package org.eclipse.aether.internal.impl.checksum;
   
   /*
    * 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.inject.Inject;
  import javax.inject.Named;
  import javax.inject.Singleton;
  
  import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.UncheckedIOException;
  import java.nio.charset.StandardCharsets;
  import java.nio.file.Files;
  import java.nio.file.Path;
  import java.util.ArrayList;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  import java.util.Objects;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.atomic.AtomicBoolean;
  
  import org.eclipse.aether.MultiRuntimeException;
  import org.eclipse.aether.RepositorySystemSession;
  import org.eclipse.aether.artifact.Artifact;
  import org.eclipse.aether.impl.RepositorySystemLifecycle;
  import org.eclipse.aether.internal.impl.LocalPathComposer;
  import org.eclipse.aether.repository.ArtifactRepository;
  import org.eclipse.aether.spi.connector.checksum.ChecksumAlgorithmFactory;
  import org.eclipse.aether.util.FileUtils;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import static java.util.Objects.requireNonNull;
  import static java.util.stream.Collectors.toList;
  
  /**
   * Compact file {@link FileTrustedChecksumsSourceSupport} implementation that use specified directory as base
   * directory, where it expects a "summary" file named as "checksums.${checksumExt}" for each checksum algorithm.
   * File format is GNU Coreutils compatible: each line holds checksum followed by two spaces and artifact relative path
   * (from local repository root, without leading "./"). This means that trusted checksums summary file can be used to
   * validate artifacts or generate it using standard GNU tools like GNU {@code sha1sum} is (for BSD derivatives same
   * file can be used with {@code -r} switch).
   * <p>
   * The format supports comments "#" (hash) and empty lines for easier structuring the file content, and both are
   * ignored. Also, their presence makes the summary file incompatible with GNU Coreutils format. On save of the
   * summary file, the comments and empty lines are lost, and file is sorted by path names for easier diffing
   * (2nd column in file).
   * <p>
   * The source by default is "origin aware", and it will factor in origin repository ID as well into summary file name,
   * for example "checksums-central.sha256".
   * <p>
   * Example commands for managing summary file (in examples will use repository ID "central"):
   * <ul>
   *     <li>To create summary file: {@code find * -not -name "checksums-central.sha256" -type f -print0 |
   *       xargs -0 sha256sum | sort -k 2 > checksums-central.sha256}</li>
   *     <li>To verify artifacts using summary file: {@code sha256sum --quiet -c checksums-central.sha256}</li>
   * </ul>
   * <p>
   * The checksums summary file is lazily loaded and remains cached during lifetime of the component, so file changes
   * during lifecycle of the component are not picked up. This implementation can be simultaneously used to lookup and
   * also record checksums. The recorded checksums will become visible for every session, and will be flushed
   * at repository system shutdown, merged with existing ones on disk.
   * <p>
   * The name of this implementation is "summaryFile".
   *
   * @see <a href="https://man7.org/linux/man-pages/man1/sha1sum.1.html">sha1sum man page</a>
   * @see <a href="https://www.gnu.org/software/coreutils/manual/coreutils.html#md5sum-invocation">GNU Coreutils: md5sum</a>
   * @since 1.9.0
   */
  @Singleton
  @Named( SummaryFileTrustedChecksumsSource.NAME )
  public final class SummaryFileTrustedChecksumsSource
          extends FileTrustedChecksumsSourceSupport
  {
      public static final String NAME = "summaryFile";
  
      private static final String CHECKSUMS_FILE_PREFIX = "checksums";
  
      private static final Logger LOGGER = LoggerFactory.getLogger( SummaryFileTrustedChecksumsSource.class );
  
      private final LocalPathComposer localPathComposer;
 
     private final RepositorySystemLifecycle repositorySystemLifecycle;
 
     private final ConcurrentHashMap<Path, ConcurrentHashMap<String, String>> checksums;
 
     private final ConcurrentHashMap<Path, Boolean> changedChecksums;
 
     private final AtomicBoolean onShutdownHandlerRegistered;
 
