#ifndef FORMAT_INL_H_
#error "Direct inclusion of this file is not allowed, include format.h"
// For the sake of sane code completion.
#include "format.h"
#endif

#include "guid.h"
#include "enum.h"
#include "string.h"

#include <library/cpp/yt/assert/assert.h>

#include <library/cpp/yt/compact_containers/compact_vector.h>

#include <library/cpp/yt/containers/enum_indexed_array.h>

#include <library/cpp/yt/misc/concepts.h>
#include <library/cpp/yt/misc/enum.h>
#include <library/cpp/yt/misc/source_location.h>

#include <util/generic/maybe.h>

#include <util/system/platform.h>

#include <cctype>
#include <optional>
#include <span>

#if __cplusplus >= 202302L
    #include <filesystem>
#endif

#ifdef __cpp_lib_source_location
#include <source_location>
#endif // __cpp_lib_source_location

namespace NYT {

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

inline void FormatValue(TStringBuilderBase* builder, const TStringBuilder& value, TStringBuf /*spec*/)
{
    builder->AppendString(value.GetBuffer());
}

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

template <class T>
TString ToStringViaBuilder(const T& value, TStringBuf spec)
{
    TStringBuilder builder;
    FormatValue(&builder, value, spec);
    return builder.Flush();
}

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

// Compatibility for users of NYT::ToString(nyt_type).
template <CFormattable T>
TString ToString(const T& t)
{
    return ToStringViaBuilder(t);
}

// Sometime we want to implement
// FormatValue using util's ToString
// However, if we inside the FormatValue
// we cannot just call the ToString since
// in this scope T is already CFormattable
// and ToString will call the very
// FormatValue we are implementing,
// causing an infinite recursion loop.
// This method is basically a call to
// util's ToString default implementation.
template <class T>
TString ToStringIgnoringFormatValue(const T& t)
{
    TString s;
    ::TStringOutput o(s);
    o << t;
    return s;
}

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

// Helper functions for formatting.
namespace NDetail {

constexpr inline char IntroductorySymbol = '%';
constexpr inline char GenericSpecSymbol = 'v';

inline bool IsQuotationSpecSymbol(char symbol)
{
    return symbol == 'Q' || symbol == 'q';
}

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

template <class TValue>
void FormatValueViaSprintf(
    TStringBuilderBase* builder,
    TValue value,
    TStringBuf spec,
    TStringBuf genericSpec);

template <class TValue>
void FormatIntValue(
    TStringBuilderBase* builder,
    TValue value,
    TStringBuf spec,
    TStringBuf genericSpec);

void FormatPointerValue(
    TStringBuilderBase* builder,
    const void* value,
    TStringBuf spec);

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

// Helper concepts for matching the correct overload.
// NB(arkady-e1ppa): We prefer to hardcode the known types
// so that someone doesn't accidentally implement the
// "SimpleRange" concept and have a non-trivial
// formatting procedure at the same time.
// Sadly, clang is bugged and thus we must do implementation by hand
// if we want to use this concept in class specializations.

template <class R>
constexpr bool CKnownRange = false;

template <class T>
    requires requires (T* t) { [] <class... Ts> (std::vector<Ts...>*) {} (t); }
constexpr bool CKnownRange<T> = true;
template <class T, size_t E>
constexpr bool CKnownRange<std::span<T, E>> = true;
template <class T, size_t N>
constexpr bool CKnownRange<std::array<T, N>> = true;
template <class T, size_t N>
constexpr bool CKnownRange<TCompactVector<T, N>> = true;
template <class T>
    requires requires (T* t) { [] <class... Ts> (std::set<Ts...>*) {} (t); }
constexpr bool CKnownRange<T> = true;
template <class T>
    requires requires (T* t) { [] <class... Ts> (std::multiset<Ts...>*) {} (t); }
constexpr bool CKnownRange<T> = true;
template <class... Ts>
constexpr bool CKnownRange<THashSet<Ts...>> = true;
template <class... Ts>
constexpr bool CKnownRange<THashMultiSet<Ts...>> = true;

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

template <class R>
constexpr bool CKnownKVRange = false;

template <class T>
    requires requires (T* t) { [] <class... Ts> (std::map<Ts...>*) {} (t); }
constexpr bool CKnownKVRange<T> = true;
template <class T>
    requires requires (T* t) { [] <class... Ts> (std::multimap<Ts...>*) {} (t); }
constexpr bool CKnownKVRange<T> = true;
template <class... Ts>
constexpr bool CKnownKVRange<THashMap<Ts...>> = true;
template <class... Ts>
constexpr bool CKnownKVRange<THashMultiMap<Ts...>> = true;

// TODO(arkady-e1ppa): Uncomment me when
// https://github.com/llvm/llvm-project/issues/58534 is shipped.
// template <class R>
// concept CKnownRange =
//     requires (R r) { [] <class... Ts> (std::vector<Ts...>) { } (r); } ||
//     requires (R r) { [] <class T, size_t E> (std::span<T, E>) { } (r); } ||
//     requires (R r) { [] <class T, size_t N> (TCompactVector<T, N>) { } (r); } ||
//     requires (R r) { [] <class... Ts> (std::set<Ts...>) { } (r); } ||
//     requires (R r) { [] <class... Ts> (THashSet<Ts...>) { } (r); } ||
//     requires (R r) { [] <class... Ts> (THashMultiSet<Ts...>) { } (r); };

