/**
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you under the Apache License, Version 2.0 (the
    * "License"); you may not use this file except in compliance
    * with the License.  You may obtain a copy of the License at
    *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.hadoop.hbase.metrics.impl;
  
  import com.google.common.base.Optional;
  import java.lang.reflect.InvocationTargetException;
  import java.lang.reflect.Method;
  import java.util.Collection;
  import java.util.HashMap;
  import java.util.Iterator;
  import java.util.Map;
  import java.util.Map.Entry;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicBoolean;
  import org.apache.commons.lang.reflect.FieldUtils;
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.metrics.MetricRegistries;
  import org.apache.hadoop.hbase.metrics.MetricRegistry;
  import org.apache.hadoop.hbase.metrics.MetricRegistryInfo;
  import org.apache.hadoop.metrics2.MetricsCollector;
  import org.apache.hadoop.metrics2.MetricsExecutor;
  import org.apache.hadoop.metrics2.MetricsSource;
  import org.apache.hadoop.metrics2.MetricsSystem;
  import org.apache.hadoop.metrics2.impl.JmxCacheBuster;
  import org.apache.hadoop.metrics2.impl.MetricsSystemImpl;
  import org.apache.hadoop.metrics2.lib.DefaultMetricsSystem;
  import org.apache.hadoop.metrics2.lib.DefaultMetricsSystemHelper;
  import org.apache.hadoop.metrics2.lib.MetricsExecutorImpl;
  
  /**
   * This class acts as an adapter to export the MetricRegistry's in the global registry. Each
   * MetricRegistry will be registered or unregistered from the metric2 system. The collection will
   * be performed via the MetricsSourceAdapter and the MetricRegistry will collected like a
   * BaseSource instance for a group of metrics  (like WAL, RPC, etc) with the MetricRegistryInfo's
   * JMX context.
   *
   * <p>Developer note:
   * Unlike the current metrics2 based approach, the new metrics approach
   * (hbase-metrics-api and hbase-metrics modules) work by having different MetricRegistries that are
   * initialized and used from the code that lives in their respective modules (hbase-server, etc).
   * There is no need to define BaseSource classes and do a lot of indirection. The MetricRegistry'es
   * will be in the global MetricRegistriesImpl, and this class will iterate over
   * MetricRegistries.global() and register adapters to the metrics2 subsystem. These adapters then
   * report the actual values by delegating to
   * {@link HBaseMetrics2HadoopMetricsAdapter#snapshotAllMetrics(MetricRegistry, MetricsCollector)}.
   *
   * We do not initialize the Hadoop Metrics2 system assuming that other BaseSources already do so
   * (see BaseSourceImpl). Once the last BaseSource is moved to the new system, the metric2
   * initialization should be moved here.
   * </p>
   */
  public class GlobalMetricRegistriesAdapter {
  
    private static final Log LOG = LogFactory.getLog(GlobalMetricRegistriesAdapter.class);
  
    private class MetricsSourceAdapter implements MetricsSource {
      private final MetricRegistry registry;
      MetricsSourceAdapter(MetricRegistry registry) {
        this.registry = registry;
      }
  
      @Override
      public void getMetrics(MetricsCollector collector, boolean all) {
        metricsAdapter.snapshotAllMetrics(registry, collector);
      }
    }
  
    private final MetricsExecutor executor;
    private final AtomicBoolean stopped;
    private final DefaultMetricsSystemHelper helper;
    private final HBaseMetrics2HadoopMetricsAdapter metricsAdapter;
    private final HashMap<MetricRegistryInfo, MetricsSourceAdapter> registeredSources;
  
    private GlobalMetricRegistriesAdapter() {
      this.executor = new MetricsExecutorImpl();
      this.stopped = new AtomicBoolean(false);
      this.metricsAdapter = new HBaseMetrics2HadoopMetricsAdapter();
      this.registeredSources = new HashMap<>();
      this.helper = new DefaultMetricsSystemHelper();
      executor.getExecutor().scheduleAtFixedRate(new Runnable(){
        @Override
        public void run() {
          doRun();
 
       }}, 10, 10, TimeUnit.SECONDS);
   }
 
   /**
    * Make sure that this global MetricSource for hbase-metrics module based metrics are initialized.
    * This should be called only once.
    */
   public static GlobalMetricRegistriesAdapter init() {
     return new GlobalMetricRegistriesAdapter();
   }
 
   public void stop() {
     stopped.set(true);
   }
 
   private void doRun() {
     if (stopped.get()) {
       executor.stop();
       return;
     }
     if (LOG.isTraceEnabled()) {
       LOG.trace("doRun called: " + registeredSources);
     }
 
