/*
 * 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.ozone;

import com.google.common.base.Preconditions;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.BlockLocation;
import org.apache.hadoop.fs.CreateFlag;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.FileChecksum;
import org.apache.hadoop.fs.FileStatus;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.InvalidPathException;
import org.apache.hadoop.fs.LocatedFileStatus;
import org.apache.hadoop.fs.Options.Rename;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.fs.PathFilter;
import org.apache.hadoop.fs.PathIsNotEmptyDirectoryException;
import org.apache.hadoop.fs.RemoteIterator;
import org.apache.hadoop.fs.permission.FsPermission;
import org.apache.hadoop.hdds.annotation.InterfaceAudience;
import org.apache.hadoop.hdds.annotation.InterfaceStability;
import org.apache.hadoop.hdds.conf.ConfigurationSource;
import org.apache.hadoop.hdds.conf.OzoneConfiguration;
import org.apache.hadoop.hdds.conf.StorageUnit;
import org.apache.hadoop.hdds.utils.LegacyHadoopConfigurationSource;
import org.apache.hadoop.ozone.om.exceptions.OMException;
import org.apache.hadoop.ozone.om.helpers.OzoneFSUtils;
import org.apache.hadoop.security.UserGroupInformation;
import org.apache.hadoop.security.token.Token;
import org.apache.hadoop.util.Progressable;
import org.apache.http.client.utils.URIBuilder;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.net.URI;
import java.net.URISyntaxException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.EnumSet;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Objects;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.stream.Collectors;

import static org.apache.hadoop.fs.ozone.Constants.LISTING_PAGE_SIZE;
import static org.apache.hadoop.fs.ozone.Constants.OZONE_DEFAULT_USER;
import static org.apache.hadoop.fs.ozone.Constants.OZONE_USER_DIR;
import static org.apache.hadoop.ozone.OzoneConfigKeys.OZONE_FS_ITERATE_BATCH_SIZE;
import static org.apache.hadoop.ozone.OzoneConfigKeys.OZONE_FS_ITERATE_BATCH_SIZE_DEFAULT;
import static org.apache.hadoop.ozone.OzoneConfigKeys.OZONE_SCM_BLOCK_SIZE;
import static org.apache.hadoop.ozone.OzoneConfigKeys.OZONE_SCM_BLOCK_SIZE_DEFAULT;
import static org.apache.hadoop.ozone.OzoneConsts.OZONE_URI_DELIMITER;
import static org.apache.hadoop.ozone.OzoneConsts.OZONE_URI_SCHEME;

/**
 * The minimal Ozone Filesystem implementation.
 * <p>
 * This is a basic version which doesn't extend
 * KeyProviderTokenIssuer and doesn't include statistics. It can be used
 * from older hadoop version. For newer hadoop version use the full featured
 * OzoneFileSystem.
 */
@InterfaceAudience.Private
@InterfaceStability.Evolving
public class BasicOzoneFileSystem extends FileSystem {
  static final Logger LOG =
      LoggerFactory.getLogger(BasicOzoneFileSystem.class);

  /**
   * The Ozone client for connecting to Ozone server.
   */

  private URI uri;
  private String userName;
  private Path workingDir;

  private OzoneClientAdapter adapter;

  private static final Pattern URL_SCHEMA_PATTERN =
      Pattern.compile("([^\\.]+)\\.([^\\.]+)\\.{0,1}(.*)");

  private static final String URI_EXCEPTION_TEXT = "Ozone file system URL " +
      "should be one of the following formats: " +
      "o3fs://bucket.volume/key  OR " +
      "o3fs://bucket.volume.om-host.example.com/key  OR " +
      "o3fs://bucket.volume.om-host.example.com:5678/key";

  @Override
  public void initialize(URI name, Configuration conf) throws IOException {
    super.initialize(name, conf);
    setConf(conf);
    Objects.requireNonNull(name.getScheme(), "No scheme provided in " + name);
    Preconditions.checkArgument(getScheme().equals(name.getScheme()),
        "Invalid scheme provided in " + name);

