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.Locale;
  
  import com.puppycrawl.tools.checkstyle.StatelessCheck;
  import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
  import com.puppycrawl.tools.checkstyle.api.DetailAST;
  import com.puppycrawl.tools.checkstyle.api.TokenTypes;
  import com.puppycrawl.tools.checkstyle.utils.JavadocUtil;
  import com.puppycrawl.tools.checkstyle.utils.TokenUtil;
  
  /**
   * <p>
   * Checks that the Javadoc content begins from the same position
   * for all Javadoc comments in the project. Any leading asterisks and spaces
   * are not counted as the beginning of the content and are therefore ignored.
   * </p>
   * <p>
   * It is possible to enforce two different styles:
   * </p>
   * <ul>
   * <li>
   * {@code first_line} - Javadoc content starts from the first line:
   * <pre>
   * &#47;** Summary text.
   *   * More details.
   *   *&#47;
   * public void method();
   * </pre>
   * </li>
   * <li>
   * {@code second_line} - Javadoc content starts from the second line:
   * <pre>
   * &#47;**
   *   * Summary text.
   *   * More details.
   *   *&#47;
   * public void method();
   * </pre>
   * </li>
   * </ul>
   * <p>
   * This check does not validate the Javadoc summary itself nor its presence.
   * The check will not report any violations for missing or malformed javadoc summary.
   * To validate the Javadoc summary use
   * <a href="https://checkstyle.org/checks/javadoc/summaryjavadoc.html#SummaryJavadoc">
   * SummaryJavadoc</a> check.
   * </p>
   * <p>
   * The <a href="https://docs.oracle.com/en/java/javase/11/docs/specs/doc-comment-spec.html">
   * Documentation Comment Specification</a> permits leading asterisks on the first line.
   * For these Javadoc comments:
   * </p>
   * <pre>
   * &#47;***
   *   * Some text.
   *   *&#47;
   * &#47;************
   *   * Some text.
   *   *&#47;
   * &#47;**           **
   *   * Some text.
   *   *&#47;
   * </pre>
   * <p>
   * The documentation generated will be just "Some text." without any asterisks.
   * Since these asterisks will not appear in the generated documentation,
   * they should not be considered as the beginning of the Javadoc content.
   * In such cases, the check assumes that the Javadoc content begins on the second line.
   * </p>
   * <ul>
   * <li>
   * Property {@code location} - Specify the policy on placement of the Javadoc content.
   * Type is {@code com.puppycrawl.tools.checkstyle.checks.javadoc.JavadocContentLocationOption}.
   * Default value is {@code second_line}.
   * </li>
   * </ul>
   * <p>
   * To configure the default check to validate that the Javadoc content starts from the second line:
   * </p>
   * <pre>
   * &lt;module name="JavadocContentLocationCheck"/&gt;
   * </pre>
   * <p>
   * This setting produces a violation for each multi-line comment starting
   * on the same line as the initial asterisks:
   * </p>
   * <pre>
   * &#47;** This comment causes a violation because it starts from the first line
   *   * and spans several lines.
   *   *&#47;
   * &#47;**
   *   * This comment is OK because it starts from the second line.
   *   *&#47;
   * &#47;** This comment is OK because it is on the single-line. *&#47;
   * </pre>
   * <p>
   * To ensure that Javadoc content starts from the first line:
   * </p>
   * <pre>
   * &lt;module name="JavadocContentLocationCheck"&gt;
   *   &lt;property name="location" value="first_line"/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>
   * This setting produces a violation for each comment not
   * starting on the same line as the initial asterisks:
   * </p>
   * <pre>
   * &#47;** This comment is OK because it starts on the first line.
   *    * There may be additional text.
   *    *&#47;
   * &#47;**
   *   * This comment causes a violation because it starts on the second line.
   *   *&#47;
   * &#47;** This single-line comment also is OK. *&#47;
   * </pre>
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code javadoc.content.first.line}
   * </li>
   * <li>
   * {@code javadoc.content.second.line}
   * </li>
   * </ul>
   *
   * @since 8.27
   */
  @StatelessCheck
  public class JavadocContentLocationCheck extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties" file.
       */
      public static final String MSG_JAVADOC_CONTENT_FIRST_LINE = "javadoc.content.first.line";
  
      /**
       * A key is pointing to the warning message text in "messages.properties" file.
       */
      public static final String MSG_JAVADOC_CONTENT_SECOND_LINE = "javadoc.content.second.line";
  
      /**
       * Specify the policy on placement of the Javadoc content.
       */
      private JavadocContentLocationOption location = JavadocContentLocationOption.SECOND_LINE;
  
      @Override
      public int[] getRequiredTokens() {
          return new int[] {
              TokenTypes.BLOCK_COMMENT_BEGIN,
          };
      }
  
      @Override
      public int[] getAcceptableTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getDefaultTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public boolean isCommentNodesRequired() {
          return true;
      }
  
      /**
       * Setter to specify the policy on placement of the Javadoc content.
       *
       * @param value string to decode location from
       * @throws IllegalArgumentException if unable to decode
       */
      public void setLocation(String value) {
          location = JavadocContentLocationOption.valueOf(value.trim().toUpperCase(Locale.ENGLISH));
      }
  
      @Override
      public void visitToken(DetailAST ast) {
          if (isMultilineComment(ast) && JavadocUtil.isJavadocComment(ast)) {
              final String commentContent = JavadocUtil.getJavadocCommentContent(ast);
              final int indexOfFirstNonBlankLine = findIndexOfFirstNonBlankLine(commentContent);
              if (indexOfFirstNonBlankLine >= 0) {
                  if (location == JavadocContentLocationOption.FIRST_LINE) {
                      if (indexOfFirstNonBlankLine != 0) {
                          log(ast, MSG_JAVADOC_CONTENT_FIRST_LINE);
                      }
                  }
                  else if (indexOfFirstNonBlankLine != 1) {
                      log(ast, MSG_JAVADOC_CONTENT_SECOND_LINE);
                  }
              }
          }
      }
  
      /**
       * Checks if a DetailAST of type {@code TokenTypes.BLOCK_COMMENT_BEGIN} span
       * more than one line. The node always has at least one child of the type
       * {@code TokenTypes.BLOCK_COMMENT_END}.
       *
       * @param node node to check
       * @return {@code true} for multi-line comment nodes
       */
      private static boolean isMultilineComment(DetailAST node) {
          return !TokenUtil.areOnSameLine(node, node.getLastChild());
      }
  
      /**
       * Returns the index of the first non-blank line.
       * All lines consists only of asterisks and whitespaces are treated as blank.
       *
       * @param commentContent Javadoc content to process
       * @return the index of the first non-blank line or {@code -1} if all lines are blank
       */
      private static int findIndexOfFirstNonBlankLine(String commentContent) {
          int lineNo = 0;
          boolean noContent = true;
          for (int i = 0; i < commentContent.length(); ++i) {
              final char character = commentContent.charAt(i);
              if (character == '\n') {
                  ++lineNo;
              }
              else if (character != '*' && !Character.isWhitespace(character)) {
                  noContent = false;
                  break;
              }
          }
          if (noContent) {
              lineNo = -1;
          }
          return lineNo;
      }
  
  }
  