#include "assets/data_loaders/obj_loader.hpp"

#include <charconv>
#include <fstream>
#include <array>

#include "assets/components/mesh_vertex_components.hpp"
#include "assets/dynamic_data_loaders/dynamic_material_loader.hpp"

#include "util/logger.hpp"
#include "util/for_each.hpp"
#include "util/uix.hpp"
#include <set>

#include "util/line_parser.hpp"

namespace obj_loader_error {

struct category : std::error_category {
	[[nodiscard]] const char* name() const noexcept override {
		return "connector";
	}

	[[nodiscard]] std::string message(int ev) const override {
		switch (static_cast<codes>(ev)) {
			using enum codes;
		case obj_cannot_open_file:
			return "Cannot open given obj file.";
		case obj_malformed_vertex:
			return "File contains malformed 'v' statement.";
		case obj_malformed_texture_coordinate:
			return "File contains malformed 'vt' statement.";
		case obj_malformed_normal:
			return "File contains malformed 'vn' statement.";
		case obj_malformed_face:
			return "File contains malformed 'f' statement.";
		case obj_face_index_out_of_range:
			return "Face index out of range.";
		case obj_unknown_line_begin:
			return "Unknown obj line begin.";
		default:
			using namespace std::string_literals;
			return "unrecognized error ("s + std::to_string(ev) + ")";
		}
	}
};

} // namespace mesh_loader_error

inline std::error_category& connector_error_category() {
	static obj_loader_error::category category;
	return category;
}

namespace obj_loader_error {

inline std::error_code make_error_code(codes e) {
	return { static_cast<int>(e), connector_error_category() };
}

} // namespace mesh_loader_error


using vertex_type = std::array<dynamic_mesh_buffer::index_type, 3>;

struct indexed_vertex_type
{
	vertex_type vertex;
	ztu::u32 buffer_index;

	friend auto operator<=>(const indexed_vertex_type& a, const indexed_vertex_type& b) {
		return a.vertex <=> b.vertex;
	}

	bool operator==(const indexed_vertex_type& other) const noexcept {
		return other.vertex == vertex;
	}
};


// TODO add compile time selection and unrolling
template<typename T, std::size_t Count>
std::errc parse_numeric_vector(std::string_view param, std::array<T, Count>& values) {
	auto it = param.begin(), end = param.end();

	for (auto& value : values)
	{
		if (it >= end)
		{
			return std::errc::invalid_argument;
		}

		const auto [ptr, ec] = std::from_chars(it, end, value);

		if (ec != std::errc{})
		{
			return ec;
		}

		it = ptr + 1; // skip space in between components
	}

	return {};
};


void find_materials(
	std::span<char> buffer,
	std::ifstream& in,
	ztu::string_list& material_filenames
) {
	static constexpr auto keyword = std::string_view{ "\nmtllib " };

	const auto buffer_view = std::string_view(buffer);

	// Add linebreak to simplify line begin search
	buffer.front() = '\n';
	auto leftover = std::size_t{ 1 };

	do
	{
		// Keep some old characters to continue matching interrupted sequence
		std::copy(buffer.end() - leftover, buffer.end(), buffer.begin());

		in.read(buffer.data() + leftover, buffer.size() - leftover);

		const auto str = buffer_view.substr(0, leftover + in.gcount());

		leftover = keyword.size();

		auto pos = std::string_view::size_type{};
		while ((pos = str.find(keyword, pos)) != std::string_view::npos)
		{
			const auto filename_begin = pos + keyword.size();
			const auto filename_end = str.find('\n', filename_begin);

			if (filename_end != std::string_view::npos)
			{
				const auto length = filename_end - filename_begin;
				const auto material_filename = str.substr(filename_begin, length);

				// TODO get base dir from param figure out how to avoid heap
				if (material_filename.is_relative())
				{
					material_filename = directory / material_filename;
				}

				material_filenames.push_back(material_filename);

				pos = filename_end;
			}
			else // string exceeds the buffer
			{
				if (pos == 0) [[unlikely]]
				{
					std::cout << "Ignoring string match, as it exceeds buffer size." << std::endl;
					leftover = 0;
				}
				else
				{
					leftover = str.size() - pos;
				}
				break;
			}
		}
	} while (not in.eof());
}


std::error_code obj_loader::prefetch(
	const file_dir_list& paths,
	prefetch_queue& queue
) {
	namespace fs = std::filesystem;
	using obj_loader_error::codes;
	using obj_loader_error::make_error_code;

	auto buffer = std::vector<char>(8 * 1024, '\0');

	auto in = std::ifstream{};

	const auto parse_file = [&](const char* filename)
	{
		in.open(filename);
		if (not in.is_open()) {
			ztu::logger::error("Could not open .obj file '%'", filename);
			return;
		}

		find_materials(buffer, in, queue.mtl_queue.files);

		in.close();
	};

	for (const auto file : paths.files)
	{
		// `file` is null-terminates by list.
		parse_file(file.data());
	}

	for (const auto directory : paths.directories)
	{
		for (const auto& file : fs::directory_iterator{ directory }) {

			const auto& file_path = std::string_view{ file.path().c_str() };

