/**
 * 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;

import java.io.FileNotFoundException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

import org.apache.hadoop.fs.PathIsNotDirectoryException;
import org.apache.hadoop.fs.permission.FsAction;
import org.apache.hadoop.fs.permission.PermissionStatus;
import org.apache.hadoop.fs.StorageType;
import org.apache.hadoop.fs.XAttr;
import org.apache.hadoop.hdfs.DFSUtil;
import org.apache.hadoop.hdfs.protocol.SnapshotException;
import org.apache.hadoop.hdfs.server.blockmanagement.BlockStoragePolicySuite;
import org.apache.hadoop.hdfs.server.namenode.INodeReference.WithCount;
import org.apache.hadoop.hdfs.server.namenode.snapshot.DirectorySnapshottableFeature;
import org.apache.hadoop.hdfs.server.namenode.snapshot.DirectoryWithSnapshotFeature;
import org.apache.hadoop.hdfs.server.namenode.snapshot.DirectoryWithSnapshotFeature.DirectoryDiffList;
import org.apache.hadoop.hdfs.server.namenode.snapshot.Snapshot;
import org.apache.hadoop.hdfs.util.ReadOnlyList;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Preconditions;
import org.apache.hadoop.security.AccessControlException;

import static org.apache.hadoop.hdfs.protocol.HdfsConstants.BLOCK_STORAGE_POLICY_ID_UNSPECIFIED;

/**
 * Directory INode class.
 */
public class INodeDirectory extends INodeWithAdditionalFields
    implements INodeDirectoryAttributes {

  /** Cast INode to INodeDirectory. */
  public static INodeDirectory valueOf(INode inode, Object path
      ) throws FileNotFoundException, PathIsNotDirectoryException {
    if (inode == null) {
      throw new FileNotFoundException("Directory does not exist: "
          + DFSUtil.path2String(path));
    }
    if (!inode.isDirectory()) {
      throw new PathIsNotDirectoryException(DFSUtil.path2String(path));
    }
    return inode.asDirectory(); 
  }

  // Profiling shows that most of the file lists are between 1 and 4 elements.
  // Thus allocate the corresponding ArrayLists with a small initial capacity.
  public static final int DEFAULT_FILES_PER_DIRECTORY = 2;

  static final byte[] ROOT_NAME = DFSUtil.string2Bytes("");

  private List<INode> children = null;
  
  /** constructor */
  public INodeDirectory(long id, byte[] name, PermissionStatus permissions,
      long mtime) {
    super(id, name, permissions, mtime, 0L);
  }
  
  /**
   * Copy constructor
   * @param other The INodeDirectory to be copied
   * @param adopt Indicate whether or not need to set the parent field of child
   *              INodes to the new node
   * @param featuresToCopy any number of features to copy to the new node.
   *              The method will do a reference copy, not a deep copy.
   */
  public INodeDirectory(INodeDirectory other, boolean adopt,
      Feature... featuresToCopy) {
    super(other);
    this.children = other.children;
    if (adopt && this.children != null) {
      for (INode child : children) {
        child.setParent(this);
      }
    }
    this.features = featuresToCopy;
    AclFeature aclFeature = getFeature(AclFeature.class);
    if (aclFeature != null) {
      // for the de-duplication of AclFeature
      removeFeature(aclFeature);
      addFeature(AclStorage.addAclFeature(aclFeature));
    }
  }

  /** @return true unconditionally. */
  @Override
  public final boolean isDirectory() {
    return true;
  }

  /** @return this object. */
  @Override
  public final INodeDirectory asDirectory() {
    return this;
  }

  @Override
  public byte getLocalStoragePolicyID() {
    XAttrFeature f = getXAttrFeature();
    XAttr xattr = f == null ? null : f.getXAttr(
        BlockStoragePolicySuite.getStoragePolicyXAttrPrefixedName());
    if (xattr != null) {
      return (xattr.getValue())[0];
    }
    return BLOCK_STORAGE_POLICY_ID_UNSPECIFIED;
  }