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

// template <class R>
// concept CKnownKVRange =
//     requires (R r) { [] <class... Ts> (std::map<Ts...>) { } (r); } ||
//     requires (R r) { [] <class... Ts> (std::multimap<Ts...>) { } (r); } ||
//     requires (R r) { [] <class... Ts> (THashMap<Ts...>) { } (r); } ||
//     requires (R r) { [] <class... Ts> (THashMultiMap<Ts...>) { } (r); };

} // namespace NDetail

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

template <class TRange, class TFormatter>
void FormatRange(TStringBuilderBase* builder, const TRange& range, const TFormatter& formatter, size_t limit = std::numeric_limits<size_t>::max())
{
    builder->AppendChar('[');
    size_t index = 0;
    for (const auto& item : range) {
        if (index > 0) {
            builder->AppendString(DefaultJoinToStringDelimiter);
        }
        if (index == limit) {
            builder->AppendString(DefaultRangeEllipsisFormat);
            break;
        }
        formatter(builder, item);
        ++index;
    }
    builder->AppendChar(']');
}

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

template <class TRange, class TFormatter>
void FormatKeyValueRange(TStringBuilderBase* builder, const TRange& range, const TFormatter& formatter, size_t limit = std::numeric_limits<size_t>::max())
{
    builder->AppendChar('{');
    size_t index = 0;
    for (const auto& item : range) {
        if (index > 0) {
            builder->AppendString(DefaultJoinToStringDelimiter);
        }
        if (index == limit) {
            builder->AppendString(DefaultRangeEllipsisFormat);
            break;
        }
        formatter(builder, item.first);
        builder->AppendString(DefaultKeyValueDelimiter);
        formatter(builder, item.second);
        ++index;
    }
    builder->AppendChar('}');
}

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

template <class TRange, class TValueGetter, class TIntervalFormatter>
void FormatCompactIntervalRange(
    TStringBuilderBase* builder,
    const TRange& range,
    const TValueGetter& valueGetter,
    const TIntervalFormatter& intervalFormatter)
{
    if (range.begin() == range.end()) {
        builder->AppendString("[]");
        return;
    }

    builder->AppendChar('[');

    auto first = range.begin();
    auto last = first;
    auto current = first + 1;

    while (current != range.end()) {
        if (valueGetter(current) != valueGetter(last) + 1) {
            bool firstInterval = first == range.begin();
            intervalFormatter(builder, first, last, valueGetter, firstInterval);
            first = current;
        }

        last = current;
        ++current;
    }

    bool firstInterval = first == range.begin();
    intervalFormatter(builder, first, last, valueGetter, firstInterval);

    builder->AppendChar(']');
}

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

template <class R>
concept CFormattableRange =
    NDetail::CKnownRange<R> &&
    CFormattable<typename R::value_type>;

template <class R>
concept CFormattableKVRange =
    NDetail::CKnownKVRange<R> &&
    CFormattable<typename R::key_type> &&
    CFormattable<typename R::value_type>;


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

// Specializations of TFormatArg for ranges
template <class R>
    requires CFormattableRange<std::remove_cvref_t<R>>
struct TFormatArg<R>
    : public TFormatArgBase
{
    using TUnderlying = typename std::remove_cvref_t<R>::value_type;

    static constexpr auto ConversionSpecifiers = TFormatArg<TUnderlying>::ConversionSpecifiers;

    static constexpr auto FlagSpecifiers = TFormatArg<TUnderlying>::FlagSpecifiers;
};

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

template <class TRange, class TFormatter>
typename TFormattableView<TRange, TFormatter>::TBegin TFormattableView<TRange, TFormatter>::begin() const
{
    return RangeBegin;
}

template <class TRange, class TFormatter>
typename TFormattableView<TRange, TFormatter>::TEnd TFormattableView<TRange, TFormatter>::end() const
{
    return RangeEnd;
}

template <class TRange, class TFormatter>
TFormattableView<TRange, TFormatter> MakeFormattableView(
    const TRange& range,
    TFormatter&& formatter)
{
    return TFormattableView<TRange, std::decay_t<TFormatter>>{range.begin(), range.end(), std::forward<TFormatter>(formatter)};
}

template <class TRange, class TFormatter>
TFormattableView<TRange, TFormatter> MakeShrunkFormattableView(
    const TRange& range,
    TFormatter&& formatter,
    size_t limit)
{
    return TFormattableView<TRange, std::decay_t<TFormatter>>{
        range.begin(),
        range.end(),
        std::forward<TFormatter>(formatter),
        limit};
}

template <class TFormatter>
TFormatterWrapper<TFormatter> MakeFormatterWrapper(
    TFormatter&& formatter)
{
    return TFormatterWrapper<TFormatter>{
        .Formatter = std::move(formatter)
    };
}

