/*
 * From https://github.com/mariusbancila/stduuid
 *
 * Copyright (c) 2017
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

module;

#include <algorithm>
#include <array>
#include <atomic>
#include <chrono>
#include <cstring>
#include <functional>
#include <iomanip>
#include <iterator>
#include <memory>
#include <numeric>
#include <optional>
#include <random>
#include <ranges>
#include <span>
#include <string>
#include <sstream>
#include <string_view>
#include <type_traits>

export module nihil.uuid;

namespace nihil {

template <typename TChar>
[[nodiscard]] constexpr unsigned char hex2char(TChar const ch) noexcept
{
	if (ch >= static_cast<TChar>('0') && ch <= static_cast<TChar>('9'))
		return static_cast<unsigned char>(ch - static_cast<TChar>('0'));
	if (ch >= static_cast<TChar>('a') && ch <= static_cast<TChar>('f'))
		return static_cast<unsigned char>(10 + ch - static_cast<TChar>('a'));
	if (ch >= static_cast<TChar>('A') && ch <= static_cast<TChar>('F'))
		return static_cast<unsigned char>(10 + ch - static_cast<TChar>('A'));
	return 0;
}

template <typename TChar>
[[nodiscard]] constexpr bool is_hex(TChar const ch) noexcept
{
	return
		(ch >= static_cast<TChar>('0') && ch <= static_cast<TChar>('9')) ||
		(ch >= static_cast<TChar>('a') && ch <= static_cast<TChar>('f')) ||
		(ch >= static_cast<TChar>('A') && ch <= static_cast<TChar>('F'));
}

template <typename TChar>
[[nodiscard]] constexpr std::basic_string_view<TChar> to_string_view(TChar const * str) noexcept
{
	if (str)
		return str;
	return {};
}

template <typename StringType>
[[nodiscard]] 
constexpr std::basic_string_view<
	typename StringType::value_type,
	typename StringType::traits_type>
to_string_view(StringType const & str) noexcept
{
	return str;
}

struct sha1
{
	using digest32_t = uint32_t[5];
	using digest8_t = uint8_t[20];

	static constexpr unsigned int block_bytes = 64;

	[[nodiscard]] inline static uint32_t left_rotate(uint32_t value, size_t const count) noexcept
	{
		return (value << count) ^ (value >> (32 - count));
	}

	sha1()
	{
		reset();
	}

	void reset() noexcept
	{
		m_digest[0] = 0x67452301;
		m_digest[1] = 0xEFCDAB89;
		m_digest[2] = 0x98BADCFE;
		m_digest[3] = 0x10325476;
		m_digest[4] = 0xC3D2E1F0;
		m_blockByteIndex = 0;
		m_byteCount = 0;
	}

	void process_byte(uint8_t octet) 
	{
		this->m_block[this->m_blockByteIndex++] = octet;
		++this->m_byteCount;
		if (m_blockByteIndex == block_bytes) {
			this->m_blockByteIndex = 0;
			process_block();
		}
	}

	void process_block(void const * const start, void const * const end) 
	{
		auto *begin = static_cast<const uint8_t*>(start);
		auto *finish = static_cast<const uint8_t*>(end);
		while (begin != finish) {
			process_byte(*begin);
			begin++;
		}
	}

	void process_bytes(void const * const data, size_t const len)
	{
		auto *block = static_cast<const uint8_t*>(data);
		process_block(block, block + len);
	}

	uint32_t const * get_digest(digest32_t digest) 
	{
		size_t const bitCount = this->m_byteCount * 8;
		process_byte(0x80);
		if (this->m_blockByteIndex > 56) {
			while (m_blockByteIndex != 0)
				process_byte(0);
			while (m_blockByteIndex < 56)
				process_byte(0);
		} else {
			while (m_blockByteIndex < 56)
				process_byte(0);
		}

		process_byte(0);
		process_byte(0);
		process_byte(0);
		process_byte(0);
		process_byte(static_cast<unsigned char>((bitCount >> 24) & 0xFF));
		process_byte(static_cast<unsigned char>((bitCount >> 16) & 0xFF));
		process_byte(static_cast<unsigned char>((bitCount >> 8) & 0xFF));
		process_byte(static_cast<unsigned char>((bitCount) & 0xFF));

