#include "../../../include/assets/data_parsers"

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

#include "util/logger.hpp"
#include "util/for_each.hpp"
#include "util/line_parser.hpp"

#include "../../../include/assets/data_loaders"

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

	[[nodiscard]] std::string message(int ev) const override
	{
		switch (static_cast<codes>(ev))
		{
			using enum codes;
		case cannot_open_file:
			return "Cannot open mtl file.";
		case cannot_open_texture:
			return "Cannot open texture file.";
		case malformed_ambient_color:
			return "File contains malformed 'Ka' statement.";
		case malformed_diffuse_color:
			return "File contains malformed 'Kd' statement.";
		case malformed_specular_color:
			return "File contains malformed 'Ks' statement.";
		case malformed_specular_exponent:
			return "File contains malformed 'Ns' statement.";
		case malformed_dissolve:
			return "File contains malformed 'd' statement.";
		case unknown_line_begin:
			return "Unknown mtl 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 mtl_loader_error::category category;
	return category;
}

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


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 mtl_loader::find_textures(
	std::span<char> buffer,
	std::filesystem::path& path_buffer,
	const std::filesystem::path& base_directory,
	std::ifstream& in,
	ztu::string_list& texture_filenames
) {
	using namespace std::string_view_literals;

	// TODO 'bump' is missing!!!

	static constexpr auto keyword = "\nmap_"sv;

	using long_postfix_type = std::array<char, 2>;

	static constexpr auto postfix_length = std::tuple_size_v<long_postfix_type>;

	static constexpr auto make_postfix = [](const std::string_view str) static constexpr
	{
		auto postfix = long_postfix_type{};
		assert(str.length() >= postfix_length);
		std::copy_n(str.begin(), postfix.size(), postfix.begin());
		return postfix;
	};

	static constexpr auto postfixes = std::array{
		make_postfix("d "),
		make_postfix("Ka"),
		make_postfix("Kd"),
		make_postfix("Ks"),
		make_postfix("Ns")
	};

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

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

	enum class match {
		exact,
		overflowed,
		none
	};

	const auto check_match = [](std::string_view& potential_match) static -> match
	{
		std::cout << '\'' << potential_match.substr(0, std::min(40ul, potential_match.size())) << '\'' << std::endl;

		if (potential_match.length() < postfix_length)
		{
			return match::overflowed;
		}

		const auto postfix = make_postfix(potential_match);

		// Optimized for SIMD.
		if (not std::ranges::contains(postfixes, postfix))
		{
			return match::none;
		}

		const auto long_match = postfix.back() != ' ';

		if (long_match and (
			potential_match.length() < postfix_length + sizeof(' ') or
			potential_match[postfix_length] != ' '
		)) {
			return match::overflowed;
		}

		const auto actual_postfix_length = std::size_t{ 1 } + static_cast<std::size_t>(long_match);

		const auto filename_begin = actual_postfix_length + sizeof(' ');
		const auto filename_end = potential_match.find('\n', filename_begin);

		if (filename_end == std::string_view::npos)
		{
			return match::overflowed;
		}

		const auto length = filename_end - filename_begin;
		potential_match = potential_match.substr(filename_begin, length);

		return match::exact;
	};

	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());

		auto pos = std::string_view::size_type{};
		while ((pos = str.find(keyword, pos)) != std::string_view::npos)
		{
			const auto keyword_end = pos + keyword.size();
			auto potential_match = str.substr(keyword_end);

			const auto match_type = check_match(potential_match);

			if (match_type == match::exact)
			{
				path_buffer.assign(potential_match);

				if (path_buffer.is_relative())
				{
					path_buffer = base_directory;
					path_buffer /= potential_match;
				}

				texture_filenames.push_back(path_buffer.c_str());

				pos += potential_match.size();

				leftover = 0;
			}
			else if (match_type == match::overflowed)
			{
				if (pos == 0) [[unlikely]]
				{
					ztu::logger::error("Ignoring string match, as it exceeds buffer size of % characters.", buffer.size());
					leftover = 0;
				}
				else
				{
					leftover = str.size() - pos;
				}
				break;
			}
			else
			{
				leftover = keyword.size();
			}
		}
	} while (not in.eof());
}