  @Override
  public byte getStoragePolicyID() {
    byte id = getLocalStoragePolicyID();
    if (id != BLOCK_STORAGE_POLICY_ID_UNSPECIFIED) {
      return id;
    }
    // if it is unspecified, check its parent
    return getParent() != null ? getParent().getStoragePolicyID() : BLOCK_STORAGE_POLICY_ID_UNSPECIFIED;
  }

  void setQuota(BlockStoragePolicySuite bsps, long nsQuota, long ssQuota, StorageType type) {
    DirectoryWithQuotaFeature quota = getDirectoryWithQuotaFeature();
    if (quota != null) {
      // already has quota; so set the quota to the new values
      if (type != null) {
        quota.setQuota(ssQuota, type);
      } else {
        quota.setQuota(nsQuota, ssQuota);
      }
      if (!isQuotaSet() && !isRoot()) {
        removeFeature(quota);
      }
    } else {
      final QuotaCounts c = computeQuotaUsage(bsps);
      DirectoryWithQuotaFeature.Builder builder =
          new DirectoryWithQuotaFeature.Builder().nameSpaceQuota(nsQuota);
      if (type != null) {
        builder.typeQuota(type, ssQuota);
      } else {
        builder.storageSpaceQuota(ssQuota);
      }
      addDirectoryWithQuotaFeature(builder.build()).setSpaceConsumed(c);
    }
  }

  @Override
  public QuotaCounts getQuotaCounts() {
    final DirectoryWithQuotaFeature q = getDirectoryWithQuotaFeature();
    return q != null? q.getQuota(): super.getQuotaCounts();
  }

  @Override
  public void addSpaceConsumed(QuotaCounts counts) {
    super.addSpaceConsumed(counts);

    final DirectoryWithQuotaFeature q = getDirectoryWithQuotaFeature();
    if (q != null && isQuotaSet()) {
      q.addSpaceConsumed2Cache(counts);
    }
  }

  /**
   * If the directory contains a {@link DirectoryWithQuotaFeature}, return it;
   * otherwise, return null.
   */
  public final DirectoryWithQuotaFeature getDirectoryWithQuotaFeature() {
    return getFeature(DirectoryWithQuotaFeature.class);
  }

  /** Is this directory with quota? */
  final boolean isWithQuota() {
    return getDirectoryWithQuotaFeature() != null;
  }

  DirectoryWithQuotaFeature addDirectoryWithQuotaFeature(
      DirectoryWithQuotaFeature q) {
    Preconditions.checkState(!isWithQuota(), "Directory is already with quota");
    addFeature(q);
    return q;
  }

  int searchChildren(byte[] name) {
    return children == null? -1: Collections.binarySearch(children, name);
  }
  
  public DirectoryWithSnapshotFeature addSnapshotFeature(
      DirectoryDiffList diffs) {
    Preconditions.checkState(!isWithSnapshot(), 
        "Directory is already with snapshot");
    DirectoryWithSnapshotFeature sf = new DirectoryWithSnapshotFeature(diffs);
    addFeature(sf);
    return sf;
  }
  
  /**
   * If feature list contains a {@link DirectoryWithSnapshotFeature}, return it;
   * otherwise, return null.
   */
  public final DirectoryWithSnapshotFeature getDirectoryWithSnapshotFeature() {
    return getFeature(DirectoryWithSnapshotFeature.class);
  }

  /** Is this file has the snapshot feature? */
  public final boolean isWithSnapshot() {
    return getDirectoryWithSnapshotFeature() != null;
  }

  public DirectoryDiffList getDiffs() {
    DirectoryWithSnapshotFeature sf = getDirectoryWithSnapshotFeature();
    return sf != null ? sf.getDiffs() : null;
  }
  
  @Override
  public INodeDirectoryAttributes getSnapshotINode(int snapshotId) {
    DirectoryWithSnapshotFeature sf = getDirectoryWithSnapshotFeature();
    return sf == null ? this : sf.getDiffs().getSnapshotINode(snapshotId, this);
  }
  
  @Override
  public String toDetailString() {
    DirectoryWithSnapshotFeature sf = this.getDirectoryWithSnapshotFeature();
    return super.toDetailString() + (sf == null ? "" : ", " + sf.getDiffs()); 
  }

  public DirectorySnapshottableFeature getDirectorySnapshottableFeature() {
    return getFeature(DirectorySnapshottableFeature.class);
  }

  public boolean isSnapshottable() {
    return getDirectorySnapshottableFeature() != null;
  }