		std::memcpy(digest, m_digest, 5 * sizeof(uint32_t));
		return digest;
	}

	uint8_t const * get_digest_bytes(digest8_t digest) 
	{
		digest32_t d32;
		get_digest(d32);
		size_t di = 0;
		digest[di++] = static_cast<uint8_t>(d32[0] >> 24);
		digest[di++] = static_cast<uint8_t>(d32[0] >> 16);
		digest[di++] = static_cast<uint8_t>(d32[0] >> 8);
		digest[di++] = static_cast<uint8_t>(d32[0] >> 0);

		digest[di++] = static_cast<uint8_t>(d32[1] >> 24);
		digest[di++] = static_cast<uint8_t>(d32[1] >> 16);
		digest[di++] = static_cast<uint8_t>(d32[1] >> 8);
		digest[di++] = static_cast<uint8_t>(d32[1] >> 0);

		digest[di++] = static_cast<uint8_t>(d32[2] >> 24);
		digest[di++] = static_cast<uint8_t>(d32[2] >> 16);
		digest[di++] = static_cast<uint8_t>(d32[2] >> 8);
		digest[di++] = static_cast<uint8_t>(d32[2] >> 0);

		digest[di++] = static_cast<uint8_t>(d32[3] >> 24);
		digest[di++] = static_cast<uint8_t>(d32[3] >> 16);
		digest[di++] = static_cast<uint8_t>(d32[3] >> 8);
		digest[di++] = static_cast<uint8_t>(d32[3] >> 0);

		digest[di++] = static_cast<uint8_t>(d32[4] >> 24);
		digest[di++] = static_cast<uint8_t>(d32[4] >> 16);
		digest[di++] = static_cast<uint8_t>(d32[4] >> 8);
		digest[di++] = static_cast<uint8_t>(d32[4] >> 0);

		return digest;
	}

private:
	void process_block() 
	{
		uint32_t w[80];
		for (size_t i = 0; i < 16; i++) {
			w[i] = static_cast<uint32_t>(m_block[i * 4 + 0] << 24);
			w[i] |= static_cast<uint32_t>(m_block[i * 4 + 1] << 16);
			w[i] |= static_cast<uint32_t>(m_block[i * 4 + 2] << 8);
			w[i] |= static_cast<uint32_t>(m_block[i * 4 + 3]);
		}
		for (size_t i = 16; i < 80; i++) {
			w[i] = left_rotate((w[i - 3] ^ w[i - 8] ^ w[i - 14] ^ w[i - 16]), 1);
		}

		uint32_t a = m_digest[0];
		uint32_t b = m_digest[1];
		uint32_t c = m_digest[2];
		uint32_t d = m_digest[3];
		uint32_t e = m_digest[4];

		for (std::size_t i = 0; i < 80; ++i) {
			uint32_t f = 0;
			uint32_t k = 0;

			if (i < 20) {
				f = (b & c) | (~b & d);
				k = 0x5A827999;
			} else if (i < 40) {
				f = b ^ c ^ d;
				k = 0x6ED9EBA1;
			} else if (i < 60) {
				f = (b & c) | (b & d) | (c & d);
				k = 0x8F1BBCDC;
			} else {
				f = b ^ c ^ d;
				k = 0xCA62C1D6;
			}

			uint32_t temp = left_rotate(a, 5) + f + e + k + w[i];
			e = d;
			d = c;
			c = left_rotate(b, 30);
			b = a;
			a = temp;
		}

		m_digest[0] += a;
		m_digest[1] += b;
		m_digest[2] += c;
		m_digest[3] += d;
		m_digest[4] += e;
	}

	digest32_t m_digest;
	uint8_t m_block[64];
	size_t m_blockByteIndex;
	size_t m_byteCount;
};

template <typename CharT>
inline constexpr CharT empty_guid[37] = "00000000-0000-0000-0000-000000000000";

template <>
inline constexpr wchar_t empty_guid<wchar_t>[37] = L"00000000-0000-0000-0000-000000000000";

template <typename CharT>
inline constexpr CharT guid_encoder[17] = "0123456789abcdef";

template <>
inline constexpr wchar_t guid_encoder<wchar_t>[17] = L"0123456789abcdef";

