Refactor project structure and enhance functionality

Changed the project namespace from `Ghost.Editor` to `Ghost.App` across multiple files.
Changed the `InternalsVisibleTo` attribute in `AssemblyInfo.cs` to include `Ghost.App`.
Changed the `ProjectRepository` class to add new asynchronous methods for retrieving projects by ID, name, and metadata path.
Changed the `ProjectService` class to utilize the new asynchronous project loading methods.
Changed the `SceneGraph` classes to improve node management and serialization.
Changed the `EntityManager` class to enhance entity management with new component handling methods.
Added new test classes, `EntityTest` and `SerializationTest`, to ensure reliability in entity and serialization systems.
Added the `Ghost.App` project file to establish a modular project structure.
Added the `Ghost.Generator` project for automated component serialization code generation.
Updated UI components to reflect the new namespace for proper functionality.

Ghost.Editor/SceneGraph/EntityNode.cs

@@ -0,0 +1,21 @@
+using Ghost.Entities;
+
+namespace Ghost.Editor.SceneGraph;
+
+public partial class EntityNode : SceneGraphNode
+{
+    private readonly Entity _entity;
+
+    public Entity Entity => _entity;
+    public override SceneGraphNodeType NodeType => SceneGraphNodeType.Entity;
+
+    public EntityNode(Entity entity, string name)
+    {
+        _entity = entity;
+        Name = name;
+    }
+
+    internal EntityNode()
+    {
+    }
+}

Ghost.Editor/SceneGraph/SceneGraphHelpers.cs

@@ -0,0 +1,112 @@
+using Ghost.Engine.Components;
+using Ghost.Entities;
+
+namespace Ghost.Editor.SceneGraph;
+
+public 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(WorldNode 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.AddChild(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(WorldNode 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].RemoveChild(node);
+    }
+}

Ghost.Editor/SceneGraph/SceneGraphNode.cs

@@ -0,0 +1,54 @@
+using CommunityToolkit.Mvvm.ComponentModel;
+using System.Collections.ObjectModel;
+
+namespace Ghost.Editor.SceneGraph;
+
+public enum SceneGraphNodeType
+{
+    Scene,
+    Entity,
+}
+
+public abstract partial class SceneGraphNode : ObservableObject
+{
+    public ObservableCollection<SceneGraphNode>? Children
+    {
+        get;
+        private set;
+    }
+
+    [ObservableProperty]
+    public partial string Name
+    {
+        get;
+        set;
+    }
+
+    public abstract SceneGraphNodeType NodeType
+    {
+        get;
+    }
+
+    public int ChildCount => Children?.Count ?? 0;
+
+    public virtual void AddChild(SceneGraphNode child)
+    {
+        Children ??= new();
+        Children.Add(child);
+    }
+
+    public virtual bool RemoveChild(SceneGraphNode child)
+    {
+        return Children?.Remove(child) ?? false;
+    }
+
+    public SceneGraphNode GetChild(int index)
+    {
+        if (Children == null || index < 0 || index >= Children.Count)
+        {
+            throw new ArgumentOutOfRangeException(nameof(index), "Index is out of range.");
+        }
+
+        return Children[index];
+    }
+}

Ghost.Editor/SceneGraph/WorldNode.cs

@@ -0,0 +1,112 @@
+using Ghost.Editor.Serializer;
+using Ghost.Engine.Components;
+using Ghost.Entities;
+using System.Text.Json.Serialization;
+
+namespace Ghost.Editor.SceneGraph;
+
+[JsonConverter(typeof(WorldNodeSerializer))]
+public partial class WorldNode : SceneGraphNode
+{
+    private readonly World _world;
+    private Dictionary<Entity, EntityNode> _entityNodeLookup = new();
+
+    public World World => _world;
+    public Dictionary<Entity, EntityNode> EntityNodeLookup => _entityNodeLookup;
+
+    public override SceneGraphNodeType NodeType => SceneGraphNodeType.Scene;
+
+    public WorldNode(World world, string name)
+    {
+        _world = world;
+        Name = name;
+    }
+
+    internal WorldNode()
+    {
+        _world = World.Create();
+    }
+
+    private void UpdateLookup(Entity key, EntityNode value)
+    {
+        _entityNodeLookup[key] = value;
+        if (value.Children == null)
+        {
+            return;
+        }
+
+        foreach (var child in value.Children)
+        {
+            if (child is EntityNode entityChild)
+            {
+                UpdateLookup(entityChild.Entity, entityChild);
+            }
+        }
+    }
+
+    public override void AddChild(SceneGraphNode child)
+    {
+        if (child is not EntityNode entityNode)
+        {
+            throw new ArgumentException("Child must be of type EntityNode.", nameof(child));
+        }
+
+        base.AddChild(entityNode);
+        UpdateLookup(entityNode.Entity, entityNode);
+    }
+
+    public override bool RemoveChild(SceneGraphNode child)
+    {
+        if (child is not EntityNode entityNode)
+        {
+            throw new ArgumentException("Child must be of type EntityNode.", nameof(child));
+        }
+
+        var result = base.RemoveChild(child);
+        if (result)
+        {
+            _entityNodeLookup.Remove(entityNode.Entity);
+        }
+
+        return result;
+    }
+
+    private EntityNode BuildNodeRecursive(Entity entity, World world)
+    {
+        // TODO: Node serialization.
+        if (!_entityNodeLookup.TryGetValue(entity, out var node))
+        {
+            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.AddChild(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);
+                AddChild(node);
+            }
+        }
+    }
+
+    public void Load()
+    {
+        BuildGraph();
+    }
+}