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.regexp;
  
  import java.util.regex.Matcher;
  
  import com.puppycrawl.tools.checkstyle.api.FileText;
  
  /**
   * A detector that matches individual lines.
   */
  class SinglelineDetector {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_REGEXP_EXCEEDED = "regexp.exceeded";
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_REGEXP_MINIMUM = "regexp.minimum";
  
      /** The detection options to use. */
      private final DetectorOptions options;
      /** Tracks the number of matches. */
      private int currentMatches;
  
      /**
       * Creates an instance.
       *
       * @param options the options to use.
       */
      /* package */ SinglelineDetector(DetectorOptions options) {
          this.options = options;
      }
  
      /**
       * Processes a set of lines looking for matches.
       *
       * @param fileText {@link FileText} object contains the lines to process.
       */
      public void processLines(FileText fileText) {
          resetState();
          int lineNo = 0;
          for (int index = 0; index < fileText.size(); index++) {
              final String line = fileText.get(index);
              lineNo++;
              checkLine(lineNo, line, options.getPattern().matcher(line), 0);
          }
          finish();
      }
  
      /** Perform processing at the end of a set of lines. */
      private void finish() {
          if (currentMatches < options.getMinimum()) {
              if (options.getMessage().isEmpty()) {
                  options.getReporter().log(1, MSG_REGEXP_MINIMUM,
                          options.getMinimum(), options.getFormat());
              }
              else {
                  options.getReporter().log(1, options.getMessage());
              }
          }
      }
  
      /**
       * Reset the state of the detector.
       */
      private void resetState() {
          currentMatches = 0;
      }
  
      /**
       * Check a line for matches.
       *
       * @param lineNo the line number of the line to check
       * @param line the line to check
       * @param matcher the matcher to use
       * @param startPosition the position to start searching from.
       */
      private void checkLine(int lineNo, String line, Matcher matcher,
              int startPosition) {
          final boolean foundMatch = matcher.find(startPosition);
          if (foundMatch) {
              // match is found, check for intersection with comment
              final int startCol = matcher.start(0);
              final int endCol = matcher.end(0);
              // Note that Matcher.end(int) returns the offset AFTER the
              // last matched character, but shouldSuppress()
              // needs column number of the last character.
              // So we need to use (endCol - 1) here.
              if (options.getSuppressor()
                      .shouldSuppress(lineNo, startCol, lineNo, endCol - 1)) {
                  checkLine(lineNo, line, matcher, endCol);
              }
              else {
                  currentMatches++;
                  if (currentMatches > options.getMaximum()) {
                      if (options.getMessage().isEmpty()) {
                          options.getReporter().log(lineNo, MSG_REGEXP_EXCEEDED,
                                  matcher.pattern().toString());
                      }
                      else {
                          options.getReporter().log(lineNo, options.getMessage());
                      }
                  }
              }
          }
      }
  
  }
  