/**
 * 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.fs;

import java.util.Iterator;
import java.util.NoSuchElementException;

import com.google.common.base.Preconditions;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.fs.FileSystem.Statistics.StatisticsData;

/**
 * A basic StorageStatistics instance which simply returns data from
 * FileSystem#Statistics.
 */
@InterfaceAudience.Private
@InterfaceStability.Unstable
public class FileSystemStorageStatistics extends StorageStatistics {
  /**
   * The per-class FileSystem statistics.
   */
  private final FileSystem.Statistics stats;

  private static final String[] KEYS = {
      "bytesRead",
      "bytesWritten",
      "readOps",
      "largeReadOps",
      "writeOps",
  };

  private static class LongStatisticIterator
      implements Iterator<LongStatistic> {
    private final StatisticsData data;

    private int keyIdx;

    LongStatisticIterator(StatisticsData data) {
      this.data = data;
      this.keyIdx = 0;
    }

    @Override
    public boolean hasNext() {
      return (this.keyIdx < KEYS.length);
    }

    @Override
    public LongStatistic next() {
      if (this.keyIdx >= KEYS.length) {
        throw new NoSuchElementException();
      }
      String key = KEYS[this.keyIdx++];
      Long val = fetch(data, key);
      return new LongStatistic(key, val.longValue());
    }

    @Override
    public void remove() {
      throw new UnsupportedOperationException();
    }
  }

  private static Long fetch(StatisticsData data, String key) {
    Preconditions.checkArgument(key != null,
        "The stat key of FileSystemStorageStatistics should not be null!");

    switch (key) {
    case "bytesRead":
      return data.getBytesRead();
    case "bytesWritten":
      return data.getBytesWritten();
    case "readOps":
      return (long) (data.getReadOps() + data.getLargeReadOps());
    case "largeReadOps":
      return Long.valueOf(data.getLargeReadOps());
    case "writeOps":
      return Long.valueOf(data.getWriteOps());
    default:
      return null;
    }
  }

  FileSystemStorageStatistics(String name, FileSystem.Statistics stats) {
    super(name);
    Preconditions.checkArgument(stats != null,
        "FileSystem.Statistics can not be null");
    Preconditions.checkArgument(stats.getData() != null,
        "FileSystem.Statistics can not have null data");
    this.stats = stats;
  }

  @Override
  public String getScheme() {
    return stats.getScheme();
  }

  @Override
  public Iterator<LongStatistic> getLongStatistics() {
    return new LongStatisticIterator(stats.getData());
  }

  @Override
  public Long getLong(String key) {
    return fetch(stats.getData(), key);
  }

  /**
   * Return true if a statistic is being tracked.
   *
   * @return         True only if the statistic is being tracked.
   */
  @Override
  public boolean isTracked(String key) {
    for (String k: KEYS) {
      if (k.equals(key)) {
        return true;
      }
    }
    return false;
  }

  @Override
  public void reset() {
    stats.reset();
  }
}