Z3D/include/util/binary_ifstream.hpp

#pragma once

#include <filesystem>
#include <fstream>
#include <span>
#include <algorithm>
#include <cstring>

class binary_ifstream {
public:
	using char_type = char;
	using size_type = std::streamsize;

	[[nodiscard]] inline std::error_code open(
		const std::filesystem::path& filename,
		bool check_file_before_open
	);

	[[nodiscard]] inline std::error_code read(std::span<char_type> buffer);

	template<std::endian E, std::integral T>
	[[nodiscard]] std::error_code read(T& integer);

	template<std::endian E, std::floating_point T>
	[[nodiscard]] std::error_code read_ieee754(T& floating_point);

	[[nodiscard]] inline std::error_code skip(size_type count);

	template<std::integral T>
	[[nodiscard]] std::error_code skip();

	template<std::floating_point T>
	[[nodiscard]] std::error_code skip();

	inline void close();

protected:
	[[nodiscard]] inline static std::error_code check_file(
		const std::filesystem::path& filename
	);

	[[nodiscard]] inline std::errc get_stream_error_code() const;

private:
	std::basic_ifstream<char_type> in{};
};

inline std::errc binary_ifstream::get_stream_error_code() const {
	const auto state = in.rdstate();

	auto code = std::errc{};

	if (state != std::ios::goodbit)
	{
		code = std::errc::state_not_recoverable;

		if (state & std::ios::failbit) // irrecoverable stream error
		{
			code = std::errc::state_not_recoverable;
		}
		else if (state & std::ios::badbit) // input/output operation failed
		{
			code = std::errc::io_error;
		}
		else if (state & std::ios::eofbit) // input sequence has reached end-of-file
		{
			code = std::errc::result_out_of_range;
		}
	}

	return code;
}

inline std::error_code binary_ifstream::check_file(const std::filesystem::path& filename)
{
	auto error = std::error_code{};

	const auto is_file = std::filesystem::exists(filename, error);

	if (error)
	{
		return error;
	}

	if (not is_file)
	{
		return std::make_error_code(std::errc::invalid_argument);
	}

	const auto files_exists = std::filesystem::exists(filename, error);

	if (error)
	{
		return error;
	}

	if (not files_exists)
	{
		return std::make_error_code(std::errc::no_such_file_or_directory);
	}

	return {};
}

inline std::error_code binary_ifstream::open(
	const std::filesystem::path& filename,
	bool check_file_before_open
) {
	if (check_file_before_open)
	{
		if (const auto error = check_file(filename))
		{
			return error;
		}
	}

	in = {};

	// Turn of exceptions, as errors are handled via the stream state.
	in.exceptions(std::ios::goodbit);

	in.open(filename, std::ios::binary | std::ios::in);

	if (const auto error = std::make_error_code(get_stream_error_code()))
	{
		return error;
	}

	if (not in.is_open())
	{
		// Unknown error, so 'state_not_recoverable' is assumed.
		return std::make_error_code(std::errc::state_not_recoverable);
	}

	return {};
}

inline void binary_ifstream::close()
{
	in.close();
}

inline std::error_code binary_ifstream::skip(size_type count)
{
	in.ignore(count);
	return std::make_error_code(get_stream_error_code());
}

template<std::floating_point T>
std::error_code binary_ifstream::skip()
{
	return skip(sizeof(T));
}

template<std::integral T>
std::error_code binary_ifstream::skip()
{
	return skip(sizeof(T));
}

inline std::error_code binary_ifstream::read(std::span<char_type> buffer)
{
	in.read(buffer.data(), static_cast<size_type>(buffer.size()));
	return std::make_error_code(get_stream_error_code());
}

template<std::endian E, std::integral T>
std::error_code binary_ifstream::read(T& integer)
{
	std::array<char_type, sizeof(T)> buffer;
	if (const auto error = read(buffer))
	{
		return error;
	}

	if constexpr (std::endian::native != E)
	{
		std::reverse(buffer.begin(), buffer.end());
	}

	// Use memcpy to avoid UB.
	std::memcpy(static_cast<void*>(&integer), buffer.data(), buffer.size());

	return {};
}

template<std::endian E, std::floating_point T>
std::error_code binary_ifstream::read_ieee754(T& floating_point)
{
	static_assert(std::numeric_limits<T>::is_iec559);

	std::array<char_type, sizeof(T)> buffer;
	if (const auto error = read(buffer))
	{
		return error;
	}

	if constexpr (std::endian::native != E)
	{
		std::reverse(buffer.begin(), buffer.end());
	}

	// Use memcpy to avoid UB.
	std::memcpy(static_cast<void*>(&floating_point), buffer.data(), buffer.size());

	return {};
}