// --------------------------------------------------------------------------------------------------------------------------
// UUID format https://tools.ietf.org/html/rfc4122
// --------------------------------------------------------------------------------------------------------------------------

// --------------------------------------------------------------------------------------------------------------------------
// Field                         NDR Data Type     Octet #   Note
// --------------------------------------------------------------------------------------------------------------------------
// time_low                      unsigned long     0 - 3     The low field of the timestamp.
// time_mid                      unsigned short    4 - 5     The middle field of the timestamp.
// time_hi_and_version           unsigned short    6 - 7     The high field of the timestamp multiplexed with the version number.
// clock_seq_hi_and_reserved     unsigned small    8         The high field of the clock sequence multiplexed with the variant.
// clock_seq_low                 unsigned small    9         The low field of the clock sequence.
// node                          character         10 - 15   The spatially unique node identifier.
// --------------------------------------------------------------------------------------------------------------------------
// 0                   1                   2                   3
//  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// |                          time_low                             |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// |       time_mid                |         time_hi_and_version   |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// |clk_seq_hi_res |  clk_seq_low  |         node (0-1)            |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// |                         node (2-5)                            |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

// --------------------------------------------------------------------------------------------------------------------------
// enumerations
// --------------------------------------------------------------------------------------------------------------------------

// indicated by a bit pattern in octet 8, marked with N in xxxxxxxx-xxxx-xxxx-Nxxx-xxxxxxxxxxxx
export enum struct uuid_variant {
	// NCS backward compatibility (with the obsolete Apollo Network Computing System 1.5 UUID format)
	// N bit pattern: 0xxx
	// > the first 6 octets of the UUID are a 48-bit timestamp (the number of 4 microsecond units of time since 1 Jan 1980 UTC);
	// > the next 2 octets are reserved;
	// > the next octet is the "address family"; 
	// > the final 7 octets are a 56-bit host ID in the form specified by the address family
	ncs,

	// RFC 4122/DCE 1.1 
	// N bit pattern: 10xx
	// > big-endian byte order
	rfc,

	// Microsoft Corporation backward compatibility
	// N bit pattern: 110x
	// > little endian byte order
	// > formely used in the Component Object Model (COM) library      
	microsoft,

	// reserved for possible future definition
	// N bit pattern: 111x      
	reserved
};

// indicated by a bit pattern in octet 6, marked with M in xxxxxxxx-xxxx-Mxxx-xxxx-xxxxxxxxxxxx   
export enum struct uuid_version {
	none = 0, // only possible for nil or invalid uuids
	time_based = 1,  // The time-based version specified in RFC 4122
	dce_security = 2,  // DCE Security version, with embedded POSIX UIDs.
	name_based_md5 = 3,  // The name-based version specified in RFS 4122 with MD5 hashing
	random_number_based = 4,  // The randomly or pseudo-randomly generated version specified in RFS 4122
	name_based_sha1 = 5   // The name-based version specified in RFS 4122 with SHA1 hashing
};

// Forward declare uuid & to_string so that we can declare to_string as a friend later.
export struct uuid;
export template <typename CharT = char,
	  typename Traits = std::char_traits<CharT>,
	  typename Allocator = std::allocator<CharT>>
std::basic_string<CharT, Traits, Allocator> to_string(uuid const &id);

// --------------------------------------------------------------------------------------------------------------------------
// uuid class
// --------------------------------------------------------------------------------------------------------------------------
export struct uuid {
	using value_type = uint8_t;

	constexpr uuid() noexcept = default;

	uuid(value_type(&arr)[16]) noexcept
	{
		std::ranges::copy(arr, std::ranges::begin(data));
	}

	constexpr uuid(std::array<value_type, 16> const & arr) noexcept
		: data{arr}
	{
	}

	explicit uuid(std::span<value_type, 16> bytes)
	{
		std::ranges::copy(bytes, std::ranges::begin(data));
	}

	template<typename ForwardIterator>
	explicit uuid(ForwardIterator first, ForwardIterator last)
	{
		if (std::distance(first, last) == 16)
			std::copy(first, last, std::begin(data));
	}