  /**
   * Check if this directory is a descendant directory
   * of a snapshot root directory.
   * @param snapshotRootDir the snapshot root directory
   * @return true if this directory is a descendant of snapshot root
   */
  public boolean isDescendantOfSnapshotRoot(INodeDirectory snapshotRootDir) {
    Preconditions.checkArgument(snapshotRootDir.isSnapshottable());
    INodeDirectory dir = this;
    while(dir != null) {
      if (dir.equals(snapshotRootDir)) {
        return true;
      }
      dir = dir.getParent();
    }
    return false;
  }

  public Snapshot getSnapshot(byte[] snapshotName) {
    return getDirectorySnapshottableFeature().getSnapshot(snapshotName);
  }

  public void setSnapshotQuota(int snapshotQuota) {
    getDirectorySnapshottableFeature().setSnapshotQuota(snapshotQuota);
  }

  public Snapshot addSnapshot(int id, String name,
      final LeaseManager leaseManager, final boolean captureOpenFiles,
      int maxSnapshotLimit)
      throws SnapshotException {
    return getDirectorySnapshottableFeature().addSnapshot(this, id, name,
        leaseManager, captureOpenFiles, maxSnapshotLimit);
  }

  public Snapshot removeSnapshot(
      ReclaimContext reclaimContext, String snapshotName)
      throws SnapshotException {
    return getDirectorySnapshottableFeature().removeSnapshot(
        reclaimContext, this, snapshotName);
  }

  public void renameSnapshot(String path, String oldName, String newName)
      throws SnapshotException {
    getDirectorySnapshottableFeature().renameSnapshot(path, oldName, newName);
  }

  /** add DirectorySnapshottableFeature */
  public void addSnapshottableFeature() {
    Preconditions.checkState(!isSnapshottable(),
        "this is already snapshottable, this=%s", this);
    DirectoryWithSnapshotFeature s = this.getDirectoryWithSnapshotFeature();
    final DirectorySnapshottableFeature snapshottable =
        new DirectorySnapshottableFeature(s);
    if (s != null) {
      this.removeFeature(s);
    }
    this.addFeature(snapshottable);
  }

  /** remove DirectorySnapshottableFeature */
  public void removeSnapshottableFeature() {
    DirectorySnapshottableFeature s = getDirectorySnapshottableFeature();
    Preconditions.checkState(s != null,
        "The dir does not have snapshottable feature: this=%s", this);
    this.removeFeature(s);
    if (s.getDiffs().asList().size() > 0) {
      // add a DirectoryWithSnapshotFeature back
      DirectoryWithSnapshotFeature sf = new DirectoryWithSnapshotFeature(
          s.getDiffs());
      addFeature(sf);
    }
  }

  /** 
   * Replace the given child with a new child. Note that we no longer need to
   * replace an normal INodeDirectory or INodeFile into an
   * INodeDirectoryWithSnapshot or INodeFileUnderConstruction. The only cases
   * for child replacement is for reference nodes.
   */
  public void replaceChild(INode oldChild, final INode newChild,
      final INodeMap inodeMap) {
    Preconditions.checkNotNull(children);
    final int i = searchChildren(newChild.getLocalNameBytes());
    Preconditions.checkState(i >= 0);
    Preconditions.checkState(oldChild == children.get(i)
        || oldChild == children.get(i).asReference().getReferredINode()
            .asReference().getReferredINode());
    oldChild = children.get(i);
    
    if (oldChild.isReference() && newChild.isReference()) {
      // both are reference nodes, e.g., DstReference -> WithName
      final INodeReference.WithCount withCount = 
          (WithCount) oldChild.asReference().getReferredINode();
      withCount.removeReference(oldChild.asReference());
    }
    children.set(i, newChild);
    
    // replace the instance in the created list of the diff list
    DirectoryWithSnapshotFeature sf = this.getDirectoryWithSnapshotFeature();
    if (sf != null) {
      sf.getDiffs().replaceCreatedChild(oldChild, newChild);
    }
    
    // update the inodeMap
    if (inodeMap != null) {
      inodeMap.put(newChild);
    }    
  }

  INodeReference.WithName replaceChild4ReferenceWithName(INode oldChild,
      int latestSnapshotId) {
    Preconditions.checkArgument(latestSnapshotId != Snapshot.CURRENT_STATE_ID);
    if (oldChild instanceof INodeReference.WithName) {
      return (INodeReference.WithName)oldChild;
    }

    final INodeReference.WithCount withCount;
    if (oldChild.isReference()) {
      Preconditions.checkState(oldChild instanceof INodeReference.DstReference);
      withCount = (INodeReference.WithCount) oldChild.asReference()
          .getReferredINode();
    } else {
      withCount = new INodeReference.WithCount(null, oldChild);
    }
    final INodeReference.WithName ref = new INodeReference.WithName(this,
        withCount, oldChild.getLocalNameBytes(), latestSnapshotId);
    replaceChild(oldChild, ref, null);
    return ref;
  }

