/**
 * 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.hdfs.server.namenode.sps;

import java.io.IOException;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Queue;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.util.Daemon;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.google.common.annotations.VisibleForTesting;

/**
 * A Class to track the block collection IDs (Inode's ID) for which physical
 * storage movement needed as per the Namespace and StorageReports from DN.
 * It scan the pending directories for which storage movement is required and
 * schedule the block collection IDs for movement. It track the info of
 * scheduled items and remove the SPS xAttr from the file/Directory once
 * movement is success.
 */
@InterfaceAudience.Private
public class BlockStorageMovementNeeded {

  public static final Logger LOG =
      LoggerFactory.getLogger(BlockStorageMovementNeeded.class);

  private final Queue<ItemInfo> storageMovementNeeded =
      new LinkedList<ItemInfo>();

  /**
   * Map of startPath and number of child's. Number of child's indicate the
   * number of files pending to satisfy the policy.
   */
  private final Map<Long, DirPendingWorkInfo> pendingWorkForDirectory =
      new HashMap<>();

  private final Context ctxt;

  private Daemon pathIdCollector;

  private SPSPathIdProcessor pathIDProcessor;

  // Amount of time to cache the SUCCESS status of path before turning it to
  // NOT_AVAILABLE.
  private static long statusClearanceElapsedTimeMs = 300000;

  public BlockStorageMovementNeeded(Context context) {
    this.ctxt = context;
    pathIDProcessor = new SPSPathIdProcessor();
  }

  /**
   * Add the candidate to tracking list for which storage movement
   * expected if necessary.
   *
   * @param trackInfo
   *          - track info for satisfy the policy
   */
  public synchronized void add(ItemInfo trackInfo) {
    if (trackInfo != null) {
      storageMovementNeeded.add(trackInfo);
    }
  }

  /**
   * Add the itemInfo list to tracking list for which storage movement expected
   * if necessary.
   *
   * @param startPath
   *          - start path
   * @param itemInfoList
   *          - List of child in the directory
   * @param scanCompleted
   *          -Indicates whether the start id directory has no more elements to
   *          scan.
   */
  @VisibleForTesting
  public synchronized void addAll(long startPath, List<ItemInfo> itemInfoList,
      boolean scanCompleted) {
    storageMovementNeeded.addAll(itemInfoList);
    updatePendingDirScanStats(startPath, itemInfoList.size(), scanCompleted);
  }

  /**
   * Add the itemInfo to tracking list for which storage movement expected if
   * necessary.
   *
   * @param itemInfoList
   *          - List of child in the directory
   * @param scanCompleted
   *          -Indicates whether the ItemInfo start id directory has no more
   *          elements to scan.
   */
  @VisibleForTesting
  public synchronized void add(ItemInfo itemInfo, boolean scanCompleted) {
    storageMovementNeeded.add(itemInfo);
    // This represents sps start id is file, so no need to update pending dir
    // stats.
    if (itemInfo.getStartPath() == itemInfo.getFile()) {
      return;
    }
    updatePendingDirScanStats(itemInfo.getStartPath(), 1, scanCompleted);
  }

  private void updatePendingDirScanStats(long startPath, int numScannedFiles,
      boolean scanCompleted) {
    DirPendingWorkInfo pendingWork = pendingWorkForDirectory.get(startPath);
    if (pendingWork == null) {
      pendingWork = new DirPendingWorkInfo();
      pendingWorkForDirectory.put(startPath, pendingWork);
    }
    pendingWork.addPendingWorkCount(numScannedFiles);
    if (scanCompleted) {
      pendingWork.markScanCompleted();
    }
  }

  /**
   * Gets the satisfier files for which block storage movements check necessary
   * and make the movement if required.
   *
   * @return satisfier files
   */
  public synchronized ItemInfo get() {
    return storageMovementNeeded.poll();
  }

  /**
   * Returns queue size.
   */
  public synchronized int size() {
    return storageMovementNeeded.size();
  }

  public synchronized void clearAll() {
    storageMovementNeeded.clear();
    pendingWorkForDirectory.clear();
  }

  /**
   * Decrease the pending child count for directory once one file blocks moved
   * successfully. Remove the SPS xAttr if pending child count is zero.
   */
  public synchronized void removeItemTrackInfo(ItemInfo trackInfo,
      boolean isSuccess) throws IOException {
    if (trackInfo.isDir()) {
      // If track is part of some start inode then reduce the pending
      // directory work count.
      long startId = trackInfo.getStartPath();
      if (!ctxt.isFileExist(startId)) {
        // directory deleted just remove it.
        this.pendingWorkForDirectory.remove(startId);
      } else {
        DirPendingWorkInfo pendingWork = pendingWorkForDirectory.get(startId);
        if (pendingWork != null) {
          pendingWork.decrementPendingWorkCount();
          if (pendingWork.isDirWorkDone()) {
            ctxt.removeSPSHint(startId);
            pendingWorkForDirectory.remove(startId);
          }
        }
      }
    } else {
      // Remove xAttr if trackID doesn't exist in
      // storageMovementAttemptedItems or file policy satisfied.
      ctxt.removeSPSHint(trackInfo.getFile());
    }
  }