			// TODO remove heap allocation
			if (not file_path.ends_with(".obj"))
			{
				continue;
			}

			// Null terminated by fs::path.
			parse_file(file_path.data());
		}
	}

	return {};
}

std::error_code obj_loader::load_directory(
	dynamic_data_loader_ctx& ctx,
	dynamic_mesh_store& store,
	components::mesh_vertex::flags enabled_components,
	const std::filesystem::path& path,
	const bool pedantic
) {
	namespace fs = std::filesystem;

	if (not fs::exists(path))
	{
		return make_error_code(std::errc::no_such_file_or_directory);
	}

	for (const auto& file : fs::directory_iterator{ path })
	{
		const auto& file_path = file.path();

		if (file_path.extension() != ".obj")
		{
			continue;
		}

		if (const auto e = load(
			ctx,
			store,
			enabled_components,
			path,
			pedantic
		)) {
			ztu::logger::error(
				"Error while loading obj file '%': [%] %",
				file_path,
				e.category().name(),
				e.message()
			);
		}
	}

	return {};
}

[[nodiscard]] static std::error_code load(
	components::mesh_vertex::flags enabled_components,
	dynamic_mesh_buffer& buffer,
	const file_dir_list& paths,
	prefetch_lookup& id_lookup,
	dynamic_data_store& store,
	bool pedantic = false
) {


	auto in = std::ifstream{};
	std::set<indexed_vertex_type> vertex_ids;

	const auto parse_file = [&](const char* filename)
	{
		in.open(filename);
		if (not in.is_open()) {
			ztu::logger::error("Could not open .obj file '%'", filename);
			return;
		}


		vertex_ids.clear();

		in.close();
	};

	for (const auto file : paths.files)
	{
		// `file` is null-terminates by list.
		parse_file(file.data());
	}

	for (const auto directory : paths.directories)
	{
		for (const auto& file : fs::directory_iterator{ directory }) {

			const auto& file_path = std::string_view{ file.path().c_str() };

			// TODO remove heap allocation
			if (not file_path.ends_with(".obj"))
			{
				continue;
			}

			// Null terminated by fs::path.
			parse_file(file_path.data());
		}
	}

}

// TODO refactor so there is a function like parse_normals etc.

std::error_code obj_loader::load(
	components::mesh_vertex::flags enabled_components,
	dynamic_mesh_buffer& buffer,
	const char* filename,
	prefetch_lookup& id_lookup,
	dynamic_data_store& store,
	bool pedantic
) {
	using obj_loader_error::codes;
	using obj_loader_error::make_error_code;

	auto in = std::ifstream{ filename };
	if (not in.is_open()) {
		return make_error_code(codes::obj_cannot_open_file);
	}

	namespace fs = std::filesystem;
	const auto directory = fs::path(filename).parent_path();

	// Each vertex of a face can represent a unique combination of vertex-/texture-/normal-coordinates.
	// But some combinations may occur more than once, for example on every corner of a cube 3 triangles will
	// reference the exact same corner vertex.
	// To get the best rendering performance and lowest final memory footprint these duplicates
	// need to be removed. So this std::set lookup is used to identify the aforementioned duplicates
	// and only push unique combinations to the buffers.
	std::set<indexed_vertex_type> vertex_ids;

	// Buffers
	// TODO find out if this is still relevant
	auto position_buffer = buffer.positions();
	auto normal_buffer = buffer.normals();
	auto tex_coord_buffer = buffer.tex_coords();

	std::unordered_map<std::string, ztu::u32> material_name_lookup;

	std::string material_name;

	const auto push_mesh = [&](const bool clear_buffers = false) {

		if (not buffer.positions().empty())
		{
			// Copy buffers instead of moving to keep capacity for further parsing
			// and have the final buffers be shrunk to size.
			if (not material_name.empty()) {
				if (const auto id = material_loader.find_id(material_name))
				{
					buffer.material_id() = *id;
				}
				else
				{
					ztu::logger::warn(
						"Could not find material '%'.",
						material_name
					);
				}
			}

			ztu::logger::debug("Parsed % positions.", mesh.positions().size());
			ztu::logger::debug("Parsed % normals.", mesh.normals().size());
			ztu::logger::debug("Parsed % tex_coords.", mesh.tex_coords().size());

			if (not buffer.positions().empty())
			{
				buffer.components() |= components::mesh_vertex::flags::position;
			}

			if (not buffer.normals().empty())
			{
				buffer.components() |= components::mesh_vertex::flags::normal;
			}

			if (not buffer.tex_coords().empty())
			{
				buffer.components() |= components::mesh_vertex::flags::tex_coord;
			}

			ztu::logger::debug("Pushing obj mesh with % triangles.", buffer.triangles().size());

			store.meshes.add(buffer);
		}

		if (clear_buffers)
		{
			position_buffer.clear();
			normal_buffer.clear();
			tex_coord_buffer.clear();
		}

		buffer.clear();

		vertex_ids.clear();
		material_name.clear();
	};

	const auto find_or_push_vertex = [&](const vertex_type& vertex) -> ztu::u32 {

		auto indexed_vid = indexed_vertex_type{
			.vertex = vertex,
			.buffer_index = static_cast<ztu::u32>(buffer.positions().size())
		};