    String authority = name.getAuthority();
    if (authority == null) {
      // authority is null when fs.defaultFS is not a qualified o3fs URI and
      // o3fs:/// is passed to the client. matcher will NPE if authority is null
      throw new IllegalArgumentException(URI_EXCEPTION_TEXT);
    }

    Matcher matcher = URL_SCHEMA_PATTERN.matcher(authority);

    if (!matcher.matches()) {
      throw new IllegalArgumentException(URI_EXCEPTION_TEXT);
    }
    String bucketStr = matcher.group(1);
    String volumeStr = matcher.group(2);
    String remaining = matcher.groupCount() == 3 ? matcher.group(3) : null;

    String omHost = null;
    int omPort = -1;
    if (!isEmpty(remaining)) {
      String[] parts = remaining.split(":");
      // Array length should be either 1(hostname or service id) or 2(host:port)
      if (parts.length > 2) {
        throw new IllegalArgumentException(URI_EXCEPTION_TEXT);
      }
      omHost = parts[0];
      if (parts.length == 2) {
        try {
          omPort = Integer.parseInt(parts[1]);
        } catch (NumberFormatException e) {
          throw new IllegalArgumentException(URI_EXCEPTION_TEXT);
        }
      }
    }

    try {
      uri = new URIBuilder().setScheme(OZONE_URI_SCHEME)
          .setHost(authority)
          .build();
      LOG.trace("Ozone URI for ozfs initialization is {}", uri);

      ConfigurationSource source = getConfSource();
      this.adapter =
          createAdapter(source, bucketStr,
              volumeStr, omHost, omPort);

      try {
        this.userName =
            UserGroupInformation.getCurrentUser().getShortUserName();
      } catch (IOException e) {
        this.userName = OZONE_DEFAULT_USER;
      }
      this.workingDir = new Path(OZONE_USER_DIR, this.userName)
          .makeQualified(this.uri, this.workingDir);

    } catch (URISyntaxException ue) {
      final String msg = "Invalid Ozone endpoint " + name;
      LOG.error(msg, ue);
      throw new IOException(msg, ue);
    }
  }

  protected OzoneClientAdapter createAdapter(ConfigurationSource conf,
      String bucketStr,
      String volumeStr, String omHost, int omPort) throws IOException {

    return new BasicOzoneClientAdapterImpl(omHost, omPort, conf,
        volumeStr, bucketStr);
  }

  @Override
  public void close() throws IOException {
    try {
      adapter.close();
    } finally {
      super.close();
    }
  }

  @Override
  public URI getUri() {
    return uri;
  }

  @Override
  public String getScheme() {
    return OZONE_URI_SCHEME;
  }

  @Override
  public FSDataInputStream open(Path f, int bufferSize) throws IOException {
    incrementCounter(Statistic.INVOCATION_OPEN, 1);
    statistics.incrementReadOps(1);
    LOG.trace("open() path:{}", f);
    final String key = pathToKey(f);
    InputStream inputStream = adapter.readFile(key);
    return new FSDataInputStream(createFSInputStream(inputStream));
  }

  protected InputStream createFSInputStream(InputStream inputStream) {
    return new OzoneFSInputStream(inputStream, statistics);
  }

  protected void incrementCounter(Statistic statistic) {
    incrementCounter(statistic, 1);
  }

  protected void incrementCounter(Statistic statistic, long count) {
    //don't do anything in this default implementation.
  }

  @Override
  public FSDataOutputStream create(Path f, FsPermission permission,
      boolean overwrite, int bufferSize,
      short replication, long blockSize,
      Progressable progress) throws IOException {
    LOG.trace("create() path:{}", f);
    incrementCounter(Statistic.INVOCATION_CREATE, 1);
    statistics.incrementWriteOps(1);
    final String key = pathToKey(f);
    return createOutputStream(key, replication, overwrite, true);
  }