	[[nodiscard]] constexpr uuid_variant variant() const noexcept
	{
		if ((data[8] & 0x80) == 0x00)
			return uuid_variant::ncs;
		else if ((data[8] & 0xC0) == 0x80)
			return uuid_variant::rfc;
		else if ((data[8] & 0xE0) == 0xC0)
			return uuid_variant::microsoft;
		else
			return uuid_variant::reserved;
	}

	[[nodiscard]] constexpr uuid_version version() const noexcept
	{
		if ((data[6] & 0xF0) == 0x10)
			return uuid_version::time_based;
		else if ((data[6] & 0xF0) == 0x20)
			return uuid_version::dce_security;
		else if ((data[6] & 0xF0) == 0x30)
			return uuid_version::name_based_md5;
		else if ((data[6] & 0xF0) == 0x40)
			return uuid_version::random_number_based;
		else if ((data[6] & 0xF0) == 0x50)
			return uuid_version::name_based_sha1;
		else
			return uuid_version::none;
	}

	[[nodiscard]] constexpr bool is_nil() const noexcept
	{
		for (size_t i = 0; i < data.size(); ++i)
			if (data[i] != 0)
				return false;
		return true;
	}

	void swap(uuid &other) noexcept
	{
		data.swap(other.data);
	}

	[[nodiscard]] inline std::span<std::byte const, 16> as_bytes() const
	{
		return std::span<std::byte const, 16>(reinterpret_cast<std::byte const*>(data.data()), 16);
	}

	template <typename StringType>
	[[nodiscard]] constexpr static bool is_valid_uuid(StringType const & in_str) noexcept
	{
		auto str = to_string_view(in_str);
		bool firstDigit = true;
		size_t hasBraces = 0;
		size_t index = 0;

		if (str.empty())
			return false;

		if (str.front() == '{')
			hasBraces = 1;
		if (hasBraces && str.back() != '}')
			return false;

		for (size_t i = hasBraces; i < str.size() - hasBraces; ++i) {
			if (str[i] == '-')
				continue;

			if (index >= 16 || !is_hex(str[i]))
				return false;

			if (firstDigit) {
				firstDigit = false;
			} else {
				index++;
				firstDigit = true;
			}
		}

		if (index < 16)
			return false;

		return true;
	}

	template <typename StringType>
	[[nodiscard]] constexpr static std::optional<uuid> from_string(StringType const & in_str) noexcept
	{
		auto str = to_string_view(in_str);
		bool firstDigit = true;
		size_t hasBraces = 0;
		size_t index = 0;

		std::array<uint8_t, 16> data{ { 0 } };

		if (str.empty())
			return {};

		if (str.front() == '{')
			hasBraces = 1;
		if (hasBraces && str.back() != '}')
			return {};

		for (size_t i = hasBraces; i < str.size() - hasBraces; ++i) {
			if (str[i] == '-')
				continue;

			if (index >= 16 || !is_hex(str[i])) {
				return {};
			}

			if (firstDigit) {
				data[index] = static_cast<uint8_t>(hex2char(str[i]) << 4);
				firstDigit = false;
			} else {
				data[index] = static_cast<uint8_t>(data[index] | hex2char(str[i]));
				index++;
				firstDigit = true;
			}
		}

		if (index < 16) {
			return {};
		}

		return uuid{data};
	}

private:
	std::array<value_type, 16> data{ { 0 } };

	friend bool operator==(uuid const & lhs, uuid const & rhs) noexcept;
	friend bool operator<(uuid const & lhs, uuid const & rhs) noexcept;

	template <class Elem, class Traits>
	friend std::basic_ostream<Elem, Traits> & operator<<(std::basic_ostream<Elem, Traits> &s, uuid const & id);

	template<class CharT, class Traits, class Allocator>
	friend std::basic_string<CharT, Traits, Allocator> to_string(uuid const& id);

	friend std::hash<uuid>;
};