template <class TRange, class TValueGetter, class TIntervalFormatter>
auto TCompactIntervalView<TRange, TValueGetter, TIntervalFormatter>::begin() const
    -> TBegin
{
    return RangeBegin;
}

template <class TRange, class TValueGetter, class TIntervalFormatter>
auto TCompactIntervalView<TRange, TValueGetter, TIntervalFormatter>::end() const
    -> TEnd
{
    return RangeEnd;
}

template <class TRange>
auto TDefaultValueGetter<TRange>::operator()(const TIterator& iterator) const
    -> typename std::iterator_traits<TIterator>::value_type
{
    return *iterator;
}

template <class TRange, class TValueGetter>
void TDefaultIntervalFormatter<TRange, TValueGetter>::operator()(
    TStringBuilderBase* builder,
    const TIterator& first,
    const TIterator& last,
    const TValueGetter& valueGetter,
    bool firstInterval) const
{
    if (!firstInterval) {
        builder->AppendString(DefaultJoinToStringDelimiter);
    }

    if (first == last) {
        builder->AppendFormat("%v", valueGetter(first));
    } else {
        builder->AppendFormat("%v-%v", valueGetter(first), valueGetter(last));
    }
}

template <class TRange, class TValueGetter, class TIntervalFormatter>
TCompactIntervalView<TRange, TValueGetter, TIntervalFormatter> MakeCompactIntervalView(
    const TRange& range,
    TValueGetter&& valueGetter,
    TIntervalFormatter&& intervalFormatter)
{
    return TCompactIntervalView<TRange, TValueGetter, TIntervalFormatter>{
        range.begin(),
        range.end(),
        std::forward<TValueGetter>(valueGetter),
        std::forward<TIntervalFormatter>(intervalFormatter)};
}

template <class... TArgs>
TLazyMultiValueFormatter<TArgs...>::TLazyMultiValueFormatter(
    TStringBuf format,
    TArgs&&... args)
    : Format_(format)
    , Args_(std::forward<TArgs>(args)...)
{ }

template <class... TArgs>
auto MakeLazyMultiValueFormatter(TStringBuf format, TArgs&&... args)
{
    return TLazyMultiValueFormatter<TArgs...>(format, std::forward<TArgs>(args)...);
}

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

// Non-container objects.

#define XX(valueType, castType, genericSpec) \
    inline void FormatValue(TStringBuilderBase* builder, valueType value, TStringBuf spec) \
    { \
        NYT::NDetail::FormatIntValue(builder, static_cast<castType>(value), spec, genericSpec); \
    }

XX(i8,                  i32,      TStringBuf("d"))
XX(ui8,                 ui32,     TStringBuf("u"))
XX(i16,                 i32,      TStringBuf("d"))
XX(ui16,                ui32,     TStringBuf("u"))
XX(i32,                 i32,      TStringBuf("d"))
XX(ui32,                ui32,     TStringBuf("u"))
XX(long,                i64,      TStringBuf(PRIdLEAST64))
XX(long long,           i64,      TStringBuf(PRIdLEAST64))
XX(unsigned long,       ui64,     TStringBuf(PRIuLEAST64))
XX(unsigned long long,  ui64,     TStringBuf(PRIuLEAST64))

#undef XX

#define XX(valueType, castType, genericSpec) \
    inline void FormatValue(TStringBuilderBase* builder, valueType value, TStringBuf spec) \
    { \
        NYT::NDetail::FormatValueViaSprintf(builder, static_cast<castType>(value), spec, genericSpec); \
    }

XX(double,              double,   TStringBuf("lf"))
XX(float,               float,    TStringBuf("f"))

#undef XX

// Pointer
template <class T>
void FormatValue(TStringBuilderBase* builder, T* value, TStringBuf spec)
{
    NYT::NDetail::FormatPointerValue(builder, static_cast<const void*>(value), spec);
}

// TStringBuf
inline void FormatValue(TStringBuilderBase* builder, TStringBuf value, TStringBuf spec)
{
    if (!spec) {
        builder->AppendString(value);
        return;
    }

    // Parse alignment.
    bool alignLeft = false;
    const char* current = spec.begin();
    if (*current == '-') {
        alignLeft = true;
        ++current;
    }

    bool hasAlign = false;
    int alignSize = 0;
    while (*current >= '0' && *current <= '9') {
        hasAlign = true;
        alignSize = 10 * alignSize + (*current - '0');
        if (alignSize > 1000000) {
            builder->AppendString(TStringBuf("<alignment overflow>"));
            return;
        }
        ++current;
    }

    int padding = 0;
    bool padLeft = false;
    bool padRight = false;
    if (hasAlign) {
        padding = alignSize - value.size();
        if (padding < 0) {
            padding = 0;
        }
        padLeft = !alignLeft;
        padRight = alignLeft;
    }

    bool singleQuotes = false;
    bool doubleQuotes = false;
    bool escape = false;
    while (current < spec.end()) {
        switch (*current++) {
            case 'q':
                singleQuotes = true;
                break;
            case 'Q':
                doubleQuotes = true;
                break;
            case 'h':
                escape =  true;
                break;
        }
    }

