code: ///////////////////////////////////////////////////////////////////////////////////////////////
  // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
  // Copyright (C) 2001-2023 the original author or authors.
  //
  // This library is free software; you can redistribute it and/or
  // modify it under the terms of the GNU Lesser General Public
  // License as published by the Free Software Foundation; either
  // version 2.1 of the License, or (at your option) any later version.
  //
  // This library is distributed in the hope that it will be useful,
  // but WITHOUT ANY WARRANTY; without even the implied warranty of
  // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  // Lesser General Public License for more details.
  //
  // You should have received a copy of the GNU Lesser General Public
  // License along with this library; if not, write to the Free Software
  // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  ///////////////////////////////////////////////////////////////////////////////////////////////
  
  package com.puppycrawl.tools.checkstyle.checks.javadoc;
  
  import java.util.ArrayList;
  import java.util.List;
  
  import com.puppycrawl.tools.checkstyle.StatelessCheck;
  import com.puppycrawl.tools.checkstyle.api.DetailNode;
  import com.puppycrawl.tools.checkstyle.api.JavadocTokenTypes;
  import com.puppycrawl.tools.checkstyle.utils.CommonUtil;
  import com.puppycrawl.tools.checkstyle.utils.JavadocUtil;
  
  /**
   * <p>
   * Checks the indentation of the continuation lines in block tags. That is whether the continued
   * description of at clauses should be indented or not. If the text is not properly indented it
   * throws a violation. A continuation line is when the description starts/spans past the line with
   * the tag. Default indentation required is at least 4, but this can be changed with the help of
   * properties below.
   * </p>
   * <ul>
   * <li>
   * Property {@code violateExecutionOnNonTightHtml} - Control when to print violations
   * if the Javadoc being examined by this check violates the tight html rules defined at
   * <a href="https://checkstyle.org/writingjavadocchecks.html#Tight-HTML_rules">Tight-HTML Rules</a>.
   * Type is {@code boolean}.
   * Default value is {@code false}.
   * </li>
   * <li>
   * Property {@code offset} - Specify how many spaces to use for new indentation level.
   * Type is {@code int}.
   * Default value is {@code 4}.
   * </li>
   * </ul>
   * <p>
   * To configure the default check:
   * </p>
   * <pre>
   * &lt;module name="JavadocTagContinuationIndentation"/&gt;
   * </pre>
   * <p>
   * Example:
   * </p>
   * <pre>
   * &#47;**
   *  * @tag comment
   *  *  Indentation spacing is 1. Line with violation
   *  *   Indentation spacing is 2. Line with violation
   *  *     Indentation spacing is 4. OK
   *  *&#47;
   * public class Test {
   * }
   * </pre>
   * <p>
   * To configure the check with two spaces indentation:
   * </p>
   * <pre>
   * &lt;module name="JavadocTagContinuationIndentation"&gt;
   *   &lt;property name="offset" value="2"/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>
   * Example:
   * </p>
   * <pre>
   * &#47;**
   *  * @tag comment
   *  * Indentation spacing is 0. Line with violation
   *  *   Indentation spacing is 2. OK
   *  *  Indentation spacing is 1. Line with violation
   *  *&#47;
   * public class Test {
   * }
   * </pre>
   * <p>
   * To configure the check to show violations for Tight-HTML Rules:
   * </p>
   * <pre>
   * &lt;module name="JavadocTagContinuationIndentation"&gt;
   *   &lt;property name="violateExecutionOnNonTightHtml" value="true"/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>
   * Example:
   * </p>
   * <pre>
   * &#47;**
   *  * &lt;p&gt; 'p' tag is unclosed. Line with violation, this html tag needs closing tag.
   *  * &lt;p&gt; 'p' tag is closed&lt;/p&gt;. OK
   *  *&#47;
   * public class Test {
   * }
   * </pre>
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code javadoc.missed.html.close}
   * </li>
   * <li>
   * {@code javadoc.parse.rule.error}
   * </li>
   * <li>
   * {@code javadoc.wrong.singleton.html.tag}
   * </li>
   * <li>
   * {@code tag.continuation.indent}
   * </li>
   * </ul>
   *
   * @since 6.0
   *
   */
  @StatelessCheck
  public class JavadocTagContinuationIndentationCheck extends AbstractJavadocCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_KEY = "tag.continuation.indent";
  