  /**
   * Clean all the movements in spsDirsToBeTraveresed/storageMovementNeeded
   * and notify to clean up required resources.
   * @throws IOException
   */
  public synchronized void clearQueuesWithNotification() {
    // Remove xAttr from directories
    Long trackId;
    while ((trackId = ctxt.getNextSPSPath()) != null) {
      try {
        // Remove xAttr for file
        ctxt.removeSPSHint(trackId);
      } catch (IOException ie) {
        LOG.warn("Failed to remove SPS xattr for track id " + trackId, ie);
      }
    }

    // File's directly added to storageMovementNeeded, So try to remove
    // xAttr for file
    ItemInfo itemInfo;
    while ((itemInfo = get()) != null) {
      try {
        // Remove xAttr for file
        if (!itemInfo.isDir()) {
          ctxt.removeSPSHint(itemInfo.getFile());
        }
      } catch (IOException ie) {
        LOG.warn(
            "Failed to remove SPS xattr for track id "
                + itemInfo.getFile(), ie);
      }
    }
    this.clearAll();
  }

  /**
   * Take dir tack ID from the spsDirsToBeTraveresed queue and collect child
   * ID's to process for satisfy the policy.
   */
  private class SPSPathIdProcessor implements Runnable {

    @Override
    public void run() {
      LOG.info("Starting SPSPathIdProcessor!.");
      Long startINode = null;
      while (ctxt.isRunning()) {
        try {
          if (!ctxt.isInSafeMode()) {
            if (startINode == null) {
              startINode = ctxt.getNextSPSPath();
            } // else same id will be retried
            if (startINode == null) {
              // Waiting for SPS path
              Thread.sleep(3000);
            } else {
              ctxt.scanAndCollectFiles(startINode);
              // check if directory was empty and no child added to queue
              DirPendingWorkInfo dirPendingWorkInfo =
                  pendingWorkForDirectory.get(startINode);
              if (dirPendingWorkInfo != null
                  && dirPendingWorkInfo.isDirWorkDone()) {
                ctxt.removeSPSHint(startINode);
                pendingWorkForDirectory.remove(startINode);
              }
            }
            startINode = null; // Current inode successfully scanned.
          }
        } catch (Throwable t) {
          String reClass = t.getClass().getName();
          if (InterruptedException.class.getName().equals(reClass)) {
            LOG.info("SPSPathIdProcessor thread is interrupted. Stopping..");
            break;
          }
          LOG.warn("Exception while scanning file inodes to satisfy the policy",
              t);
          try {
            Thread.sleep(3000);
          } catch (InterruptedException e) {
            LOG.info("Interrupted while waiting in SPSPathIdProcessor", t);
            break;
          }
        }
      }
    }
  }

  /**
   * Info for directory recursive scan.
   */
  public static class DirPendingWorkInfo {

    private int pendingWorkCount = 0;
    private boolean fullyScanned = false;

    /**
     * Increment the pending work count for directory.
     */
    public synchronized void addPendingWorkCount(int count) {
      this.pendingWorkCount = this.pendingWorkCount + count;
    }

    /**
     * Decrement the pending work count for directory one track info is
     * completed.
     */
    public synchronized void decrementPendingWorkCount() {
      this.pendingWorkCount--;
    }

    /**
     * Return true if all the pending work is done and directory fully
     * scanned, otherwise false.
     */
    public synchronized boolean isDirWorkDone() {
      return (pendingWorkCount <= 0 && fullyScanned);
    }

    /**
     * Mark directory scan is completed.
     */
    public synchronized void markScanCompleted() {
      this.fullyScanned = true;
    }
  }

  public void activate() {
    pathIdCollector = new Daemon(pathIDProcessor);
    pathIdCollector.setName("SPSPathIdProcessor");
    pathIdCollector.start();
  }

  public void close() {
    if (pathIdCollector != null) {
      pathIdCollector.interrupt();
    }
  }

  @VisibleForTesting
  public static void setStatusClearanceElapsedTimeMs(
      long statusClearanceElapsedTimeMs) {
    BlockStorageMovementNeeded.statusClearanceElapsedTimeMs =
        statusClearanceElapsedTimeMs;
  }

  @VisibleForTesting
  public static long getStatusClearanceElapsedTimeMs() {
    return statusClearanceElapsedTimeMs;
  }

  public void markScanCompletedForDir(long inode) {
    DirPendingWorkInfo pendingWork = pendingWorkForDirectory.get(inode);
    if (pendingWork != null) {
      pendingWork.markScanCompleted();
    }
  }
}