 
     @Inject
     public SummaryFileTrustedChecksumsSource( LocalPathComposer localPathComposer,
                                               RepositorySystemLifecycle repositorySystemLifecycle )
     {
         super( NAME );
         this.localPathComposer = requireNonNull( localPathComposer );
         this.repositorySystemLifecycle = requireNonNull( repositorySystemLifecycle );
         this.checksums = new ConcurrentHashMap<>();
         this.changedChecksums = new ConcurrentHashMap<>();
         this.onShutdownHandlerRegistered = new AtomicBoolean( false );
     }
 
     @Override
     protected Map<String, String> doGetTrustedArtifactChecksums(
             RepositorySystemSession session, Artifact artifact, ArtifactRepository artifactRepository,
             List<ChecksumAlgorithmFactory> checksumAlgorithmFactories )
     {
         final HashMap<String, String> result = new HashMap<>();
         final Path basedir = getBasedir( session, false );
         if ( Files.isDirectory( basedir ) )
         {
             final String artifactPath = localPathComposer.getPathForArtifact( artifact, false );
             final boolean originAware = isOriginAware( session );
             for ( ChecksumAlgorithmFactory checksumAlgorithmFactory : checksumAlgorithmFactories )
             {
                 Path summaryFile = summaryFile( basedir, originAware, artifactRepository.getId(),
                         checksumAlgorithmFactory.getFileExtension() );
                 ConcurrentHashMap<String, String> algorithmChecksums = checksums.computeIfAbsent( summaryFile, f ->
                         {
                             ConcurrentHashMap<String, String> loaded = loadProvidedChecksums( summaryFile );
                             if ( Files.isRegularFile( summaryFile ) )
                             {
                                 LOGGER.info( "Loaded {} {} trusted checksums for remote repository {}",
                                         loaded.size(), checksumAlgorithmFactory.getName(), artifactRepository.getId() );
                             }
                             return loaded;
                         }
                 );
                 String checksum = algorithmChecksums.get( artifactPath );
                 if ( checksum != null )
                 {
                     result.put( checksumAlgorithmFactory.getName(), checksum );
                 }
             }
         }
         return result;
     }
 
     @Override
     protected SummaryFileWriter doGetTrustedArtifactChecksumsWriter( RepositorySystemSession session )
     {
         if ( onShutdownHandlerRegistered.compareAndSet( false, true ) )
         {
             repositorySystemLifecycle.addOnSystemEndedHandler( this::saveRecordedLines );
         }
         return new SummaryFileWriter( checksums, getBasedir( session, true ), isOriginAware( session ) );
     }
 
     /**
      * Returns the summary file path. The file itself and its parent directories may not exist, this method merely
      * calculate the path.
      */
     private Path summaryFile( Path basedir, boolean originAware, String repositoryId, String checksumExtension )
     {
         String fileName = CHECKSUMS_FILE_PREFIX;
         if ( originAware )
         {
             fileName += "-" + repositoryId;
         }
         return basedir.resolve( fileName + "." + checksumExtension );
     }
 
     private ConcurrentHashMap<String, String> loadProvidedChecksums( Path summaryFile )
     {
         ConcurrentHashMap<String, String> result = new ConcurrentHashMap<>();
         if ( Files.isRegularFile( summaryFile ) )
         {
             try ( BufferedReader reader = Files.newBufferedReader( summaryFile, StandardCharsets.UTF_8 ) )
             {
                 String line;
                 while ( ( line = reader.readLine() ) != null )
                 {
                     if ( !line.startsWith( "#" ) && !line.isEmpty() )
                     {
                         String[] parts = line.split( "  ", 2 );
                         if ( parts.length == 2 )
                         {
                             String newChecksum = parts[0];
                             String artifactPath = parts[1];
                             String oldChecksum = result.put( artifactPath, newChecksum );
                             if ( oldChecksum != null )
                             {
                                 if ( Objects.equals( oldChecksum, newChecksum ) )
                                 {
                                     LOGGER.warn(
                                             "Checksums file '{}' contains duplicate checksums for artifact {}: {}",
                                             summaryFile, artifactPath, oldChecksum );
                                 }
                                 else
                                 {
                                     LOGGER.warn(
                                             "Checksums file '{}' contains different checksums for artifact {}: "
                                                     + "old '{}' replaced by new '{}'", summaryFile, artifactPath,
                                             oldChecksum, newChecksum );
                                 }
                             }
                         }
                         else
                         {
                             LOGGER.warn( "Checksums file '{}' ignored malformed line '{}'", summaryFile, line );
                         }
                     }
                 }
             }
             catch ( IOException e )
             {
                 throw new UncheckedIOException( e );
             }
         }
         return result;
     }
 
