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.header;
  
  import java.io.File;
  import java.util.BitSet;
  
  import com.puppycrawl.tools.checkstyle.StatelessCheck;
  import com.puppycrawl.tools.checkstyle.api.FileText;
  import com.puppycrawl.tools.checkstyle.utils.TokenUtil;
  
  /**
   * <p>
   * Checks that a source file begins with a specified header.
   * Property {@code headerFile} specifies a file that contains the required header.
   * Alternatively, the header specification can be set directly in the
   * {@code header} property without the need for an external file.
   * </p>
   * <p>
   * Property {@code ignoreLines} specifies the line numbers to ignore when matching
   * lines in a header file. This property is very useful for supporting headers
   * that contain copyright dates. For example, consider the following header:
   * </p>
   * <pre>
   * line 1: ////////////////////////////////////////////////////////////////////
   * line 2: // checkstyle:
   * line 3: // Checks Java source code for adherence to a set of rules.
   * line 4: // Copyright (C) 2002  Oliver Burn
   * line 5: ////////////////////////////////////////////////////////////////////
   * </pre>
   * <p>
   * Since the year information will change over time, you can tell Checkstyle
   * to ignore line 4 by setting property {@code ignoreLines} to {@code 4}.
   * </p>
   * <p>
   * In default configuration, if header is not specified, the default value
   * of header is set to {@code null} and the check does not rise any violations.
   * </p>
   * <ul>
   * <li>
   * Property {@code headerFile} - Specify the name of the file containing the required header.
   * Type is {@code java.net.URI}.
   * Default value is {@code null}.
   * </li>
   * <li>
   * Property {@code charset} - Specify the character encoding to use when reading the headerFile.
   * Type is {@code java.lang.String}.
   * Default value is {@code the charset property of the parent
   * <a href="https://checkstyle.org/config.html#Checker">Checker</a> module}.
   * </li>
   * <li>
   * Property {@code header} - Specify the required header specified inline.
   * Individual header lines must be separated by the string {@code "\n"}
   * (even on platforms with a different line separator), see examples below.
   * Type is {@code java.lang.String}.
   * Default value is {@code null}.
   * </li>
   * <li>
   * Property {@code ignoreLines} - Specify the line numbers to ignore.
   * Type is {@code int[]}.
   * Default value is {@code ""}.
   * </li>
   * <li>
   * Property {@code fileExtensions} - Specify the file type extension of files to process.
   * Type is {@code java.lang.String[]}.
   * Default value is {@code ""}.
   * </li>
   * </ul>
   * <p>
   * To configure the check such that no violations arise.
   * Default values of properties are used.
   * </p>
   * <pre>
   * &lt;module name="Header"/&gt;
   * </pre>
   * <p>
   * To configure the check to use header file {@code "config/java.header"}
   * and ignore lines {@code 2}, {@code 3}, and {@code 4} and only process Java files:
   * </p>
   * <pre>
   * &lt;module name="Header"&gt;
   *   &lt;property name="headerFile" value="config/java.header"/&gt;
   *   &lt;property name="ignoreLines" value="2, 3, 4"/&gt;
   *   &lt;property name="fileExtensions" value="java"/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>
   * To configure the check to verify that each file starts with the header
   * </p>
   * <pre>
   * // Copyright (C) 2004 MyCompany
   * // All rights reserved
   * </pre>
   * <p>
   * without the need for an external header file:
   * </p>
   * <pre>
   * &lt;module name="Header"&gt;
   *   &lt;property name="header"
   *     value="// Copyright (C) 2004 MyCompany\n// All rights reserved"/&gt;
   * &lt;/module&gt;
   * </pre>
   * <p>
   * Parent is {@code com.puppycrawl.tools.checkstyle.Checker}
   * </p>
   * <p>
   * Violation Message Keys:
   * </p>
   * <ul>
   * <li>
   * {@code header.mismatch}
   * </li>
   * <li>
   * {@code header.missing}
   * </li>
   * </ul>
   *
   * @since 6.9
   */
  @StatelessCheck
  public class HeaderCheck extends AbstractHeaderCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_MISSING = "header.missing";
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_MISMATCH = "header.mismatch";
  
      /** Specify the line numbers to ignore. */
      private BitSet ignoreLines = new BitSet();
  
      /**
       * Returns true if lineNo is header lines or false.
       *
       * @param lineNo a line number
       * @return if {@code lineNo} is one of the ignored header lines.
       */
      private boolean isIgnoreLine(int lineNo) {
          return ignoreLines.get(lineNo);
      }
  
      /**
       * Checks if a code line matches the required header line.
       *
       * @param lineNumber the line number to check against the header
       * @param line the line contents
       * @return true if and only if the line matches the required header line
       */
      private boolean isMatch(int lineNumber, String line) {
          // skip lines we are meant to ignore
          return isIgnoreLine(lineNumber + 1)
              || getHeaderLines().get(lineNumber).equals(line);
      }
  
      /**
       * Setter to specify the line numbers to ignore.
       *
       * @param lines line numbers to ignore in header.
       */
      public void setIgnoreLines(int... lines) {
          ignoreLines = TokenUtil.asBitSet(lines);
      }
  
      @Override
      protected void processFiltered(File file, FileText fileText) {
          if (getHeaderLines().size() > fileText.size()) {
              log(1, MSG_MISSING);
          }
          else {
              for (int i = 0; i < getHeaderLines().size(); i++) {
                  if (!isMatch(i, fileText.get(i))) {
                      log(i + 1, MSG_MISMATCH, getHeaderLines().get(i));
                      break;
                  }
              }
          }
      }
  
      @Override
      protected void postProcessHeaderLines() {
          // no code
      }
  
  }
  