGraph;
+using Ghost.Editor.ViewModels.Pages.EngineEditor;
+using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Controls;
+
+// To learn more about WinUI, the WinUI project structure,
+// and more about our project templates, see: http://aka.ms/winui-project-info.
+
+namespace Ghost.Editor.View.Pages.EngineEditor;
+/// <summary>
+/// An empty page that can be used on its own or navigated to within a Frame.
+/// </summary>
+internal sealed partial class HierarchyPage : Page
+{
+    public HierarchyViewModel ViewModel
+    {
+        get;
+    }
+
+    public HierarchyPage()
+    {
+        ViewModel = App.GetService<HierarchyViewModel>();
+
+        InitializeComponent();
+    }
+}
+
+internal partial class HierarchyTemplateSector : DataTemplateSelector
+{
+    public DataTemplate? SceneTemplate
+    {
+        get;
+        set;
+    }
+
+    public DataTemplate? EntityTemplate
+    {
+        get;
+        set;
+    }
+
+    protected override DataTemplate SelectTemplateCore(object item)
+    {
+        if (SceneTemplate == null || EntityTemplate == null)
+        {
+            return base.SelectTemplateCore(item);
+        }
+
+        var node = (SceneGraphNode)item;
+        return node.Type switch
+        {
+            SceneGraphNode.NodeType.Scene => SceneTemplate,
+            SceneGraphNode.NodeType.Entity => EntityTemplate,
+            _ => base.SelectTemplateCore(item)
+        };
+    }
+}

Ghost.Editor/View/Pages/EngineEditor/ProjectPage.xaml

@@ -3,11 +3,17 @@
     x:Class="Ghost.Editor.View.Pages.EngineEditor.ProjectPage"
     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+    xmlns:converter="using:Ghost.Editor.Helpers.Converters"
     xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
     xmlns:local="using:Ghost.Editor.View.Pages.EngineEditor"
     xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+    xmlns:model="using:Ghost.Editor.Models"
     mc:Ignorable="d">
 
+    <Page.Resources>
+        <converter:AssetPathToGlyphConverter x:Key="AssetPathToGlyphConverter" />
+    </Page.Resources>
+
     <Grid Background="{ThemeResource LayerFillColorDefaultBrush}">
         <Grid.ColumnDefinitions>
             <ColumnDefinition Width="250" />
@@ -17,55 +23,116 @@
         <!--  Folder Tree View  -->
         <Grid
             Grid.Column="0"
+            Padding="4"
+            Background="{ThemeResource CardBackgroundFillColorSecondaryBrush}"
             BorderBrush="{ThemeResource CardStrokeColorDefaultSolid}"
             BorderThickness="0,0,1,0">
             <TreeView
                 HorizontalAlignment="Stretch"
                 VerticalAlignment="Stretch"
-                Background="{ThemeResource CardBackgroundFillColorSecondaryBrush}"
+                ItemsSource="{x:Bind ViewModel.SubDirectories}"
-                ScrollViewer.HorizontalScrollBarVisibility="Disabled"
+                ScrollViewer.HorizontalScrollBarVisibility="Hidden"
-                ScrollViewer.VerticalScrollBarVisibility="Auto">
+                ScrollViewer.VerticalScrollBarVisibility="Auto"
-                <TreeView.ItemContainerStyle>
+                SelectedItem="{x:Bind ViewModel.SelectedDirectory, Mode=TwoWay}">
-                    <Style TargetType="TreeViewItem">
+                <TreeView.ItemTemplate>
-                        <Setter Property="Padding" Value="4,2" />
+                    <DataTemplate x:DataType="model:ExplorerItem">
-                        <Setter Property="Margin" Value="0,0,0,2" />
+                        <TreeViewItem ItemsSource="{x:Bind Children}">
-                    </Style>
+                            <StackPanel Orientation="Horizontal">
-                </TreeView.ItemContainerStyle>
+                                <FontIcon
+                                    VerticalAlignment="Center"
+                                    FontSize="14"
+                                    Glyph="&#xE8B7;" />
+                                <TextBlock
+                                    Margin="8,0,0,0"
+                                    VerticalAlignment="Center"
+                                    Style="{StaticResource CaptionTextBlockStyle}"
+                                    Text="{x:Bind Name}"
+                                    TextTrimming="CharacterEllipsis" />
+                            </StackPanel>
+                        </TreeViewItem>
+                    </DataTemplate>
+                </TreeView.ItemTemplate>
             </TreeView>
         </Grid>
 
         <!--  Files  -->
-        <ScrollViewer
+        <Grid Grid.Column="1">
-            Grid.Column="1"
+            <Grid.RowDefinitions>
-            HorizontalScrollBarVisibility="Auto"
+                <RowDefinition Height="Auto" />
-            VerticalScrollBarVisibility="Auto">
+                <RowDefinition Height="*" />
-            <GridView HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
+                <RowDefinition Height="Auto" />
-                <GridView.ItemContainerStyle>
+            </Grid.RowDefinitions>
-                    <Style BasedOn="{StaticResource DefaultGridViewItemStyle}" TargetType="GridViewItem">
-                        <Setter Property="Margin" Value="5,5,5,5" />
-                    </Style>
-                </GridView.ItemContainerStyle>
 
-                <GridView.ItemTemplate>
+            <Grid
-                    <DataTemplate>
+                Grid.Row="0"
-                        <Grid>
+                Padding="4"
-                            <Grid.RowDefinitions>
+                HorizontalAlignment="Stretch"
-                                <RowDefinition Height="*" />
+                VerticalAlignment="Stretch"
-                                <RowDefinition Height="0.2*" />
+                Background="{ThemeResource CardBackgroundFillColorSecondaryBrush}"
-                            </Grid.RowDefinitions>
+                BorderBrush="{ThemeResource CardStrokeColorDefaultSolid}"
-                            <ImageIcon
+                BorderThickness="0,0,0,1">
-                                Grid.Row="0"
+                <BreadcrumbBar Height="15" />
-                                Width="24"
+            </Grid>
-                                Height="24" />
+
-                            <TextBlock
+            <ScrollViewer
-                                Grid.Row="1"
+                Grid.Row="1"
-                                Margin="8,0"
+                Padding="8"
-                                VerticalAlignment="Center"
+                VerticalAlignment="Stretch"
-                                TextTrimming="CharacterEllipsis" />
+                HorizontalScrollBarVisibility="Auto"
-                        </Grid>
+                VerticalScrollBarVisibility="Auto">
-                    </DataTemplate>
+                <GridView
-                </GridView.ItemTemplate>
+                    HorizontalAlignment="Stretch"
-            </GridView>
+                    VerticalAlignment="Stretch"
-        </ScrollViewer>
+                    ItemsSource="{x:Bind ViewModel.DirectoryAssets, Mode=OneWay}"
+                    SelectedItem="{x:Bind ViewModel.SelectedAsset, Mode=TwoWay}">
+                    <GridView.ItemContainerStyle>
+                        <Style BasedOn="{StaticResource DefaultGridViewItemStyle}" TargetType="GridViewItem">
+                            <Setter Property="Margin" Value="2" />
+                        </Style>
+                    </GridView.ItemContainerStyle>
+
+                    <GridView.ItemTemplate>
+                        <DataTemplate x:DataType="model:ExplorerItem">
+                            <Grid
+                                Width="100"
+                                Height="100"
+                                Padding="8"
+                                DoubleTapped="GridViewItem_DoubleTapped"
+                                IsDoubleTapEnabled="True">
+                                <Grid.RowDefinitions>
+                                    <RowDefinition Height="*" />
+                                    <RowDefinition Height="0.25*" />
+                                </Grid.RowDefinitions>
+                                <FontIcon FontSize="42" Glyph="{x:Bind Path, Converter={StaticResource AssetPathToGlyphConverter}}" />
+                                <TextBlock
+                                    Grid.Row="1"
+                                    Margin="8,0"
+                                    HorizontalAlignment="Center"
+                                    VerticalAlignment="Center"
+                                    Style="{StaticResource CaptionTextBlockStyle}"
+                                    Text="{x:Bind Name}"
+                                    TextTrimming="CharacterEllipsis" />
+                            </Grid>
+                        </DataTemplate>
+                    </GridView.ItemTemplate>
+                </GridView>
+            </ScrollViewer>
+
+            <Grid
+                Grid.Row="2"
+                Padding="4"
+                HorizontalAlignment="Stretch"
+                VerticalAlignment="Stretch"
+                Background="{ThemeResource CardBackgroundFillColorSecondaryBrush}"
+                BorderBrush="{ThemeResource CardStrokeColorDefaultSolid}"
+                BorderThickness="0,1,0,0">
+                <TextBlock
+                    VerticalAlignment="Center"
+                    HorizontalTextAlignment="Left"
+                    Style="{StaticResource CaptionTextBlockStyle}"
+                    Text="{x:Bind ViewModel.SelectedAsset.Path, Mode=OneWay}"
+                    TextTrimming="CharacterEllipsis" />
+            </Grid>
+        </Grid>
     </Grid>
 </Page>

Ghost.Editor/View/Pages/EngineEditor/ProjectPage.xaml.cs

@@ -1,30 +1,25 @@
-using System;
+using Ghost.Editor.ViewModels.Pages.EngineEditor;
-using System.Collections.Generic;
-using System.IO;
-using System.Linq;
-using System.Runtime.InteropServices.WindowsRuntime;
-using Windows.Foundation;
-using Windows.Foundation.Collections;
-using Microsoft.UI.Xaml;
 using Microsoft.UI.Xaml.Controls;
-using Microsoft.UI.Xaml.Controls.Primitives;
-using Microsoft.UI.Xaml.Data;
 using Microsoft.UI.Xaml.Input;
-using Microsoft.UI.Xaml.Media;
-using Microsoft.UI.Xaml.Navigation;
-
-// To learn more about WinUI, the WinUI project structure,
-// and more about our project templates, see: http://aka.ms/winui-project-info.
 
 namespace Ghost.Editor.View.Pages.EngineEditor;
 
-/// <summary>
+internal sealed partial class ProjectPage : Page
-/// An empty page that can be used on its own or navigated to within a Frame.
-/// </summary>
-public sealed partial class ProjectPage : Page
 {
+    public ProjectViewModel ViewModel
+    {
+        get;
+    }
+
     public ProjectPage()
     {
+        ViewModel = App.GetService<ProjectViewModel>();
+
         InitializeComponent();
     }
+
+    private void GridViewItem_DoubleTapped(object sender, DoubleTappedRoutedEventArgs e)
+    {
+        ViewModel.NavigateToSelected();
+    }
 }

Ghost.Editor/View/Pages/Landing/CreateProjectPage.xaml.cs

@@ -1,4 +1,4 @@
-using Ghost.Editor.ViewModel.Pages.Landing;
+using Ghost.Editor.ViewModels.Pages.Landing;
 using Microsoft.UI.Xaml.Controls;
 using Microsoft.UI.Xaml.Navigation;
 

Ghost.Editor/View/Pages/Landing/OpenProjectPage.xaml

@@ -6,6 +6,7 @@
     xmlns:converters="using:Ghost.Editor.Helpers.Converters"
     xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
     xmlns:data="using:Ghost.Data.Models"
+    xmlns:interactivity="using:Microsoft.Xaml.Interactivity"
     xmlns:local="using:Ghost.Editor.View.Pages.Landing"
     xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
     NavigationCacheMode="Enabled"
@@ -73,7 +74,7 @@
                 CornerRadius="{StaticResource OverlayCornerRadius}"
                 IsItemClickEnabled="True"
                 ItemClick="ListView_ItemClick"
-                ItemsSource="{x:Bind projects}"
+                ItemsSource="{x:Bind ViewModel.projects}"
                 SelectionMode="None">
                 <ListView.ItemTemplate>
                     <DataTemplate x:DataType="data:ProjectMetadataInfo">

