package com.atlassian.plugin.instrumentation;
   
   import com.atlassian.instrumentation.operations.OpSnapshot;
   import com.atlassian.instrumentation.operations.OpTimer;
   import org.apache.log4j.MDC;
   import org.slf4j.Logger;
   import org.slf4j.LoggerFactory;
   
   import javax.annotation.Nonnull;
  import java.util.Optional;
  import java.util.concurrent.TimeUnit;
  
  /**
   * Wrapper around an {@link com.atlassian.instrumentation.operations.OpTimer} that may be safely used even if that
   * class is not present in the class loader.
   * <p>
   * This wrapper implements {@link java.io.Closeable}. On close it logs elapsed time and elapsed cpu time
   * <p>
   * Note to maintainers: extreme care must be taken to ensure that <code>OpTimer</code> not accessed at runtime if it is
   * not present.
   *
   * @see PluginSystemInstrumentation
   * @since 4.1
   */
  public class SingleTimer extends Timer {
      private static final Logger log = LoggerFactory.getLogger(SingleTimer.class);
      // We cannot rely on OpTimer name for logging as it contains timestamps
      private String name;
  
      SingleTimer(@Nonnull Optional<OpTimer> opTimer, String name) {
          super(opTimer);
          this.name = name;
      }
  
      public String getName() {
          return name;
      }
      
      /**
       * End the timer, if instrumentation is present and enabled log clock time and cpu time
       */
      @Override
      public void close() {
          Optional<OpTimer> timerOption = this.getOpTimer();
          if (timerOption.isPresent()) {
              OpSnapshot snapshot = timerOption.get().snapshot();
              long cpuTime = snapshot.getCpuTotalTime(TimeUnit.MILLISECONDS);
              long elapsedTime = snapshot.getElapsedTotalTime(TimeUnit.MILLISECONDS);
              String logKey = "com.atlassian.plugin." + name;
              String cpuKey = logKey + ".cpu-ms";
              String clockKey = logKey + ".clock-ms";
  
              MDC.put(cpuKey, cpuTime);
              MDC.put(clockKey, elapsedTime);
              // Kibana does not register DEBUG messages. This is safe as instrumentation won't be enabled in PROD
              log.info("Timer {} took {}ms ({} cpu ns)", snapshot.getName(), elapsedTime, cpuTime);
              MDC.remove(clockKey);
              MDC.remove(cpuKey);
          }
          super.close();
      }
  }