From 7251f954597b91cedaf465d21bcdcc63bee9ce70 Mon Sep 17 00:00:00 2001
From: "Timur A. Fatkhullin" <timur@sao.ru>
Date: Tue, 12 Nov 2024 18:07:00 +0300
Subject: [PATCH] add AdcOstreamLogger class (std::basic_stream based
 multithread-safe simple logger)

---
 common/adc_utils.h     | 82 ++++++++++++++++++++++++++++++++++++++++++
 net/adc_net_concepts.h | 17 +++++++--
 2 files changed, 97 insertions(+), 2 deletions(-)

diff --git a/common/adc_utils.h b/common/adc_utils.h
index 9dbaed8..b4693cf 100644
--- a/common/adc_utils.h
+++ b/common/adc_utils.h
@@ -2,7 +2,9 @@
 
 #include <algorithm>
 #include <charconv>
+#include <iostream>
 #include <limits>
+#include <mutex>
 #include <ranges>
 #include <regex>
 #include <utility>
@@ -674,5 +676,85 @@ static constexpr size_t AdcFNV1aHash(const R& r)
     return hash;
 }
 
+/*  std::basic_ostream based multithread-safe simple logger  */
+
+template <typename CharT = char, typename CharTraitsT = std::char_traits<CharT>>
+class AdcOstreamLogger
+{
+public:
+    typedef CharT char_t;
+    typedef CharTraitsT char_traits_t;
+
+    enum loglevel_t { NULL_LEVEL, ERROR_LEVEL, INFO_LEVEL, DEBUG_LEVEL };
+    static constexpr std::array logLevelMark{"null", "error", "info", "debug"};
+
+    AdcOstreamLogger(std::basic_ostream<CharT, CharTraitsT>& stream = std::cout, loglevel_t log_level = INFO_LEVEL)
+        : _logStream(stream), _currentLogLevel(log_level)
+    {
+    }
+
+    AdcOstreamLogger(loglevel_t log_level) : _logStream(std::cout), _currentLogLevel(log_level) {}
+
+    virtual ~AdcOstreamLogger() = default;
+
+    void setLogLevel(loglevel_t log_level)
+    {
+        std::lock_guard<std::mutex> lock(_logMutex);
+
+        _currentLogLevel = log_level;
+    }
+
+    loglevel_t getLogLevel() const
+    {
+        return _currentLogLevel;
+    }
+
+    template <traits::formattable... Ts>
+    void logMessage(loglevel_t level, std::string_view fmt, Ts&&... args)
+    {
+        std::lock_guard<std::mutex> lock(_logMutex);
+
+        if (_currentLogLevel < level)
+            return;
+
+        std::string s;
+        std::format_to(std::back_inserter(s), fmt, std::forward<Ts>(args)...);
+
+        const std::time_t now = std::chrono::system_clock::to_time_t(std::chrono::system_clock::now());
+
+        // format log-message in form:
+        //    [YYYY-MM-DD HH:MM:SS][level] log-message
+        //
+        _logStream << std::put_time(std::localtime(&now), "[%F %T]") << "[" << logLevelMark[_currentLogLevel] << "] "
+                   << s;
+    }
+
+
+    template <traits::formattable... Ts>
+    void logError(std::string_view fmt, Ts&&... args)
+    {
+        logMessage(ERROR_LEVEL, fmt, std::forward<Ts>(args)...);
+    }
+
+    template <traits::formattable... Ts>
+    void logInfo(std::string_view fmt, Ts&&... args)
+    {
+        logMessage(INFO_LEVEL, fmt, std::forward<Ts>(args)...);
+    }
+
+    template <traits::formattable... Ts>
+    void logDebug(std::string_view fmt, Ts&&... args)
+    {
+        logMessage(DEBUG_LEVEL, fmt, std::forward<Ts>(args)...);
+    }
+
+
+protected:
+    std::basic_ostream<CharT, CharTraitsT>& _logStream;
+    loglevel_t _currentLogLevel;
+
+    std::mutex _logMutex;
+};
+
 
 }  // namespace adc::utils
diff --git a/net/adc_net_concepts.h b/net/adc_net_concepts.h
index b35e570..fcbf4d0 100644
--- a/net/adc_net_concepts.h
+++ b/net/adc_net_concepts.h
@@ -227,12 +227,25 @@ concept adc_netsession_proto_c =
 /*  LOGGER  */
 
 template <typename LOGGERT>
-concept adc_logger_c = requires(LOGGERT log) {
-    // logging method must accept at least the single argument - formating string
+concept adc_logger_c = requires(LOGGERT log, const LOGGERT log_const) {
+    typename LOGGERT::loglevel_t;
+
+    log.setLogLevel(std::declval<typename LOGGERT::loglevel_t>());
+    { log_const.getLogLevel() } -> std::same_as<typename LOGGERT::loglevel_t>;
+
+    // logging method signature:
+    //     void method(std::string_view fmt, traits::formattable auto&& args...)
+
+
+    // logging method must accept at least the single argument - formatting string
     log.logInfo(std::declval<std::string_view>());
+    // method must be defined at least for std::string as its argument
     log.logInfo(std::declval<std::string_view>(), std::declval<std::string>());
 
+    log.logWarn(std::declval<std::string_view>());
     log.logWarn(std::declval<std::string_view>(), std::declval<std::string>());
+
+    log.logError(std::declval<std::string_view>());
     log.logError(std::declval<std::string_view>(), std::declval<std::string>());
 };