Ghost.Editor/View/Pages/Landing/OpenProjectPage.xaml.cs

@@ -1,68 +1,47 @@
 using Ghost.Data.Models;
-using Ghost.Data.Services;
+using Ghost.Editor.ViewModels.Pages.Landing;
-using Ghost.Editor.AppStates;
-using Ghost.Editor.Services;
 using Microsoft.UI.Xaml;
 using Microsoft.UI.Xaml.Controls;
 using Microsoft.UI.Xaml.Navigation;
-using System;
-using System.Collections.ObjectModel;
-using System.Linq;
 using Windows.ApplicationModel.DataTransfer;
-using Windows.Storage;
 
 namespace Ghost.Editor.View.Pages.Landing;
 
 internal sealed partial class OpenProjectPage : Page
 {
-    private readonly ProjectService _projectService;
+    public OpenProjectViewModel ViewModel
-    private readonly StackedNotificationService _notificationService;
+    {
-    private readonly AppStateService _stateService;
+        get;
-
+    }
-    public readonly ObservableCollection<ProjectMetadataInfo> projects = new();
 
     public OpenProjectPage()
     {
-        _notificationService = App.GetService<StackedNotificationService>();
+        ViewModel = App.GetService<OpenProjectViewModel>();
-        _projectService = App.GetService<ProjectService>();
-        _stateService = App.GetService<AppStateService>();
         InitializeComponent();
     }
 
-    private void UpdateEmptyPlaceHolderVisibility()
+    protected override void OnNavigatedTo(NavigationEventArgs e)
-    {
-        EmptyPlaceHolder.Visibility = projects.Count == 0 ? Visibility.Visible : Visibility.Collapsed;
-    }
-
-    protected override async void OnNavigatedTo(NavigationEventArgs e)
     {
         base.OnNavigatedTo(e);
+        ViewModel.OnNavigatedTo(e.Parameter);
+    }
 
-        projects.Clear();
+    override protected void OnNavigatedFrom(NavigationEventArgs e)
-        await foreach (var projectInfo in _projectService.LoadAllProjectAsync())
+    {
-        {
+        base.OnNavigatedFrom(e);
-            var metadata = await ProjectService.LoadMetadataAsync(projectInfo.MetadataPath);
+        ViewModel.OnNavigatedFrom();
-            if (metadata == null)
-            {
-                continue;
-            }
-
-            projects.Add(new(projectInfo.MetadataPath, metadata));
-        }
-
-        UpdateEmptyPlaceHolderVisibility();
     }
 
     private void ProjectContainer_DragEnter(object sender, DragEventArgs e)
     {
-        DragVisual.Visibility = Visibility.Visible;
+        ViewModel.DragVisibility = Visibility.Visible;
-        EmptyPlaceHolder.Visibility = Visibility.Collapsed;
+        ViewModel.EmptyVisibility = Visibility.Collapsed;
     }
 
     private void ProjectContainer_DragLeave(object sender, DragEventArgs e)
     {
-        DragVisual.Visibility = Visibility.Collapsed;
+        ViewModel.DragVisibility = Visibility.Collapsed;
-        UpdateEmptyPlaceHolderVisibility();
+        ViewModel.UpdateEmptyPlaceHolderVisibility();
     }
 
     private void ProjectContainer_DragOver(object sender, DragEventArgs e)
@@ -79,55 +58,14 @@ internal sealed partial class OpenProjectPage : Page
 
     private async void ProjectContainer_Drop(object sender, DragEventArgs e)
     {
-        var errorMessage = string.Empty;
+        await ViewModel.ContentDrop(e.DataView);
-        if (e.DataView.Contains(StandardDataFormats.StorageItems))
-        {
-            var items = await e.DataView.GetStorageItemsAsync();
-            var rootFolder = items.OfType<StorageFolder>().FirstOrDefault();
-            if (rootFolder != null)
-            {
-                var result = await _projectService.AddProjectFromDirectoryAsync(rootFolder.Path);
-                if (result.success)
-                {
-                    projects.Add(result.data);
-                    DragVisual.Visibility = Visibility.Collapsed;
-                    goto CloseDropPanel;
-                }
-                else
-                {
-                    errorMessage = result.message;
-                }
-            }
-        }
-        else
-        {
-            errorMessage = "Unsupported data format. Please drop a folder containing a project.";
-        }
-
-        _notificationService.ShowNotification(errorMessage, InfoBarSeverity.Error);
-
-    CloseDropPanel:
-        DragVisual.Visibility = Visibility.Collapsed;
-        UpdateEmptyPlaceHolderVisibility();
     }
 
     private async void ListView_ItemClick(object sender, ItemClickEventArgs e)
     {
-        if (e.ClickedItem is not ProjectMetadataInfo project)
+        if (e.ClickedItem is ProjectMetadataInfo project)
         {
-            return;
+            await ViewModel.LoadProject(project);
-        }
-
-        try
-        {
-            project.Metadata.LastOpened = DateTime.Now;
-            await ProjectService.CreateMetadataFileAsync(project.Path, project.Metadata);
-
-            await _stateService.TransitionToAsync(StateKey.EngineEditor, project.Metadata);
-        }
-        catch (Exception exp)
-        {
-            _notificationService.ShowNotification($"Failed to load project: {exp.Message}", InfoBarSeverity.Error);
         }
     }
 }

Ghost.Editor/View/Windows/EngineEditorWindow.xaml

@@ -43,7 +43,7 @@
                 Margin="8,0,0,0"
                 VerticalAlignment="Center"
                 Style="{StaticResource CaptionTextBlockStyle}"
-                Text="{x:Bind ViewModel.CurrentProject.Name, Mode=OneWay}" />
+                Text="{x:Bind ViewModel.CurrentProject.Metadata.Name, Mode=OneWay}" />
         </StackPanel>
 
         <!--  Toolbar  -->
@@ -83,13 +83,26 @@
                     <ColumnDefinition Width="Auto" />
                 </Grid.ColumnDefinitions>
 
-                <Grid
+                <TabView
                     Grid.Column="0"
                     Width="350"
-                    Background="Aquamarine" />
+                    HorizontalAlignment="Stretch"
+                    VerticalAlignment="Stretch"
+                    TabWidthMode="Compact">
+                    <TabView.TabItems>
+                        <TabViewItem Header="Hierarchy">
+                            <TabViewItem.IconSource>
+                                <FontIconSource Glyph="&#xE8A4;" />
+                            </TabViewItem.IconSource>
+                            <ee:HierarchyPage />
+                        </TabViewItem>
+                    </TabView.TabItems>
+                </TabView>
+
                 <Grid Grid.Column="1">
                     <Image Source="C:\Users\Misaki\OneDrive\Pictures\Screenshots\Screenshot 2024-07-20 021657.png" Stretch="UniformToFill" />
                 </Grid>
+
                 <Grid
                     Grid.Column="2"
                     Width="350"
@@ -103,7 +116,7 @@
                 <TabView.TabItems>
                     <TabViewItem Header="Project">
                         <TabViewItem.IconSource>
-                            <FontIconSource Glyph="&#xE8B7;" />
+                            <FontIconSource Glyph="&#xEC50;" />
                         </TabViewItem.IconSource>
                         <ee:ProjectPage />
                     </TabViewItem>

Ghost.Editor/View/Windows/EngineEditorWindow.xaml.cs

@@ -1,5 +1,5 @@
 using Ghost.Data.Resources;
-using Ghost.Editor.ViewModel.Windows;
+using Ghost.Editor.ViewModels.Windows;
 using Ghost.Engine.Resources;
 using WinUIEx;
 

Ghost.Editor/ViewModel/Pages/EngineEditor/ProjectViewModel.cs

@@ -1,5 +0,0 @@
-namespace Ghost.Editor.ViewModel.Pages.EngineEditor;
-
-internal class ProjectViewModel
-{
-}

Ghost.Editor/ViewModels/Pages/EngineEditor/ConsoleViewModel.cs

@@ -0,0 +1,92 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+using CommunityToolkit.Mvvm.Input;
+using Ghost.Engine.Models;
+using Ghost.Engine.Services;
+using System.Collections.ObjectModel;
+
+namespace Ghost.Editor.ViewModels.Pages.EngineEditor;
+
+internal partial class ConsoleViewModel : ObservableObject
+{
+    [ObservableProperty]
+    public partial ObservableCollection<LogMessage> Logs
+    {
+        get; set;
+    } = new();
+
+    [ObservableProperty]
+    public partial bool ShowInfo
+    {
+        get; set;
+    } = true;
+
+    [ObservableProperty]
+    public partial bool ShowWarning
+    {
+        get; set;
+    } = true;
+
+    [ObservableProperty]
+    public partial bool ShowError
+    {
+        get; set;
+    } = true;
+
+    [ObservableProperty]
+    public partial bool ShowStackTrace
+    {
+        get; set;
+    } = false;
+
+    [ObservableProperty]
+    public partial LogMessage? SelectedLog
+    {
+        get; set;
+    }
+
+    public ConsoleViewModel()
+    {
+        foreach (var log in Logger.Logs)
+        {
+            Logs.Add(log);
+        }
+
+        Logger.OnLogsUpdate += UpdateLogs;
+    }
+
+    ~ConsoleViewModel()
+    {
+        Logger.OnLogsUpdate -= UpdateLogs;
+    }
+
+    private void UpdateLogs(LogChangeType updateType)
+    {
+        switch (updateType)
+        {
+            case LogChangeType.LogAdded:
+                Logs.Add(Logger.Logs[^1]);
+                break;
+            case LogChangeType.LogRemoved:
+                if (Logs.Count > 0)
+                {
+                    Logs.RemoveAt(0);
+                }
+                break;
+            case LogChangeType.LogsCleared:
+                Logs.Clear();
+                break;
+        }
+    }
+
+    partial void OnShowStackTraceChanged(bool value)
+    {
+        Logger.HasStackTrace = value;
+        Logger.LogInfo($"Stack trace visibility set to {value}.");
+    }
+
+    [RelayCommand]
+    private void ClearLogs()
+    {
+        Logger.Clear();
+    }
+}

Ghost.Editor/ViewModels/Pages/EngineEditor/HierarchyViewModel.cs

@@ -0,0 +1,38 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+using Ghost.Editor.Infrastructures.SceneGraph;
+using Ghost.Entities;
+using System.Collections.ObjectModel;
+
+namespace Ghost.Editor.ViewModels.Pages.EngineEditor;
+
+internal partial class HierarchyViewModel : ObservableObject
+{
+    [ObservableProperty]
+    public partial ObservableCollection<SceneNode> SceneList
+    {
+        get;
+        private set;
+    } = new();
+
+    public HierarchyViewModel()
+    {
+        // Test only
+        var testWorld = World.Create();
+        var entity1 = SceneGraphHelpers.CreateEntityNode(testWorld, "entity 1");
+        var entity2 = SceneGraphHelpers.CreateEntityNode(testWorld, "entity 3");
+        var entity3 = SceneGraphHelpers.CreateEntityNode(testWorld, "entity 4");
+        var entity4 = SceneGraphHelpers.CreateEntityNode(testWorld, "entity 5");
+        var entity5 = SceneGraphHelpers.CreateEntityNode(testWorld, "entity 2");
+
+        var testScene = new SceneNode(testWorld, "Test Scene");
+
+        SceneGraphHelpers.AttachChild(testScene, entity1, entity2);
+        SceneGraphHelpers.AttachChild(testScene, entity1, entity3);
+        SceneGraphHelpers.AttachChild(testScene, entity2, entity4);
+
+        testScene.Children.Add(entity1);
+        testScene.Children.Add(entity5);
+
+        SceneList.Add(testScene);
+    }
+}