  @Override
  public FSDataOutputStream createNonRecursive(Path path,
      FsPermission permission,
      EnumSet<CreateFlag> flags,
      int bufferSize,
      short replication,
      long blockSize,
      Progressable progress) throws IOException {
    incrementCounter(Statistic.INVOCATION_CREATE_NON_RECURSIVE, 1);
    statistics.incrementWriteOps(1);
    final String key = pathToKey(path);
    return createOutputStream(key,
        replication, flags.contains(CreateFlag.OVERWRITE), false);
  }

  private FSDataOutputStream createOutputStream(String key, short replication,
      boolean overwrite, boolean recursive) throws IOException {
    return new FSDataOutputStream(adapter.createFile(key,
        replication, overwrite, recursive), statistics);
  }

  @Override
  public FSDataOutputStream append(Path f, int bufferSize,
      Progressable progress) throws IOException {
    throw new UnsupportedOperationException("append() Not implemented by the "
        + getClass().getSimpleName() + " FileSystem implementation");
  }

  private class RenameIterator extends OzoneListingIterator {
    private final String srcKey;
    private final String dstKey;

    RenameIterator(Path srcPath, Path dstPath)
        throws IOException {
      super(srcPath);
      srcKey = pathToKey(srcPath);
      dstKey = pathToKey(dstPath);
      LOG.trace("rename from:{} to:{}", srcKey, dstKey);
    }

    @Override
    boolean processKey(List<String> keyList) throws IOException {
      // TODO RenameKey needs to be changed to batch operation
      for(String key : keyList) {
        String newKeyName = dstKey.concat(key.substring(srcKey.length()));
        adapter.renameKey(key, newKeyName);
      }
      return true;
    }
  }

  /**
   * Check whether the source and destination path are valid and then perform
   * rename from source path to destination path.
   * <p>
   * The rename operation is performed by renaming the keys with src as prefix.
   * For such keys the prefix is changed from src to dst.
   *
   * @param src source path for rename
   * @param dst destination path for rename
   * @return true if rename operation succeeded or
   * if the src and dst have the same path and are of the same type
   * @throws IOException on I/O errors or if the src/dst paths are invalid.
   */
  @Override
  public boolean rename(Path src, Path dst) throws IOException {
    incrementCounter(Statistic.INVOCATION_RENAME, 1);
    statistics.incrementWriteOps(1);
    super.checkPath(src);
    super.checkPath(dst);

    String srcPath = src.toUri().getPath();
    String dstPath = dst.toUri().getPath();
    if (srcPath.equals(dstPath)) {
      return true;
    }

    LOG.trace("rename() from:{} to:{}", src, dst);
    if (src.isRoot()) {
      // Cannot rename root of file system
      LOG.trace("Cannot rename the root of a filesystem");
      return false;
    }

    // Check if the source exists
    FileStatus srcStatus;
    try {
      srcStatus = getFileStatus(src);
    } catch (FileNotFoundException fnfe) {
      // source doesn't exist, return
      return false;
    }

    // Cannot rename a directory to its own subdirectory
    if (srcStatus.isDirectory()) {
      Path dstParent = dst.getParent();
      while (dstParent != null && !src.equals(dstParent)) {
        dstParent = dstParent.getParent();
      }
      Preconditions.checkArgument(dstParent == null,
          "Cannot rename a directory to its own subdirectory");
    }
    // Check if the destination exists
    FileStatus dstStatus;
    try {
      dstStatus = getFileStatus(dst);
    } catch (FileNotFoundException fnde) {
      dstStatus = null;
    }

