serenity/AK/Format.h

/*
 * Copyright (c) 2020, the SerenityOS developers.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#pragma once

#include <AK/Array.h>
#include <AK/StringView.h>

// FIXME: I would really love to merge the format_value and make_type_erased_parameters functions,
//        but the compiler creates weird error messages when I do that. Here is a small snippet that
//        reproduces the issue: https://godbolt.org/z/o55crs

namespace AK {

template<typename T, typename = void>
struct Formatter;

struct TypeErasedParameter {
    enum class Type {
        UInt8,
        UInt16,
        UInt32,
        UInt64,
        Int8,
        Int16,
        Int32,
        Int64,
        Custom
    };

    template<typename T>
    static Type get_type()
    {
        if (IsSame<T, u8>::value)
            return Type::UInt8;
        if (IsSame<T, u16>::value)
            return Type::UInt16;
        if (IsSame<T, u32>::value)
            return Type::UInt32;
        if (IsSame<T, u64>::value)
            return Type::UInt64;
        if (IsSame<T, i8>::value)
            return Type::Int8;
        if (IsSame<T, i16>::value)
            return Type::Int16;
        if (IsSame<T, i32>::value)
            return Type::Int32;
        if (IsSame<T, i64>::value)
            return Type::Int64;

        return Type::Custom;
    }

    const void* value;
    Type type;
    void (*formatter)(StringBuilder& builder, const void* value, class FormatterContext&);
};

class FormatterContext {
public:
    FormatterContext(Span<const TypeErasedParameter> parameters)
        : m_parameters(parameters)
    {
    }

    const TypeErasedParameter& parameter_at(size_t index) const { return m_parameters.at(index); }
    size_t parameter_count() const { return m_parameters.size(); }

    StringView flags() const { return m_flags; }
    void set_flags(StringView value) { m_flags = value; }

    size_t take_next_index() { return m_next_index++; }

private:
    Span<const TypeErasedParameter> m_parameters;
    StringView m_flags;
    size_t m_next_index { 0 };
};

} // namespace AK

namespace AK::Detail::Format {

template<typename T>
void format_value(StringBuilder& builder, const void* value, FormatterContext& context)
{
    Formatter<T> formatter;

    formatter.parse(context);
    formatter.format(builder, *static_cast<const T*>(value), context);
}

} // namespace AK::Detail::Format

namespace AK {

constexpr size_t max_format_arguments = 256;

// We use the same format for most types for consistency. This is taken directly from std::format.
// Not all valid options do anything yet.
// https://en.cppreference.com/w/cpp/utility/format/formatter#Standard_format_specification
struct StandardFormatter {
    enum class Align {
        Default,
        Left,
        Right,
        Center,
    };
    enum class Sign {
        NegativeOnly,
        PositiveAndNegative,
        ReserveSpace,
        Default = NegativeOnly
    };
    enum class Mode {
        Default,
        Binary,
        BinaryUppercase,
        Decimal,
        Octal,
        Hexadecimal,
        HexadecimalUppercase,
        Character,
        String,
        Pointer,
    };

    static constexpr size_t value_not_set = 0;
    static constexpr size_t value_from_next_arg = NumericLimits<size_t>::max();
    static constexpr size_t value_from_arg = NumericLimits<size_t>::max() - max_format_arguments - 1;

    Align m_align = Align::Default;
    Sign m_sign = Sign::NegativeOnly;
    Mode m_mode = Mode::Default;
    bool m_alternative_form = false;
    char m_fill = ' ';
    bool m_zero_pad = false;
    size_t m_width = value_not_set;
    size_t m_precision = value_not_set;

    void parse(FormatterContext&);
};

template<>
struct Formatter<StringView> : StandardFormatter {
    Formatter() { }
    explicit Formatter(StandardFormatter formatter)
        : StandardFormatter(formatter)
    {
    }

    void format(StringBuilder& builder, StringView value, FormatterContext&);
};
template<>
struct Formatter<const char*> : Formatter<StringView> {
};
template<>
struct Formatter<char*> : Formatter<StringView> {
};
template<size_t Size>
struct Formatter<char[Size]> : Formatter<StringView> {
};
template<>
struct Formatter<String> : Formatter<StringView> {
};

template<typename T>
struct Formatter<T, typename EnableIf<IsIntegral<T>::value>::Type> : StandardFormatter {
    Formatter() { }
    explicit Formatter(StandardFormatter formatter)
        : StandardFormatter(formatter)
    {
    }

    void format(StringBuilder&, T value, FormatterContext&);
};

template<typename T>
struct Formatter<T*> : StandardFormatter {
    void format(StringBuilder& builder, T* value, FormatterContext& context)
    {
        Formatter<FlatPtr> formatter { *this };
        formatter.format(builder, reinterpret_cast<FlatPtr>(value), context);
    }
};

template<>
struct Formatter<bool> : StandardFormatter {
    void format(StringBuilder&, bool value, FormatterContext&);
};

template<typename... Parameters>
Array<TypeErasedParameter, sizeof...(Parameters)> make_type_erased_parameters(const Parameters&... parameters)
{
    static_assert(sizeof...(Parameters) <= max_format_arguments);

    return { TypeErasedParameter { &parameters, TypeErasedParameter::get_type<Parameters>(), Detail::Format::format_value<Parameters> }... };
}

void vformat(StringBuilder& builder, StringView fmtstr, Span<const TypeErasedParameter>);
void vformat(const LogStream& stream, StringView fmtstr, Span<const TypeErasedParameter>);

} // namespace AK