Ghost.Editor/ViewModels/Pages/EngineEditor/ProjectViewModel.cs

@@ -0,0 +1,142 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+using Ghost.Data.Services;
+using Ghost.Editor.Models;
+using System;
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.IO;
+using System.Threading.Tasks;
+
+namespace Ghost.Editor.ViewModels.Pages.EngineEditor;
+
+internal partial class ProjectViewModel : ObservableObject
+{
+    public ObservableCollection<ExplorerItem> SubDirectories
+    {
+        get;
+    } = new();
+
+    [ObservableProperty]
+    public partial ObservableCollection<ExplorerItem> DirectoryAssets
+    {
+        get;
+        set;
+    } = new();
+
+    [ObservableProperty]
+    public partial ExplorerItem? SelectedDirectory
+    {
+        get;
+        set;
+    }
+
+    [ObservableProperty]
+    public partial ExplorerItem? SelectedAsset
+    {
+        get;
+        set;
+    }
+
+    public ProjectViewModel()
+    {
+        if (ProjectService.CurrentProject.Metadata == null)
+        {
+            throw new InvalidOperationException("Current project is not set.");
+        }
+
+        var assetsItem = new ExplorerItem("Assets", Path.Combine(Path.GetDirectoryName(ProjectService.CurrentProject.Path)!, ProjectService.ASSETS_FOLDER), true);
+        LoadSubFolderRecursive(ref assetsItem);
+
+        SubDirectories.Add(assetsItem);
+    }
+
+    private void LoadSubFolderRecursive(ref ExplorerItem parentItem)
+    {
+        foreach (var directory in Directory.EnumerateDirectories(parentItem.Path))
+        {
+            var item = new ExplorerItem(Path.GetFileName(directory), directory, true);
+            LoadSubFolderRecursive(ref item);
+
+            parentItem.Children ??= new();
+            parentItem.Children.Add(item);
+        }
+    }
+
+    public static Task<ExplorerItem?> FindNodeIterative(ExplorerItem root, Func<ExplorerItem, bool> predicate)
+    {
+        var stack = new Stack<ExplorerItem>();
+        stack.Push(root);
+
+        return Task.Run(() =>
+        {
+            while (stack.Count > 0)
+            {
+                var node = stack.Pop();
+                if (predicate(node))
+                {
+                    return node;
+                }
+
+                if (node.Children == null || node.Children.Count == 0)
+                {
+                    continue;
+                }
+
+                for (var i = node.Children.Count - 1; i >= 0; i--)
+                {
+                    stack.Push(node.Children[i]);
+                }
+            }
+
+            return null;
+        });
+    }
+
+    private void NavigateToDirectory(string? path)
+    {
+        App.Window?.DispatcherQueue.TryEnqueue(async () =>
+        {
+            DirectoryAssets.Clear();
+
+            if (!Directory.Exists(path))
+            {
+                return;
+            }
+
+            foreach (var directory in Directory.EnumerateDirectories(path))
+            {
+                var directoryItem = new ExplorerItem(Path.GetFileName(directory), directory, true);
+                DirectoryAssets.Add(directoryItem);
+            }
+
+            foreach (var file in Directory.EnumerateFiles(path))
+            {
+                var fileItem = new ExplorerItem(Path.GetFileName(file), file, false);
+                DirectoryAssets.Add(fileItem);
+            }
+
+            SelectedDirectory = await FindNodeIterative(SubDirectories[0], x => x.Path == path);
+        });
+    }
+
+    public void NavigateToSelected()
+    {
+        if (SelectedAsset == null || !SelectedAsset.IsDirectory)
+        {
+            return;
+        }
+
+        NavigateToDirectory(SelectedAsset.Path);
+    }
+
+    partial void OnSelectedDirectoryChanged(ExplorerItem? value)
+    {
+        DirectoryAssets.Clear();
+        if (value == null)
+        {
+            return;
+        }
+
+        NavigateToDirectory(value.Path);
+    }
+}

Ghost.Editor/ViewModels/Pages/Landing/CreateProjectViewModel.cs

@@ -2,9 +2,9 @@
 using CommunityToolkit.Mvvm.Input;
 using Ghost.Data.Models;
 using Ghost.Data.Services;
-using Ghost.Editor.AppStates;
 using Ghost.Editor.Contracts;
 using Ghost.Editor.Helpers;
+using Ghost.Editor.Infrastructures.AppState;
 using Ghost.Editor.Services;
 using Ghost.Engine.Resources;
 using Microsoft.UI.Xaml.Controls;
@@ -13,9 +13,9 @@ using System.IO;
 using System.Linq;
 using System.Threading.Tasks;
 
-namespace Ghost.Editor.ViewModel.Pages.Landing;
+namespace Ghost.Editor.ViewModels.Pages.Landing;
 
-internal partial class CreateProjectViewModel(StackedNotificationService notificationService, ProjectService projectService, AppStateService stateService) : ObservableRecipient, INavigationAware
+internal partial class CreateProjectViewModel(StackedNotificationService notificationService, ProjectService projectService, AppStateMachine stateService) : ObservableObject, INavigationAware
 {
     public ObservableCollection<TemplateData> templates = new();
 
@@ -77,16 +77,15 @@ internal partial class CreateProjectViewModel(StackedNotificationService notific
         }
 
         var result = await projectService.CreateProjectAsync(ProjectName, ProjectLocation, EngineData.s_engineVersion, SelectedTemplate.Value.directory);
-        if (!result.success || result.data == null)
+        if (!result.success)
         {
             notificationService.ShowNotification(result.message, InfoBarSeverity.Error);
             return;
         }
 
-        var metadata = await ProjectService.LoadMetadataAsync(result.data.MetadataPath); // Metadata should not be null here if create project succeeded
         try
         {
-            await stateService.TransitionToAsync(StateKey.EngineEditor, metadata);
+            await stateService.TransitionToAsync(StateKey.EngineEditor, result.data);
         }
         catch (System.Exception e)
         {

Ghost.Editor/ViewModels/Pages/Landing/OpenProjectViewModel.cs

@@ -0,0 +1,109 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+using Ghost.Data.Models;
+using Ghost.Data.Services;
+using Ghost.Editor.Contracts;
+using Ghost.Editor.Infrastructures.AppState;
+using Ghost.Editor.Services;
+using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Controls;
+using System;
+using System.Collections.ObjectModel;
+using System.Linq;
+using System.Threading.Tasks;
+using Windows.ApplicationModel.DataTransfer;
+using Windows.Storage;
+
+namespace Ghost.Editor.ViewModels.Pages.Landing;
+
+internal partial class OpenProjectViewModel(ProjectService projectService, StackedNotificationService _notificationService, AppStateMachine _stateService) : ObservableObject, INavigationAware
+{
+    public readonly ObservableCollection<ProjectMetadataInfo> projects = new();
+
+    [ObservableProperty]
+    public partial Visibility EmptyVisibility
+    {
+        get;
+        set;
+    }
+
+    [ObservableProperty]
+    public partial Visibility DragVisibility
+    {
+        get;
+        set;
+    }
+
+    public void UpdateEmptyPlaceHolderVisibility()
+    {
+        EmptyVisibility = projects.Count == 0 ? Visibility.Visible : Visibility.Collapsed;
+    }
+
+    public async void OnNavigatedTo(object? parameter)
+    {
+        projects.Clear();
+        await foreach (var projectInfo in projectService.LoadAllProjectAsync())
+        {
+            var metadata = await ProjectService.LoadMetadataAsync(projectInfo.MetadataPath);
+            if (metadata == null)
+            {
+                continue;
+            }
+
+            projects.Add(new(projectInfo.MetadataPath, metadata));
+        }
+
+        UpdateEmptyPlaceHolderVisibility();
+    }
+
+    public void OnNavigatedFrom()
+    {
+    }
+
+    public async Task ContentDrop(DataPackageView dataView)
+    {
+        var errorMessage = string.Empty;
+        if (dataView.Contains(StandardDataFormats.StorageItems))
+        {
+            var items = await dataView.GetStorageItemsAsync();
+            var rootFolder = items.OfType<StorageFolder>().FirstOrDefault();
+            if (rootFolder != null)
+            {
+                var result = await projectService.AddProjectFromDirectoryAsync(rootFolder.Path);
+                if (result.success)
+                {
+                    projects.Add(result.data);
+                    goto CloseDropPanel;
+                }
+                else
+                {
+                    errorMessage = result.message;
+                }
+            }
+        }
+        else
+        {
+            errorMessage = "Unsupported data format. Please drop a folder containing a project.";
+        }
+
+        _notificationService.ShowNotification(errorMessage, InfoBarSeverity.Error);
+
+    CloseDropPanel:
+        DragVisibility = Visibility.Collapsed;
+        UpdateEmptyPlaceHolderVisibility();
+    }
+
+    public async Task LoadProject(ProjectMetadataInfo project)
+    {
+        try
+        {
+            project.Metadata.LastOpened = DateTime.Now;
+            await ProjectService.CreateMetadataFileAsync(project.Path, project.Metadata);
+
+            await _stateService.TransitionToAsync(StateKey.EngineEditor, project);
+        }
+        catch (Exception e)
+        {
+            _notificationService.ShowNotification($"Failed to load project: {e.Message}", InfoBarSeverity.Error);
+        }
+    }
+}

Ghost.Editor/ViewModels/Windows/EngineEditorViewModel.cs

@@ -1,17 +1,13 @@
 using CommunityToolkit.Mvvm.ComponentModel;
 using Ghost.Data.Models;
+using Ghost.Data.Services;
 using Ghost.Engine.Resources;
 
-namespace Ghost.Editor.ViewModel.Windows;
+namespace Ghost.Editor.ViewModels.Windows;
 
 internal partial class EngineEditorViewModel : ObservableRecipient
 {
     public string engineVersionDescriptor = $"{EngineData.ENGINE_NAME} - {EngineData.s_engineVersion}";
 
-    [ObservableProperty]
+    public ProjectMetadataInfo CurrentProject => ProjectService.CurrentProject;
-    public partial ProjectMetadata CurrentProject
-    {
-        get;
-        set;
-    }
 }

Ghost.Engine/Components/Hierarchy.cs

@@ -0,0 +1,24 @@
+using Ghost.Entities;
+using Ghost.Entities.Components;
+using System.Runtime.CompilerServices;
+
+namespace Ghost.Engine.Components;
+
+[SkipLocalsInit]
+public struct Hierarchy : IComponentData
+{
+    public Entity parent;
+    public Entity firstChild;
+    public Entity nextSibling;
+
+    public static Hierarchy Root
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        get => new()
+        {
+            parent = Entity.Invalid,
+            firstChild = Entity.Invalid,
+            nextSibling = Entity.Invalid
+        };
+    }
+}

Ghost.Engine/Components/LocalToWorld.cs

@@ -0,0 +1,21 @@
+using Ghost.Engine.Helpers;
+using Ghost.Entities.Components;
+using System.Numerics;
+using System.Runtime.CompilerServices;
+
+namespace Ghost.Engine.Components;
+
+[SkipLocalsInit]
+public struct LocalToWorld : IComponentData
+{
+    public Matrix4x4 matrix;
+
+    public static LocalToWorld Identity
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        get => new()
+        {
+            matrix = MatrixHelpers.CreateTRS(Vector3.Zero, Quaternion.Identity, Vector3.One)
+        };
+    }
+}

