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? motionFrameOverride = null)
    {
        // Pose source priority:
        //   1. motionFrameOverride — caller has resolved an idle/animation
        //      frame from the entity's MotionTable (Phase 6). This is the
        //      best source for creatures and characters because their
        //      Setup.PlacementFrames don't define an upright idle pose.
        //   2. Setup.PlacementFrames[Resting] — used by static objects
        //      that have a Resting frame defined (e.g. signs, doors).
        //   3. Setup.PlacementFrames[Default] — fallback for everything
        //      else (most scenery), which is the only frame those setups
        //      define and renders correctly.
        //
        // Without an override, creatures used to render in their Default
        // pose (T-pose-ish or aggressive crouch) because their MotionTable
        // wasn't consulted. The Phase 6 MotionResolver provides the override
        // by walking Setup.DefaultMotionTable → MotionTable.Cycles →
        // Animation.PartFrames[LowFrame].
        AnimationFrame? defaultAnim = motionFrameOverride;
        if (defaultAnim is null && setup.PlacementFrames.TryGetValue(Placement.Resting, out var resting))
            defaultAnim = resting;
        if (defaultAnim is null && setup.PlacementFrames.TryGetValue(Placement.Default, out var af))
            defaultAnim = af;
        // Last resort: use the first available placement frame (matches ACME's
        // StaticObjectManager.GetDefaultPlacementFrame third fallback). Handles
        // rare Setups that define only an unusual placement frame key.
        if (defaultAnim is null)
        {
            foreach (var kvp in setup.PlacementFrames)
            {
                defaultAnim = kvp.Value;
                break;
            }
        }

        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;
    }
}