logging.h

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/*
 * Copyright (C) 2017 Original author K. Henriksson @n
 * Copyright (C) 2017-2024 Norbert Schlia (nschlia@oblivion-software.de)
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 * On Debian systems, the complete text of the GNU General Public License
 * Version 3 can be found in `/usr/share/common-licenses/GPL-3'.
 */
 
#ifndef LOGGING_H
#define LOGGING_H
 
#pragma once
 
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
 
#include <map>
#include <fstream>
#include <sstream>
#include <regex>
#include <mutex>
 
class Logging
{
public:
    enum class LOGLEVEL
    {
        LOGERROR = 1,       
        LOGWARN = 2,        
        LOGINFO = 3,        
        LOGDEBUG = 4,       
        LOGTRACE = 5        
    };
 
    explicit Logging(const std::string & logfile, LOGLEVEL max_level, bool to_stderr, bool to_syslog);
 
    bool GetFail() const;
 
private:
    class Logger : public std::ostringstream
    {
    public:
        Logger(LOGLEVEL loglevel, const std::string & filename) :
            m_loglevel(loglevel),
            m_filename(filename) {}
        explicit Logger() :
            m_loglevel(LOGLEVEL::LOGDEBUG) {}
        virtual ~Logger();
 
    private:
        const LOGLEVEL      m_loglevel;                                     
        const std::string   m_filename;                                     
        static const std::map<LOGLEVEL, int>           m_syslog_level_map;  
        static const std::map<LOGLEVEL, std::string>   m_level_name_map;    
        static const std::map<LOGLEVEL, std::string>   m_level_colour_map;  
    };
 
public:
    static bool init_logging(const std::string & logfile, LOGLEVEL max_level, bool to_stderr, bool to_syslog);
 
    template <typename T, typename... Args>
    static void trace(const T filename, const std::string &format_string, Args &&...args)
    {
        LOGLEVEL loglevel = LOGLEVEL::LOGTRACE;
 
        if (!show(loglevel))
        {
            return;
        }
 
        log_with_level(loglevel, filename, format_helper(format_string, 1, std::forward<Args>(args)...));
    }
 
    template <typename T, typename... Args>
    static void debug(const T filename, const std::string &format_string, Args &&...args)
    {
        LOGLEVEL loglevel = LOGLEVEL::LOGDEBUG;
 
        if (!show(loglevel))
        {
            return;
        }
 
        log_with_level(loglevel, filename, format_helper(format_string, 1, std::forward<Args>(args)...));
    }
 
    template <typename T, typename... Args>
    static void info(const T filename, const std::string &format_string, Args &&...args)
    {
        LOGLEVEL loglevel = LOGLEVEL::LOGINFO;
 
        if (!show(loglevel))
        {
            return;
        }
 
        log_with_level(loglevel, filename, format_helper(format_string, 1, std::forward<Args>(args)...));
    }
 
    template <typename T, typename... Args>
    static void warning(const T filename, const std::string &format_string, Args &&...args)
    {
        LOGLEVEL loglevel = LOGLEVEL::LOGWARN;
 
        if (!show(loglevel))
        {
            return;
        }
 
        log_with_level(loglevel, filename, format_helper(format_string, 1, std::forward<Args>(args)...));
    }
 
    template <typename T, typename... Args>
    static void error(const T filename, const std::string &format_string, Args &&...args)
    {
        LOGLEVEL loglevel = LOGLEVEL::LOGERROR;
 
        if (!show(loglevel))
        {
            return;
        }
 
        log_with_level(loglevel, filename, format_helper(format_string, 1, std::forward<Args>(args)...));
    }
 
    static void log_with_level(LOGLEVEL loglevel, const char *filename, const std::string & message);
 
    static void log_with_level(LOGLEVEL loglevel, const std::string & filename, const std::string & message);
 
    static bool show(LOGLEVEL loglevel)
    {
        return (m_logging && loglevel <= m_logging->m_max_level);
    }
 
private:
    template<typename T>
    static T & convert(T & val)
    {
        return val;
    }
 
    static std::string convert(const char * val)
    {
        if (val != nullptr)
        {
            return val;
        }
        else
        {
            return "(null)";
        }
    }
 
    static std::string convert(char * val)
    {
        if (val != nullptr)
        {
            return val;
        }
        else
        {
            return "(null)";
        }
    }
 