    if (dstStatus == null) {
      // If dst doesn't exist, check whether dst parent dir exists or not
      // if the parent exists, the source can still be renamed to dst path
      dstStatus = getFileStatus(dst.getParent());
      if (!dstStatus.isDirectory()) {
        throw new IOException(String.format(
            "Failed to rename %s to %s, %s is a file", src, dst,
            dst.getParent()));
      }
    } else {
      // if dst exists and source and destination are same,
      // check both the src and dst are of same type
      if (srcStatus.getPath().equals(dstStatus.getPath())) {
        return !srcStatus.isDirectory();
      } else if (dstStatus.isDirectory()) {
        // If dst is a directory, rename source as subpath of it.
        // for example rename /source to /dst will lead to /dst/source
        dst = new Path(dst, src.getName());
        dstPath = dst.toUri().getPath();
        FileStatus[] statuses;
        try {
          statuses = listStatus(dst);
        } catch (FileNotFoundException fnde) {
          statuses = null;
        }

        if (statuses != null && statuses.length > 0) {
          // If dst exists and not a directory not empty
          LOG.warn("Failed to rename {} to {}, file already exists" +
              " or not empty!", src, dst);
          return false;
        }
      } else {
        // If dst is not a directory
        LOG.warn("Failed to rename {} to {}, file already exists!", src, dst);
        return false;
      }
    }

    if (srcStatus.isDirectory()) {
      if (dstPath.toString()
          .startsWith(srcPath.toString() + OZONE_URI_DELIMITER)) {
        LOG.trace("Cannot rename a directory to a subdirectory of self");
        return false;
      }
    }
    RenameIterator iterator = new RenameIterator(src, dst);
    boolean result = iterator.iterate();
    if (result) {
      createFakeParentDirectory(src);
    }
    return result;
  }

  /**
   * Intercept rename to trash calls from TrashPolicyDefault.
   */
  @Deprecated
  protected void rename(final Path src, final Path dst,
      final Rename... options) throws IOException {
    boolean hasMoveToTrash = false;
    if (options != null) {
      for (Rename option : options) {
        if (option == Rename.TO_TRASH) {
          hasMoveToTrash = true;
          break;
        }
      }
    }
    if (!hasMoveToTrash) {
      // if doesn't have TO_TRASH option, just pass the call to super
      super.rename(src, dst, options);
    } else {
      rename(src, dst);
    }
  }

  private class DeleteIterator extends OzoneListingIterator {
    private boolean recursive;

    DeleteIterator(Path f, boolean recursive)
        throws IOException {
      super(f);
      this.recursive = recursive;
      if (getStatus().isDirectory()
          && !this.recursive
          && listStatus(f).length != 0) {
        throw new PathIsNotEmptyDirectoryException(f.toString());
      }
    }

    @Override
    boolean processKey(List<String> key) throws IOException {
      LOG.trace("deleting key:{}", key);
      boolean succeed = adapter.deleteObjects(key);
      // if recursive delete is requested ignore the return value of
      // deleteObject and issue deletes for other keys.
      return recursive || succeed;
    }
  }

  /**
   * Deletes the children of the input dir path by iterating though the
   * DeleteIterator.
   *
   * @param f directory path to be deleted
   * @return true if successfully deletes all required keys, false otherwise
   * @throws IOException
   */
  private boolean innerDelete(Path f, boolean recursive) throws IOException {
    LOG.trace("delete() path:{} recursive:{}", f, recursive);
    try {
      DeleteIterator iterator = new DeleteIterator(f, recursive);

      if (f.isRoot()) {
        LOG.warn("Cannot delete root directory.");
        return false;
      }

      return iterator.iterate();
    } catch (FileNotFoundException e) {
      if (LOG.isDebugEnabled()) {
        LOG.debug("Couldn't delete {} - does not exist", f);
      }
      return false;
    }
  }

  @Override
  public boolean delete(Path f, boolean recursive) throws IOException {
    incrementCounter(Statistic.INVOCATION_DELETE, 1);
    statistics.incrementWriteOps(1);
    LOG.debug("Delete path {} - recursive {}", f, recursive);
    FileStatus status;
    try {
      status = getFileStatus(f);
    } catch (FileNotFoundException ex) {
      LOG.warn("delete: Path does not exist: {}", f);
      return false;
    }