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

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

	auto in = std::ifstream{};

	auto path_buffer = fs::path{};
	auto filename_buffer = fs::path{};

	const auto process_file = [&]()
	{
		in.open(filename_buffer);
		if (not in.is_open()) {
			ztu::logger::error("Could not open .mtl file '%'", filename_buffer);
			return;
		}

		filename_buffer.remove_filename();

		find_textures(buffer, path_buffer, filename_buffer, in, queue.texture.files);

		in.close();
	};


	for (const auto file : paths.files)
	{
		filename_buffer.assign(file);
		process_file();
	}

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

			filename_buffer.assign(file.path());

			// Avoid heap allocation of .extension()
			if (not std::string_view(filename_buffer.c_str()).ends_with(".obj"))
			{
				continue;
			}

			process_file();
		}
	}

	return {};
}

std::error_code mtl_loader::load_directory(
	dynamic_data_loader_ctx& ctx,
	dynamic_material_store& store,
	material_components::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 {};
}

std::error_code mtl_loader::load(
	dynamic_data_loader_ctx& ctx,
	dynamic_material_store& store,
	material_components::flags enabled_components,
	const std::filesystem::path& filename,
	const bool pedantic
) {
	using mtl_loader_error::codes;
	using mtl_loader_error::make_error_code;

	using flags = material_components::flags;

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

	// TODO unroll stuff
	const auto textures_disabled = component_disabled(flags::ambient_filter_texture);
	const auto surface_properties_disabled = component_disabled(flags::surface_properties);
	const auto transparencies_disabled = component_disabled(flags::transparency);

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

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

	auto name = std::string{};
	auto material = dynamic_material_data{};

	const auto push_material = [&]()
	{
		if (not name.empty())
		{
			const auto id = store.add(std::move(material));
			m_id_lookup.emplace(std::move(name), id);
		}
		name = std::string{};
		material = dynamic_material_data{};
	};

	const auto load_texture = [&](
		const std::string_view path,
		std::string_view texture_type_name,
		auto&& f
	) {
		auto texture_filename = fs::path(path);
		if (texture_filename.is_relative())
		{
			texture_filename = directory / texture_filename;
		}

		const auto extension = texture_filename.extension().string();

		auto texture_type = std::string_view{ extension };
		if (not texture_type.empty() and texture_type.front() == '.')
		{
			texture_type = texture_type.substr(1);
		}

		if (const auto loader_id = ctx.texture_loader.find_loader(texture_type))
		{
			if (auto res = ctx.texture_loader.read(
				ctx,
				*loader_id,
				texture_filename,
				pedantic
			)) {
				f(*res);
			}
			else
			{
				const auto error = res.error();
				ztu::logger::warn(
					"Error while loading % texture '%': [%] %",
					texture_type_name,
					path,
					error.category().name(),
					error.message()
				);
			}
		}
		else
		{
			ztu::logger::warn(
				"Failed to load % texture '%' because extension is not supported.",
				texture_type_name,
				path
			);
		}
	};

	const auto ec = ztu::parse_lines<codes>(
		in,
		pedantic,
		ztu::make_line_parser("newmtl ", ztu::is_not_repeating, [&](const auto& param)
		{
			push_material();
			name = param;

		   return codes::ok;
		}),
		ztu::make_line_parser("Ka ", ztu::is_not_repeating, [&](const auto& param)
		{
			if (surface_properties_disabled) return codes::ok;

			auto& properties = material.initialized_surface_properties();
			if (parse_numeric_vector(param, properties.ambient_filter) != std::errc{}) [[unlikely]]
			{
				return codes::malformed_ambient_color;
			}

			material.components() |= flags::surface_properties;

