#pragma once

#include <util/generic/string.h>
#include <util/generic/typetraits.h>

#include <array>

namespace NYT {

////////////////////////////////////////////////////////////////////////////////

//! TGuid is 16-byte value that might be interpreted as four little-endian 32-bit integers or two 64-bit little-endian integers.
/*!
 *    *-------------------------*-------------------------*
 *    |       Parts64[0]        |       Parts64[1]        |
 *    *------------*------------*------------*------------*
 *    | Parts32[0] | Parts32[1] | Parts32[2] | Parts32[3] |
 *    *------------*------------*------------*------------*
 *    | 15..............................................0 |
 *    *---------------------------------------------------*
 *
 *  Note, that bytes are kept in memory in reverse order.
 *
 *  Canonical text representation of guid consists of four base-16 numbers.
 *  In text form, Parts32[3] comes first, and Parts32[0] comes last.
 *
 *  For example:
 *
 *    xxyyzzaa-0-1234-ff
 *
 *      xx is byte [0]
 *      yy is byte [1]
 *      zz is byte [2]
 *      12 is byte [8]
 *      34 is byte [9]
 *      ff is byte [15]
 */
struct TGuid
{
    union
    {
        ui32 Parts32[4];
        ui64 Parts64[2];
        ui8 ReversedParts8[16];
    };

    //! Constructs a null (zero) guid.
    constexpr TGuid();

    //! Constructs guid from parts.
    constexpr TGuid(ui32 part0, ui32 part1, ui32 part2, ui32 part3);

    //! Constructs guid from parts.
    constexpr TGuid(ui64 part0, ui64 part1);

    //! Copies an existing guid.
    constexpr TGuid(const TGuid& other) noexcept = default;
    constexpr TGuid& operator=(const TGuid& other) noexcept = default;

    //! Checks if TGuid is zero.
    bool IsEmpty() const;

    //! Converts TGuid to bool, returns |false| iff TGuid is zero.
    explicit operator bool() const;

    //! Creates a new instance.
    static TGuid Create();

    //! Parses guid from TStringBuf, throws an exception if something went wrong.
    static TGuid FromString(TStringBuf str);

    //! Parses guid from TStringBuf, returns |true| if everything was ok.
    static bool FromString(TStringBuf str, TGuid* guid);

    //! Same as FromString, but expects exactly 32 hex digits without dashes.
    static TGuid FromStringHex32(TStringBuf str);

    //! Same as TryFromString, but expects exactly 32 hex digits without dashes.
    static bool FromStringHex32(TStringBuf str, TGuid* guid);
};

bool operator == (TGuid lhs, TGuid rhs) noexcept;
std::strong_ordering operator <=> (TGuid lhs, TGuid rhs) noexcept;

////////////////////////////////////////////////////////////////////////////////

constexpr int MaxGuidStringSize = 4 * 8 + 3;
char* WriteGuidToBuffer(char* ptr, TGuid value);

////////////////////////////////////////////////////////////////////////////////

//! Enables TGuid-to-TStringBuf conversion without allocation.
class TFormattableGuid
{
public:
    explicit TFormattableGuid(TGuid guid);
    TStringBuf ToStringBuf() const;

private:
    std::array<char, MaxGuidStringSize> Buffer_;
    const char* const End_;
};

////////////////////////////////////////////////////////////////////////////////

} // namespace NYT

////////////////////////////////////////////////////////////////////////////////

Y_DECLARE_PODTYPE(NYT::TGuid);

//! A hasher for TGuid.
template <>
struct THash<NYT::TGuid>
{
    size_t operator()(const NYT::TGuid& guid) const;
};

////////////////////////////////////////////////////////////////////////////////

#define GUID_INL_H_
#include "guid-inl.h"
#undef GUID_INL_H_