////////////////////////////////////////////////////////////////////////////////
   // 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;
  
  import java.io.BufferedInputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.net.URL;
  import java.util.ArrayDeque;
  import java.util.Deque;
  import java.util.Enumeration;
  import java.util.HashMap;
  import java.util.Iterator;
  import java.util.LinkedHashSet;
  import java.util.Map;
  import java.util.Set;
  
  import javax.xml.parsers.ParserConfigurationException;
  
  import org.xml.sax.Attributes;
  import org.xml.sax.InputSource;
  import org.xml.sax.SAXException;
  
  import com.puppycrawl.tools.checkstyle.api.CheckstyleException;
  import com.puppycrawl.tools.checkstyle.utils.CommonUtil;
  
  /**
   * Loads a list of package names from a package name XML file.
   */
  public final class PackageNamesLoader
      extends XmlLoader {
  
      /** The public ID for the configuration dtd. */
      private static final String DTD_PUBLIC_ID =
          "-//Puppy Crawl//DTD Package Names 1.0//EN";
  
      /** The new public ID for the configuration dtd. */
      private static final String DTD_PUBLIC_CS_ID =
          "-//Checkstyle//DTD Package Names Configuration 1.0//EN";
  
      /** The resource for the configuration dtd. */
      private static final String DTD_RESOURCE_NAME =
          "com/puppycrawl/tools/checkstyle/packages_1_0.dtd";
  
      /** Name of default checkstyle package names resource file.
       * The file must be in the classpath.
       */
      private static final String CHECKSTYLE_PACKAGES =
          "checkstyle_packages.xml";
  
      /** Qualified name for element 'package'. */
      private static final String PACKAGE_ELEMENT_NAME = "package";
  
      /** The temporary stack of package name parts. */
      private final Deque<String> packageStack = new ArrayDeque<>();
  
      /** The fully qualified package names. */
      private final Set<String> packageNames = new LinkedHashSet<>();
  
      /**
       * Creates a new {@code PackageNamesLoader} instance.
       * @throws ParserConfigurationException if an error occurs
       * @throws SAXException if an error occurs
       */
      private PackageNamesLoader()
              throws ParserConfigurationException, SAXException {
          super(createIdToResourceNameMap());
      }
  
      @Override
      public void startElement(String uri,
                               String localName,
                               String qName,
                               Attributes attributes) {
          if (PACKAGE_ELEMENT_NAME.equals(qName)) {
              //push package name, name is mandatory attribute with not empty value by DTD
              final String name = attributes.getValue("name");
              packageStack.push(name);
          }
      }
  
      /**
      * Creates a full package name from the package names on the stack.
      * @return the full name of the current package.
      */
     private String getPackageName() {
         final StringBuilder buf = new StringBuilder(256);
         final Iterator<String> iterator = packageStack.descendingIterator();
         while (iterator.hasNext()) {
             final String subPackage = iterator.next();
             buf.append(subPackage);
             if (!CommonUtil.endsWithChar(subPackage, '.') && iterator.hasNext()) {
                 buf.append('.');
             }
         }
         return buf.toString();
     }
 
     @Override
     public void endElement(String uri,
                            String localName,
                            String qName) {
         if (PACKAGE_ELEMENT_NAME.equals(qName)) {
             packageNames.add(getPackageName());
             packageStack.pop();
         }
     }
 
     /**
      * Returns the set of package names, compiled from all
      * checkstyle_packages.xml files found on the given class loaders
      * classpath.
      * @param classLoader the class loader for loading the
      *          checkstyle_packages.xml files.
      * @return the set of package names.
      * @throws CheckstyleException if an error occurs.
      */
     public static Set<String> getPackageNames(ClassLoader classLoader)
             throws CheckstyleException {
         final Set<String> result;
         try {
             //create the loader outside the loop to prevent PackageObjectFactory
             //being created anew for each file
             final PackageNamesLoader namesLoader = new PackageNamesLoader();
 
             final Enumeration<URL> packageFiles = classLoader.getResources(CHECKSTYLE_PACKAGES);
 
             while (packageFiles.hasMoreElements()) {
                 processFile(packageFiles.nextElement(), namesLoader);
             }
 
             result = namesLoader.packageNames;
         }
         catch (IOException ex) {
             throw new CheckstyleException("unable to get package file resources", ex);
         }
         catch (ParserConfigurationException | SAXException ex) {
             throw new CheckstyleException("unable to open one of package files", ex);
         }
 
         return result;
     }
 
     /**
      * Reads the file provided and parses it with package names loader.
      * @param packageFile file from package
      * @param namesLoader package names loader
      * @throws SAXException if an error while parsing occurs
      * @throws CheckstyleException if unable to open file
      */
     private static void processFile(URL packageFile, PackageNamesLoader namesLoader)
             throws SAXException, CheckstyleException {
         try (InputStream stream = new BufferedInputStream(packageFile.openStream())) {
             final InputSource source = new InputSource(stream);
             namesLoader.parseInputSource(source);
         }
         catch (IOException ex) {
             throw new CheckstyleException("unable to open " + packageFile, ex);
         }
     }
 
     /**
      * Creates mapping between local resources and dtd ids.
      * @return map between local resources and dtd ids.
      */
     private static Map<String, String> createIdToResourceNameMap() {
         final Map<String, String> map = new HashMap<>();
         map.put(DTD_PUBLIC_ID, DTD_RESOURCE_NAME);
         map.put(DTD_PUBLIC_CS_ID, DTD_RESOURCE_NAME);
         return map;
     }
 
 }