  @Override
  public void recordModification(int latestSnapshotId) {
    if (isInLatestSnapshot(latestSnapshotId)
        && !shouldRecordInSrcSnapshot(latestSnapshotId)) {
      // add snapshot feature if necessary
      DirectoryWithSnapshotFeature sf = getDirectoryWithSnapshotFeature();
      if (sf == null) {
        sf = addSnapshotFeature(null);
      }
      // record self in the diff list if necessary
      sf.getDiffs().saveSelf2Snapshot(latestSnapshotId, this, null);
    }
  }

  /**
   * Save the child to the latest snapshot.
   * 
   * @return the child inode, which may be replaced.
   */
  public INode saveChild2Snapshot(final INode child, final int latestSnapshotId,
      final INode snapshotCopy) {
    if (latestSnapshotId == Snapshot.CURRENT_STATE_ID) {
      return child;
    }
    
    // add snapshot feature if necessary
    DirectoryWithSnapshotFeature sf = getDirectoryWithSnapshotFeature();
    if (sf == null) {
      sf = this.addSnapshotFeature(null);
    }
    return sf.saveChild2Snapshot(this, child, latestSnapshotId, snapshotCopy);
  }

  /**
   * @param name the name of the child
   * @param snapshotId
   *          if it is not {@link Snapshot#CURRENT_STATE_ID}, get the result
   *          from the corresponding snapshot; otherwise, get the result from
   *          the current directory.
   * @return the child inode.
   */
  public INode getChild(byte[] name, int snapshotId) {
    DirectoryWithSnapshotFeature sf;
    if (snapshotId == Snapshot.CURRENT_STATE_ID || 
        (sf = getDirectoryWithSnapshotFeature()) == null) {
      ReadOnlyList<INode> c = getCurrentChildrenList();
      final int i = ReadOnlyList.Util.binarySearch(c, name);
      return i < 0 ? null : c.get(i);
    }
    
    return sf.getChild(this, name, snapshotId);
  }

  /**
   * Search for the given INode in the children list and the deleted lists of
   * snapshots.
   * @return {@link Snapshot#CURRENT_STATE_ID} if the inode is in the children
   * list; {@link Snapshot#NO_SNAPSHOT_ID} if the inode is neither in the
   * children list nor in any snapshot; otherwise the snapshot id of the
   * corresponding snapshot diff list.
   */
  public int searchChild(INode inode) {
    INode child = getChild(inode.getLocalNameBytes(), Snapshot.CURRENT_STATE_ID);
    if (child != inode) {
      // inode is not in parent's children list, thus inode must be in
      // snapshot. identify the snapshot id and later add it into the path
      DirectoryDiffList diffs = getDiffs();
      if (diffs == null) {
        return Snapshot.NO_SNAPSHOT_ID;
      }
      return diffs.findSnapshotDeleted(inode);
    } else {
      return Snapshot.CURRENT_STATE_ID;
    }
  }
  
  /**
   * @param snapshotId
   *          if it is not {@link Snapshot#CURRENT_STATE_ID}, get the result
   *          from the corresponding snapshot; otherwise, get the result from
   *          the current directory.
   * @return the current children list if the specified snapshot is null;
   *         otherwise, return the children list corresponding to the snapshot.
   *         Note that the returned list is never null.
   */
  public ReadOnlyList<INode> getChildrenList(final int snapshotId) {
    DirectoryWithSnapshotFeature sf;
    if (snapshotId == Snapshot.CURRENT_STATE_ID
        || (sf = this.getDirectoryWithSnapshotFeature()) == null) {
      return getCurrentChildrenList();
    }
    return sf.getChildrenList(this, snapshotId);
  }
  
  private ReadOnlyList<INode> getCurrentChildrenList() {
    return children == null ? ReadOnlyList.Util.<INode> emptyList()
        : ReadOnlyList.Util.asReadOnlyList(children);
  }

  /**
   * Given a child's name, return the index of the next child
   *
   * @param name a child's name
   * @return the index of the next child
   */
  static int nextChild(ReadOnlyList<INode> children, byte[] name) {
    if (name.length == 0) { // empty name
      return 0;
    }
    int nextPos = ReadOnlyList.Util.binarySearch(children, name) + 1;
    if (nextPos >= 0) {
      return nextPos;
    }
    return -nextPos;
  }
  
