#include <psemek/gfx/gltf_mesh.hpp>

#include <stdexcept>

namespace psemek::gfx
{

	void gltf_mesh::mesh::primitive::draw()
	{
		vao.bind();
		gl::DrawElements(gl::TRIANGLES, index_count, index_type, reinterpret_cast<void const *>(index_offset));
	}

	gltf_mesh::gltf_mesh(gltf_asset const & asset, std::vector<util::span<char const>> const & buffers)
	{
		if (buffers.size() != asset.buffers.size())
			throw std::runtime_error("wrong number of glTF buffers");

		for (auto buffer : buffers)
			this->buffers.emplace_back().load(buffer.data(), buffer.size(), gl::STATIC_DRAW);

		for (auto const & node : asset.nodes)
		{
			auto & target_mesh = meshes[node.name];

			auto const & mesh = asset.meshes[node.mesh];

			for (auto const & primitive : mesh.primitives)
			{
				auto & target_primitive = target_mesh.primitives.emplace_back();
				target_primitive.material = primitive.material;

				target_primitive.vao.bind();

				{
					auto const & indices_accessor = asset.accessors[primitive.indices];
					auto const & indices_view = asset.buffer_views[indices_accessor.buffer_view];

					gl::BindBuffer(gl::ELEMENT_ARRAY_BUFFER, this->buffers[indices_view.buffer].id());
					target_primitive.index_offset = indices_view.offset;
					target_primitive.index_type = indices_accessor.component_type;
					target_primitive.index_count = indices_accessor.count;
				}

				std::pair<GLuint, std::optional<std::size_t>> attributes[3] =
				{
					{0, primitive.position},
					{1, primitive.normal},
					{2, primitive.texcoord},
				};

				for (auto const & attribute : attributes)
				{
					if (!attribute.second) continue;

					auto const & accessor = asset.accessors[*attribute.second];
					auto const & view = asset.buffer_views[accessor.buffer_view];

					gl::BindBuffer(gl::ARRAY_BUFFER, this->buffers[view.buffer].id());
					gl::EnableVertexAttribArray(attribute.first);
					gl::VertexAttribPointer(attribute.first, accessor.type, accessor.component_type, accessor.normalized, 0, reinterpret_cast<void const *>(view.offset));
				}
			}
		}
	}

}