    if (padLeft) {
        builder->AppendChar(' ', padding);
    }

    if (singleQuotes || doubleQuotes || escape) {
        for (const char* valueCurrent = value.begin(); valueCurrent < value.end(); ++valueCurrent) {
            char ch = *valueCurrent;
            if (ch == '\n') {
                builder->AppendString("\\n");
            } else if (ch == '\t') {
                builder->AppendString("\\t");
            } else if (ch == '\\') {
                builder->AppendString("\\\\");
            } else if (ch < PrintableASCIILow || ch > PrintableASCIIHigh) {
                builder->AppendString("\\x");
                builder->AppendChar(IntToHexLowercase[static_cast<ui8>(ch) >> 4]);
                builder->AppendChar(IntToHexLowercase[static_cast<ui8>(ch) & 0xf]);
            } else if ((singleQuotes && ch == '\'') || (doubleQuotes && ch == '\"')) {
                builder->AppendChar('\\');
                builder->AppendChar(ch);
            } else {
                builder->AppendChar(ch);
            }
        }
    } else {
        builder->AppendString(value);
    }

    if (padRight) {
        builder->AppendChar(' ', padding);
    }
}

// TString
inline void FormatValue(TStringBuilderBase* builder, const TString& value, TStringBuf spec)
{
    FormatValue(builder, TStringBuf(value), spec);
}

// const char*
inline void FormatValue(TStringBuilderBase* builder, const char* value, TStringBuf spec)
{
    FormatValue(builder, TStringBuf(value), spec);
}

template <size_t N>
inline void FormatValue(TStringBuilderBase* builder, const char (&value)[N], TStringBuf spec)
{
    FormatValue(builder, TStringBuf(value), spec);
}

// char*
inline void FormatValue(TStringBuilderBase* builder, char* value, TStringBuf spec)
{
    FormatValue(builder, TStringBuf(value), spec);
}

// std::string
inline void FormatValue(TStringBuilderBase* builder, const std::string& value, TStringBuf spec)
{
    FormatValue(builder, TStringBuf(value), spec);
}

// std::string_view
inline void FormatValue(TStringBuilderBase* builder, const std::string_view& value, TStringBuf spec)
{
    FormatValue(builder, TStringBuf(value), spec);
}

#if __cplusplus >= 202302L
// std::filesystem::path
inline void FormatValue(TStringBuilderBase* builder, const std::filesystem::path& value, TStringBuf spec)
{
    FormatValue(builder, std::string(value), spec);
}
#endif

#ifdef __cpp_lib_source_location
// std::source_location
inline void FormatValue(TStringBuilderBase* builder, const std::source_location& location, TStringBuf /*spec*/)
{
    if (location.file_name() != nullptr) {
        builder->AppendFormat(
            "%v:%v:%v",
            location.file_name(),
            location.line(),
            location.column());
    } else {
        builder->AppendString("<unknown>");
    }
}
#endif // __cpp_lib_source_location

// TSourceLocation
inline void FormatValue(TStringBuilderBase* builder, const TSourceLocation& location, TStringBuf /*spec*/)
{
    if (location.GetFileName() != nullptr) {
        builder->AppendFormat(
            "%v:%v",
            location.GetFileName(),
            location.GetLine());
    } else {
        builder->AppendString("<unknown>");
    }
}

// std::monostate
inline void FormatValue(TStringBuilderBase* builder, const std::monostate&, TStringBuf /*spec*/)
{
    builder->AppendString(TStringBuf("<monostate>"));
}

// std::variant
template <class... Ts>
    requires (CFormattable<Ts> && ...)
void FormatValue(TStringBuilderBase* builder, const std::variant<Ts...>& variant, TStringBuf spec)
{
    [&] <size_t... Ids> (std::index_sequence<Ids...>) {
        ([&] {
            if (variant.index() == Ids) {
                FormatValue(builder, std::get<Ids>(variant), spec);
                return false;
            }

            return true;
        } () && ...);
    } (std::index_sequence_for<Ts...>());
}

// char
inline void FormatValue(TStringBuilderBase* builder, char value, TStringBuf spec)
{
    FormatValue(builder, TStringBuf(&value, 1), spec);
}

// bool
inline void FormatValue(TStringBuilderBase* builder, bool value, TStringBuf spec)
{
    // Parse custom flags.
    bool lowercase = false;
    const char* current = spec.begin();
    while (current != spec.end()) {
        if (*current == 'l') {
            ++current;
            lowercase = true;
        } else if (NYT::NDetail::IsQuotationSpecSymbol(*current)) {
            ++current;
        } else
            break;
    }

    auto str = lowercase
        ? (value ? TStringBuf("true") : TStringBuf("false"))
        : (value ? TStringBuf("True") : TStringBuf("False"));

    builder->AppendString(str);
}

// TDuration
inline void FormatValue(TStringBuilderBase* builder, TDuration value, TStringBuf /*spec*/)
{
    builder->AppendFormat("%vus", value.MicroSeconds());
}

