package org.apache.maven.surefire.providerapi;
   
   /*
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you under the Apache License, Version 2.0 (the
    * "License"); you may not use this file except in compliance
   * with the License.  You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing,
   * software distributed under the License is distributed on an
   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
   * KIND, either express or implied.  See the License for the
   * specific language governing permissions and limitations
   * under the License.
   */
  
  import javax.annotation.Nonnull;
  import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InputStreamReader;
  import java.net.URL;
  import java.util.Enumeration;
  import java.util.HashSet;
  import java.util.Set;
  
  import static java.lang.Character.isJavaIdentifierPart;
  import static java.lang.Character.isJavaIdentifierStart;
  import static java.util.Collections.emptySet;
  import static org.apache.maven.surefire.util.ReflectionUtils.getConstructor;
  
  /**
   * SPI loader for Surefire/Failsafe should use {@link Thread#getContextClassLoader() current ClassLoader}.
   * <br>
   * The {@link java.util.ServiceLoader} embedded in JVM uses
   * {@link ClassLoader#getSystemClassLoader() System ClassLoader} and cannot be used in Surefire/Failsafe.
   *
   * @since 2.20
   */
  public final class ServiceLoader
  {
  
      @Nonnull
      @SuppressWarnings( "unchecked" )
      public <T> Set<T> load( Class<T> clazz, ClassLoader classLoader )
      {
          try
          {
              Set<T> implementations = new HashSet<>();
              for ( String fullyQualifiedClassName : lookup( clazz, classLoader ) )
              {
                  Class<?> implClass = classLoader.loadClass( fullyQualifiedClassName );
                  implementations.add( (T) getConstructor( implClass ).newInstance() );
              }
              return implementations;
          }
          catch ( IOException | ReflectiveOperationException e )
          {
              throw new IllegalStateException( e.getLocalizedMessage(), e );
          }
      }
  
      @Nonnull
      public Set<String> lookup( Class<?> clazz, ClassLoader classLoader )
              throws IOException
      {
          final String resourceName = "META-INF/services/" + clazz.getName();
  
          if ( classLoader == null )
          {
              return emptySet();
          }
          final Enumeration<URL> urls = classLoader.getResources( resourceName );
          return lookupSpiImplementations( urls );
      }
  
      /**
       * Method loadServices loads the services of a class that are
       * defined using the SPI mechanism.
       *
       * @param urlEnumeration The urls from the resource
       * @return The set of service provider names
       * @throws IOException When reading the streams fails
       */
      @Nonnull
      @SuppressWarnings( "checkstyle:innerassignment" )
      private static Set<String> lookupSpiImplementations( final Enumeration<URL> urlEnumeration )
              throws IOException
      {
          final Set<String> names = new HashSet<>();
          nextUrl:
          while ( urlEnumeration.hasMoreElements() )
          {
              final URL url = urlEnumeration.nextElement();
             try ( BufferedReader reader = getReader( url ) )
             {
                 for ( String line; ( line = reader.readLine() ) != null; )
                 {
                     int ci = line.indexOf( '#' );
                     if ( ci >= 0 )
                     {
                         line = line.substring( 0, ci );
                     }
                     line = line.trim();
                     int n = line.length();
                     if ( n == 0 )
                     {
                         continue; // next line
                     }
 
                     if ( line.indexOf( ' ' ) >= 0 || line.indexOf( '\t' ) >= 0 )
                     {
                         continue nextUrl; // next url
                     }
                     char cp = line.charAt( 0 ); // should use codePointAt but this was JDK1.3
                     if ( !isJavaIdentifierStart( cp ) )
                     {
                         continue nextUrl; // next url
                     }
                     for ( int i = 1; i < n; i++ )
                     {
                         cp = line.charAt( i );  // should use codePointAt but this was JDK1.3
                         if ( !isJavaIdentifierPart( cp ) && cp != '.' )
                         {
                             continue nextUrl; // next url
                         }
                     }
                     if ( !names.contains( line ) )
                     {
                         names.add( line );
                     }
                 }
             }
         }
 
         return names;
     }
 
     @Nonnull
     private static BufferedReader getReader( @Nonnull URL url )
             throws IOException
     {
         final InputStream inputStream = url.openStream();
         final InputStreamReader inputStreamReader = new InputStreamReader( inputStream );
         return new BufferedReader( inputStreamReader );
     }
 }