  /**
   * Remove the specified child from this directory.
   */
  public boolean removeChild(INode child, int latestSnapshotId) {
    if (isInLatestSnapshot(latestSnapshotId)) {
      // create snapshot feature if necessary
      DirectoryWithSnapshotFeature sf = this.getDirectoryWithSnapshotFeature();
      if (sf == null) {
        sf = this.addSnapshotFeature(null);
      }
      return sf.removeChild(this, child, latestSnapshotId);
    }
    return removeChild(child);
  }
  
  /** 
   * Remove the specified child from this directory.
   * The basic remove method which actually calls children.remove(..).
   *
   * @param child the child inode to be removed
   * 
   * @return true if the child is removed; false if the child is not found.
   */
  public boolean removeChild(final INode child) {
    final int i = searchChildren(child.getLocalNameBytes());
    if (i < 0) {
      return false;
    }

    final INode removed = children.remove(i);
    Preconditions.checkState(removed == child);
    return true;
  }

  /**
   * Add a child inode to the directory.
   * 
   * @param node INode to insert
   * @param setModTime set modification time for the parent node
   *                   not needed when replaying the addition and 
   *                   the parent already has the proper mod time
   * @return false if the child with this name already exists; 
   *         otherwise, return true;
   */
  public boolean addChild(INode node, final boolean setModTime,
      final int latestSnapshotId) {
    final int low = searchChildren(node.getLocalNameBytes());
    if (low >= 0) {
      return false;
    }

    if (isInLatestSnapshot(latestSnapshotId)) {
      // create snapshot feature if necessary
      DirectoryWithSnapshotFeature sf = this.getDirectoryWithSnapshotFeature();
      if (sf == null) {
        sf = this.addSnapshotFeature(null);
      }
      return sf.addChild(this, node, setModTime, latestSnapshotId);
    }
    addChild(node, low);
    if (setModTime) {
      // update modification time of the parent directory
      updateModificationTime(node.getModificationTime(), latestSnapshotId);
    }
    return true;
  }

  public boolean addChild(INode node) {
    final int low = searchChildren(node.getLocalNameBytes());
    if (low >= 0) {
      return false;
    }
    addChild(node, low);
    return true;
  }

  /**
   * During image loading, the search is unnecessary since the insert position
   * should always be at the end of the map given the sequence they are
   * serialized on disk.
   */
  public boolean addChildAtLoading(INode node) {
    int pos;
    if (!node.isReference()) {
      pos = (children == null) ? (-1) : (-children.size() - 1);
      addChild(node, pos);
      return true;
    } else {
      return addChild(node);
    }
  }

  /**
   * Add the node to the children list at the given insertion point.
   * The basic add method which actually calls children.add(..).
   */
  private void addChild(final INode node, final int insertionPoint) {
    if (children == null) {
      children = new ArrayList<>(DEFAULT_FILES_PER_DIRECTORY);
    }
    node.setParent(this);
    children.add(-insertionPoint - 1, node);

    if (node.getGroupName() == null) {
      node.setGroup(getGroupName());
    }
  }

  @Override
  public QuotaCounts computeQuotaUsage(BlockStoragePolicySuite bsps,
      byte blockStoragePolicyId, boolean useCache, int lastSnapshotId) {
    final DirectoryWithSnapshotFeature sf = getDirectoryWithSnapshotFeature();

    QuotaCounts counts = new QuotaCounts.Builder().build();
    // we are computing the quota usage for a specific snapshot here, i.e., the
    // computation only includes files/directories that exist at the time of the
    // given snapshot
    if (sf != null && lastSnapshotId != Snapshot.CURRENT_STATE_ID
        && !(useCache && isQuotaSet())) {
      ReadOnlyList<INode> childrenList = getChildrenList(lastSnapshotId);
      for (INode child : childrenList) {
        final byte childPolicyId = child.getStoragePolicyIDForQuota(
            blockStoragePolicyId);
        counts.add(child.computeQuotaUsage(bsps, childPolicyId, useCache,
            lastSnapshotId));
      }
      counts.addNameSpace(1);
      return counts;
    }
    