    // std::string cannot actually be passed to %s. That's how it works...
 
    template<class T, typename std::enable_if<!std::is_same<T, std::string>::value, bool>::type = true>
    static T & fix_std_string(T & val)
    {
        return val;
    }
 
    static const char * fix_std_string(const std::string & val)
    {
        return val.c_str();
    }
 
    static std::string format_helper(
            const std::string &string_to_update,
            const size_t __attribute__((unused)) index_to_replace);
 
    template <typename T, typename... Args>
    static std::string format_helper(
            const std::string &string_to_search,
            const size_t index_to_replace,
            T &&val,
            Args &&...args)
    {
        // Match %# exactly (e.g. %12 and %123 literally)
 
        std::regex exp("%(<([^>]+)>)*" + std::to_string(index_to_replace) + "(?=[^0-9]|$)");
        std::smatch res;
        std::string string_to_update(string_to_search);
        std::string::const_iterator searchStart(string_to_search.cbegin());
        size_t offset = 0;
 
        while (std::regex_search(searchStart, string_to_search.cend(), res, exp))
        {
            std::ostringstream ostr;
 
            if (res[2].length())
            {
                // Found match with printf format in res[2]
                std::vector<char> fmt;
                std::string ftmspec = res[2].str();
 
                if (ftmspec.front() != '%')
                {
                    fmt.push_back('%');
                }
 
 
                fmt.insert(fmt.end(), ftmspec.begin(), ftmspec.end());
                fmt.push_back('\0');
 
                size_t size = static_cast<size_t>(std::snprintf(nullptr, 0, fmt.data(), fix_std_string(val))) + 1;
                std::vector<char> buffer;
                buffer.resize(size);
                std::snprintf(buffer.data(), size, fmt.data(), fix_std_string(val));
                ostr << buffer.data();
            }
            else
            {
                // No printf format, replace literally
                ostr << convert(val);
            }
 
            string_to_update.replace(static_cast<size_t>(res.position()) + offset, static_cast<size_t>(res[0].length()), ostr.str());
 
            offset += static_cast<size_t>(res.position()) + ostr.str().length();
 
            searchStart = res.suffix().first;
        }
 
        return format_helper(
                    string_to_update,
                    index_to_replace + 1,
                    std::forward<Args>(args)...);
    }
 
    template <typename... Args>
    static std::string format(const std::string &format_string, Args &&...args)
    {
        return format_helper(format_string, 1, std::forward<Args>(args)...);
    }
 
protected:
    friend Logger Log(LOGLEVEL loglevel, const std::string & filename);
    friend Logger;                                                          
    static std::unique_ptr<Logging> m_logging;                              
    static std::recursive_mutex     m_mutex;                                
    std::ofstream                   m_logfile;                              
    const LOGLEVEL                  m_max_level;                            
    const bool                      m_to_stderr;                            
    const bool                      m_to_syslog;                            
};
 
constexpr Logging::LOGLEVEL LOGERROR    = Logging::LOGLEVEL::LOGERROR;      
constexpr Logging::LOGLEVEL LOGWARN     = Logging::LOGLEVEL::LOGWARN;       
constexpr Logging::LOGLEVEL LOGINFO     = Logging::LOGLEVEL::LOGINFO;       
constexpr Logging::LOGLEVEL LOGDEBUG    = Logging::LOGLEVEL::LOGDEBUG;      
constexpr Logging::LOGLEVEL LOGTRACE    = Logging::LOGLEVEL::LOGTRACE;      
#endif