Ghost.Engine/Components/Transform.cs

@@ -1,77 +0,0 @@
-using Ghost.Engine.Helpers;
-using Ghost.Entities;
-using System.Numerics;
-using System.Runtime.CompilerServices;
-
-namespace Ghost.Engine.Components;
-
-public struct Transform : IComponentData
-{
-    private Vector3 _position = Vector3.Zero;
-    public Vector3 Position
-    {
-        get => _position;
-        set
-        {
-            _position = value;
-            hasChanged = true;
-            UpdateMatrices();
-        }
-    }
-
-    private Quaternion _rotation = Quaternion.Identity;
-    public Quaternion Rotation
-    {
-        get => _rotation;
-        set
-        {
-            _rotation = value;
-            hasChanged = true;
-            UpdateMatrices();
-        }
-    }
-
-    private Vector3 _scale = Vector3.One;
-    public Vector3 Scale
-    {
-        get => _scale;
-        set
-        {
-            _scale = value;
-            hasChanged = true;
-            UpdateMatrices();
-        }
-    }
-
-    public bool hasChanged;
-
-    private Matrix4x4 _localToWorldMatrix;
-    private Matrix4x4 _worldToLocalMatrix;
-
-    public readonly Matrix4x4 LocalToWorldMatrix => _localToWorldMatrix;
-    public readonly Matrix4x4 WorldToLocalMatrix => _worldToLocalMatrix;
-
-    public static Transform Default
-    {
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        get => new(Vector3.Zero, Quaternion.Identity, Vector3.One);
-    }
-
-    public Transform(Vector3 position, Quaternion rotation, Vector3 scale)
-    {
-        _position = position;
-        _rotation = rotation;
-        _scale = scale;
-        hasChanged = false;
-        _localToWorldMatrix = Matrix4x4.Identity;
-        _worldToLocalMatrix = Matrix4x4.Identity;
-
-        UpdateMatrices();
-    }
-
-    private void UpdateMatrices()
-    {
-        _localToWorldMatrix = MatrixHelpers.CreateTRS(_position, _rotation, _scale);
-        Matrix4x4.Invert(_localToWorldMatrix, out _worldToLocalMatrix);
-    }
-}

Ghost.Engine/EngineCore.cs

@@ -1,25 +1,16 @@
 using Ghost.Engine.Models;
+using Ghost.Engine.Services;
 
 namespace Ghost.Engine;
 
-internal class EngineCore
+internal class EngineCore : IDisposable, IAsyncDisposable
 {
-    public static EngineCore? Current
+    public async Task StartAsync(LaunchArgument args)
     {
-        get;
-        private set;
-    }
-
-    public static async Task StartAsync(LaunchArgument args)
-    {
-        if (Current != null)
-        {
-            return;
-        }
-
-        Current = new EngineCore();
-
         ActivationHandler.Handle(args);
+
+        Logger.LogInfo("Engine started successfully.");
+
         await Task.CompletedTask;
     }
 
@@ -27,4 +18,14 @@ internal class EngineCore
     {
         await Task.CompletedTask;
     }
+
+    public void Dispose()
+    {
+        ShutDownAsync().GetAwaiter().GetResult();
+    }
+
+    public async ValueTask DisposeAsync()
+    {
+        await ShutDownAsync();
+    }
 }

Ghost.Engine/Models/LogMessage.cs

@@ -0,0 +1,56 @@
+using System.Diagnostics;
+
+namespace Ghost.Engine.Models;
+
+public enum LogLevel
+{
+    Info,
+    Warning,
+    Error
+}
+
+internal class LogMessage
+{
+    public LogLevel Level
+    {
+        get; set;
+    }
+
+    public string Message
+    {
+        get; set;
+    }
+
+    public StackTrace? StackTrace
+    {
+        get; set;
+    }
+
+    public DateTime Timestamp
+    {
+        get; set;
+    }
+
+    public LogMessage(LogLevel level, string message, StackTrace? stackTrace = null)
+    {
+        Level = level;
+        Message = message;
+        StackTrace = stackTrace;
+        Timestamp = DateTime.Now;
+    }
+
+    public override string ToString()
+    {
+        return $"{Timestamp:HH:mm:ss} [{Level}] {Message}";
+    }
+
+    public string ToStringWithStackTrace()
+    {
+        if (StackTrace == null)
+        {
+            return ToString();
+        }
+
+        return $"{ToString()}\n{StackTrace}";
+    }
+}

Ghost.Engine/Services/Logger.cs

@@ -0,0 +1,73 @@
+using Ghost.Engine.Models;
+using System.Diagnostics;
+
+namespace Ghost.Engine.Services;
+
+internal enum LogChangeType
+{
+    LogAdded,
+    LogRemoved,
+    LogsCleared
+}
+
+public static class Logger
+{
+
+    private const int _MAX_LOGS = 4096;
+
+    private static readonly List<LogMessage> _logs = new();
+    internal static List<LogMessage> Logs => _logs;
+
+    internal static event Action<LogChangeType>? OnLogsUpdate;
+
+    internal static bool HasStackTrace
+    {
+        get; set;
+    }
+
+    private static void LogInternal(LogLevel level, string message, int skipFrame)
+    {
+        if (_logs.Count >= _MAX_LOGS)
+        {
+            _logs.RemoveAt(0);
+            OnLogsUpdate?.Invoke(LogChangeType.LogRemoved);
+        }
+
+        StackTrace? stackTrace = null;
+        if (HasStackTrace)
+        {
+            stackTrace = new StackTrace(skipFrame, true);
+        }
+
+        var logMessage = new LogMessage(level, message, stackTrace);
+        _logs.Add(logMessage);
+
+        OnLogsUpdate?.Invoke(LogChangeType.LogAdded);
+    }
+
+    public static void Log(LogLevel level, string message)
+    {
+        LogInternal(level, message, 2);
+    }
+
+    public static void LogInfo(string message)
+    {
+        LogInternal(LogLevel.Info, message, 3);
+    }
+
+    public static void LogWarning(string message)
+    {
+        LogInternal(LogLevel.Warning, message, 3);
+    }
+
+    public static void LogError(string message)
+    {
+        LogInternal(LogLevel.Error, message, 3);
+    }
+
+    internal static void Clear()
+    {
+        _logs.Clear();
+        OnLogsUpdate?.Invoke(LogChangeType.LogsCleared);
+    }
+}

Ghost.Entities/AssemblyInfo.cs

@@ -1,5 +1,5 @@
 global using EntityID = System.Int32;
-global using GenerationID = System.UInt16;
+global using GenerationID = System.Byte;
 global using WorldID = System.UInt16;
 
 using System.Runtime.CompilerServices;

Ghost.Entities/Components/ComponentStorage.cs

@@ -3,12 +3,7 @@ using Misaki.HighPerformance.Unsafe.Collections;
 using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 
-namespace Ghost.Entities;
+namespace Ghost.Entities.Components;
-
-public interface IComponentData
-{
-
-}
 
 internal static class SingletonContainer<T>
     where T : struct, IComponentData
@@ -50,7 +45,7 @@ internal class ComponentPool<T> : IComponentPool<T>
 
     public EntityID Count => _nextId;
 
-    public ComponentPool(int initialSize = 16)
+    public ComponentPool(int initialSize)
     {
         _nextId = 0;
         _capacity = initialSize;
@@ -144,7 +139,7 @@ internal class ComponentPool<T> : IComponentPool<T>
         return index != Entity.INVALID_ID && _components[index].owner.Generation == entity.Generation;
     }
 
-    public void Set(Entity entity, T component)
+    public void Set(Entity entity, in T component)
     {
         if (!entity.IsValid || entity.ID >= _lookup.Length || GetComponentIndex(entity) == Entity.INVALID_ID)
         {
@@ -334,7 +329,8 @@ internal class ScriptComponentPool : IComponentPool<ScriptComponent>
     }
 }
 
-internal class ComponentStorage : IDisposable
+[SkipLocalsInit]
+internal readonly struct ComponentStorage : IDisposable
 {
     private readonly Dictionary<nint, IComponentPool> _componentPools = new();
     private readonly Dictionary<nint, BitSet> _componentEntityMasks = new();
@@ -360,25 +356,25 @@ internal class ComponentStorage : IDisposable
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public bool TryGetPool(Type type, [MaybeNullWhen(false)] out IComponentPool pool)
     {
-        return TryGetPool(type.TypeHandle.Value, out pool);
+        return TryGetPool(TypeHandle.Get(type), out pool);
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public bool TryGetPool<T>([MaybeNullWhen(false)] out ComponentPool<T> pool)
         where T : struct, IComponentData
     {
-        var result = TryGetPool(TypeHandle<T>.Value, out var obj);
+        var result = TryGetPool(TypeHandle.Get<T>(), out var obj);
-        pool = (ComponentPool<T>?)obj;
+        pool = (ComponentPool<T>?)obj ?? default;
         return result;
     }
 
     public ComponentPool<T> GetOrCreateComponentPool<T>()
         where T : struct, IComponentData
     {
-        var key = TypeHandle<T>.Value;
+        var key = TypeHandle.Get<T>();
         if (!_componentPools.TryGetValue(key, out var obj))
         {
-            var pool = new ComponentPool<T>();
+            var pool = new ComponentPool<T>(16);
             _componentPools[key] = pool;
             return pool;
         }
@@ -402,7 +398,7 @@ internal class ComponentStorage : IDisposable
     public bool TryGetMask<T>([MaybeNullWhen(false)] out BitSet bitSet)
         where T : struct, IComponentData
     {
-        return TryGetMask(TypeHandle<T>.Value, out bitSet);
+        return TryGetMask(TypeHandle.Get<T>(), out bitSet);
     }
 
     public BitSet GetOrCreateMask(nint typeHandle)

Ghost.Entities/Components/IComponentData.cs

@@ -0,0 +1,4 @@
+namespace Ghost.Entities.Components;
+public interface IComponentData
+{
+}

Ghost.Entities/Components/ScriptComponent.cs

@@ -1,4 +1,4 @@
-namespace Ghost.Entities;
+namespace Ghost.Entities.Components;
 
 public abstract class ScriptComponent : IComponentData
 {

Ghost.Entities/Entity.cs

@@ -1,18 +1,14 @@
-using Ghost.Entities.Query;
+using System.Runtime.CompilerServices;
-using Ghost.Entities.Utilities;
-using System.Runtime.CompilerServices;
-using System.Runtime.InteropServices;
 
 namespace Ghost.Entities;
 
 [SkipLocalsInit]
 public struct Entity : IEquatable<Entity>, IComparable<Entity>
 {
-    public const int WORLD_INDEX_BITS = 4;
+    // Is 256 generations enough? If not, increase the size of GenerationID or make generation as a separate int field.
-    public const int GENERATION_BITS = 8;
+    public const int GENERATION_BITS = sizeof(GenerationID) * 8;
-    public const int INDEX_BITS = sizeof(EntityID) * 8 - WORLD_INDEX_BITS - GENERATION_BITS;
+    public const int INDEX_BITS = sizeof(EntityID) * 8 - GENERATION_BITS;
 
-    private const int _WORLD_INDEX_MASK = (1 << WORLD_INDEX_BITS) - 1;
     private const int _GENERATION_MASK = (1 << GENERATION_BITS) - 1;
     private const int _INDEX_MASK = (1 << INDEX_BITS) - 1;
 
@@ -38,24 +34,18 @@ public struct Entity : IEquatable<Entity>, IComparable<Entity>
         get => (GenerationID)(_id >> INDEX_BITS & _GENERATION_MASK);
     }
 
-    public readonly WorldID WorldID
-    {
-        [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        get => (WorldID)(_id >> (INDEX_BITS + GENERATION_BITS) & _WORLD_INDEX_MASK);
-    }
-
     public static Entity Invalid
     {
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        get => new(INVALID_ID, 0, 0);
+        get => new(INVALID_ID, 0);
     }
 