      /** Default tag continuation indentation. */
      private static final int DEFAULT_INDENTATION = 4;
  
      /**
       * Specify how many spaces to use for new indentation level.
       */
      private int offset = DEFAULT_INDENTATION;
  
      /**
       * Setter to specify how many spaces to use for new indentation level.
       *
       * @param offset custom value.
       */
      public void setOffset(int offset) {
          this.offset = offset;
      }
  
      @Override
      public int[] getDefaultJavadocTokens() {
          return new int[] {JavadocTokenTypes.DESCRIPTION };
      }
  
      @Override
      public int[] getRequiredJavadocTokens() {
          return getAcceptableJavadocTokens();
      }
  
      @Override
      public void visitJavadocToken(DetailNode ast) {
          if (!isInlineDescription(ast)) {
              final List<DetailNode> textNodes = getAllNewlineNodes(ast);
              for (DetailNode newlineNode : textNodes) {
                  final DetailNode textNode = JavadocUtil.getNextSibling(newlineNode);
                  if (textNode.getType() == JavadocTokenTypes.TEXT && isViolation(textNode)) {
                      log(textNode.getLineNumber(), MSG_KEY, offset);
                  }
              }
          }
      }
  
      /**
       * Checks if a text node meets the criteria for a violation.
       * If the text is shorter than {@code offset} characters, then a violation is
       * detected if the text is not blank or the next node is not a newline.
       * If the text is longer than {@code offset} characters, then a violation is
       * detected if any of the first {@code offset} characters are not blank.
       *
       * @param textNode the node to check.
       * @return true if the node has a violation.
       */
      private boolean isViolation(DetailNode textNode) {
          boolean result = false;
          final String text = textNode.getText();
          if (text.length() <= offset) {
              if (CommonUtil.isBlank(text)) {
                  final DetailNode nextNode = JavadocUtil.getNextSibling(textNode);
                  if (nextNode != null && nextNode.getType() != JavadocTokenTypes.NEWLINE) {
                      // text is blank but line hasn't ended yet
                      result = true;
                  }
              }
              else {
                  // text is not blank
                  result = true;
              }
          }
          else if (!CommonUtil.isBlank(text.substring(1, offset + 1))) {
              // first offset number of characters are not blank
              result = true;
          }
          return result;
      }
  
      /**
       * Finds and collects all NEWLINE nodes inside DESCRIPTION node.
       *
       * @param descriptionNode DESCRIPTION node.
       * @return List with NEWLINE nodes.
       */
      private static List<DetailNode> getAllNewlineNodes(DetailNode descriptionNode) {
          final List<DetailNode> textNodes = new ArrayList<>();
          DetailNode node = JavadocUtil.getFirstChild(descriptionNode);
          while (JavadocUtil.getNextSibling(node) != null) {
              if (node.getType() == JavadocTokenTypes.HTML_ELEMENT) {
                  final DetailNode descriptionNodeChild = JavadocUtil.getFirstChild(node);
                  textNodes.addAll(getAllNewlineNodes(descriptionNodeChild));
              }
              if (node.getType() == JavadocTokenTypes.LEADING_ASTERISK) {
                  textNodes.add(node);
              }
              node = JavadocUtil.getNextSibling(node);
          }
          return textNodes;
      }
  
      /**
       * Checks, if description node is a description of in-line tag.
       *
       * @param description DESCRIPTION node.
       * @return true, if description node is a description of in-line tag.
       */
      private static boolean isInlineDescription(DetailNode description) {
          boolean isInline = false;
          DetailNode inlineTag = description.getParent();
          while (inlineTag != null) {
              if (inlineTag.getType() == JavadocTokenTypes.JAVADOC_INLINE_TAG) {
                  isInline = true;
                  break;
              }
              inlineTag = inlineTag.getParent();
          }
          return isInline;
      }
  
  }
  