mini_format.h

#pragma once
#include <sstream>
#include <functional>
#include <vector>
#include <thread>
#include <chrono>
#include <cstdio>
#include <ctime>
#include <iomanip>

using arg_builder_t = std::function<void(std::ostream &)>;
inline std::string mini_format_impl(const std::string &fmt, const std::vector<arg_builder_t> &arg_builders) {
    std::ostringstream ss;
    size_t start = 0;
    for(size_t i = 0; i < arg_builders.size(); ++i) {
        std::size_t pos = fmt.find("{}", start);
        if (pos == std::string::npos) break;
        ss << fmt.substr(start, pos - start);
        arg_builders[i](ss);
        start = pos + 2 /* length of "{}" */;
    }
    ss << fmt.substr(start);
    return ss.str();
}

template<typename Arg>
inline arg_builder_t mini_format_arg(const Arg &arg) {
    return [&arg](std::ostream &ss) { ss << arg; };
}

template<typename ...Args>
inline std::string mini_format(const std::string &fmt, const Args &...args) {
    return mini_format_impl(fmt, {mini_format_arg(args)...});
}

template<typename ...Args>
inline void mini_print(const std::string &fmt, const Args &...args) {
    printf("%s", mini_format(fmt, args...).c_str());
}

inline void mini_log_info(const std::string &file, int line) {
    auto pos = file.find_last_of("\\/");
    auto now = time(0);
    mini_print("[{}] [{}] [{}:{}] ",
        std::put_time(localtime(&now), "%Y-%m-%d_%H:%M:%S"), 
        std::this_thread::get_id(),
        (pos == std::string::npos ? file : file.substr(pos + 1)), line);
}

#define MINI_LOG(...) do { mini_log_info(__FILE__, __LINE__); mini_print(__VA_ARGS__); } while(0)