Logger.cpp

#pragma once

#include <xzero/Api.h>

/*
 * <xzero/logging/...>
 *   LogSource      the logging source, that initiates/triggers the log msgs
 *   LogLevel       the log level (none, error, warn, info, debug)
 *   LogTarget      the logging target, where to log to
 *   LogAggregator  logging aggregator, that manages the sources and their target.
 *
 * The logging user app/lib itself *only* needs to know about LogSource.
 */

namespace xzero {

/**
 * A logging source.
 *
 * Creates a log message such as "[$ClassName] $LogMessage"
 */
class LogSource {
 public:
  explicit LogSource(const std::string& className);
  ~LogSource();

  void debug(const char* fmt, ...);
  void info(const char* fmt, ...);
  void warn(const char* fmt, ...);
  void error(const char* fmt, ...);

  void enable();
  bool isEnabled() const noexcept;
  void disable();

  const std::string& className() const noexcept { return className_; }

 private:
  std::string className_;
  bool enabled_;
};

/**
 * Log Target Interface.
 *
 * Logging target implementations (such as a console logger or syslog logger)
 * must implement this interface.
 */
class XZERO_API LogTarget {
 public:
  virtual ~LogTarget() {}

  virtual void debug(const std::string& msg) = 0;
  virtual void info(const std::string& msg) = 0;
  virtual void warn(const std::string& msg) = 0;
  virtual void error(const std::string& msg) = 0;

  static LogTarget* console(); // standard console logger
  static LogTarget* syslog();  // standard syslog logger
};

enum class LogLevel {
  None = 0,
  Error = 1,
  Warning = 2,
  Info = 3,
  Debug = 4,
};

/**
 * Logging Aggregator Service.
 */
class XZERO_API LogAggregator {
 public:
  LogAggregator() : LogAggregator(LogLevel::Warning, nullptr) {}
  LogAggregator(LogLevel logLevel, LogTarget* logTarget);

  LogLevel logLevel() const noexcept { return logLevel_; }
  void setLogLevel(LogLevel level) { logLevel_ = level; }

  LogTarget* logTarget() const { return target_; }
  void setLogTarget(LogTarget* target);

  void declareSource(LogSource* source);
  void undeclareSource(LogSource* source);
  LogSource* findSource(const std::string& className) const;

  static LogAggregator& get();

 private:
  LogTarget* target;
  LogLevel logLevel_;
  std::unordered_map<std::string, bool> enabledSources_;
};

}  // namespace xzero