// --------------------------------------------------------------------------------------------------------------------------
// operators and non-member functions
// --------------------------------------------------------------------------------------------------------------------------

export [[nodiscard]]
auto operator== (uuid const& lhs, uuid const& rhs) noexcept -> bool
{
	return lhs.data == rhs.data;
}

export [[nodiscard]] 
auto operator!= (uuid const& lhs, uuid const& rhs) noexcept -> bool
{
	return !(lhs == rhs);
}

export [[nodiscard]]
auto operator< (uuid const& lhs, uuid const& rhs) noexcept -> bool
{
	return lhs.data < rhs.data;
}

export template <typename CharT, typename Traits, typename Allocator>
[[nodiscard]] auto to_string(uuid const &id)
	-> std::basic_string<CharT, Traits, Allocator>
{
	std::basic_string<CharT, Traits, Allocator> uustr{empty_guid<CharT>};

	for (size_t i = 0, index = 0; i < 36; ++i) {
		if (i == 8 || i == 13 || i == 18 || i == 23)
			continue;

		uustr[i] = guid_encoder<CharT>[id.data[index] >> 4 & 0x0f];
		uustr[++i] = guid_encoder<CharT>[id.data[index] & 0x0f];
		index++;
	}

	return uustr;
}

export template <class Elem, class Traits>
auto operator<<(std::basic_ostream<Elem, Traits>& s, uuid const &id)
	-> std::basic_ostream<Elem, Traits>&
{
	s << to_string(id);
	return s;
}

export void swap(uuid & lhs, uuid & rhs) noexcept
{
	lhs.swap(rhs);   
}

/***********************************************************************
 * namespace IDs that could be used for generating name-based uuids
 */

// Name string is a fully-qualified domain name
export uuid uuid_namespace_dns{{
	0x6b, 0xa7, 0xb8, 0x10, 0x9d, 0xad, 0x11, 0xd1,
	0x80, 0xb4, 0x00, 0xc0, 0x4f, 0xd4, 0x30, 0xc8
}};

// Name string is a URL
export uuid uuid_namespace_url{{
	0x6b, 0xa7, 0xb8, 0x11, 0x9d, 0xad, 0x11, 0xd1,
	0x80, 0xb4, 0x00, 0xc0, 0x4f, 0xd4, 0x30, 0xc8
}};

// Name string is an ISO OID (See https://oidref.com/,
// https://en.wikipedia.org/wiki/Object_identifier)
export uuid uuid_namespace_oid{{
	0x6b, 0xa7, 0xb8, 0x12, 0x9d, 0xad, 0x11, 0xd1,
	0x80, 0xb4, 0x00, 0xc0, 0x4f, 0xd4, 0x30, 0xc8
}};

// Name string is an X.500 DN, in DER or a text output format (See
// https://en.wikipedia.org/wiki/X.500,
// https://en.wikipedia.org/wiki/Abstract_Syntax_Notation_One)
export uuid uuid_namespace_x500{{
	0x6b, 0xa7, 0xb8, 0x14, 0x9d, 0xad, 0x11, 0xd1,
	0x80, 0xb4, 0x00, 0xc0, 0x4f, 0xd4, 0x30, 0xc8
}};

/***********************************************************************
 * uuid generators
 */

export template <typename UniformRandomNumberGenerator>
struct basic_uuid_random_generator
{
	using engine_type = UniformRandomNumberGenerator;

	explicit basic_uuid_random_generator(engine_type& gen)
		: generator(&gen, [](auto) {})
	{
	}

	explicit basic_uuid_random_generator(engine_type* gen)
		: generator(gen, [](auto) {})
	{
	}

	[[nodiscard]] uuid operator()()
	{
		alignas(uint32_t) uint8_t bytes[16];
		for (int i = 0; i < 16; i += 4)
			*reinterpret_cast<uint32_t*>(bytes + i) = distribution(*generator);

		// variant must be 10xxxxxx
		bytes[8] &= 0xBF;
		bytes[8] |= 0x80;

