include <string>
  include <Logger.h>
  
  using namespace std;
  
  const string Logger::kLogLevelDebug = "DEBUG";
  const string Logger::kLogLevelInfo = "INFO";
  const string Logger::kLogLevelError = "ERROR";
  
  const char* const Logger::kLogFileName = "log.out";
  
  // The static instance will be constructed when the program starts and
  // destructed when it ends.
  Logger Logger::sInstance;
  
  Logger& Logger::instance()
  {
    return sInstance;
  }
  
  Logger::~Logger()
  {
    mOutputStream.close();
  }
  
  Logger::Logger()
  {
    mOutputStream.open(kLogFileName, ios_base::app);
    if (!mOutputStream.good()) {
      cerr << "Unable to initialize the Logger!" << endl;
    } 
  }
  
  void Logger::log(const string& inMessage, const string& inLogLevel)
  {
    mOutputStream << inLogLevel << ": " << inMessage << endl;
  }
  
  void Logger::log(const vector<string>& inMessages, const string& inLogLevel)
  {
    for (size_t i = 0; i < inMessages.size(); i++) {
      log(inMessages[i], inLogLevel);
    }
  }
  
  int main(int argc, char** argv)
  {
    Logger::instance().log("test message", Logger::kLogLevelDebug);
  
    vector<string> items;
    items.push_back("item1");
    items.push_back("item2");
  
    Logger::instance().log(items, Logger::kLogLevelError);
  }