     Collection<MetricRegistry> registries = MetricRegistries.global().getMetricRegistries();
     for (MetricRegistry registry : registries) {
       MetricRegistryInfo info = registry.getMetricRegistryInfo();
 
       if (info.isExistingSource()) {
         // If there is an already existing BaseSource for this MetricRegistry, skip it here. These
         // types of registries are there only due to existing BaseSource implementations in the
         // source code (like MetricsRegionServer, etc). This is to make sure that we can transition
         // iteratively to the new hbase-metrics system. These type of MetricRegistry metrics will be
         // exported from the BaseSource.getMetrics() call directly because there is already a
         // MetricRecordBuilder there (see MetricsRegionServerSourceImpl).
         continue;
       }
 
       if (!registeredSources.containsKey(info)) {
         if (LOG.isDebugEnabled()) {
           LOG.debug("Registering adapter for the MetricRegistry: " + info.getMetricsJmxContext());
         }
         // register this as a MetricSource under different JMX Context'es.
         MetricsSourceAdapter adapter = new MetricsSourceAdapter(registry);
         LOG.info("Registering " + info.getMetricsJmxContext() + " " + info.getMetricsDescription());
         DefaultMetricsSystem.instance().register(info.getMetricsJmxContext(),
             info.getMetricsDescription(), adapter);
         registeredSources.put(info, adapter);
         // next collection will collect the newly registered MetricSource. Doing this here leads to
         // ConcurrentModificationException.
       }
     }
 
     boolean removed = false;
     // Remove registered sources if it is removed from the global registry
     for (Iterator<Entry<MetricRegistryInfo, MetricsSourceAdapter>> it =
          registeredSources.entrySet().iterator(); it.hasNext();) {
       Entry<MetricRegistryInfo, MetricsSourceAdapter> entry = it.next();
       MetricRegistryInfo info = entry.getKey();
       Optional<MetricRegistry> found = MetricRegistries.global().get(info);
       if (!found.isPresent()) {
         if (LOG.isDebugEnabled()) {
           LOG.debug("Removing adapter for the MetricRegistry: " + info.getMetricsJmxContext());
         }
         synchronized(DefaultMetricsSystem.instance()) {
           unregisterSource(info);
           helper.removeSourceName(info.getMetricsJmxContext());
           helper.removeObjectName(info.getMetricsJmxContext());
           it.remove();
           removed = true;
         }
       }
     }
     if (removed) {
       JmxCacheBuster.clearJmxCache();
     }
   }
 
   /**
    * Use reflection to unregister the Hadoop metric source, since MetricsSystem#unregisterSource()
    * is only available in Hadoop 2.6+ (HADOOP-10839)
    */
   protected void unregisterSource(MetricRegistryInfo info) {
     // unregisterSource is only available in Hadoop 2.6+ (HADOOP-10839). Don't unregister for now
     MetricsSystem metricsSystem = DefaultMetricsSystem.instance();
     if (metricsSystem instanceof MetricsSystemImpl) {
       try {
         // it's actually a Map<String, MetricsSourceAdapter> , but MetricsSourceAdapter isn't
         // accessible
         @SuppressWarnings("unchecked")
         Map<String, Object> sources =
             (Map<String, Object>) FieldUtils.readField(metricsSystem, "sources", true);
         String sourceName = info.getMetricsJmxContext();
         if (sources.containsKey(sourceName)) {
           Object sourceAdapter = sources.get(sourceName);
           Method method = null;
           try {
             method = sourceAdapter.getClass().getDeclaredMethod("stop");
           } catch (NoSuchMethodException e) {
             LOG.info("Stop method not found on MetricsSourceAdapter");
           } catch (SecurityException e) {
             LOG.info("Don't have access to call stop method not found on MetricsSourceAdapter", e);
           }
           if (method != null) {
             method.setAccessible(true);
             try {
               method.invoke(sourceAdapter);
             } catch (IllegalArgumentException | InvocationTargetException e) {
               LOG.warn("Couldn't invoke stop on metrics source adapter: " + sourceName);
               e.printStackTrace();
             }
           }
           sources.remove(sourceName);
 
         }
         @SuppressWarnings("unchecked")
         Map<String, MetricsSource> allSources =
             (Map<String, MetricsSource>) FieldUtils.readField(metricsSystem, "allSources", true);
         if (allSources.containsKey(sourceName)) {
           allSources.remove(sourceName);
         }
       } catch (IllegalAccessException e) {
         LOG.warn("Error unregistering metric source " + info.getMetricsJmxContext());
       }
     }
   }
 }