    String key = pathToKey(f);
    boolean result;

    if (status.isDirectory()) {
      LOG.debug("delete: Path is a directory: {}", f);

      result = innerDelete(f, recursive);
    } else {
      LOG.debug("delete: Path is a file: {}", f);
      result = adapter.deleteObject(key);
    }

    if (result) {
      // If this delete operation removes all files/directories from the
      // parent directory, then an empty parent directory must be created.
      createFakeParentDirectory(f);
    }

    return result;
  }

  /**
   * Create a fake parent directory key if it does not already exist and no
   * other child of this parent directory exists.
   *
   * @param f path to the fake parent directory
   * @throws IOException
   */
  private void createFakeParentDirectory(Path f) throws IOException {
    Path parent = f.getParent();
    if (parent != null && !parent.isRoot()) {
      createFakeDirectoryIfNecessary(parent);
    }
  }

  /**
   * Create a fake directory key if it does not already exist.
   *
   * @param f path to the fake directory
   * @throws IOException
   */
  private void createFakeDirectoryIfNecessary(Path f) throws IOException {
    String key = pathToKey(f);
    if (!key.isEmpty() && !o3Exists(f)) {
      LOG.debug("Creating new fake directory at {}", f);
      String dirKey = addTrailingSlashIfNeeded(key);
      adapter.createDirectory(dirKey);
    }
  }

  /**
   * Check if a file or directory exists corresponding to given path.
   *
   * @param f path to file/directory.
   * @return true if it exists, false otherwise.
   * @throws IOException
   */
  private boolean o3Exists(final Path f) throws IOException {
    Path path = makeQualified(f);
    try {
      getFileStatus(path);
      return true;
    } catch (FileNotFoundException ex) {
      return false;
    }
  }

  @Override
  public FileStatus[] listStatus(Path f) throws IOException {
    incrementCounter(Statistic.INVOCATION_LIST_STATUS, 1);
    statistics.incrementReadOps(1);
    LOG.trace("listStatus() path:{}", f);
    int numEntries = LISTING_PAGE_SIZE;
    LinkedList<FileStatus> statuses = new LinkedList<>();
    List<FileStatus> tmpStatusList;
    String startKey = "";

    do {
      tmpStatusList =
          adapter.listStatus(pathToKey(f), false, startKey, numEntries, uri,
              workingDir, getUsername())
              .stream()
              .map(this::convertFileStatus)
              .collect(Collectors.toList());

      if (!tmpStatusList.isEmpty()) {
        if (startKey.isEmpty()) {
          statuses.addAll(tmpStatusList);
        } else {
          statuses.addAll(tmpStatusList.subList(1, tmpStatusList.size()));
        }
        startKey = pathToKey(statuses.getLast().getPath());
      }
      // listStatus returns entries numEntries in size if available.
      // Any lesser number of entries indicate that the required entries have
      // exhausted.
    } while (tmpStatusList.size() == numEntries);


    return statuses.toArray(new FileStatus[0]);
  }

  @Override
  public void setWorkingDirectory(Path newDir) {
    workingDir = newDir;
  }

  @Override
  public Path getWorkingDirectory() {
    return workingDir;
  }

  @Override
  public Token<?> getDelegationToken(String renewer) throws IOException {
    return adapter.getDelegationToken(renewer);
  }

  /**
   * Get a canonical service name for this file system. If the URI is logical,
   * the hostname part of the URI will be returned.
   *
   * @return a service string that uniquely identifies this file system.
   */
  @Override
  public String getCanonicalServiceName() {
    return adapter.getCanonicalServiceName();
  }

  /**
   * Get the username of the FS.
   *
   * @return the short name of the user who instantiated the FS
   */
  public String getUsername() {
    return userName;
  }