// TInstant
inline void FormatValue(TStringBuilderBase* builder, TInstant value, TStringBuf spec)
{
    // TODO(babenko): Optimize.
    FormatValue(builder, NYT::ToStringIgnoringFormatValue(value), spec);
}

// Enum
template <class TEnum>
    requires (TEnumTraits<TEnum>::IsEnum)
void FormatValue(TStringBuilderBase* builder, TEnum value, TStringBuf spec)
{
    // Parse custom flags.
    bool lowercase = false;
    const char* current = spec.begin();
    while (current != spec.end()) {
        if (*current == 'l') {
            ++current;
            lowercase = true;
        } else if (NYT::NDetail::IsQuotationSpecSymbol(*current)) {
            ++current;
        } else {
            break;
        }
    }

    FormatEnum(builder, value, lowercase);
}

template <class TArcadiaEnum>
    requires (std::is_enum_v<TArcadiaEnum> && !TEnumTraits<TArcadiaEnum>::IsEnum)
void FormatValue(TStringBuilderBase* builder, TArcadiaEnum value, TStringBuf /*spec*/)
{
    // NB(arkady-e1ppa): This can catch normal enums which
    // just want to be serialized as numbers.
    // Unfortunately, we have no way of determining that other than
    // marking every relevant arcadia enum in the code by trait
    // or writing their complete trait and placing such trait in
    // every single file where it is formatted.
    // We gotta figure something out but until that
    // we will just have to make a string for such enums.
    // If only arcadia enums provided compile-time check
    // if enum is serializable :(((((.
    builder->AppendString(NYT::ToStringIgnoringFormatValue(value));
}

// Container objects.
// NB(arkady-e1ppa): In order to support container combinations
// we forward-declare them before defining.

// TMaybe
template <class T, class TPolicy>
void FormatValue(TStringBuilderBase* builder, const TMaybe<T, TPolicy>& value, TStringBuf spec);

// std::optional
template <CFormattable T>
void FormatValue(TStringBuilderBase* builder, const std::optional<T>& value, TStringBuf spec);

// std::pair
template <CFormattable A, CFormattable B>
void FormatValue(TStringBuilderBase* builder, const std::pair<A, B>& value, TStringBuf spec);

// std::tuple
template <CFormattable... Ts>
void FormatValue(TStringBuilderBase* builder, const std::tuple<Ts...>& value, TStringBuf spec);

// TEnumIndexedArray
template <class E, CFormattable T>
void FormatValue(TStringBuilderBase* builder, const TEnumIndexedArray<E, T>& collection, TStringBuf spec);

// One-valued ranges
template <CFormattableRange TRange>
void FormatValue(TStringBuilderBase* builder, const TRange& collection, TStringBuf spec);

// Two-valued ranges
template <CFormattableKVRange TRange>
void FormatValue(TStringBuilderBase* builder, const TRange& collection, TStringBuf spec);

// FormattableView
template <class TRange, class TFormatter>
void FormatValue(
    TStringBuilderBase* builder,
    const TFormattableView<TRange, TFormatter>& formattableView,
    TStringBuf spec);

// TFormatterWrapper
template <class TFormatter>
void FormatValue(
    TStringBuilderBase* builder,
    const TFormatterWrapper<TFormatter>& wrapper,
    TStringBuf spec);

// TCompactIntervalView

template <class TRange, class TValueGetter, class TIntervalFormatter>
concept CCompactIntervalView = requires (
    TRange range,
    TValueGetter valueGetter,
    TIntervalFormatter intervalFormatter)
{
    { valueGetter(range.begin()) } -> std::integral;
    {
        intervalFormatter(nullptr, range.begin(), range.begin(), valueGetter, true)
    } -> std::same_as<void>;
};

template <class TRange, class TValueGetter, class TIntervalFormatter>
    requires CCompactIntervalView<TRange, TValueGetter, TIntervalFormatter>
void FormatValue(
    TStringBuilderBase* builder,
    const TCompactIntervalView<TRange, TValueGetter, TIntervalFormatter>& compactIntervalView,
    TStringBuf spec);

// TLazyMultiValueFormatter
template <class... TArgs>
void FormatValue(
    TStringBuilderBase* builder,
    const TLazyMultiValueFormatter<TArgs...>& value,
    TStringBuf /*spec*/);

// TMaybe
template <class T, class TPolicy>
void FormatValue(TStringBuilderBase* builder, const TMaybe<T, TPolicy>& value, TStringBuf spec)
{
    FormatValue(builder, NYT::ToStringIgnoringFormatValue(value), spec);
}

// std::optional: nullopt
inline void FormatValue(TStringBuilderBase* builder, std::nullopt_t, TStringBuf /*spec*/)
{
    builder->AppendString(TStringBuf("<null>"));
}

// std::optional: generic T
template <CFormattable T>
void FormatValue(TStringBuilderBase* builder, const std::optional<T>& value, TStringBuf spec)
{
    if (value.has_value()) {
        FormatValue(builder, *value, spec);
    } else {
        FormatValue(builder, std::nullopt, spec);
    }
}

