Refactor folder structure

src/Runtime/Ghost.Engine/Core/Scene.cs

@@ -0,0 +1,154 @@
+using Ghost.Entities;
+using Misaki.HighPerformance.LowLevel.Buffer;
+using Misaki.HighPerformance.LowLevel.Collections;
+
+namespace Ghost.Engine.Core;
+
+/// <summary>
+/// Represents a runtime scene - a collection of entities with the same SceneID.
+/// </summary>
+public readonly struct Scene : IEquatable<Scene>
+{
+    private readonly short _id;
+
+    /// <summary>
+    /// Gets the unique identifier of this scene.
+    /// </summary>
+    public short ID => _id;
+
+    /// <summary>
+    /// Gets whether this scene is valid.
+    /// </summary>
+    public bool IsValid => _id >= 0;
+
+    /// <summary>
+    /// Gets an invalid scene instance.
+    /// </summary>
+    public static Scene Invalid => new(-1);
+
+    internal Scene(short id)
+    {
+        _id = id;
+    }
+
+    public bool Equals(Scene other)
+    {
+        return _id == other._id;
+    }
+
+    public override bool Equals(object? obj)
+    {
+        return obj is Scene other && Equals(other);
+    }
+
+    public override int GetHashCode()
+    {
+        return _id.GetHashCode();
+    }
+
+    public static bool operator ==(Scene left, Scene right)
+    {
+        return left.Equals(right);
+    }
+
+    public static bool operator !=(Scene left, Scene right)
+    {
+        return !left.Equals(right);
+    }
+
+    public override string ToString()
+    {
+        return $"Scene(ID: {_id})";
+    }
+}
+
+/// <summary>
+/// Manages scenes within a world.
+/// </summary>
+/// <remarks>
+/// This is a minimal runtime representation. All metadata (like scene names) 
+/// should be stored in editor-only classes (SceneNode).
+/// </remarks>
+public static class SceneManager
+{
+    private static short s_nextSceneID;
+    private static readonly Queue<short> s_recycledSceneIDs = new();
+
+    /// <summary>
+    /// Creates a new scene in the world.
+    /// </summary>
+    /// <returns>The created scene.</returns>
+    public static Scene CreateScene()
+    {
+        if (!s_recycledSceneIDs.TryDequeue(out var id))
+        {
+            id = s_nextSceneID++;
+        }
+
+        return new Scene(id);
+    }
+
+    /// <summary>
+    /// Destroys all entities belonging to the specified scene.
+    /// </summary>
+    /// <param name="scene">The scene to unload.</param>
+    /// <param name="world">The world containing the entities.</param>
+    public static void UnloadScene(Scene scene, World world)
+    {
+        var queryID = new QueryBuilder().WithAll<Components.SceneID>().Build(world);
+        ref var query = ref world.ComponentManager.GetEntityQueryReference(queryID);
+
+        using var scope = AllocationManager.CreateStackScope();
+        var entitiesToDestroy = new UnsafeList<Entity>(128, scope.AllocationHandle);
+
+        // Iterate through all matching entities
+        foreach (var chunk in query.GetChunkIterator())
+        {
+            var entities = chunk.GetEntities();
+            var sceneIDs = chunk.GetComponentData<Components.SceneID>();
+
+            for (var i = 0; i < chunk.Count; i++)
+            {
+                if (sceneIDs[i].scene.ID == scene.ID)
+                {
+                    entitiesToDestroy.Add(entities[i]);
+                }
+            }
+        }
+
+        world.EntityManager.DestroyEntities(entitiesToDestroy.AsSpan());
+        s_recycledSceneIDs.Enqueue(scene.ID);
+    }
+
+    /// <summary>
+    /// Gets all entities belonging to the specified scene.
+    /// </summary>
+    /// <param name="scene">The scene to query.</param>
+    /// <param name="world">The world containing the entities.</param>
+    /// <param name="entities">Span to store the entities.</param>
+    /// <returns>The number of entities written to the span.</returns>
+    public static UnsafeList<Entity> GetSceneEntities(Scene scene, World world, AllocationHandle handle)
+    {
+        var queryID = new QueryBuilder().WithAll<Components.SceneID>().Build(world);
+        ref var query = ref world.ComponentManager.GetEntityQueryReference(queryID);
+
+        var entities = new UnsafeList<Entity>(128, handle);
+
+        // Iterate through all matching entities
+        foreach (var chunk in query.GetChunkIterator())
+        {
+            var chunkEntities = chunk.GetEntities();
+            var sceneIDs = chunk.GetComponentData<Components.SceneID>();
+
+            for (var i = 0; i < chunk.Count; i++)
+            {
+                if (sceneIDs[i].scene.ID == scene.ID)
+                {
+                    entities.Add(chunkEntities[i]);
+                }
+            }
+        }
+
+        return entities;
+    }
+}