  /**
   * Get the root directory of Trash for a path.
   * Returns /.Trash/<username>
   * Caller appends either Current or checkpoint timestamp for trash destination
   * @param path the trash root of the path to be determined.
   * @return trash root
   */
  @Override
  public Path getTrashRoot(Path path) {
    final Path pathToTrash = new Path(OZONE_URI_DELIMITER, TRASH_PREFIX);
    return new Path(pathToTrash, getUsername());
  }

  /**
   * Get all the trash roots for current user or all users.
   *
   * @param allUsers return trash roots for all users if true.
   * @return all the trash root directories.
   *         Returns .Trash of users if {@code /.Trash/$USER} exists.
   */
  @Override
  public Collection<FileStatus> getTrashRoots(boolean allUsers) {
    Path trashRoot = new Path(OZONE_URI_DELIMITER, TRASH_PREFIX);
    List<FileStatus> ret = new ArrayList<>();
    try {
      if (!allUsers) {
        Path userTrash = new Path(trashRoot, userName);
        if (exists(userTrash) && getFileStatus(userTrash).isDirectory()) {
          ret.add(getFileStatus(userTrash));
        }
      } else {
        if (exists(trashRoot)) {
          FileStatus[] candidates = listStatus(trashRoot);
          for (FileStatus candidate : candidates) {
            if (candidate.isDirectory()) {
              ret.add(candidate);
            }
          }
        }
      }
    } catch (IOException ex) {
      LOG.warn("Can't get all trash roots", ex);
    }
    return ret;
  }

  /**
   * Creates a directory. Directory is represented using a key with no value.
   *
   * @param path directory path to be created
   * @return true if directory exists or created successfully.
   * @throws IOException
   */
  private boolean mkdir(Path path) throws IOException {
    return adapter.createDirectory(pathToKey(path));
  }

  @Override
  public boolean mkdirs(Path f, FsPermission permission) throws IOException {
    incrementCounter(Statistic.INVOCATION_MKDIRS);
    LOG.trace("mkdir() path:{} ", f);
    String key = pathToKey(f);
    if (isEmpty(key)) {
      return false;
    }
    return mkdir(f);
  }

  @Override
  public long getDefaultBlockSize() {
    return (long)getConfSource().getStorageSize(
        OZONE_SCM_BLOCK_SIZE, OZONE_SCM_BLOCK_SIZE_DEFAULT, StorageUnit.BYTES);
  }

  @Override
  public FileStatus getFileStatus(Path f) throws IOException {
    incrementCounter(Statistic.INVOCATION_GET_FILE_STATUS, 1);
    statistics.incrementReadOps(1);
    LOG.trace("getFileStatus() path:{}", f);
    Path qualifiedPath = f.makeQualified(uri, workingDir);
    String key = pathToKey(qualifiedPath);
    FileStatus fileStatus = null;
    try {
      fileStatus = convertFileStatus(
          adapter.getFileStatus(key, uri, qualifiedPath, getUsername()));
    } catch (OMException ex) {
      if (ex.getResult().equals(OMException.ResultCodes.KEY_NOT_FOUND)) {
        throw new FileNotFoundException("File not found. path:" + f);
      }
    }
    return fileStatus;
  }

  @Override
  public BlockLocation[] getFileBlockLocations(FileStatus fileStatus,
                                               long start, long len)
      throws IOException {
    if (fileStatus instanceof LocatedFileStatus) {
      return ((LocatedFileStatus) fileStatus).getBlockLocations();
    } else {
      return super.getFileBlockLocations(fileStatus, start, len);
    }
  }

  @Override
  public short getDefaultReplication() {
    return adapter.getDefaultReplication();
  }

  @Override
  public void copyFromLocalFile(boolean delSrc, boolean overwrite, Path[] srcs,
      Path dst) throws IOException {
    incrementCounter(Statistic.INVOCATION_COPY_FROM_LOCAL_FILE);
    super.copyFromLocalFile(delSrc, overwrite, srcs, dst);
  }

