using Stride.Games;
using Stride.Rendering;
using System;
using Stride.Core.Serialization;
using Stride.Core;
using Stride.Physics;
using System.Collections.Generic;
using Stride.Core.Mathematics;

public static class MeshExtensions
{
	public static (List<Vector3> verts, List<int> indices) GetMeshVerticesAndIndices(this Model model, IGame game)
	{
		return GetMeshData(model, game.Services, game);
	}

	static unsafe (List<Vector3> verts, List<int> indices) GetMeshData(Model model, IServiceRegistry services, IGame game)
	{
		Matrix[] nodeTransforms = null;

		int totalVerts = 0, totalIndices = 0;
		foreach (var meshData in model.Meshes)
		{
			totalVerts += meshData.Draw.VertexBuffers[0].Count;
			totalIndices += meshData.Draw.IndexBuffer.Count;
		}

		var combinedVerts = new List<Vector3>(totalVerts);
		var combinedIndices = new List<int>(totalIndices);

		foreach (var meshData in model.Meshes)
		{
			var vBuffer = meshData.Draw.VertexBuffers[0].Buffer;
			var iBuffer = meshData.Draw.IndexBuffer.Buffer;
			byte[] verticesBytes = vBuffer.GetData<byte>(game.GraphicsContext.CommandList); ;
			byte[] indicesBytes = iBuffer.GetData<byte>(game.GraphicsContext.CommandList); ;

			if ((verticesBytes?.Length ?? 0) == 0 || (indicesBytes?.Length ?? 0) == 0)
			{
				throw new InvalidOperationException(
					$"Failed to find mesh buffers while attempting to build a {nameof(StaticMeshColliderShape)}. " +
					$"Make sure that the {nameof(model)} is either an asset on disk, or has its buffer data attached to the buffer through '{nameof(AttachedReference)}'\n" +
					$"You can also explicitly build a {nameof(StaticMeshColliderShape)} using the second constructor instead of this one.");
			}

			int vertMappingStart = combinedVerts.Count;

			fixed (byte* bytePtr = verticesBytes)
			{
				var vBindings = meshData.Draw.VertexBuffers[0];
				int count = vBindings.Count;
				int stride = vBindings.Declaration.VertexStride;
				for (int i = 0, vHead = vBindings.Offset; i < count; i++, vHead += stride)
				{
					var pos = *(Vector3*)(bytePtr + vHead);
					if (nodeTransforms != null)
					{
						Matrix posMatrix = Matrix.Translation(pos);
						Matrix.Multiply(ref posMatrix, ref nodeTransforms[meshData.NodeIndex], out var finalMatrix);
						pos = finalMatrix.TranslationVector;
					}

					combinedVerts.Add(pos);
				}
			}

			fixed (byte* bytePtr = indicesBytes)
			{
				if (meshData.Draw.IndexBuffer.Is32Bit)
				{
					foreach (int i in new Span<int>(bytePtr + meshData.Draw.IndexBuffer.Offset, meshData.Draw.IndexBuffer.Count))
					{
						combinedIndices.Add(vertMappingStart + i);
					}
				}
				else
				{
					foreach (ushort i in new Span<ushort>(bytePtr + meshData.Draw.IndexBuffer.Offset, meshData.Draw.IndexBuffer.Count))
					{
						combinedIndices.Add(vertMappingStart + i);
					}
				}
			}
		}
		return (combinedVerts, combinedIndices);
	}
}