// std::pair
template <CFormattable A, CFormattable B>
void FormatValue(TStringBuilderBase* builder, const std::pair<A, B>& value, TStringBuf spec)
{
    builder->AppendChar('{');
    FormatValue(builder, value.first, spec);
    builder->AppendString(TStringBuf(", "));
    FormatValue(builder, value.second, spec);
    builder->AppendChar('}');
}

// std::tuple
template <CFormattable... Ts>
void FormatValue(TStringBuilderBase* builder, const std::tuple<Ts...>& value, TStringBuf spec)
{
    builder->AppendChar('{');

    [&] <size_t... Idx> (std::index_sequence<Idx...>) {
        ([&] {
            FormatValue(builder, std::get<Idx>(value), spec);
            if constexpr (Idx != sizeof...(Ts) - 1) {
                builder->AppendString(TStringBuf(", "));
            }
        } (), ...);
    } (std::index_sequence_for<Ts...>());

    builder->AppendChar('}');
}

// TEnumIndexedArray
template <class E, CFormattable T>
void FormatValue(TStringBuilderBase* builder, const TEnumIndexedArray<E, T>& collection, TStringBuf spec)
{
    builder->AppendChar('{');
    bool firstItem = true;
    for (const auto& index : TEnumTraits<E>::GetDomainValues()) {
        if (!firstItem) {
            builder->AppendString(DefaultJoinToStringDelimiter);
        }
        FormatValue(builder, index, spec);
        builder->AppendString(": ");
        FormatValue(builder, collection[index], spec);
        firstItem = false;
    }
    builder->AppendChar('}');
}

// One-valued ranges
template <CFormattableRange TRange>
void FormatValue(TStringBuilderBase* builder, const TRange& collection, TStringBuf spec)
{
    NYT::FormatRange(builder, collection, TSpecBoundFormatter(spec));
}

// Two-valued ranges
template <CFormattableKVRange TRange>
void FormatValue(TStringBuilderBase* builder, const TRange& collection, TStringBuf /*spec*/)
{
    NYT::FormatKeyValueRange(builder, collection, TDefaultFormatter());
}

// FormattableView
template <class TRange, class TFormatter>
void FormatValue(
    TStringBuilderBase* builder,
    const TFormattableView<TRange, TFormatter>& formattableView,
    TStringBuf /*spec*/)
{
    NYT::FormatRange(builder, formattableView, formattableView.Formatter, formattableView.Limit);
}

// TCompactIntervalView
template <class TRange, class TValueGetter, class TIntervalFormatter>
    requires CCompactIntervalView<TRange, TValueGetter, TIntervalFormatter>
void FormatValue(
    TStringBuilderBase* builder,
    const TCompactIntervalView<TRange, TValueGetter, TIntervalFormatter>& compactIntervalView,
    TStringBuf /*spec*/)
{
    NYT::FormatCompactIntervalRange(
        builder,
        compactIntervalView,
        compactIntervalView.ValueGetter,
        compactIntervalView.IntervalFormatter);
}

// TFormatterWrapper
template <class TFormatter>
void FormatValue(
    TStringBuilderBase* builder,
    const TFormatterWrapper<TFormatter>& wrapper,
    TStringBuf /*spec*/)
{
    wrapper.Formatter(builder);
}

// TLazyMultiValueFormatter
template <class... TArgs>
void FormatValue(
    TStringBuilderBase* builder,
    const TLazyMultiValueFormatter<TArgs...>& value,
    TStringBuf /*spec*/)
{
    std::apply(
        [&] <class... TInnerArgs> (TInnerArgs&&... args) {
            builder->AppendFormat(value.Format_, std::forward<TInnerArgs>(args)...);
        },
        value.Args_);
}

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

namespace NDetail {

template <size_t HeadPos, class... TArgs>
class TValueFormatter;

template <size_t HeadPos>
class TValueFormatter<HeadPos>
{
public:
    void operator() (size_t /*index*/, TStringBuilderBase* builder, TStringBuf /*spec*/) const
    {
        builder->AppendString(TStringBuf("<missing argument>"));
    }
};

template <size_t HeadPos, class THead, class... TTail>
class TValueFormatter<HeadPos, THead, TTail...>
{
public:
    explicit TValueFormatter(const THead& head, const TTail&... tail) noexcept
        : Head_(head)
        , TailFormatter_(tail...)
    { }

    void operator() (size_t index, TStringBuilderBase* builder, TStringBuf spec) const
    {
        YT_ASSERT(index >= HeadPos);
        if (index == HeadPos) {
            FormatValue(builder, Head_, spec);
        } else {
            TailFormatter_(index, builder, spec);
        }
    }

private:
    const THead& Head_;
    TValueFormatter<HeadPos + 1, TTail...> TailFormatter_;
};