  @Override
  public void copyFromLocalFile(boolean delSrc, boolean overwrite, Path src,
      Path dst) throws IOException {
    incrementCounter(Statistic.INVOCATION_COPY_FROM_LOCAL_FILE);
    super.copyFromLocalFile(delSrc, overwrite, src, dst);
  }

  @Override
  public boolean exists(Path f) throws IOException {
    incrementCounter(Statistic.INVOCATION_EXISTS);
    return super.exists(f);
  }

  @Override
  public FileChecksum getFileChecksum(Path f, long length) throws IOException {
    incrementCounter(Statistic.INVOCATION_GET_FILE_CHECKSUM);
    return super.getFileChecksum(f, length);
  }

  @Override
  public FileStatus[] globStatus(Path pathPattern) throws IOException {
    incrementCounter(Statistic.INVOCATION_GLOB_STATUS);
    return super.globStatus(pathPattern);
  }

  @Override
  public FileStatus[] globStatus(Path pathPattern, PathFilter filter)
      throws IOException {
    incrementCounter(Statistic.INVOCATION_GLOB_STATUS);
    return super.globStatus(pathPattern, filter);
  }

  @Override
  @SuppressWarnings("deprecation")
  public boolean isDirectory(Path f) throws IOException {
    incrementCounter(Statistic.INVOCATION_IS_DIRECTORY);
    return super.isDirectory(f);
  }

  @Override
  @SuppressWarnings("deprecation")
  public boolean isFile(Path f) throws IOException {
    incrementCounter(Statistic.INVOCATION_IS_FILE);
    return super.isFile(f);
  }

  @Override
  public RemoteIterator<LocatedFileStatus> listFiles(Path f, boolean recursive)
      throws IOException {
    incrementCounter(Statistic.INVOCATION_LIST_FILES);
    return super.listFiles(f, recursive);
  }

  @Override
  public RemoteIterator<LocatedFileStatus> listLocatedStatus(Path f)
      throws IOException {
    incrementCounter(Statistic.INVOCATION_LIST_LOCATED_STATUS);
    return super.listLocatedStatus(f);
  }

  /**
   * Turn a path (relative or otherwise) into an Ozone key.
   *
   * @param path the path of the file.
   * @return the key of the object that represents the file.
   */
  public String pathToKey(Path path) {
    Objects.requireNonNull(path, "Path can not be null!");
    if (!path.isAbsolute()) {
      path = new Path(workingDir, path);
    }
    // removing leading '/' char
    String key = path.toUri().getPath();

    if (!OzoneFSUtils.isValidName(key)) {
      throw new InvalidPathException("Invalid path Name " + key);
    }
    LOG.trace("path for key:{} is:{}", key, path);
    return key.substring(1);
  }

  /**
   * Add trailing delimiter to path if it is already not present.
   *
   * @param key the ozone Key which needs to be appended
   * @return delimiter appended key
   */
  private String addTrailingSlashIfNeeded(String key) {
    if (!isEmpty(key) && !key.endsWith(OZONE_URI_DELIMITER)) {
      return key + OZONE_URI_DELIMITER;
    } else {
      return key;
    }
  }

  public ConfigurationSource getConfSource() {
    Configuration conf = super.getConf();
    ConfigurationSource source;
    if (conf instanceof OzoneConfiguration) {
      source = (ConfigurationSource) conf;
    } else {
      source = new LegacyHadoopConfigurationSource(conf);
    }
    return source;
  }

  @Override
  public String toString() {
    return "OzoneFileSystem{URI=" + uri + ", "
        + "workingDir=" + workingDir + ", "
        + "userName=" + userName + ", "
        + "statistics=" + statistics
        + "}";
  }