-    internal Entity(EntityID id, GenerationID generation, WorldID worldID)
+    internal Entity(EntityID id, GenerationID generation)
     {
-        _id = worldID << (INDEX_BITS + GENERATION_BITS) | generation << INDEX_BITS | id;
+        _id = generation << INDEX_BITS | id;
     }
 
-    public void IncrementGeneration()
+    internal void IncrementGeneration()
     {
         var generation = Generation + 1;
         if (generation >= _GENERATION_MASK)
@@ -98,263 +88,6 @@ public struct Entity : IEquatable<Entity>, IComparable<Entity>
 
     public override readonly string ToString()
     {
-        return $"Entity {{ Index: {ID}, Generation: {Generation}, WorldIndex: {WorldID} }}";
+        return $"Entity {{ Index: {ID}, Generation: {Generation} }}";
-    }
-}
-
-public class EntityManager : IDisposable
-{
-    private readonly List<Entity> _entities;
-    private readonly Queue<EntityID> _freeEntitySlots;
-
-    private readonly World _world;
-
-    public int EntityCount => _entities.Count;
-    public ReadOnlySpan<Entity> Entities => CollectionsMarshal.AsSpan(_entities);
-
-    public event Action<Entity, Type>? OnComponentAdded;
-    public event Action<Entity, Type>? OnComponentRemoved;
-    public event Action<Entity>? OnEntityCreated;
-    public event Action<EntityID>? OnEntityRemoved;
-
-    internal EntityManager(World world, int initialCapacity)
-    {
-        _entities = new(initialCapacity);
-        _freeEntitySlots = new(initialCapacity);
-        _world = world;
-    }
-
-    /// <summary>
-    /// Adds a new <see cref="Entity"/> to the world.
-    /// </summary>
-    /// <returns>The created <see cref="Entity"/>.</returns>
-    public Entity CreateEntity()
-    {
-        Entity entity;
-        if (_freeEntitySlots.TryDequeue(out var id))
-        {
-            entity = _entities[id];
-        }
-        else
-        {
-            id = _entities.Count;
-            entity = new Entity(id, 0, _world.ID);
-            _entities.Add(entity);
-        }
-
-        OnEntityCreated?.Invoke(entity);
-        return entity;
-    }
-
-    /// <summary>
-    /// Removes the specified <see cref="Entity"/> from the world.
-    /// </summary>
-    /// <param name="entity"></param>
-    public void RemoveEntity(ref Entity entity)
-    {
-        if (entity.ID >= _entities.Count || _entities[entity.ID].Generation != entity.Generation)
-        {
-            return;
-        }
-
-        _world.ComponentStorage.Remove(entity);
-
-        var slot = _entities[entity.ID];
-        slot.IncrementGeneration();
-        _entities[entity.ID] = slot;
-        _freeEntitySlots.Enqueue(entity.ID);
-
-        OnEntityRemoved?.Invoke(entity.ID);
-        entity = Entity.Invalid;
-    }
-
-    /// <summary>
-    /// Checks if the given <see cref="Entity"/> is valid and belongs to this <see cref="World"/>.
-    /// </summary>
-    /// <param name="entity">The entity to check.</param>
-    /// <returns>True if the entity is valid and belongs to this world; otherwise, false.</returns>
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public bool HasEntity(Entity entity)
-    {
-        if (!entity.IsValid
-            || entity.WorldID != _world.ID
-            || entity.ID >= _entities.Count)
-        {
-            return false;
-        }
-
-        return _entities[entity.ID].Generation == entity.Generation;
-    }
-
-    /// <summary>
-    /// Adds a component of type <typeparamref name="T"/> to the given <see cref="Entity"/>.
-    /// </summary>
-    /// <typeparam name="T">The type of the component to set.</typeparam>
-    /// <param name="entity">The entity for which the component is to be add.</param>
-    /// <param name="component">The component value to add.</param>
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void AddComponent<T>(Entity entity, T component)
-        where T : struct, IComponentData
-    {
-        _world.ComponentStorage.GetOrCreateComponentPool<T>().Add(entity, component);
-        _world.ComponentStorage.GetOrCreateMask(TypeHandle<T>.Value).SetBit(entity.ID);
-        OnComponentAdded?.Invoke(entity, typeof(T));
-    }
-
-    /// <summary>
-    /// Removes a component of type <typeparamref name="T"/> from the given <see cref="Entity"/>.
-    /// </summary>
-    /// <typeparam name="T">The type of the component to remove.</typeparam>
-    /// <param name="entity">The entity for which the component is to be remove.</param>
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public bool RemoveComponent<T>(Entity entity)
-        where T : struct, IComponentData
-    {
-        if (!_world.ComponentStorage.TryGetPool<T>(out var pool) || !pool.Has(entity))
-        {
-            return false;
-        }
-
-        if (!pool.Remove(entity))
-        {
-            return false;
-        }
-
-        _world.ComponentStorage.GetOrCreateMask(TypeHandle<T>.Value).ClearBit(entity.ID);
-        OnComponentRemoved?.Invoke(entity, typeof(T));
-
-        return true;
-    }
-
-    /// <summary>
-    /// Sets a component of type <typeparamref name="T"/> for the given <see cref="Entity"/>.
-    /// </summary>
-    /// <typeparam name="T">The type of the component to set.</typeparam>
-    /// <param name="entity">The entity for which the component is to be set.</param>
-    /// <param name="component">The component value to set.</param>
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void SetComponent<T>(Entity entity, T component)
-        where T : struct, IComponentData
-    {
-        _world.ComponentStorage.GetOrCreateComponentPool<T>().Set(entity, component);
-    }
-
-    /// <summary>
-    /// Checks if the given <see cref="Entity"/> has a component of the specified type.
-    /// </summary>
-    /// <param name="entity">The entity to check.</param>
-    /// <param name="typeHandle">The handle of the component type.</param>
-    /// <returns>True if the entity has the component; otherwise, false.</returns>
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public bool HasComponent(Entity entity, nint typeHandle)
-    {
-        return _world.ComponentStorage.TryGetMask(typeHandle, out var bitSet) && bitSet.IsSet(entity.ID);
-    }
-
-    /// <summary>
-    /// Retrieves a reference to a component of type <typeparamref name="T"/> associated with the given <see cref="Entity"/>.
-    /// </summary>
-    /// <typeparam name="T">The type of the component to retrieve.</typeparam>
-    /// <param name="entity">The entity whose component is to be retrieved.</param>
-    /// <returns>A <see cref="Ref{T}"/> to the component, or a null reference if the component does not exist.</returns>
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public Ref<T> GetComponent<T>(Entity entity)
-        where T : struct, IComponentData
-    {
-        if (_world.ComponentStorage.TryGetPool<T>(out var pool) && pool.Has(entity))
-        {
-            return new Ref<T>(ref pool.GetRef(entity));
-        }
-        else
-        {
-            return new Ref<T>(ref Unsafe.NullRef<T>(), false);
-        }
-    }
-
-    /// <summary>
-    /// Adds a script of type <typeparamref name="T"/> to the given <see cref="Entity"/>.
-    /// </summary>
-    /// <typeparam name="T">The type of the script to add.</typeparam>
-    /// <param name="entity">The entity to which the script is to be added.</param>
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void AddScript<T>(Entity entity)
-        where T : ScriptComponent, new()
-    {
-        _world.ComponentStorage.ScriptComponentPool.Add(entity, new T());
-        OnComponentAdded?.Invoke(entity, typeof(ScriptComponent));
-    }
-
-    /// <summary>
-    /// Adds a script of the specified type to the given <see cref="Entity"/>.
-    /// </summary>
-    /// <param name="entity">The entity to which the script is to be added.</param>
-    /// <param name="type">The type of the script to add.</param>
-    /// <exception cref="ArgumentException">Thrown if the specified type does not inherit from <see cref="ScriptComponent"/>.</exception>
-    /// <exception cref="InvalidOperationException">Thrown if the script instance could not be created.</exception>
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void AddScript(Entity entity, Type type)
-    {
-        if (!typeof(ScriptComponent).IsAssignableFrom(type))
-        {
-            throw new ArgumentException($"Type {type} must inherit from ScriptComponent.", nameof(type));
-        }
-
-        var instance = (ScriptComponent?)Activator.CreateInstance(type) ?? throw new InvalidOperationException($"Failed to create instance of {type}.");
-        _world.ComponentStorage.ScriptComponentPool.Add(entity, instance);
-        OnComponentAdded?.Invoke(entity, typeof(ScriptComponent));
-    }
-
-    public bool RemoveScript<T>(Entity entity)
-        where T : ScriptComponent
-    {
-        if (!_world.ComponentStorage.ScriptComponentPool.Remove<T>(entity))
-        {
-            return false;
-        }
-
-        OnComponentRemoved?.Invoke(entity, typeof(ScriptComponent));
-        return true;
-    }
-
-    public bool RemoveScriptAt(Entity entity, int index)
-    {
-        if (!_world.ComponentStorage.ScriptComponentPool.RemoveAt(entity, index))
-        {
-            return false;
-        }
-
-        OnComponentRemoved?.Invoke(entity, typeof(ScriptComponent));
-        return true;
-    }
-
-    /// <summary>
-    /// Retrieves the first script of type <typeparamref name="T"/> associated with the given <see cref="Entity"/>.
-    /// </summary>
-    /// <typeparam name="T">The type of the script to retrieve.</typeparam>
-    /// <param name="entity">The entity whose script is to be retrieved.</param>
-    /// <returns>The script of type <typeparamref name="T"/>, or null if no such script exists.</returns>
-    public T? GetScript<T>(Entity entity)
-        where T : ScriptComponent
-    {
-        return (T?)_world.ComponentStorage.ScriptComponentPool.Get(entity)?
-            .FirstOrDefault(script => script is T tScript);
-    }
-
-    /// <summary>
-    /// Retrieves all scripts of type <typeparamref name="T"/> associated with the given <see cref="Entity"/>.
-    /// </summary>
-    /// <typeparam name="T">The type of the scripts to retrieve.</typeparam>
-    /// <param name="entity">The entity whose scripts are to be retrieved.</param>
-    /// <returns>An enumerable of scripts of type <typeparamref name="T"/>.</returns>
-    public IEnumerable<T> GetScripts<T>(Entity entity)
-        where T : ScriptComponent
-    {
-        return (IEnumerable<T>?)_world.ComponentStorage.ScriptComponentPool.Get(entity)?.Where(script => script is T tScript) ?? Enumerable.Empty<T>();
-    }
-
-    public void Dispose()
-    {
-        _entities.Clear();
-        _freeEntitySlots.Clear();
     }
 }