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

template <class TRangeValue>
class TRangeFormatter
{
public:
    template <class... TArgs>
        requires std::constructible_from<std::span<const TRangeValue>, TArgs...>
    explicit TRangeFormatter(TArgs&&... args) noexcept
        : Span_(std::forward<TArgs>(args)...)
    { }

    void operator() (size_t index, TStringBuilderBase* builder, TStringBuf spec) const
    {
        if (index >= Span_.size()) {
            builder->AppendString(TStringBuf("<missing argument>"));
        } else {
            FormatValue(builder, *(Span_.begin() + index), spec);
        }
    }

private:
    std::span<const TRangeValue> Span_;
};

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

template <class T>
concept CFormatter = CInvocable<T, void(size_t, TStringBuilderBase*, TStringBuf)>;

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

template <CFormatter TFormatter>
void RunFormatterAt(
    const TFormatter& formatter,
    size_t index,
    TStringBuilderBase* builder,
    TStringBuf spec,
    bool singleQuotes,
    bool doubleQuotes)
{
    // 'n' means 'nothing'; skip the argument.
    if (!spec.Contains('n')) {
        if (singleQuotes) {
            builder->AppendChar('\'');
        }
        if (doubleQuotes) {
            builder->AppendChar('"');
        }

        formatter(index, builder, spec);

        if (singleQuotes) {
            builder->AppendChar('\'');
        }
        if (doubleQuotes) {
            builder->AppendChar('"');
        }
    }
}

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

template <CFormatter TFormatter>
void RunFormatterFullScan(
    TStringBuilderBase* builder,
    TStringBuf format,
    const TFormatter& formatter,
    int argIndex = 0)
{
    auto current = std::begin(format);
    auto end = std::end(format);
    while (true) {
        // Scan verbatim part until stop symbol.
        auto verbatimBegin = current;
        auto verbatimEnd = std::find(current, end, IntroductorySymbol);

        // Copy verbatim part, if any.
        size_t verbatimSize = verbatimEnd - verbatimBegin;
        if (verbatimSize > 0) {
            builder->AppendString(TStringBuf(verbatimBegin, verbatimSize));
        }

        // Handle stop symbol.
        current = verbatimEnd;
        if (current == end) {
            break;
        }

        YT_ASSERT(*current == IntroductorySymbol);
        ++current;

        if (*current == IntroductorySymbol) {
            // Verbatim %.
            builder->AppendChar(IntroductorySymbol);
            ++current;
            continue;
        }

        // Scan format part until stop symbol.
        auto argFormatBegin = current;
        auto argFormatEnd = argFormatBegin;
        bool singleQuotes = false;
        bool doubleQuotes = false;

        static constexpr TStringBuf conversionSpecifiers =
            "diuoxXfFeEgGaAcspn";

        while (
            argFormatEnd != end &&
            *argFormatEnd != GenericSpecSymbol &&            // value in generic format
            !conversionSpecifiers.Contains(*argFormatEnd)) // others are standard specifiers supported by printf
        {
            switch (*argFormatEnd) {
                case 'q':
                    singleQuotes = true;
                    break;
                case 'Q':
                    doubleQuotes = true;
                    break;
                case 'h':
                    break;
            }
            ++argFormatEnd;
        }

        // Handle end of format string.
        if (argFormatEnd != end) {
            ++argFormatEnd;
        }

        RunFormatterAt(
            formatter,
            argIndex++,
            builder,
            TStringBuf{argFormatBegin, argFormatEnd},
            singleQuotes,
            doubleQuotes);

        current = argFormatEnd;
    }
}

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

template <CFormatter TFormatter, class... TArgs>
void RunFormatter(
    TStringBuilderBase* builder,
    TBasicFormatString<TArgs...> formatString,
    const TFormatter& formatter)
{
    auto isValidLocations = [] (const auto& t) {
        return std::get<0>(t) != std::get<1>(t);
    };
    // Generally marker is simply "%v" e.g. 2 symbols.
    // We assume it is used to insert something for roughly 5 symbols
    // of size.
    builder->Preallocate(std::size(formatString.Get()) + sizeof...(TArgs) * (5 - 2));

    // Empty marker positions -- fallback to the normal impl.
    if constexpr (sizeof...(TArgs) != 0) {
        if (!isValidLocations(formatString.Markers[0])) {
            RunFormatterFullScan(builder, formatString.Get(), formatter);
            return;
        }
    } else {
        if (formatString.Escapes[0] == -2) {
            RunFormatterFullScan(builder, formatString.Get(), formatter);
            return;
        }
    }

    int escapesFound = 0;
    int currentPos = 0;

    auto beginIt = formatString.Get().begin();
    auto size = formatString.Get().size();

    const auto& [markers, escapes] = std::tie(formatString.Markers, formatString.Escapes);

    auto appendVerbatim = [&] (int offsetToEnd) {
        builder->AppendString(TStringBuf{beginIt + currentPos, beginIt + offsetToEnd});
    };

    auto processEscape = [&] () mutable {
        // OpenMP doesn't support structured bindings :(.
        auto escapePos = formatString.Escapes[escapesFound];

        // Append everything that's present until %%.
        appendVerbatim(escapePos);

        // Append '%'.
        builder->AppendChar('%');

        // Advance position to first '%' pos + 2.
        currentPos = escapePos + 2;
    };

    int argIndex = 0;

    while(argIndex < std::ssize(markers)) {
        auto [markerStart, markerEnd] = markers[argIndex];

        if (
            escapes[escapesFound] != -1 &&
            escapes[escapesFound] - currentPos < markerStart - currentPos)
        {
            // Escape sequence is closer.
            processEscape();
            ++escapesFound;
        } else {
            // Normal marker is closer.

