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.utils;
  
  import java.util.ArrayList;
  import java.util.List;
  import java.util.regex.Matcher;
  import java.util.regex.Pattern;
  
  import com.puppycrawl.tools.checkstyle.api.LineColumn;
  
  /**
   * Tools for extracting inline tags from Javadoc comments.
   *
   */
  public final class InlineTagUtil {
  
      /**
       * Inline tag pattern.
       */
      private static final Pattern INLINE_TAG_PATTERN = Pattern.compile(
              "\\{@(\\p{Alpha}+)\\b(.*?)}", Pattern.DOTALL);
  
      /** Pattern to recognize leading "*" characters in Javadoc. */
      private static final Pattern JAVADOC_PREFIX_PATTERN = Pattern.compile(
          "^\\s*\\*", Pattern.MULTILINE);
  
      /** Pattern matching whitespace, used by {@link InlineTagUtil#collapseWhitespace(String)}. */
      private static final Pattern WHITESPACE_PATTERN = Pattern.compile("\\s+");
  
      /** Pattern matching a newline. */
      private static final Pattern NEWLINE_PATTERN = Pattern.compile("\\n");
  
      /** Line feed character. */
      private static final char LINE_FEED = '\n';
  
      /** Carriage return character. */
      private static final char CARRIAGE_RETURN = '\r';
  
      /** Prevent instantiation. */
      private InlineTagUtil() {
      }
  
      /**
       * Extract inline Javadoc tags from the given comment.
       *
       * @param lines The Javadoc comment (as lines).
       * @return The extracted inline Javadoc tags.
       * @throws IllegalArgumentException when comment lines contain newlines
       */
      public static List<TagInfo> extractInlineTags(String... lines) {
          for (String line : lines) {
              if (line.indexOf(LINE_FEED) != -1 || line.indexOf(CARRIAGE_RETURN) != -1) {
                  throw new IllegalArgumentException("comment lines cannot contain newlines");
              }
          }
  
          final String commentText = convertLinesToString(lines);
          final Matcher inlineTagMatcher = INLINE_TAG_PATTERN.matcher(commentText);
  
          final List<TagInfo> tags = new ArrayList<>();
  
          while (inlineTagMatcher.find()) {
              final String tagName = inlineTagMatcher.group(1);
  
              // Remove the leading asterisks (in case the tag spans a line) and collapse
              // the whitespace.
              String matchedTagValue = inlineTagMatcher.group(2);
              matchedTagValue = removeLeadingJavaDoc(matchedTagValue);
              matchedTagValue = collapseWhitespace(matchedTagValue);
  
              final String tagValue = matchedTagValue;
  
              final int startIndex = inlineTagMatcher.start(1);
              final LineColumn position = getLineColumnOfIndex(commentText,
                  // correct start index offset
                  startIndex - 1);
  
              tags.add(new TagInfo(tagName, tagValue, position));
          }
  
          return tags;
      }
  
      /**
       * Convert array of string to single String.
       *
       * @param lines A number of lines, in order.
       * @return The lines, joined together with newlines, as a single string.
       */
      private static String convertLinesToString(String... lines) {
          final StringBuilder builder = new StringBuilder(1024);
          for (String line : lines) {
              builder.append(line);
              builder.append(LINE_FEED);
          }
          return builder.toString();
      }
  
      /**
       * Get LineColumn from string till index.
       *
       * @param source Source string.
       * @param index An index into the string.
       * @return A position in the source representing what line and column that index appears on.
       */
      private static LineColumn getLineColumnOfIndex(String source, int index) {
          final String precedingText = source.subSequence(0, index).toString();
          final String[] precedingLines = NEWLINE_PATTERN.split(precedingText);
          final String lastLine = precedingLines[precedingLines.length - 1];
          return new LineColumn(precedingLines.length, lastLine.length());
      }
  
      /**
       * Collapse whitespaces.
       *
       * @param str Source string.
       * @return The given string with all whitespace collapsed.
       */
      private static String collapseWhitespace(String str) {
          final Matcher matcher = WHITESPACE_PATTERN.matcher(str);
          return matcher.replaceAll(" ").trim();
      }
  
      /**
       * Remove leading JavaDoc.
       *
       * @param source A string to remove leading Javadoc from.
       * @return The given string with leading Javadoc "*" characters from each line removed.
       */
      private static String removeLeadingJavaDoc(String source) {
          final Matcher matcher = JAVADOC_PREFIX_PATTERN.matcher(source);
          return matcher.replaceAll("");
      }
  
  }
  