content: /*
   * 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.
   */
  
  package org.apache.cassandra.io.sstable.format;
  
  import java.io.FileNotFoundException;
  import java.io.IOError;
  import java.io.IOException;
  import java.nio.file.Files;
  import java.nio.file.NoSuchFileException;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.List;
  import java.util.Set;
  import java.util.TreeSet;
  
  import com.google.common.collect.Collections2;
  import com.google.common.collect.Sets;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import org.apache.cassandra.io.FSWriteError;
  import org.apache.cassandra.io.sstable.Component;
  import org.apache.cassandra.io.sstable.Descriptor;
  import org.apache.cassandra.io.sstable.format.SSTableFormat.Components;
  import org.apache.cassandra.io.util.File;
  import org.apache.cassandra.io.util.FileUtils;
  
  import static java.nio.file.StandardOpenOption.CREATE;
  import static java.nio.file.StandardOpenOption.SYNC;
  import static java.nio.file.StandardOpenOption.TRUNCATE_EXISTING;
  
  public class TOCComponent
  {
      private static final Logger logger = LoggerFactory.getLogger(TOCComponent.class);
  
      /**
       * Reads the list of components from the TOC component.
       *
       * @return set of components found in the TOC
       */
      public static Set<Component> loadTOC(Descriptor descriptor) throws IOException
      {
          return loadTOC(descriptor, true);
      }
  
      /**
       * Reads the list of components from the TOC component.
       *
       * @param skipMissing skip adding the component to the returned set if the corresponding file is missing.
       * @return set of components found in the TOC
       */
      public static Set<Component> loadTOC(Descriptor descriptor, boolean skipMissing) throws IOException
      {
          File tocFile = descriptor.fileFor(Components.TOC);
          List<String> componentNames = Files.readAllLines(tocFile.toPath());
          Set<Component> components = Sets.newHashSetWithExpectedSize(componentNames.size());
          for (String componentName : componentNames)
          {
              Component component = Component.parse(componentName, descriptor.version.format);
              if (skipMissing && !descriptor.fileFor(component).exists())
                  logger.error("Missing component: {}", descriptor.fileFor(component));
              else
                  components.add(component);
          }
          return components;
      }
  
      /**
       * Updates the TOC file by reading existing component entries, merging them with the given components,
       * sorting the combined list in lexicographic order for deterministic output.
       *
       * @param descriptor the SSTable descriptor for which to update the TOC
       * @param components new components to merge into the TOC (existing TOC entries are preserved)
       * @throws FSWriteError if an I/O error occurs when creating or overwriting the TOC file
       */
      public static void updateTOC(Descriptor descriptor, Collection<Component> components)
      {
          if (components.isEmpty())
              return;
  
          File tocFile = descriptor.fileFor(Components.TOC);
  
          Set<String> componentNames = new TreeSet<>(Collections2.transform(components, Component::name));
  
          if (tocFile.exists())
              componentNames.addAll(FileUtils.readLines(tocFile));
  
          try
          {
              FileUtils.write(tocFile, new ArrayList<>(componentNames), CREATE, TRUNCATE_EXISTING, SYNC);
          }
          catch (RuntimeException ex)
          {
              throw new RuntimeException("Exception occurred while writing to " + tocFile,
                                         ex.getCause() != null ? ex.getCause() : ex);
          }
      }
  
      /**
       * Loads existing TOC file or creates a new one.
       *
       * @param descriptor descriptor to load TOC for
       * @return set of loaded or discovered components
       * @throws IOError when loading of a component is erroneous
       * @throws FSWriteError when creating of a new TOC file is erroneous
       */
      public static Set<Component> loadOrCreate(Descriptor descriptor)
      {
          try
          {
              return TOCComponent.loadTOC(descriptor);
          }
          catch (FileNotFoundException | NoSuchFileException e)
          {
              // if TOC is missing, we might create a new one
          }
          catch (IOException ex)
          {
              throw new IOError(ex);
          }
  
          Set<Component> components = descriptor.discoverComponents();
          if (components.isEmpty())
              return components; // sstable doesn't exist yet
  
          components.add(Components.TOC);
          TOCComponent.updateTOC(descriptor, components);
          return components;
      }
  
      /**
       * Rewrites the TOC component by deleting and recreating it only with provided component names.
       */
      public static void rewriteTOC(Descriptor descriptor, Collection<Component> components)
      {
          File tocFile = descriptor.fileFor(Components.TOC);
          if (!tocFile.tryDelete())
              logger.error("Failed to delete TOC component for {}", descriptor);
          updateTOC(descriptor, components);
      }
  }
  