		// Search through sorted lookup to check if index combination is unique
		const auto [ id_it, unique ] = vertex_ids.insert(indexed_vid);

		if (unique)
		{
			const auto& [ position_index, tex_coord_index, normal_index ] = vertex;

			if (position_index < position_buffer.size())
			{
				buffer.positions().emplace_back(position_buffer[position_index]);
			}

			if (normal_index < normal_buffer.size())
			{
				buffer.normals().emplace_back(normal_buffer[normal_index]);
			}

			if (tex_coord_index < tex_coord_buffer.size())
			{
				buffer.tex_coords().emplace_back(tex_coord_buffer[tex_coord_index]);
			}
		}

		return id_it->buffer_index;
	};

	using flags = components::mesh_vertex::flags;

	const auto component_disabled = [&](const flags component) {
		return (enabled_components & component) == flags::none;
	};

	const auto positions_disabled = component_disabled(flags::position);
	const auto normals_disabled = component_disabled(flags::normal);
	const auto tex_coords_disabled = component_disabled(flags::tex_coord);

	const auto ec = ztu::parse_lines<codes>(
		in,
		pedantic,
		ztu::make_line_parser("v ", ztu::is_repeating, [&](const auto& param)
		{
			if (positions_disabled) return codes::ok;

			components::mesh_vertex::position position;
			if (parse_numeric_vector(param, position) != std::errc{}) [[unlikely]]
			{
				return codes::obj_malformed_vertex;
			}

			position_buffer.push_back(position);

			return codes::ok;
		}),
		ztu::make_line_parser("vt ", ztu::is_repeating, [&](const auto& param) {
			if (tex_coords_disabled) return codes::ok;

			components::mesh_vertex::tex_coord coord;
			if (parse_numeric_vector(param, coord) != std::errc{}) [[unlikely]]
			{
				return codes::obj_malformed_texture_coordinate;
			}

			tex_coord_buffer.push_back(coord);

			return codes::ok;
		}),
		ztu::make_line_parser("vn ", ztu::is_repeating, [&](const auto& param)
		{
			if (normals_disabled) return codes::ok;

			components::mesh_vertex::normal normal;
			if (parse_numeric_vector(param, normal) != std::errc{}) [[unlikely]]
			{
				return codes::obj_malformed_normal;
			}

			normal_buffer.push_back(normal);

			return codes::ok;
		}),
		ztu::make_line_parser("o ", ztu::is_not_repeating, [&](const auto&)
		{
			push_mesh(); // Name is currently ignored
			return codes::ok;
		}),
		ztu::make_line_parser("f ", ztu::is_repeating, [&](const auto& param)
		{
			const auto begin = param.begin().base();
			const auto end = param.end().base();

			auto vertex = vertex_type{};

			ztu::u32 first_index{}, prev_index{};

			auto vertex_count = std::size_t{};

			for (auto it = begin; it <= end; ++it)
			{

				for (auto& component_index : vertex)
				{
					if (it != end and *it == '/')
					{
						++it;
						continue;
					}

					const auto [ptr, ec] = std::from_chars(it, end, component_index);
					if (ec != std::errc()) [[unlikely]]
					{
						// Discard whole face if one index is malformed
						return codes::obj_malformed_face;
					}

					--component_index; // Indices start at one
					it = ptr;

					if (it == end or *it != '/')
					{
						break;
					}

					++it;
				}

				++vertex_count;

				if (it != end and *it != ' ') [[unlikely]]
				{
					return codes::obj_malformed_face;
				}

				const auto curr_index = find_or_push_vertex(vertex);

				if (vertex_count >= 3)
				{
					 auto& triangle = mesh.triangles().emplace_back();
					triangle[0] = first_index;
					triangle[1] = prev_index;
					triangle[2] = curr_index;
				}
				else if (vertex_count == 1)
				{
					first_index = curr_index;
				}

				prev_index = curr_index;
		   }

			return codes::ok;
		}),
		ztu::make_line_parser("usemtl ", ztu::is_not_repeating, [&](const auto& param)
		{
			push_mesh(false);

			material_name = param;

			return codes::ok;
		}),
		ztu::make_line_parser("mtllib ", ztu::is_not_repeating, [&](const auto& param)
		{
			auto material_filename = fs::path(param);
			if (material_filename.is_relative())
			{
				material_filename = directory / material_filename;
			}

			if (const auto error = ctx.material_loader.read(
				ctx,
				mtl_loader_id,
				material_filename,
				pedantic
			)) {
				ztu::logger::warn(
					"Error occurred while loading mtl files '%': [%] %",
					material_filename,
					error.category().name(),
					error.message()
				);
			}
		})
	);

	if (ec != codes::ok)
	{
		return make_error_code(ec);
	}

	push_mesh();

	return {};
}