////////////////////////////////////////////////////////////////////////////////
   // checkstyle: Checks Java source code for adherence to a set of rules.
   // Copyright (C) 2001-2019 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.BufferedInputStream;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.io.LineNumberReader;
  import java.io.Reader;
  import java.io.StringReader;
  import java.io.UnsupportedEncodingException;
  import java.net.URI;
  import java.nio.charset.Charset;
  import java.nio.charset.StandardCharsets;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  import java.util.Set;
  import java.util.regex.Pattern;
  
  import com.puppycrawl.tools.checkstyle.api.AbstractFileSetCheck;
  import com.puppycrawl.tools.checkstyle.api.CheckstyleException;
  import com.puppycrawl.tools.checkstyle.api.ExternalResourceHolder;
  import com.puppycrawl.tools.checkstyle.utils.CommonUtil;
  
  /**
   * Abstract super class for header checks.
   * Provides support for header and headerFile properties.
   */
  public abstract class AbstractHeaderCheck extends AbstractFileSetCheck
      implements ExternalResourceHolder {
  
      /** Pattern to detect occurrences of '\n' in text. */
      private static final Pattern ESCAPED_LINE_FEED_PATTERN = Pattern.compile("\\\\n");
  
      /** The lines of the header file. */
      private final List<String> readerLines = new ArrayList<>();
  
      /** The file that contains the header to check against. */
      private URI headerFile;
  
      /** Name of a charset to use for loading the header from a file. */
      private String charset = System.getProperty("file.encoding", StandardCharsets.UTF_8.name());
  
      /**
       * Hook method for post processing header lines.
       * This implementation does nothing.
       */
      protected abstract void postProcessHeaderLines();
  
      /**
       * Return the header lines to check against.
       * @return the header lines to check against.
       */
      protected List<String> getHeaderLines() {
          final List<String> copy = new ArrayList<>(readerLines);
          return Collections.unmodifiableList(copy);
      }
  
      /**
       * Set the charset to use for loading the header from a file.
       * @param charset the charset to use for loading the header from a file
       * @throws UnsupportedEncodingException if charset is unsupported
       */
      public void setCharset(String charset) throws UnsupportedEncodingException {
          if (!Charset.isSupported(charset)) {
              final String message = "unsupported charset: '" + charset + "'";
              throw new UnsupportedEncodingException(message);
          }
          this.charset = charset;
      }
  
      /**
       * Set the header file to check against.
       * @param uri the uri of the header to load.
       * @throws CheckstyleException if fileName is empty.
       */
      public void setHeaderFile(URI uri) throws CheckstyleException {
          if (uri == null) {
              throw new CheckstyleException(
                  "property 'headerFile' is missing or invalid in module "
                      + getConfiguration().getName());
         }
 
         headerFile = uri;
     }
 
     /**
      * Load the header from a file.
      * @throws CheckstyleException if the file cannot be loaded
      */
     private void loadHeaderFile() throws CheckstyleException {
         checkHeaderNotInitialized();
         try (Reader headerReader = new InputStreamReader(new BufferedInputStream(
                     headerFile.toURL().openStream()), charset)) {
             loadHeader(headerReader);
         }
         catch (final IOException ex) {
             throw new CheckstyleException(
                     "unable to load header file " + headerFile, ex);
         }
     }
 
     /**
      * Called before initializing the header.
      * @throws IllegalArgumentException if header has already been set
      */
     private void checkHeaderNotInitialized() {
         if (!readerLines.isEmpty()) {
             throw new IllegalArgumentException(
                     "header has already been set - "
                     + "set either header or headerFile, not both");
         }
     }
 
     /**
      * Set the header to check against. Individual lines in the header
      * must be separated by '\n' characters.
      * @param header header content to check against.
      * @throws IllegalArgumentException if the header cannot be interpreted
      */
     public void setHeader(String header) {
         if (!CommonUtil.isBlank(header)) {
             checkHeaderNotInitialized();
 
             final String headerExpandedNewLines = ESCAPED_LINE_FEED_PATTERN
                     .matcher(header).replaceAll("\n");
 
             try (Reader headerReader = new StringReader(headerExpandedNewLines)) {
                 loadHeader(headerReader);
             }
             catch (final IOException ex) {
                 throw new IllegalArgumentException("unable to load header", ex);
             }
         }
     }
 
     /**
      * Load header to check against from a Reader into readerLines.
      * @param headerReader delivers the header to check against
      * @throws IOException if
      */
     private void loadHeader(final Reader headerReader) throws IOException {
         try (LineNumberReader lnr = new LineNumberReader(headerReader)) {
             String line;
             do {
                 line = lnr.readLine();
                 if (line != null) {
                     readerLines.add(line);
                 }
             } while (line != null);
             postProcessHeaderLines();
         }
     }
 
     @Override
     protected final void finishLocalSetup() throws CheckstyleException {
         if (headerFile != null) {
             loadHeaderFile();
         }
     }
 
     @Override
     public Set<String> getExternalResourceLocations() {
         final Set<String> result;
 
         if (headerFile == null) {
             result = Collections.emptySet();
         }
         else {
             result = Collections.singleton(headerFile.toString());
         }
 
         return result;
     }
 
 }