Ghost.Entities/EntityManager.cs

@@ -0,0 +1,262 @@
+using Ghost.Entities.Components;
+using Ghost.Entities.Query;
+using Ghost.Entities.Utilities;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+namespace Ghost.Entities;
+public struct EntityManager : IDisposable
+{
+    private readonly List<Entity> _entities;
+    private readonly Queue<EntityID> _freeEntitySlots;
+
+    private readonly World _world;
+
+    public readonly int EntityCount => _entities.Count;
+    public readonly ReadOnlySpan<Entity> Entities => CollectionsMarshal.AsSpan(_entities);
+
+    public event Action<Entity>? OnEntityCreated;
+    public event Action<EntityID>? OnEntityRemoved;
+    public event Action<Entity, Type>? OnComponentAdded;
+    public event Action<Entity, Type>? OnComponentRemoved;
+
+    internal EntityManager(World world, int initialCapacity)
+    {
+        _entities = new(initialCapacity);
+        _freeEntitySlots = new(initialCapacity);
+        _world = world;
+    }
+
+    /// <summary>
+    /// Adds a new <see cref="Entity"/> to the world.
+    /// </summary>
+    /// <returns>The created <see cref="Entity"/>.</returns>
+    public readonly Entity CreateEntity()
+    {
+        Entity entity;
+        if (_freeEntitySlots.TryDequeue(out var id))
+        {
+            entity = _entities[id];
+        }
+        else
+        {
+            id = _entities.Count;
+            entity = new Entity(id, 0);
+            _entities.Add(entity);
+        }
+
+        OnEntityCreated?.Invoke(entity);
+        return entity;
+    }
+
+    /// <summary>
+    /// Removes the specified <see cref="Entity"/> from the world.
+    /// </summary>
+    /// <param name="entity"></param>
+    public readonly void RemoveEntity(ref Entity entity)
+    {
+        if (entity.ID >= _entities.Count || _entities[entity.ID].Generation != entity.Generation)
+        {
+            return;
+        }
+
+        _world.ComponentStorage.Remove(entity);
+
+        var slot = _entities[entity.ID];
+        slot.IncrementGeneration();
+        _entities[entity.ID] = slot;
+        _freeEntitySlots.Enqueue(entity.ID);
+
+        OnEntityRemoved?.Invoke(entity.ID);
+        entity = Entity.Invalid;
+    }
+
+    /// <summary>
+    /// Checks if the given <see cref="Entity"/> is valid and belongs to this <see cref="World"/>.
+    /// </summary>
+    /// <param name="entity">The entity to check.</param>
+    /// <returns>True if the entity is valid and belongs to this world; otherwise, false.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public readonly bool HasEntity(Entity entity)
+    {
+        if (!entity.IsValid
+            || entity.ID >= _entities.Count)
+        {
+            return false;
+        }
+
+        return _entities[entity.ID].Generation == entity.Generation;
+    }
+
+    /// <summary>
+    /// Adds a component of type <typeparamref name="T"/> to the given <see cref="Entity"/>.
+    /// </summary>
+    /// <typeparam name="T">The type of the component to set.</typeparam>
+    /// <param name="entity">The entity for which the component is to be add.</param>
+    /// <param name="component">The component value to add.</param>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public readonly void AddComponent<T>(Entity entity, T component)
+        where T : struct, IComponentData
+    {
+        _world.ComponentStorage.GetOrCreateComponentPool<T>().Add(entity, component);
+        _world.ComponentStorage.GetOrCreateMask(TypeHandle.Get<T>()).SetBit(entity.ID);
+        OnComponentAdded?.Invoke(entity, typeof(T));
+    }
+
+    /// <summary>
+    /// Removes a component of type <typeparamref name="T"/> from the given <see cref="Entity"/>.
+    /// </summary>
+    /// <typeparam name="T">The type of the component to remove.</typeparam>
+    /// <param name="entity">The entity for which the component is to be remove.</param>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public readonly bool RemoveComponent<T>(Entity entity)
+        where T : struct, IComponentData
+    {
+        if (!_world.ComponentStorage.TryGetPool<T>(out var pool) || !pool.Has(entity))
+        {
+            return false;
+        }
+
+        if (!pool.Remove(entity))
+        {
+            return false;
+        }
+
+        _world.ComponentStorage.GetOrCreateMask(TypeHandle.Get<T>()).ClearBit(entity.ID);
+        OnComponentRemoved?.Invoke(entity, typeof(T));
+
+        return true;
+    }
+
+    /// <summary>
+    /// Sets a component of type <typeparamref name="T"/> for the given <see cref="Entity"/>.
+    /// </summary>
+    /// <typeparam name="T">The type of the component to set.</typeparam>
+    /// <param name="entity">The entity for which the component is to be set.</param>
+    /// <param name="component">The component value to set.</param>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public readonly void SetComponent<T>(Entity entity, in T component)
+        where T : struct, IComponentData
+    {
+        _world.ComponentStorage.GetOrCreateComponentPool<T>().Set(entity, in component);
+    }
+
+    /// <summary>
+    /// Checks if the given <see cref="Entity"/> has a component of the specified type.
+    /// </summary>
+    /// <param name="entity">The entity to check.</param>
+    /// <param name="typeHandle">The handle of the component type.</param>
+    /// <returns>True if the entity has the component; otherwise, false.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public readonly bool HasComponent(Entity entity, nint typeHandle)
+    {
+        return _world.ComponentStorage.TryGetMask(typeHandle, out var bitSet) && bitSet.IsSet(entity.ID);
+    }
+
+    /// <summary>
+    /// Retrieves a reference to a component of type <typeparamref name="T"/> associated with the given <see cref="Entity"/>.
+    /// </summary>
+    /// <typeparam name="T">The type of the component to retrieve.</typeparam>
+    /// <param name="entity">The entity whose component is to be retrieved.</param>
+    /// <returns>A <see cref="Ref{T}"/> to the component, or a null reference if the component does not exist.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public readonly Ref<T> GetComponent<T>(Entity entity)
+        where T : struct, IComponentData
+    {
+        if (_world.ComponentStorage.TryGetPool<T>(out var pool) && pool.Has(entity))
+        {
+            return new Ref<T>(ref pool.GetRef(entity));
+        }
+        else
+        {
+            return new Ref<T>(ref Unsafe.NullRef<T>(), false);
+        }
+    }
+
+    /// <summary>
+    /// Adds a script of type <typeparamref name="T"/> to the given <see cref="Entity"/>.
+    /// </summary>
+    /// <typeparam name="T">The type of the script to add.</typeparam>
+    /// <param name="entity">The entity to which the script is to be added.</param>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public readonly void AddScript<T>(Entity entity)
+        where T : ScriptComponent, new()
+    {
+        _world.ComponentStorage.ScriptComponentPool.Add(entity, new T());
+        OnComponentAdded?.Invoke(entity, typeof(ScriptComponent));
+    }
+
+    /// <summary>
+    /// Adds a script of the specified type to the given <see cref="Entity"/>.
+    /// </summary>
+    /// <param name="entity">The entity to which the script is to be added.</param>
+    /// <param name="type">The type of the script to add.</param>
+    /// <exception cref="ArgumentException">Thrown if the specified type does not inherit from <see cref="ScriptComponent"/>.</exception>
+    /// <exception cref="InvalidOperationException">Thrown if the script instance could not be created.</exception>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public readonly void AddScript(Entity entity, Type type)
+    {
+        if (!typeof(ScriptComponent).IsAssignableFrom(type))
+        {
+            throw new ArgumentException($"Type {type} must inherit from ScriptComponent.", nameof(type));
+        }
+
+        var instance = (ScriptComponent?)Activator.CreateInstance(type) ?? throw new InvalidOperationException($"Failed to create instance of {type}.");
+        _world.ComponentStorage.ScriptComponentPool.Add(entity, instance);
+        OnComponentAdded?.Invoke(entity, typeof(ScriptComponent));
+    }
+
+    public readonly bool RemoveScript<T>(Entity entity)
+        where T : ScriptComponent
+    {
+        if (!_world.ComponentStorage.ScriptComponentPool.Remove<T>(entity))
+        {
+            return false;
+        }
+
+        OnComponentRemoved?.Invoke(entity, typeof(ScriptComponent));
+        return true;
+    }
+
+    public readonly bool RemoveScriptAt(Entity entity, int index)
+    {
+        if (!_world.ComponentStorage.ScriptComponentPool.RemoveAt(entity, index))
+        {
+            return false;
+        }
+
+        OnComponentRemoved?.Invoke(entity, typeof(ScriptComponent));
+        return true;
+    }
+
+    /// <summary>
+    /// Retrieves the first script of type <typeparamref name="T"/> associated with the given <see cref="Entity"/>.
+    /// </summary>
+    /// <typeparam name="T">The type of the script to retrieve.</typeparam>
+    /// <param name="entity">The entity whose script is to be retrieved.</param>
+    /// <returns>The script of type <typeparamref name="T"/>, or null if no such script exists.</returns>
+    public readonly T? GetScript<T>(Entity entity)
+        where T : ScriptComponent
+    {
+        return (T?)_world.ComponentStorage.ScriptComponentPool.Get(entity)?
+            .FirstOrDefault(script => script is T tScript);
+    }
+
+    /// <summary>
+    /// Retrieves all scripts of type <typeparamref name="T"/> associated with the given <see cref="Entity"/>.
+    /// </summary>
+    /// <typeparam name="T">The type of the scripts to retrieve.</typeparam>
+    /// <param name="entity">The entity whose scripts are to be retrieved.</param>
+    /// <returns>An enumerable of scripts of type <typeparamref name="T"/>.</returns>
+    public readonly IEnumerable<T> GetScripts<T>(Entity entity)
+        where T : ScriptComponent
+    {
+        return (IEnumerable<T>?)_world.ComponentStorage.ScriptComponentPool.Get(entity)?.Where(script => script is T tScript) ?? Enumerable.Empty<T>();
+    }
+
+    public readonly void Dispose()
+    {
+        _entities.Clear();
+        _freeEntitySlots.Clear();
+    }
+}