  /**
   * This class provides an interface to iterate through all the keys in the
   * bucket prefixed with the input path key and process them.
   * <p>
   * Each implementing class should define how the keys should be processed
   * through the processKey() function.
   */
  private abstract class OzoneListingIterator {
    private final Path path;
    private final FileStatus status;
    private String pathKey;
    private Iterator<BasicKeyInfo> keyIterator;

    OzoneListingIterator(Path path)
        throws IOException {
      this.path = path;
      this.status = getFileStatus(path);
      this.pathKey = pathToKey(path);
      if (status.isDirectory()) {
        this.pathKey = addTrailingSlashIfNeeded(pathKey);
      }
      keyIterator = adapter.listKeys(pathKey);
    }

    /**
     * The output of processKey determines if further iteration through the
     * keys should be done or not.
     *
     * @return true if we should continue iteration of keys, false otherwise.
     * @throws IOException
     */
    abstract boolean processKey(List<String> key) throws IOException;

    /**
     * Iterates thorugh all the keys prefixed with the input path's key and
     * processes the key though processKey().
     * If for any key, the processKey() returns false, then the iteration is
     * stopped and returned with false indicating that all the keys could not
     * be processed successfully.
     *
     * @return true if all keys are processed successfully, false otherwise.
     * @throws IOException
     */
    boolean iterate() throws IOException {
      LOG.trace("Iterating path {}", path);
      List<String> keyList = new ArrayList<>();
      int batchSize = getConf().getInt(OZONE_FS_ITERATE_BATCH_SIZE,
          OZONE_FS_ITERATE_BATCH_SIZE_DEFAULT);
      if (status.isDirectory()) {
        LOG.trace("Iterating directory:{}", pathKey);
        while (keyIterator.hasNext()) {
          BasicKeyInfo key = keyIterator.next();
          LOG.trace("iterating key:{}", key.getName());
          if (!key.getName().equals("")) {
            keyList.add(key.getName());
          }
          if (keyList.size() >= batchSize) {
            if (!processKey(keyList)) {
              return false;
            } else {
              keyList.clear();
            }
          }
        }
        if (keyList.size() > 0) {
          if (!processKey(keyList)) {
            return false;
          }
        }
        return true;
      } else {
        LOG.trace("iterating file:{}", path);
        keyList.add(pathKey);
        return processKey(keyList);
      }
    }

    String getPathKey() {
      return pathKey;
    }

    boolean pathIsDirectory() {
      return status.isDirectory();
    }

    FileStatus getStatus() {
      return status;
    }
  }

  public OzoneClientAdapter getAdapter() {
    return adapter;
  }

  public boolean isEmpty(CharSequence cs) {
    return cs == null || cs.length() == 0;
  }

  public boolean isNumber(String number) {
    try {
      Integer.parseInt(number);
    } catch (NumberFormatException ex) {
      return false;
    }
    return true;
  }

  private FileStatus convertFileStatus(
      FileStatusAdapter fileStatusAdapter) {

    Path symLink = null;
    try {
      fileStatusAdapter.getSymlink();
    } catch (Exception ex) {
      //NOOP: If not symlink symlink remains null.
    }

    FileStatus fileStatus =  new FileStatus(
        fileStatusAdapter.getLength(),
        fileStatusAdapter.isDir(),
        fileStatusAdapter.getBlockReplication(),
        fileStatusAdapter.getBlocksize(),
        fileStatusAdapter.getModificationTime(),
        fileStatusAdapter.getAccessTime(),
        new FsPermission(fileStatusAdapter.getPermission()),
        fileStatusAdapter.getOwner(),
        fileStatusAdapter.getGroup(),
        symLink,
        fileStatusAdapter.getPath()
    );

    BlockLocation[] blockLocations = fileStatusAdapter.getBlockLocations();
    if (blockLocations == null || blockLocations.length == 0) {
      return fileStatus;
    }
    return new LocatedFileStatus(fileStatus, blockLocations);
  }

}