/**
 * 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.hive.common.metrics.metrics2;

import com.codahale.metrics.MetricRegistry;
import com.codahale.metrics.json.MetricsModule;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.ObjectWriter;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.net.URI;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.fs.permission.FsPermission;
import org.apache.hadoop.hive.conf.HiveConf;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;


/**
 * A metrics reporter for CodahaleMetrics that dumps metrics periodically into a file in JSON format.
 */

public class JsonFileMetricsReporter implements CodahaleReporter {

  private final MetricRegistry metricRegistry;
  private final ObjectWriter jsonWriter;
  private final ScheduledExecutorService executorService;
  private final HiveConf conf;
  private final long interval;
  private final String pathString;
  private final Path path;

  private static final Logger LOGGER = LoggerFactory.getLogger(JsonFileMetricsReporter.class);

  public JsonFileMetricsReporter(MetricRegistry registry, HiveConf conf) {
    this.metricRegistry = registry;
    this.jsonWriter =
        new ObjectMapper().registerModule(new MetricsModule(TimeUnit.MILLISECONDS,
            TimeUnit.MILLISECONDS, false)).writerWithDefaultPrettyPrinter();
    executorService = Executors.newSingleThreadScheduledExecutor();
    this.conf = conf;

    interval = conf.getTimeVar(HiveConf.ConfVars.HIVE_METRICS_JSON_FILE_INTERVAL, TimeUnit.MILLISECONDS);
    pathString = conf.getVar(HiveConf.ConfVars.HIVE_METRICS_JSON_FILE_LOCATION);
    path = new Path(pathString);
  }

  @Override
  public void start() {

    final Path tmpPath = new Path(pathString + ".tmp");
    URI tmpPathURI = tmpPath.toUri();
    final FileSystem fs;
    try {
      if (tmpPathURI.getScheme() == null && tmpPathURI.getAuthority() == null) {
        //default local
        fs = FileSystem.getLocal(conf);
      } else {
        fs = FileSystem.get(tmpPathURI, conf);
      }
    }
    catch (IOException e) {
        LOGGER.error("Unable to access filesystem for path " + tmpPath + ". Aborting reporting", e);
        return;
    }

    Runnable task = new Runnable() {
      public void run() {
        try {
          String json = null;
          try {
            json = jsonWriter.writeValueAsString(metricRegistry);
          } catch (JsonProcessingException e) {
            LOGGER.error("Unable to convert json to string ", e);
            return;
          }

          BufferedWriter bw = null;
          try {
            fs.delete(tmpPath, true);
            bw = new BufferedWriter(new OutputStreamWriter(fs.create(tmpPath, true)));
            bw.write(json);
            fs.setPermission(tmpPath, FsPermission.createImmutable((short) 0644));
          } catch (IOException e) {
            LOGGER.error("Unable to write to temp file " + tmpPath, e);
            return;
          } finally {
            if (bw != null) {
              bw.close();
            }
          }

          try {
            fs.rename(tmpPath, path);
            fs.setPermission(path, FsPermission.createImmutable((short) 0644));
          } catch (IOException e) {
            LOGGER.error("Unable to rename temp file " + tmpPath + " to " + pathString, e);
            return;
          }
        } catch (Throwable t) {
          // catch all errors (throwable and execptions to prevent subsequent tasks from being suppressed)
          LOGGER.error("Error executing scheduled task ", t);
        }
      }
    };

    executorService.scheduleWithFixedDelay(task,0, interval, TimeUnit.MILLISECONDS);
  }

  @Override
  public void close() {
    executorService.shutdown();
  }
}