Ghost.Entities/Helpers/EntityHelpers.cs

@@ -1,147 +0,0 @@
-using Ghost.Entities.Query;
-using System.Runtime.CompilerServices;
-
-namespace Ghost.Entities.Helpers;
-
-/// <summary>
-/// Provides extension methods for working with entities in the Ghost framework.
-/// </summary>
-public static class EntityHelpers
-{
-    public static World GetWorld(this Entity entity)
-    {
-        return World.GetWorld(entity.WorldID);
-    }
-
-    /// <summary>
-    /// Adds a component of type <typeparamref name="T"/> to the given <see cref="Entity"/>.
-    /// </summary>
-    /// <typeparam name="T">The type of the component to set.</typeparam>
-    /// <param name="entity">The entity for which the component is to be add.</param>
-    /// <param name="component">The component value to add.</param>
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public static void AddComponent<T>(this Entity entity, T component)
-        where T : struct, IComponentData
-    {
-        var world = entity.GetWorld();
-        world.EntityManager.AddComponent<T>(entity, component);
-    }
-
-    /// <summary>
-    /// Removes a component of type <typeparamref name="T"/> from the given <see cref="Entity"/>.
-    /// </summary>
-    /// <typeparam name="T">The type of the component to remove.</typeparam>
-    /// <param name="entity">The entity for which the component is to be remove.</param>
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public static bool RemoveComponent<T>(this Entity entity)
-        where T : struct, IComponentData
-    {
-        var world = entity.GetWorld();
-        return world.EntityManager.RemoveComponent<T>(entity);
-    }
-
-    /// <summary>
-    /// Sets a component of type <typeparamref name="T"/> for the given <see cref="Entity"/>.
-    /// </summary>
-    /// <typeparam name="T">The type of the component to set.</typeparam>
-    /// <param name="entity">The entity for which the component is to be set.</param>
-    /// <param name="component">The component value to set.</param>
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public static void SetComponent<T>(this Entity entity, T component)
-        where T : struct, IComponentData
-    {
-        var world = entity.GetWorld();
-        world.EntityManager.SetComponent<T>(entity, component);
-    }
-
-    /// <summary>
-    /// Checks if the given <see cref="Entity"/> has a component of the specified type.
-    /// </summary>
-    /// <param name="entity">The entity to check.</param>
-    /// <param name="typeHandle">The handle of the component type.</param>
-    /// <returns>True if the entity has the component; otherwise, false.</returns>
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public static bool HasComponent(this Entity entity, nint typeHandle)
-    {
-        var world = entity.GetWorld();
-        return world.EntityManager.HasComponent(entity, typeHandle);
-    }
-
-    /// <summary>
-    /// Retrieves a reference to a component of type <typeparamref name="T"/> associated with the given <see cref="Entity"/>.
-    /// </summary>
-    /// <typeparam name="T">The type of the component to retrieve.</typeparam>
-    /// <param name="entity">The entity whose component is to be retrieved.</param>
-    /// <returns>A <see cref="Ref{T}"/> to the component, or a null reference if the component does not exist.</returns>
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public static Ref<T> GetComponent<T>(this Entity entity)
-        where T : struct, IComponentData
-    {
-        var world = entity.GetWorld();
-        return world.EntityManager.GetComponent<T>(entity);
-    }
-
-    /// <summary>
-    /// Adds a script of type <typeparamref name="T"/> to the given <see cref="Entity"/>.
-    /// </summary>
-    /// <typeparam name="T">The type of the script to add.</typeparam>
-    /// <param name="entity">The entity to which the script is to be added.</param>
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public static void AddScript<T>(this Entity entity)
-        where T : ScriptComponent, new()
-    {
-        var world = entity.GetWorld();
-        world.EntityManager.AddScript<T>(entity);
-    }
-
-    /// <summary>
-    /// Adds a script of the specified type to the given <see cref="Entity"/>.
-    /// </summary>
-    /// <param name="entity">The entity to which the script is to be added.</param>
-    /// <param name="type">The type of the script to add.</param>
-    /// <exception cref="ArgumentException">Thrown if the specified type does not inherit from <see cref="ScriptComponent"/>.</exception>
-    /// <exception cref="InvalidOperationException">Thrown if the script instance could not be created.</exception>
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public static void AddScript(this Entity entity, Type type)
-    {
-        var world = entity.GetWorld();
-        world.EntityManager.AddScript(entity, type);
-    }
-
-    /// <summary>
-    /// Retrieves the first script of type <typeparamref name="T"/> associated with the given <see cref="Entity"/>.
-    /// </summary>
-    /// <typeparam name="T">The type of the script to retrieve.</typeparam>
-    /// <param name="entity">The entity whose script is to be retrieved.</param>
-    /// <returns>The script of type <typeparamref name="T"/>, or null if no such script exists.</returns>
-    public static T? GetScript<T>(this Entity entity)
-        where T : ScriptComponent
-    {
-        var world = entity.GetWorld();
-        return world.EntityManager.GetScript<T>(entity);
-    }
-
-    /// <summary>
-    /// Retrieves all scripts of type <typeparamref name="T"/> associated with the given <see cref="Entity"/>.
-    /// </summary>
-    /// <typeparam name="T">The type of the scripts to retrieve.</typeparam>
-    /// <param name="entity">The entity whose scripts are to be retrieved.</param>
-    /// <returns>An enumerable of scripts of type <typeparamref name="T"/>.</returns>
-    public static IEnumerable<T> GetScripts<T>(this Entity entity)
-        where T : ScriptComponent
-    {
-        var world = entity.GetWorld();
-        return world.EntityManager.GetScripts<T>(entity);
-    }
-
-    /// <summary>
-    /// Destroys the given <see cref="Entity"/> by removing it from its associated <see cref="World"/>.
-    /// </summary>
-    /// <param name="entity">The entity to destroy.</param>
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public static void Destroy(this Entity entity)
-    {
-        var world = entity.GetWorld();
-        world.EntityManager.RemoveEntity(ref entity);
-    }
-}

Ghost.Entities/Query/QueryTypeParameter.cs

@@ -1,4 +1,5 @@
-using System.Runtime.CompilerServices;
+using Ghost.Entities.Components;
+using System.Runtime.CompilerServices;
 
 namespace Ghost.Entities.Query;
 

Ghost.Entities/System.cs

@@ -1,135 +0,0 @@
-using System.Runtime.CompilerServices;
-
-namespace Ghost.Entities;
-
-public abstract class SystemBase
-{
-    /// <summary>
-    /// Gets the execution order of the current operation or component.
-    /// </summary>
-    public virtual int ExecutionOrder => 0;
-
-    /// <summary>
-    /// Gets or sets a value indicating whether the feature is enabled.
-    /// </summary>
-    public virtual bool Enable
-    {
-        get;
-        set;
-    } = true;
-
-    /// <summary>
-    /// The world that this system belongs to.
-    /// </summary>
-    public World World
-    {
-        get;
-        internal set;
-    } = null!;
-
-    public virtual void OnCreate()
-    {
-    }
-
-    public virtual void OnUpdate()
-    {
-    }
-
-    public virtual void OnDestroy()
-    {
-    }
-}
-
-public class SystemStorage : IDisposable
-{
-    private readonly List<SystemBase> _systems = new();
-    private readonly List<SystemBase> _executionList = new();
-
-    private readonly World _world;
-
-    public event Action<SystemBase>? SystemAdded;
-    public event Action<SystemBase>? SystemRemoved;
-
-    internal SystemStorage(World world)
-    {
-        _world = world;
-    }
-
-    public void AddSystem<T>(T system)
-        where T : SystemBase
-    {
-        _systems.Add(system);
-        system.World = _world;
-        if (system.Enable)
-        {
-            system.OnCreate();
-        }
-
-        SystemAdded?.Invoke(system);
-    }
-
-
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void AddSystem<T>()
-        where T : SystemBase, new()
-    {
-        AddSystem(new T());
-    }
-
-    public void RemoveSystem<T>(T system)
-        where T : SystemBase
-    {
-        system.World = null!;
-        _systems.Remove(system);
-        if (system.Enable)
-        {
-            system.OnDestroy();
-        }
-
-        SystemRemoved?.Invoke(system);
-    }
-
-    [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    public void RemoveSystem<T>()
-        where T : SystemBase, new()
-    {
-        var system = _systems.FirstOrDefault(s => s is T);
-        if (system != null)
-        {
-            RemoveSystem(system);
-        }
-    }
-
-    internal void RebuildExecutionList()
-    {
-        _executionList.Clear();
-        _executionList.AddRange(_systems.OrderBy(s => s.ExecutionOrder));
-    }
-
-    internal void UpdateSystems()
-    {
-        foreach (var system in _systems)
-        {
-            if (!system.Enable)
-            {
-                continue;
-            }
-            system.OnUpdate();
-        }
-    }
-
-    public void Dispose()
-    {
-        foreach (var system in _systems)
-        {
-            if (!system.Enable)
-            {
-                continue;
-            }
-            system.OnDestroy();
-        }
-
-        _systems.Clear();
-        _executionList.Clear();
-    }
-}

Ghost.Entities/Systems/ISystem.cs

@@ -0,0 +1,27 @@
+namespace Ghost.Entities.Systems;
+
+/// <summary>
+/// Attribute to declare that a system depends on one or more other systems.
+/// </summary>
+[AttributeUsage(AttributeTargets.Struct | AttributeTargets.Class, AllowMultiple = false)]
+public class DependsOnAttribute : Attribute
+{
+    public Type[] Prerequisites
+    {
+        get;
+    }
+
+    public DependsOnAttribute(params Type[] prerequisites)
+    {
+        Prerequisites = prerequisites;
+    }
+}
+
+public interface ISystem
+{
+    public void OnCreate(in SystemState state);
+
+    public void OnUpdate(in SystemState state);
+
+    public void OnDestroy(in SystemState state);
+}

Ghost.Entities/Systems/SystemDependencyBuilder.cs

@@ -0,0 +1,92 @@
+using System.Reflection;
+
+namespace Ghost.Entities.Systems;
+
+internal class SystemDependencyBuilder(List<Type> allSystemTypes)
+{
+    private Dictionary<Type, List<Type>> _dependencies = new();
+
+    public void BuildDependencyGraph()
+    {
+        foreach (var systemType in allSystemTypes)
+        {
+            if (!typeof(ISystem).IsAssignableFrom(systemType) || systemType.IsAbstract || systemType.IsInterface)
+            {
+                throw new ArgumentException($"{systemType.Name} is not a concrete ISystem type.");
+            }
+
+            var directDependencies = new List<Type>();
+            var dependsOnAttributes = systemType.GetCustomAttributes<DependsOnAttribute>(false);
+            foreach (var attr in dependsOnAttributes)
+            {
+                directDependencies.AddRange(attr.Prerequisites);
+            }
+
+            _dependencies[systemType] = directDependencies;
+        }
+    }
+
+    private void Visit(Type systemType, HashSet<Type> visited, HashSet<Type> permanentMark, List<Type> executionOrder)
+    {
+        if (permanentMark.Contains(systemType))
+        {
+            return;
+        }
+
+        if (visited.Contains(systemType))
+        {
+            throw new InvalidOperationException($"Circular dependency detected involving system: {systemType.Name}");
+        }
+
+        visited.Add(systemType); // Mark as currently visiting
+
+        if (_dependencies.TryGetValue(systemType, out var directDependencies))
+        {
+            foreach (var dependencyType in directDependencies)
+            {
+                // Ensure the dependency is a registered system type
+                if (!allSystemTypes.Contains(dependencyType))
+                {
+                    throw new InvalidOperationException($"System {systemType.Name} depends on unregistered system {dependencyType.Name}.");
+                }
+
+                Visit(dependencyType, visited, permanentMark, executionOrder);
+            }
+        }
+
+        visited.Remove(systemType); // Done visiting this node in the current path
+        permanentMark.Add(systemType); // Mark as permanently processed
+        executionOrder.Add(systemType); // Add to the sorted list (this will be reversed later for correct order)
+    }
+
+    /// <summary>
+    /// Builds the topological order of systems.
+    /// </summary>
+    /// <returns>A list of system types in the order they should be executed.</returns>
+    /// <exception cref="InvalidOperationException">Thrown if a circular dependency is detected.</exception>"
+    public List<Type> BuildExecutionOrder()
+    {
+        var executionOrder = new List<Type>(allSystemTypes.Count);
+        var visited = new HashSet<Type>(); // Tracks visited nodes in the current DFS path (for cycle detection)
+        var permanentMark = new HashSet<Type>(); // Tracks nodes whose dependencies have been fully resolved
+
+        // Initialize dependencies for all registered systems, even those without explicit attributes
+        foreach (var sysType in allSystemTypes)
+        {
+            if (!_dependencies.ContainsKey(sysType))
+            {
+                _dependencies[sysType] = new();
+            }
+        }
+
+        foreach (var systemType in allSystemTypes)
+        {
+            if (!permanentMark.Contains(systemType))
+            {
+                Visit(systemType, visited, permanentMark, executionOrder);
+            }
+        }
+
+        return executionOrder;
+    }
+}

Ghost.Entities/Systems/SystemState.cs

@@ -0,0 +1,10 @@
+namespace Ghost.Entities.Systems;
+
+public struct SystemState
+{
+    public World World
+    {
+        get;
+        init;
+    }
+}