    // compute the quota usage in the scope of the current directory tree
    final DirectoryWithQuotaFeature q = getDirectoryWithQuotaFeature();
    if (useCache && q != null && q.isQuotaSet()) { // use the cached quota
      return q.AddCurrentSpaceUsage(counts);
    } else {
      useCache = q != null && !q.isQuotaSet() ? false : useCache;
      return computeDirectoryQuotaUsage(bsps, blockStoragePolicyId, counts,
          useCache, lastSnapshotId);
    }
  }

  private QuotaCounts computeDirectoryQuotaUsage(BlockStoragePolicySuite bsps,
      byte blockStoragePolicyId, QuotaCounts counts, boolean useCache,
      int lastSnapshotId) {
    if (children != null) {
      for (INode child : children) {
        final byte childPolicyId = child.getStoragePolicyIDForQuota(
            blockStoragePolicyId);
        counts.add(child.computeQuotaUsage(bsps, childPolicyId, useCache,
            lastSnapshotId));
      }
    }
    return computeQuotaUsage4CurrentDirectory(bsps, blockStoragePolicyId,
        counts);
  }
  
  /** Add quota usage for this inode excluding children. */
  public QuotaCounts computeQuotaUsage4CurrentDirectory(
      BlockStoragePolicySuite bsps, byte storagePolicyId, QuotaCounts counts) {
    counts.addNameSpace(1);
    // include the diff list
    DirectoryWithSnapshotFeature sf = getDirectoryWithSnapshotFeature();
    if (sf != null) {
      counts.add(sf.computeQuotaUsage4CurrentDirectory(bsps, storagePolicyId));
    }
    return counts;
  }

  @Override
  public ContentSummaryComputationContext computeContentSummary(int snapshotId,
      ContentSummaryComputationContext summary) throws AccessControlException {
    final DirectoryWithSnapshotFeature sf = getDirectoryWithSnapshotFeature();
    if (sf != null && snapshotId == Snapshot.CURRENT_STATE_ID) {
      final ContentCounts counts = new ContentCounts.Builder().build();
      // if the getContentSummary call is against a non-snapshot path, the
      // computation should include all the deleted files/directories
      sf.computeContentSummary4Snapshot(summary.getBlockStoragePolicySuite(),
          counts);
      summary.getCounts().addContents(counts);
      // Also add ContentSummary to snapshotCounts (So we can extract it
      // later from the ContentSummary of all).
      summary.getSnapshotCounts().addContents(counts);
    }
    final DirectoryWithQuotaFeature q = getDirectoryWithQuotaFeature();
    if (q != null && snapshotId == Snapshot.CURRENT_STATE_ID) {
      return q.computeContentSummary(this, summary);
    } else {
      return computeDirectoryContentSummary(summary, snapshotId);
    }
  }

  protected ContentSummaryComputationContext computeDirectoryContentSummary(
      ContentSummaryComputationContext summary, int snapshotId)
      throws AccessControlException{
    // throws exception if failing the permission check
    summary.checkPermission(this, snapshotId, FsAction.READ_EXECUTE);
    ReadOnlyList<INode> childrenList = getChildrenList(snapshotId);
    // Explicit traversing is done to enable repositioning after relinquishing
    // and reacquiring locks.
    for (int i = 0;  i < childrenList.size(); i++) {
      INode child = childrenList.get(i);
      byte[] childName = child.getLocalNameBytes();

      long lastYieldCount = summary.getYieldCount();
      child.computeContentSummary(snapshotId, summary);

      // Check whether the computation was paused in the subtree.
      // The counts may be off, but traversing the rest of children
      // should be made safe.
      if (lastYieldCount == summary.getYieldCount()) {
        continue;
      }
      // The locks were released and reacquired. Check parent first.
      if (!isRoot() && getParent() == null) {
        // Stop further counting and return whatever we have so far.
        break;
      }
      // Obtain the children list again since it may have been modified.
      childrenList = getChildrenList(snapshotId);
      // Reposition in case the children list is changed. Decrement by 1
      // since it will be incremented when loops.
      i = nextChild(childrenList, childName) - 1;
    }

    // Increment the directory count for this directory.
    summary.getCounts().addContent(Content.DIRECTORY, 1);
    // Relinquish and reacquire locks if necessary.
    summary.yield();
    return summary;
  }
  
