spdlog/include/c11log/details/stack_buf.h

#pragma once

#include <array>
#include <vector>
#include <algorithm>
#include <cstring>

// Fast memory storage
// stores its contents on the stack when possible, in vector<char> otherwise
// NOTE: User should be remember that returned buffer might be on the stack!!
namespace c11log
{
namespace details
{

using bufpair_t = std::pair<const char*, std::size_t>;

template<std::size_t STACK_SIZE = 128>
class stack_buf
{
public:
    stack_buf() :_v(), _stack_array(), _stack_size(0) {}
    ~stack_buf() {};

    stack_buf& operator=(const stack_buf& other) = delete;

    stack_buf(const bufpair_t& buf_to_copy) :stack_buf()
    {
        append(buf_to_copy);
    }

    stack_buf(const stack_buf& other)
    {
        _stack_size = other._stack_size;
        if (!other._v.empty())
            _v = other._v;
        else if (_stack_size)
            std::copy(other._stack_array.begin(), other._stack_array.begin() + _stack_size, _stack_array.begin());
    }

    stack_buf(stack_buf&& other)
    {
        _stack_size = other._stack_size;
        if (!other._v.empty())
            _v = std::move(other._v);
        else if (_stack_size)
            std::copy(other._stack_array.begin(), other._stack_array.begin() + _stack_size, _stack_array.begin());
        other.clear();
    }

    void append(const char* buf, std::size_t buf_size)
    {
        //If we are aleady using _v, forget about the stack
        if (!_v.empty())
        {
            _v.insert(_v.end(), buf, buf + buf_size);
        }
        //Try use the stack
        else
        {
            if (_stack_size + buf_size <= STACK_SIZE)
            {
                std::memcpy(&_stack_array[_stack_size], buf, buf_size);
                _stack_size += buf_size;
            }
            //Not enough stack space. Copy all to _v
            else
            {
                _v.reserve(_stack_size + buf_size);
                if (_stack_size)
                    _v.insert(_v.end(), _stack_array.begin(), _stack_array.begin() + _stack_size);
                _v.insert(_v.end(), buf, buf + buf_size);
            }
        }
    }

    void append(const bufpair_t &buf)
    {
        append(buf.first, buf.second);
    }

    void clear()
    {
        _stack_size = 0;
        _v.clear();
    }

    bufpair_t get() const
    {
        if (!_v.empty())
            return bufpair_t(_v.data(), _v.size());
        else
            return bufpair_t(_stack_array.data(), _stack_size);
    }

    std::size_t size() const
    {
        if (!_v.empty())
            return _v.size();
        else
            return _stack_size;
    }

private:
    std::vector<char> _v;
    std::array<char, STACK_SIZE> _stack_array;
    std::size_t _stack_size;
};

}
} //namespace c11log { namespace details {