			return codes::ok;
		}),
		ztu::make_line_parser("Kd ", ztu::is_not_repeating, [&](const auto& param)
		{
			if (surface_properties_disabled) return codes::ok;

			auto& properties = material.initialized_surface_properties();
			if (parse_numeric_vector(param, properties.diffuse_filter) != std::errc{}) [[unlikely]]
			{
				return codes::malformed_diffuse_color;
			}

			material.components() |= flags::surface_properties;

			return codes::ok;
		}),
		ztu::make_line_parser("Ks ", ztu::is_not_repeating, [&](const auto& param)
		{
			if (surface_properties_disabled) return codes::ok;

			auto& properties = material.initialized_surface_properties();
			if (parse_numeric_vector(param, properties.specular_filter) != std::errc{}) [[unlikely]]
			{
				return codes::malformed_specular_color;
			}

			material.components() |= flags::surface_properties;

			return codes::ok;
		}),
		ztu::make_line_parser("Ns ", ztu::is_not_repeating, [&](const auto& param)
		{
			if (surface_properties_disabled) return codes::ok;

			auto& properties = material.initialized_surface_properties();
			std::array<float, 1> shininess{};
			if (parse_numeric_vector(param, shininess) != std::errc{}) [[unlikely]]
			{
				return codes::malformed_specular_exponent;
			}

			properties.shininess = shininess.front();
			material.components() |= flags::surface_properties;

			return codes::ok;
		}),
		ztu::make_line_parser("d ", ztu::is_not_repeating, [&](const auto& param)
		{
			if (transparencies_disabled) return codes::ok;

			std::array<float, 1> transparency{};
			if (parse_numeric_vector(param, transparency) != std::errc{}) [[unlikely]]
			{
				return codes::malformed_dissolve;
			}

			material.transparency().emplace(transparency.front());
			material.components() |= flags::transparency;

			return codes::ok;
		}),
		ztu::make_line_parser("map_Ka ", ztu::is_not_repeating, [&](const auto& param)
		{
			if (textures_disabled) return codes::ok;

			load_texture(param, "ambient color", [&](const auto id) {
				material.ambient_color_texture_id() = id;
				material.components() |= flags::ambient_filter_texture;
			});

			return codes::ok;
		}),
		ztu::make_line_parser("map_Kd ", ztu::is_not_repeating, [&](const auto& param)
		{
			if (textures_disabled) return codes::ok;

			load_texture(param, "diffuse color", [&](const auto id) {
				material.diffuse_color_texture_id() = id;
				material.components() |= flags::diffuse_filter_texture;
			});

			return codes::ok;
		}),
		ztu::make_line_parser("map_Ks ", ztu::is_not_repeating, [&](const auto& param)
		{
			if (textures_disabled) return codes::ok;

			load_texture(param, "specular color", [&](const auto id) {
				material.specular_color_texture_id() = id;
				material.components() |= flags::specular_filter_texture;
			});

			return codes::ok;
		}),
		ztu::make_line_parser("map_Ns ", ztu::is_not_repeating, [&](const auto& param)
		{
			if (textures_disabled) return codes::ok;

			load_texture(param, "shininess", [&](const auto id) {
				material.shininess_texture_id() = id;
				material.components() |= flags::shininess_texture;
			});

			return codes::ok;
		}),
		ztu::make_line_parser("map_d ", ztu::is_not_repeating, [&](const auto& param)
		{
			if (textures_disabled) return codes::ok;

			load_texture(param, "alpha", [&](const auto id) {
				material.alpha_texture_id() = id;
				material.components() |= flags::alpha_texture;
			});

			return codes::ok;
		}),
		ztu::make_line_parser("bump ", ztu::is_not_repeating, [&](const auto& param)
		{
			if (textures_disabled) return codes::ok;

			load_texture(param, "bump", [&](const auto id) {
				material.bump_texture_id() = id;
				material.components() |= flags::bump_texture;
			});

			return codes::ok;
		})
	);

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

	push_material();

	return {};
}