Ghost.Entities/Systems/SystemStorage.cs

@@ -0,0 +1,95 @@
+using System.Runtime.CompilerServices;
+
+namespace Ghost.Entities.Systems;
+
+[SkipLocalsInit]
+public struct SystemStorage
+{
+    private readonly List<Type> _systems = new();
+    private readonly List<ISystem> _executionList = new();
+
+    private readonly World _world;
+
+    public event Action<Type>? SystemAdded;
+    public event Action<Type>? SystemRemoved;
+
+    internal SystemStorage(World world)
+    {
+        _world = world;
+    }
+
+    public readonly void AddSystem(Type systemType)
+    {
+        _systems.Add(systemType);
+        SystemAdded?.Invoke(systemType);
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public readonly void AddSystem<T>()
+        where T : ISystem, new()
+    {
+        AddSystem(typeof(T));
+    }
+
+    public readonly void RemoveSystem(Type systemType)
+    {
+        _systems.Remove(systemType);
+        SystemRemoved?.Invoke(systemType);
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public readonly void RemoveSystem<T>()
+        where T : ISystem, new()
+    {
+        RemoveSystem(typeof(T));
+    }
+
+    internal void CreateSystems()
+    {
+        var builder = new SystemDependencyBuilder(_systems);
+        builder.BuildDependencyGraph();
+        var executionOrder = builder.BuildExecutionOrder();
+
+        var state = new SystemState()
+        {
+            World = _world,
+        };
+
+        foreach (var systemType in executionOrder)
+        {
+            var system = (ISystem?)Activator.CreateInstance(systemType) ?? throw new InvalidOperationException($"Failed to create instance of system type {systemType.Name}.");
+
+            _executionList.Add(system);
+            system.OnCreate(in state);
+        }
+    }
+
+    internal void UpdateSystems()
+    {
+        var state = new SystemState()
+        {
+            World = _world,
+        };
+
+        foreach (var system in _executionList)
+        {
+            system.OnUpdate(in state);
+        }
+    }
+
+    internal void Dispose()
+    {
+        var state = new SystemState()
+        {
+            World = _world,
+        };
+
+        foreach (var system in _executionList)
+        {
+            system.OnDestroy(in state);
+        }
+
+        _systems.Clear();
+        _executionList.Clear();
+    }
+}

Ghost.Entities/Template/QueryEnumerable.tt

@@ -5,6 +5,7 @@
 <#@ import namespace="System.Linq" #>
 <#@ include file="Helpers.ttinclude" #>
 
+using Ghost.Entities.Components;
 using Ghost.Entities.Query;
 using Ghost.Entities.Utilities;
 using Misaki.HighPerformance.Unsafe.Collections;
@@ -47,11 +48,11 @@ public struct QueryEnumerable<<#= generics #>>
         
         _filters = new();
 <# for (int i = 0; i < arity; i++) {#>
-        _filters._all.Add(TypeHandle<T<#= i #>>.Value);
+        _filters._all.Add(TypeHandle.Get<T<#= i #>>());
 <# } #>
     }
 
-    public Enumerator GetEnumerator() => new Enumerator(_world, <#= constructorParams #>, _count, _filters);
+    public readonly Enumerator GetEnumerator() => new (_world, <#= constructorParams #>, _count, _filters);
 
     public ref struct Enumerator
     {
@@ -110,7 +111,7 @@ var compRestrictions = AppendGenericRestrictions(i, "TComponent", "struct, IComp
 		<#= compRestrictions #>
 	{
 <# for (int j = 0; j < i; j++) {#>
-        _filters._all.Add(TypeHandle<TComponent<#= j #>>.Value);
+        _filters._all.Add(TypeHandle.Get<TComponent<#= j #>>());
 <# } #>
         return this;
 	}
@@ -119,7 +120,7 @@ var compRestrictions = AppendGenericRestrictions(i, "TComponent", "struct, IComp
 		<#= compRestrictions #>
 	{
 <# for (int j = 0; j < i; j++) {#>
-        _filters._any.Add(TypeHandle<TComponent<#= j #>>.Value);
+        _filters._any.Add(TypeHandle.Get<TComponent<#= j #>>());
 <# } #>
         return this;
 	}
@@ -128,7 +129,7 @@ var compRestrictions = AppendGenericRestrictions(i, "TComponent", "struct, IComp
 		<#= compRestrictions #>
 	{
 <# for (int j = 0; j < i; j++) {#>
-        _filters._absent.Add(TypeHandle<TComponent<#= j #>>.Value);
+        _filters._absent.Add(TypeHandle.Get<TComponent<#= j #>>());
 <# } #>
         return this;
 	}
@@ -137,7 +138,7 @@ var compRestrictions = AppendGenericRestrictions(i, "TComponent", "struct, IComp
 		<#= compRestrictions #>
 	{
 <# for (int j = 0; j < i; j++) {#>
-        _filters._disabled.Add(TypeHandle<TComponent<#= j #>>.Value);
+        _filters._disabled.Add(TypeHandle.Get<TComponent<#= j #>>());
 <# } #>
         return this;
 	}

Ghost.Entities/Template/QueryItem.cs

@@ -1,5 +1,6 @@
 
 
+using Ghost.Entities.Components;
 using Ghost.Entities.Query;
 
 namespace Ghost.Entities;

Ghost.Entities/Template/QueryRefComponent.cs

@@ -1,5 +1,7 @@
 
 
+using Ghost.Entities.Components;
+
 namespace Ghost.Entities;
 
 public delegate void QueryRefComponent<T0>(Entity entity, ref T0 t0Component)

Ghost.Entities/Template/World.Query.cs

@@ -1,5 +1,7 @@
 
 
+using Ghost.Entities.Components;
+
 namespace Ghost.Entities;
 
 public partial class World

Ghost.Entities/Utilities/TypeHandle.cs

@@ -1,6 +1,28 @@
-namespace Ghost.Entities.Utilities;
+using System.Runtime.CompilerServices;
 
-internal static class TypeHandle<T>
+namespace Ghost.Entities.Utilities;
+
+internal static class TypeHandle
 {
-    public static nint Value => typeof(T).TypeHandle.Value;
+    /// <summary>
+    /// Gets the type handle for the specified type.
+    /// </summary>
+    /// <typeparam name="T">The type to get the handle for.</typeparam>
+    /// <returns>The type handle as a nint.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static nint Get<T>()
+    {
+        return typeof(T).TypeHandle.Value;
+    }
+
+    /// <summary>
+    /// Gets the type handle for the specified type.
+    /// </summary>
+    /// <param name="type">The type to get the handle for.</param>
+    /// <returns>The type handle as a nint.</returns>
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static nint Get(Type type)
+    {
+        return type.TypeHandle.Value;
+    }
 }

Ghost.Entities/World.cs

@@ -1,4 +1,6 @@
-using Ghost.Entities.Query;
+using Ghost.Entities.Components;
+using Ghost.Entities.Query;
+using Ghost.Entities.Systems;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
@@ -7,11 +9,9 @@ namespace Ghost.Entities;
 // TODO: Archetype system for better performance
 public partial class World
 {
-    private static List<World> s_worlds = new(2);
+    private static List<World> s_worlds = new(4);
     private static Queue<WorldID> s_freeWorldSlots = new();
 
-    private static int s_maxWorldCount = (int)MathF.Pow(2, Entity.WORLD_INDEX_BITS);
-
     public static int WorldCount => s_worlds.Count - s_freeWorldSlots.Count;
 
     public static World Create(int entityCapacity = 16)
@@ -24,7 +24,7 @@ public partial class World
             }
             else
             {
-                if (s_worlds.Count >= s_maxWorldCount)
+                if (s_worlds.Count >= WorldID.MaxValue)
                 {
                     throw new InvalidOperationException("Maximum number of worlds reached");
                 }

Ghost.Test/Program.cs

@@ -1,5 +1,6 @@
 using Ghost.Entities;
-using Ghost.Entities.Helpers;
+using Ghost.Entities.Components;
+using Ghost.Entities.Systems;
 using System.Numerics;
 
 var t = new Test();
@@ -15,17 +16,17 @@ public partial class Test
         var entity2 = world.EntityManager.CreateEntity();
         var entity3 = world.EntityManager.CreateEntity();
 
-        entity1.AddComponent(new Transform { position = new Vector3(1, 2, 3) });
+        world.EntityManager.AddComponent(entity1, new Transform { position = new Vector3(1, 2, 3) });
-        entity1.AddComponent(new Mesh { index = 42 });
+        world.EntityManager.AddComponent(entity1, new Mesh { index = 42 });
-        entity1.AddScript<UIManager>();
+        world.EntityManager.AddScript<UIManager>(entity1);
-        entity1.AddScript<EventManager>();
+        world.EntityManager.AddScript<EventManager>(entity1);
 
-        entity2.AddComponent(new Transform { position = new Vector3(4, 5, 6) });
+        world.EntityManager.AddComponent(entity2, new Transform { position = new Vector3(4, 5, 6) });
-        entity2.AddComponent(new Mesh { index = 43 });
+        world.EntityManager.AddComponent(entity2, new Mesh { index = 43 });
-        entity2.AddScript<UserScript>();
+        world.EntityManager.AddScript<UserScript>(entity2);
 
-        entity3.AddComponent(new Transform { position = new Vector3(7, 8, 9) });
+        world.EntityManager.AddComponent(entity3, new Transform { position = new Vector3(7, 8, 9) });
-        entity3.AddScript<EventManager>();
+        world.EntityManager.AddScript<EventManager>(entity3);
 
         foreach (var (_, transform) in world.Query<Transform>())
         {
@@ -40,62 +41,56 @@ public partial class Test
         world.EntityManager.RemoveEntity(ref entity2);
 
         var entity4 = world.EntityManager.CreateEntity();
-        entity4.AddComponent(new Transform { position = new Vector3(10, 11, 12) });
+        world.EntityManager.AddComponent(entity4, new Transform { position = new Vector3(10, 11, 12) });
-        entity4.AddComponent(new Mesh { index = 44 });
+        world.EntityManager.AddComponent(entity4, new Mesh { index = 44 });
-        entity4.AddScript<UserScript>();
+        world.EntityManager.AddScript<UserScript>(entity4);
 
+        world.SystemStorage.AddSystem<TestSystem2>();
         world.SystemStorage.AddSystem<TestSystem>();
+        world.SystemStorage.CreateSystems();
         world.SystemStorage.UpdateSystems();
 
-        //world.SystemStorage.RebuildExecutionList();
-        //world.ComponentStorage.RebuildExecutionList();
-
-        //Console.WriteLine();
-        //Console.WriteLine("Starting scripts...");
-        //foreach (var component in world.QueryScript())
-        //{
-        //    if (!component.Enable)
-        //    {
-        //        continue;
-        //    }
-        //    component.Start();
-        //}
-
-        //Console.WriteLine();
-        //Console.WriteLine("Updating scripts...");
-        //foreach (var component in world.QueryScript())
-        //{
-        //    if (!component.Enable)
-        //    {
-        //        continue;
-        //    }
-        //    component.Update();
-        //}
-
-        //Console.WriteLine();
-        //Console.WriteLine("LateUpdating scripts...");
-        //foreach (var component in world.QueryScript())
-        //{
-        //    if (!component.Enable)
-        //    {
-        //        continue;
-        //    }
-        //    component.LateUpdate();
-        //}
-
         world.Dispose();
     }
 }
 
-public class TestSystem : SystemBase
+public class TestSystem : ISystem
 {
-    public override void OnUpdate()
+    public void OnCreate(in SystemState state)
     {
-        foreach (var (entity, transform) in World.Query<Transform>().WithAny<Mesh>())
+    }
+
+    public void OnUpdate(in SystemState state)
+    {
+        foreach (var (entity, transform) in state.World.Query<Transform>())
         {
             Console.WriteLine($"Entity {entity.ID}: Transform Position = {transform.ValueRO.position}");
         }
     }
+
+    public void OnDestroy(in SystemState state)
+    {
+    }
+}
+
+[DependsOn(typeof(TestSystem))]
+public class TestSystem2 : ISystem
+{
+    public void OnCreate(in SystemState state)
+    {
+    }
+
+    public void OnUpdate(in SystemState state)
+    {
+        foreach (var (entity, mesh) in state.World.Query<Mesh>())
+        {
+            Console.WriteLine($"Entity {entity.ID}: Mesh Index = {mesh.ValueRO.index}");
+        }
+    }
+
+    public void OnDestroy(in SystemState state)
+    {
+    }
 }
 
 public struct Transform : IComponentData