/**
   * Delete an existing directory including all child objects.
   *
   * @param aDir The directory to be deleted. May not be <code>null</code>.
   * @return A non-<code>null</code> error code.
   */
  @Nonnull
  public static FileIOError deleteDirRecursive(@Nonnull final File aDir) {
    ValueEnforcer.notNull(aDir, "Directory");

    // Non-existing directory?
    if (!FileUtils.existsDir(aDir))
      return EFileIOErrorCode.SOURCE_DOES_NOT_EXIST.getAsIOError(
          EFileIOOperation.DELETE_DIR_RECURSIVE, aDir);

    if (isWarnOnDeleteRoot()) {
      // Check that we're not deleting the complete hard drive...
      if (aDir.getAbsoluteFile().getParent() == null)
        throw new IllegalArgumentException(
            "Aren't we deleting the full drive: '" + aDir.getAbsolutePath() + "'");
    }

    // Is the parent directory writable?
    final File aParentDir = aDir.getParentFile();
    if (aParentDir != null && !FileUtils.canWrite(aParentDir))
      return EFileIOErrorCode.SOURCE_PARENT_NOT_WRITABLE.getAsIOError(
          EFileIOOperation.DELETE_DIR_RECURSIVE, aDir);

    // iterate directory
    for (final File aChild : FileUtils.getDirectoryContent(aDir)) {
      // is it a file or a directory or ...
      if (aChild.isDirectory()) {
        // Ignore "." and ".." directory
        if (FilenameHelper.isSystemInternalDirectory(aChild.getName())) continue;

        // recursive call
        final FileIOError eCode = deleteDirRecursive(aChild);
        if (eCode.isFailure()) return eCode;
      } else if (aChild.isFile()) {
        // delete file
        final FileIOError eCode = deleteFile(aChild);
        if (eCode.isFailure()) return eCode;
      } else {
        // Neither directory no file - don't know how to handle
        return EFileIOErrorCode.OBJECT_CANNOT_BE_HANDLED.getAsIOError(
            EFileIOOperation.DELETE_DIR_RECURSIVE, aChild);
      }
    }

    // Now this directory should be empty -> delete as if empty
    return deleteDir(aDir);
  }
  /**
   * Copy a directory including all child objects.
   *
   * @param aSourceDir The source directory to be copied. May not be <code>null</code>.
   * @param aTargetDir The destination directory where to be copied. This directory may not be
   *     existing. May not be <code>null</code>.
   * @return A non-<code>null</code> error code.
   */
  @Nonnull
  public static FileIOError copyDirRecursive(
      @Nonnull final File aSourceDir, @Nonnull final File aTargetDir) {
    ValueEnforcer.notNull(aSourceDir, "SourceDirectory");
    ValueEnforcer.notNull(aTargetDir, "TargetDirectory");

    // Does the source directory exist?
    if (!FileUtils.existsDir(aSourceDir))
      return EFileIOErrorCode.SOURCE_DOES_NOT_EXIST.getAsIOError(
          EFileIOOperation.COPY_DIR_RECURSIVE, aSourceDir);

    // Are source and target different?
    if (EqualsUtils.equals(aSourceDir, aTargetDir))
      return EFileIOErrorCode.SOURCE_EQUALS_TARGET.getAsIOError(
          EFileIOOperation.COPY_DIR_RECURSIVE, aSourceDir);

    // Is the source a parent of target?
    if (FileUtils.isParentDirectory(aSourceDir, aTargetDir))
      return EFileIOErrorCode.TARGET_IS_CHILD_OF_SOURCE.getAsIOError(
          EFileIOOperation.COPY_DIR_RECURSIVE, aSourceDir, aTargetDir);

    // Does the target directory already exist?
    if (aTargetDir.exists())
      return EFileIOErrorCode.TARGET_ALREADY_EXISTS.getAsIOError(
          EFileIOOperation.COPY_DIR_RECURSIVE, aTargetDir);

    // Is the source directory readable?
    if (!FileUtils.canRead(aSourceDir))
      return EFileIOErrorCode.SOURCE_NOT_READABLE.getAsIOError(
          EFileIOOperation.COPY_DIR_RECURSIVE, aSourceDir);

    // Is the target parent directory writable?
    final File aTargetParentDir = aTargetDir.getParentFile();
    if (aTargetParentDir != null
        && aTargetParentDir.exists()
        && !FileUtils.canWrite(aTargetParentDir))
      return EFileIOErrorCode.TARGET_PARENT_NOT_WRITABLE.getAsIOError(
          EFileIOOperation.COPY_DIR_RECURSIVE, aTargetDir);

    FileIOError eCode;

    // Ensure the targets parent directory is present
    eCode = createDirRecursive(aTargetDir);
    if (eCode.isFailure()) return eCode;

    for (final File aChild : FileUtils.getDirectoryContent(aSourceDir)) {
      if (aChild.isDirectory()) {
        // Skip "." and ".."
        if (FilenameHelper.isSystemInternalDirectory(aChild.getName())) continue;

        // Copy directory
        eCode = copyDirRecursive(aChild, new File(aTargetDir, aChild.getName()));
        if (eCode.isFailure()) return eCode;
      } else if (aChild.isFile()) {
        // Copy a file
        eCode = copyFile(aChild, new File(aTargetDir, aChild.getName()));
        if (eCode.isFailure()) return eCode;
      } else {
        // Neither directory not file - don't know how to handle
        return EFileIOErrorCode.OBJECT_CANNOT_BE_HANDLED.getAsIOError(
            EFileIOOperation.COPY_DIR_RECURSIVE, aChild);
      }
    }

    // Done
    return EFileIOErrorCode.NO_ERROR.getAsIOError(
        EFileIOOperation.COPY_DIR_RECURSIVE, aSourceDir, aTargetDir);
  }