		// version must be 0100xxxx
		bytes[6] &= 0x4F;
		bytes[6] |= 0x40;

		return uuid{std::begin(bytes), std::end(bytes)};
	}

private:
	std::uniform_int_distribution<uint32_t>  distribution;
	std::shared_ptr<UniformRandomNumberGenerator> generator;
};

export using uuid_random_generator = basic_uuid_random_generator<std::mt19937>;

export struct uuid_name_generator
{
	explicit uuid_name_generator(uuid const& namespace_uuid) noexcept
		: nsuuid(namespace_uuid)
	{
	}

	template <typename StringType>
	[[nodiscard]] uuid operator()(StringType const & name)
	{
		reset();
		process_characters(to_string_view(name));
		return make_uuid();
	}

private:
	void reset() 
	{
		hasher.reset();
		std::byte bytes[16];
		auto nsbytes = nsuuid.as_bytes();
		std::ranges::copy(nsbytes, bytes);
		hasher.process_bytes(bytes, 16);
	}

	template <typename CharT, typename Traits>
	void process_characters(std::basic_string_view<CharT, Traits> const str)
	{
		for (uint32_t c : str) {
			hasher.process_byte(static_cast<uint8_t>(c & 0xFF));
			if constexpr (!std::is_same_v<CharT, char>) {
				hasher.process_byte(static_cast<uint8_t>((c >> 8) & 0xFF));
				hasher.process_byte(static_cast<uint8_t>((c >> 16) & 0xFF));
				hasher.process_byte(static_cast<uint8_t>((c >> 24) & 0xFF));
			}
		}
	}

	[[nodiscard]] uuid make_uuid()
	{
		sha1::digest8_t digest;
		hasher.get_digest_bytes(digest);

		// variant must be 0b10xxxxxx
		digest[8] &= 0xBF;
		digest[8] |= 0x80;

		// version must be 0b0101xxxx
		digest[6] &= 0x5F;
		digest[6] |= 0x50;

		return uuid{ digest, digest + 16 };
	}

private:
	uuid nsuuid;
	sha1 hasher;
};

/*
 * Create a random UUID.
 */
export auto random_uuid() -> uuid
{
	auto rd = std::random_device();
	auto seed_data = std::array<int, std::mt19937::state_size> {};

	std::ranges::generate(seed_data, std::ref(rd));
	auto seq = std::seed_seq(std::begin(seed_data), std::end(seed_data));
	auto generator = std::mt19937(seq);
	auto gen = uuid_random_generator{generator};

	return gen();	
}

} // namespace nihil

namespace std {

export template <>
struct hash<nihil::uuid>
{
	using argument_type = nihil::uuid;
	using result_type   = std::size_t;

	[[nodiscard]] result_type operator()(argument_type const &uuid) const
	{
		uint64_t l =
			static_cast<uint64_t>(uuid.data[0]) << 56 |
			static_cast<uint64_t>(uuid.data[1]) << 48 |
			static_cast<uint64_t>(uuid.data[2]) << 40 |
			static_cast<uint64_t>(uuid.data[3]) << 32 |
			static_cast<uint64_t>(uuid.data[4]) << 24 |
			static_cast<uint64_t>(uuid.data[5]) << 16 |
			static_cast<uint64_t>(uuid.data[6]) <<  8 |
			static_cast<uint64_t>(uuid.data[7]);
		uint64_t h =
			static_cast<uint64_t>(uuid.data[8])  << 56 |
			static_cast<uint64_t>(uuid.data[9])  << 48 |
			static_cast<uint64_t>(uuid.data[10]) << 40 |
			static_cast<uint64_t>(uuid.data[11]) << 32 |
			static_cast<uint64_t>(uuid.data[12]) << 24 |
			static_cast<uint64_t>(uuid.data[13]) << 16 |
			static_cast<uint64_t>(uuid.data[14]) <<  8 |
			static_cast<uint64_t>(uuid.data[15]);

		if constexpr (sizeof(result_type) > 4) {
			return result_type(l ^ h);
		} else {
			uint64_t hash64 = l ^ h;
			return result_type(uint32_t(hash64 >> 32) ^ uint32_t(hash64));
		}
	}
};

} // namespace std