json_escape.cpp

struct SourceCodeJsonEscape
{
    const char * text;
};

template<>
struct fmt::formatter<engine::SourceCodeJsonEscape> : fmt::formatter<fmt::string_view>
{
    template<typename FormatContext>
    auto format(const engine::SourceCodeJsonEscape & sourceCodejsonEscape, FormatContext & ctx) const
    {
        auto out = ctx.out();
        std::string_view text = sourceCodejsonEscape.text;
        if (std::empty(text)) {
            return out;
        }
        using namespace std::string_view_literals;
        const auto append = [&out](std::string_view s) { out = std::copy_n(std::cbegin(s), std::size(s), out); };
        while (!std::empty(text)) {
            char c = text.front();
            switch (c) {
            case '\\':
                append("\\\\"sv);
                break;
            case '"':
                append("\\\""sv);
                break;
            case '\b':
                append("\\b"sv);
                break;
            case '\f':
                append("\\f"sv);
                break;
            case '\n':
                append("\\n"sv);
                break;
            case '\r':
                append("\\r"sv);
                break;
            case '\t':
                append("\\t"sv);
                break;
            default: {
                if (static_cast<uint8_t>(c) <= 0x1f) {
                    append("\\u"sv);
                    char buf[4] = {'0', '0', '0', '0'};
                    auto r = std::to_chars(std::begin(buf), std::end(buf), static_cast<uint8_t>(c), 16);
                    INVARIANT(r.ec == std::errc{}, "Failed to convert char('{}') to hexadecimal string of length 4", c);
                    std::rotate(std::begin(buf), r.ptr, std::end(buf));
                    append({std::data(buf), std::size(buf)});
                } else if (text.starts_with("\xE2\x80\xA8"sv)) {
                    append("\\u2028"sv);
                    text.remove_prefix(3);
                    continue;
                } else if (text.starts_with("\xE2\x80\xA9"sv)) {
                    append("\\u2029"sv);
                    text.remove_prefix(3);
                    continue;
                } else {
                    *out++ = c;
                }
            }
            }
            text.remove_prefix(1);
        }
        return out;
    }
};