  /**
   * This method is usually called by the undo section of rename.
   * 
   * Before calling this function, in the rename operation, we replace the
   * original src node (of the rename operation) with a reference node (WithName
   * instance) in both the children list and a created list, delete the
   * reference node from the children list, and add it to the corresponding
   * deleted list.
   * 
   * To undo the above operations, we have the following steps in particular:
   * 
   * <pre>
   * 1) remove the WithName node from the deleted list (if it exists) 
   * 2) replace the WithName node in the created list with srcChild 
   * 3) add srcChild back as a child of srcParent. Note that we already add 
   * the node into the created list of a snapshot diff in step 2, we do not need
   * to add srcChild to the created list of the latest snapshot.
   * </pre>
   * 
   * We do not need to update quota usage because the old child is in the 
   * deleted list before. 
   * 
   * @param oldChild
   *          The reference node to be removed/replaced
   * @param newChild
   *          The node to be added back
   */
  public void undoRename4ScrParent(final INodeReference oldChild,
      final INode newChild) {
    DirectoryWithSnapshotFeature sf = getDirectoryWithSnapshotFeature();
    assert sf != null : "Directory does not have snapshot feature";
    sf.getDiffs().removeDeletedChild(oldChild);
    sf.getDiffs().replaceCreatedChild(oldChild, newChild);
    addChild(newChild, true, Snapshot.CURRENT_STATE_ID);
  }
  
  /**
   * Undo the rename operation for the dst tree, i.e., if the rename operation
   * (with OVERWRITE option) removes a file/dir from the dst tree, add it back
   * and delete possible record in the deleted list.  
   */
  public void undoRename4DstParent(final BlockStoragePolicySuite bsps,
      final INode deletedChild, int latestSnapshotId) {
    DirectoryWithSnapshotFeature sf = getDirectoryWithSnapshotFeature();
    assert sf != null : "Directory does not have snapshot feature";
    boolean removeDeletedChild = sf.getDiffs().removeDeletedChild(deletedChild);
    int sid = removeDeletedChild ? Snapshot.CURRENT_STATE_ID : latestSnapshotId;
    final boolean added = addChild(deletedChild, true, sid);
    // update quota usage if adding is successfully and the old child has not
    // been stored in deleted list before
    if (added && !removeDeletedChild) {
      final QuotaCounts counts = deletedChild.computeQuotaUsage(bsps);
      addSpaceConsumed(counts);
    }
  }

  /** Set the children list to null. */
  public void clearChildren() {
    this.children = null;
  }

  @Override
  public void clear() {
    super.clear();
    clearChildren();
  }

  /** Call cleanSubtree(..) recursively down the subtree. */
  public void cleanSubtreeRecursively(
      ReclaimContext reclaimContext, final int snapshot, int prior,
      final Map<INode, INode> excludedNodes) {
    // in case of deletion snapshot, since this call happens after we modify
    // the diff list, the snapshot to be deleted has been combined or renamed
    // to its latest previous snapshot. (besides, we also need to consider nodes
    // created after prior but before snapshot. this will be done in 
    // DirectoryWithSnapshotFeature)
    int s = snapshot != Snapshot.CURRENT_STATE_ID
        && prior != Snapshot.NO_SNAPSHOT_ID ? prior : snapshot;
    for (INode child : getChildrenList(s)) {
      if (snapshot == Snapshot.CURRENT_STATE_ID || excludedNodes == null ||
          !excludedNodes.containsKey(child)) {
        child.cleanSubtree(reclaimContext, snapshot, prior);
      }
    }
  }

  @Override
  public void destroyAndCollectBlocks(ReclaimContext reclaimContext) {
    reclaimContext.quotaDelta().add(
        new QuotaCounts.Builder().nameSpace(1).build());
    final DirectoryWithSnapshotFeature sf = getDirectoryWithSnapshotFeature();
    if (sf != null) {
      sf.clear(reclaimContext, this);
    }
    for (INode child : getChildrenList(Snapshot.CURRENT_STATE_ID)) {
      child.destroyAndCollectBlocks(reclaimContext);
    }
    if (getAclFeature() != null) {
      AclStorage.removeAclFeature(getAclFeature());
    }
    clear();
    reclaimContext.removedINodes.add(this);
  }
  
