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   * 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.db.virtual;
  
  import java.util.Map;
  import java.util.concurrent.ConcurrentHashMap;
  import javax.annotation.Nullable;
  
  import com.google.common.collect.Iterables;
  
  import org.apache.cassandra.schema.KeyspaceMetadata;
  import org.apache.cassandra.schema.TableId;
  import org.apache.cassandra.schema.TableMetadata;
  
  public final class VirtualKeyspaceRegistry
  {
      public static final VirtualKeyspaceRegistry instance = new VirtualKeyspaceRegistry();
  
      private final Map<String, VirtualKeyspace> virtualKeyspaces = new ConcurrentHashMap<>();
      private final Map<TableId, VirtualTable> virtualTables = new ConcurrentHashMap<>();
  
      private VirtualKeyspaceRegistry()
      {
      }
  
      public void register(VirtualKeyspace keyspace)
      {
          VirtualKeyspace previous = virtualKeyspaces.put(keyspace.name(), keyspace);
          // some tests choose to replace the keyspace, if so make sure to cleanup tables as well
          if (previous != null)
              previous.tables().forEach(t -> virtualTables.remove(t));
          keyspace.tables().forEach(t -> virtualTables.put(t.metadata().id, t));
      }
  
      public void unregister(VirtualKeyspace keyspace)
      {
          VirtualKeyspace virtualKeyspace = virtualKeyspaces.get(keyspace.name());
          if (virtualKeyspace == null)
              return;
  
          keyspace.tables().forEach(t -> virtualTables.remove(t.metadata().id));
          virtualKeyspaces.remove(keyspace.name());
      }
  
      @Nullable
      public VirtualKeyspace getKeyspaceNullable(String name)
      {
          return virtualKeyspaces.get(name);
      }
  
      @Nullable
      public VirtualTable getTableNullable(TableId id)
      {
          return virtualTables.get(id);
      }
  
      @Nullable
      public KeyspaceMetadata getKeyspaceMetadataNullable(String name)
      {
          VirtualKeyspace keyspace = virtualKeyspaces.get(name);
          return null != keyspace ? keyspace.metadata() : null;
      }
  
      @Nullable
      public TableMetadata getTableMetadataNullable(TableId id)
      {
          VirtualTable table = virtualTables.get(id);
          return null != table ? table.metadata() : null;
      }
  
      public Iterable<KeyspaceMetadata> virtualKeyspacesMetadata()
      {
          return Iterables.transform(virtualKeyspaces.values(), VirtualKeyspace::metadata);
      }
  }
  