     private class SummaryFileWriter implements Writer
     {
         private final ConcurrentHashMap<Path, ConcurrentHashMap<String, String>> cache;
 
         private final Path basedir;
 
         private final boolean originAware;
 
         private SummaryFileWriter( ConcurrentHashMap<Path, ConcurrentHashMap<String, String>> cache,
                                    Path basedir,
                                    boolean originAware )
         {
             this.cache = cache;
             this.basedir = basedir;
             this.originAware = originAware;
         }
 
         @Override
         public void addTrustedArtifactChecksums( Artifact artifact,
                                                  ArtifactRepository artifactRepository,
                                                  List<ChecksumAlgorithmFactory> checksumAlgorithmFactories,
                                                  Map<String, String> trustedArtifactChecksums )
         {
             String artifactPath = localPathComposer.getPathForArtifact( artifact, false );
             for ( ChecksumAlgorithmFactory checksumAlgorithmFactory : checksumAlgorithmFactories )
             {
                 Path summaryFile = summaryFile( basedir, originAware, artifactRepository.getId(),
                         checksumAlgorithmFactory.getFileExtension() );
                 String checksum = requireNonNull(
                         trustedArtifactChecksums.get( checksumAlgorithmFactory.getName() ) );
 
                 String oldChecksum = cache.computeIfAbsent( summaryFile, k -> loadProvidedChecksums( summaryFile ) )
                         .put( artifactPath, checksum );
 
                 if ( oldChecksum == null )
                 {
                     changedChecksums.put( summaryFile, Boolean.TRUE ); // new
                 }
                 else if ( !Objects.equals( oldChecksum, checksum ) )
                 {
                     changedChecksums.put( summaryFile, Boolean.TRUE ); // replaced
                     LOGGER.info( "Trusted checksum for artifact {} replaced: old {}, new {}",
                             artifact, oldChecksum, checksum );
                 }
             }
         }
     }
 
     /**
      * On-close handler that saves recorded checksums, if any.
      */
     private void saveRecordedLines()
     {
         if ( changedChecksums.isEmpty() )
         {
             return;
         }
 
         ArrayList<Exception> exceptions = new ArrayList<>();
         for ( Map.Entry<Path, ConcurrentHashMap<String, String>> entry : checksums.entrySet() )
         {
             Path summaryFile = entry.getKey();
             if ( changedChecksums.get( summaryFile ) != Boolean.TRUE )
             {
                 continue;
             }
             ConcurrentHashMap<String, String> recordedLines = entry.getValue();
             if ( !recordedLines.isEmpty() )
             {
                 try
                 {
                     ConcurrentHashMap<String, String> result = new ConcurrentHashMap<>();
                     result.putAll( loadProvidedChecksums( summaryFile ) );
                     result.putAll( recordedLines );
 
                     LOGGER.info( "Saving {} checksums to '{}'", result.size(), summaryFile );
                     FileUtils.writeFileWithBackup(
                             summaryFile,
                             p -> Files.write( p,
                                     result.entrySet().stream()
                                             .sorted( Map.Entry.comparingByValue() )
                                             .map( e -> e.getValue() + "  " + e.getKey() )
                                             .collect( toList() )
                             )
                     );
                 }
                 catch ( IOException e )
                 {
                     exceptions.add( e );
                 }
             }
         }
         MultiRuntimeException.mayThrow( "session save checksums failure", exceptions );
     }
 }