  @Override
  public void cleanSubtree(ReclaimContext reclaimContext, final int snapshotId,
      int priorSnapshotId) {
    DirectoryWithSnapshotFeature sf = getDirectoryWithSnapshotFeature();
    // there is snapshot data
    if (sf != null) {
      sf.cleanDirectory(reclaimContext, this, snapshotId, priorSnapshotId);
    } else {
      // there is no snapshot data
      if (priorSnapshotId == Snapshot.NO_SNAPSHOT_ID &&
          snapshotId == Snapshot.CURRENT_STATE_ID) {
        // destroy the whole subtree and collect blocks that should be deleted
        destroyAndCollectBlocks(reclaimContext);
      } else {
        // make a copy the quota delta
        QuotaCounts old = reclaimContext.quotaDelta().getCountsCopy();
        // process recursively down the subtree
        cleanSubtreeRecursively(reclaimContext, snapshotId, priorSnapshotId,
            null);
        QuotaCounts current = reclaimContext.quotaDelta().getCountsCopy();
        current.subtract(old);
        if (isQuotaSet()) {
          reclaimContext.quotaDelta().addQuotaDirUpdate(this, current);
        }
      }
    }
  }
  
  /**
   * Compare the metadata with another INodeDirectory
   */
  @Override
  public boolean metadataEquals(INodeDirectoryAttributes other) {
    return other != null
        && getQuotaCounts().equals(other.getQuotaCounts())
        && getPermissionLong() == other.getPermissionLong()
        && getAclFeature() == other.getAclFeature()
        && getXAttrFeature() == other.getXAttrFeature();
  }
  
  /*
   * The following code is to dump the tree recursively for testing.
   * 
   *      \- foo   (INodeDirectory@33dd2717)
   *        \- sub1   (INodeDirectory@442172)
   *          +- file1   (INodeFile@78392d4)
   *          +- file2   (INodeFile@78392d5)
   *          +- sub11   (INodeDirectory@8400cff)
   *            \- file3   (INodeFile@78392d6)
   *          \- z_file4   (INodeFile@45848712)
   */
  static final String DUMPTREE_EXCEPT_LAST_ITEM = "+-"; 
  static final String DUMPTREE_LAST_ITEM = "\\-";
  @VisibleForTesting
  @Override
  public void dumpTreeRecursively(PrintWriter out, StringBuilder prefix,
      final int snapshot) {
    super.dumpTreeRecursively(out, prefix, snapshot);
    out.print(", childrenSize=" + getChildrenList(snapshot).size());
    final DirectoryWithQuotaFeature q = getDirectoryWithQuotaFeature();
    if (q != null) {
      out.print(", " + q);
    }
    if (this instanceof Snapshot.Root) {
      out.print(", snapshotId=" + snapshot);
    }
    out.println();

    if (prefix.length() >= 2) {
      prefix.setLength(prefix.length() - 2);
      prefix.append("  ");
    }

    final DirectoryWithSnapshotFeature snapshotFeature =
        getDirectoryWithSnapshotFeature();
    if (snapshotFeature != null) {
      out.print(prefix);
      out.print(snapshotFeature);
    }
    out.println();
    dumpTreeRecursively(out, prefix, new Iterable<SnapshotAndINode>() {
      final Iterator<INode> i = getChildrenList(snapshot).iterator();
      
      @Override
      public Iterator<SnapshotAndINode> iterator() {
        return new Iterator<SnapshotAndINode>() {
          @Override
          public boolean hasNext() {
            return i.hasNext();
          }

          @Override
          public SnapshotAndINode next() {
            return new SnapshotAndINode(snapshot, i.next());
          }

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

    final DirectorySnapshottableFeature s = getDirectorySnapshottableFeature();
    if (s != null) {
      s.dumpTreeRecursively(this, out, prefix, snapshot);
    }
  }

  /**
   * Dump the given subtrees.
   * @param prefix The prefix string that each line should print.
   * @param subs The subtrees.
   */
  @VisibleForTesting
  public static void dumpTreeRecursively(PrintWriter out,
      StringBuilder prefix, Iterable<SnapshotAndINode> subs) {
    if (subs != null) {
      for(final Iterator<SnapshotAndINode> i = subs.iterator(); i.hasNext();) {
        final SnapshotAndINode pair = i.next();
        prefix.append(i.hasNext()? DUMPTREE_EXCEPT_LAST_ITEM: DUMPTREE_LAST_ITEM);
        pair.inode.dumpTreeRecursively(out, prefix, pair.snapshotId);
        prefix.setLength(prefix.length() - 2);
      }
    }
  }

  /** A pair of Snapshot and INode objects. */
  public static class SnapshotAndINode {
    public final int snapshotId;
    public final INode inode;

    public SnapshotAndINode(int snapshot, INode inode) {
      this.snapshotId = snapshot;
      this.inode = inode;
    }
  }

  public final int getChildrenNum(final int snapshotId) {
    return getChildrenList(snapshotId).size();
  }
}