using System.Numerics;
using AcDream.Core.World;
using DatReaderWriter.DBObjs;
using DatReaderWriter.Enums;
using DatReaderWriter.Types;

namespace AcDream.Core.Meshing;

public static class SetupMesh
{
    /// <summary>
    /// Flatten a Setup into a list of (GfxObjId, PartTransform) refs.
    /// Uses the default placement frame and DefaultScale per part.
    /// Does NOT walk ParentIndex — each part's transform is local to the setup root.
    /// This is simplification for Phase 2; complex hierarchical rigs are Phase 3.
    /// </summary>
    public static IReadOnlyList<MeshRef> Flatten(Setup setup)
    {
        AnimationFrame? defaultAnim = null;
        if (setup.PlacementFrames.TryGetValue(Placement.Default, out var af))
            defaultAnim = af;

        var result = new List<MeshRef>(setup.Parts.Count);
        for (int i = 0; i < setup.Parts.Count; i++)
        {
            uint gfxObjId = (uint)setup.Parts[i];

            Frame frame;
            if (defaultAnim is not null && i < defaultAnim.Frames.Count)
                frame = defaultAnim.Frames[i];
            else
                frame = new Frame { Origin = Vector3.Zero, Orientation = Quaternion.Identity };

            Vector3 scale = i < setup.DefaultScale.Count ? setup.DefaultScale[i] : Vector3.One;

            var transform =
                Matrix4x4.CreateScale(scale) *
                Matrix4x4.CreateFromQuaternion(frame.Orientation) *
                Matrix4x4.CreateTranslation(frame.Origin);

            result.Add(new MeshRef(gfxObjId, transform));
        }
        return result;
    }
}