/**
  * @return position <code>x</code> for which <code>
  *     myDocument.getText().substring(x, startOffset)</code> contains <code>blankLinesNumber
  *     </code> line feeds and <code>myDocument.getText.charAt(x-1) == '\n'</code>
  */
 private int getBlankLineOffset(int blankLinesNumber, int startOffset) {
   int startLine = myDocument.getLineNumber(startOffset);
   if (startLine <= 0) {
     return 0;
   }
   CharSequence text = myDocument.getCharsSequence();
   for (int i = myDocument.getLineStartOffset(startLine - 1) - 1;
       i >= 0;
       i = CharArrayUtil.lastIndexOf(text, "\n", i - 1)) {
     if (--blankLinesNumber <= 0) {
       return i + 1;
     }
   }
   return 0;
 }
  @Nullable
  private TextRange findCommentedRange(final Commenter commenter) {
    final CharSequence text = myDocument.getCharsSequence();
    final FileType fileType = myFile.getFileType();
    if (fileType instanceof CustomSyntaxTableFileType) {
      Lexer lexer =
          new CustomFileTypeLexer(((CustomSyntaxTableFileType) fileType).getSyntaxTable());
      final int caretOffset = myCaret.getOffset();
      int commentStart =
          CharArrayUtil.lastIndexOf(text, commenter.getBlockCommentPrefix(), caretOffset);
      if (commentStart == -1) return null;

      lexer.start(text, commentStart, text.length());
      if (lexer.getTokenType() == CustomHighlighterTokenType.MULTI_LINE_COMMENT
          && lexer.getTokenEnd() >= caretOffset) {
        return new TextRange(commentStart, lexer.getTokenEnd());
      }
      return null;
    }

    final String prefix;
    final String suffix;
    // Custom uncommenter is able to find commented block inside of selected text
    final String selectedText = myCaret.getSelectedText();
    if ((commenter instanceof CustomUncommenter) && selectedText != null) {
      final TextRange commentedRange =
          ((CustomUncommenter) commenter).findMaximumCommentedRange(selectedText);
      if (commentedRange == null) {
        return null;
      }
      // Uncommenter returns range relative to text start, so we need to shift it to make abosolute.
      return commentedRange.shiftRight(myCaret.getSelectionStart());
    }

    if (commenter instanceof SelfManagingCommenter) {
      SelfManagingCommenter selfManagingCommenter = (SelfManagingCommenter) commenter;

      prefix =
          selfManagingCommenter.getBlockCommentPrefix(
              myCaret.getSelectionStart(), myDocument, mySelfManagedCommenterData);
      suffix =
          selfManagingCommenter.getBlockCommentSuffix(
              myCaret.getSelectionEnd(), myDocument, mySelfManagedCommenterData);
    } else {
      prefix = trim(commenter.getBlockCommentPrefix());
      suffix = trim(commenter.getBlockCommentSuffix());
    }
    if (prefix == null || suffix == null) return null;

    TextRange commentedRange;

    if (commenter instanceof SelfManagingCommenter) {
      commentedRange =
          ((SelfManagingCommenter) commenter)
              .getBlockCommentRange(
                  myCaret.getSelectionStart(),
                  myCaret.getSelectionEnd(),
                  myDocument,
                  mySelfManagedCommenterData);
    } else {
      if (!testSelectionForNonComments()) {
        return null;
      }

      commentedRange = getSelectedComments(text, prefix, suffix);
    }
    if (commentedRange == null) {
      PsiElement comment = findCommentAtCaret();
      if (comment != null) {

        String commentText = comment.getText();
        if (commentText.startsWith(prefix) && commentText.endsWith(suffix)) {
          commentedRange = comment.getTextRange();
        }
      }
    }
    return commentedRange;
  }