            // Append everything that's present until marker start.
            appendVerbatim(markerStart);

            // Parsing format string.

            // We skip '%' here since spec does not contain it.
            auto spec = TStringBuf{beginIt + markerStart + 1, beginIt + markerEnd};
            bool singleQuotes = false;
            bool doubleQuotes = false;
            for (auto c : spec) {
                if (c == 'q') {
                    singleQuotes = true;
                }
                if (c == 'Q') {
                    doubleQuotes = true;
                }
            }
            RunFormatterAt(
                formatter,
                argIndex,
                builder,
                spec,
                singleQuotes,
                doubleQuotes);

            // Advance position past marker's end.
            currentPos = markerEnd;
            ++argIndex;
            continue;
        }

        // Check if the number of escapes we have found has exceeded the recorded limit
        // e.g. we have to manually scan the rest of the formatString.
        if (escapesFound == std::ssize(escapes)) {
            break;
        }
    }

    // Process remaining escapes.
    while (escapesFound < std::ssize(escapes)) {
        if (escapes[escapesFound] == -1) {
            break;
        }

        processEscape();
        ++escapesFound;
    }

    // We either ran out of markers or reached the limit of allowed
    // escape sequences.

    // Happy path: no limit on escape sequences.
    if (escapesFound != std::ssize(escapes)) {
        // Append whatever's left until the end.
        appendVerbatim(size);
        return;
    }

    // Sad path: we have to fully parse remainder of format.
    RunFormatterFullScan(builder, TStringBuf{beginIt + currentPos, beginIt + size}, formatter, argIndex);
}

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

// For benchmarking purposes.
template <class... TArgs>
TString FormatOld(TFormatString<TArgs...> format, TArgs&&... args)
{
    TStringBuilder builder;
    if constexpr ((CFormattable<TArgs> && ...)) {
        NYT::NDetail::TValueFormatter<0, TArgs...> formatter(args...);
        NYT::NDetail::RunFormatterFullScan(&builder, format.Get(), formatter);
    }
    return builder.Flush();
}

} // namespace NDetail

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

template <class... TArgs>
void Format(TStringBuilderBase* builder, TFormatString<TArgs...> format, TArgs&&... args)
{
    // NB(arkady-e1ppa): "if constexpr" is done in order to prevent
    // compiler from emitting "No matching function to call"
    // when arguments are not formattable.
    // Compiler would crash in TFormatString ctor
    // anyway (e.g. program would not compile) but
    // for some reason it does look ahead and emits
    // a second error.
    if constexpr ((CFormattable<TArgs> && ...)) {
        NYT::NDetail::TValueFormatter<0, TArgs...> formatter(args...);
        NYT::NDetail::RunFormatter(builder, format, formatter);
    }
}

template <class... TArgs>
TString Format(TFormatString<TArgs...> format, TArgs&&... args)
{
    TStringBuilder builder;
    Format(&builder, format, std::forward<TArgs>(args)...);
    return builder.Flush();
}

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

template <size_t Length, class TVector>
void FormatVector(
    TStringBuilderBase* builder,
    const char (&format)[Length],
    const TVector& vec)
{
    NYT::NDetail::TRangeFormatter<typename TVector::value_type> formatter(vec);
    NYT::NDetail::RunFormatterFullScan(builder, format, formatter);
}

template <class TVector>
void FormatVector(
    TStringBuilderBase* builder,
    TStringBuf format,
    const TVector& vec)
{
    NYT::NDetail::TRangeFormatter<typename TVector::value_type> formatter(vec);
    NYT::NDetail::RunFormatterFullScan(builder, format, formatter);
}

template <size_t Length, class TVector>
TString FormatVector(
    const char (&format)[Length],
    const TVector& vec)
{
    TStringBuilder builder;
    FormatVector(&builder, format, vec);
    return builder.Flush();
}

template <class TVector>
TString FormatVector(
    TStringBuf format,
    const TVector& vec)
{
    TStringBuilder builder;
    FormatVector(&builder, format, vec);
    return builder.Flush();
}

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

} // namespace NYT

#include <util/string/cast.h>

// util/string/cast.h extension for yt and std types only
// TODO(arkady-e1ppa): Abolish ::ToString in
// favour of either NYT::ToString or
// automatic formatting wherever it is needed.
namespace NPrivate {

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

template <class T>
    requires (
        (NYT::NDetail::IsNYTName<T>() ||
        NYT::NDetail::IsStdName<T>()) &&
        NYT::CFormattable<T>)
struct TToString<T, false>
{
    static TString Cvt(const T& t)
    {
        return NYT::ToStringViaBuilder(t);
    }
};

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

} // namespace NPrivate