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;
  
  import java.util.Objects;
  import java.util.function.Function;
  
  import com.google.common.collect.Iterables;
  
  import com.codahale.metrics.Gauge;
  import org.apache.cassandra.db.ColumnFamilyStore;
  import org.apache.cassandra.db.Keyspace;
  import org.apache.cassandra.io.sstable.format.SSTableReader;
  
  public class SimpleGaugeProvider<T extends Number, R extends SSTableReader> extends GaugeProvider<T>
  {
      private final Function<SSTableReader, R> mapper;
      private final Function<Iterable<R>, T> combiner;
  
      public SimpleGaugeProvider(Function<SSTableReader, R> mapper, String name, Function<Iterable<R>, T> combiner)
      {
          super(name);
          this.mapper = mapper;
          this.combiner = combiner;
      }
  
      @Override
      public Gauge<T> getTableGauge(ColumnFamilyStore cfs)
      {
          return () -> combine(cfs.getLiveSSTables());
      }
  
      @Override
      public Gauge<T> getKeyspaceGauge(Keyspace keyspace)
      {
          return () -> combine(getAllReaders(keyspace));
      }
  
      @Override
      public Gauge<T> getGlobalGauge()
      {
          return () -> combine(Iterables.concat(Iterables.transform(Keyspace.all(), SimpleGaugeProvider::getAllReaders)));
      }
  
      private T combine(Iterable<SSTableReader> allReaders)
      {
          Iterable<R> readers = Iterables.filter(Iterables.transform(allReaders, mapper::apply), Objects::nonNull);
          return combiner.apply(readers);
      }
  
      private static Iterable<SSTableReader> getAllReaders(Keyspace keyspace)
      {
          return Iterables.concat(Iterables.transform(keyspace.getColumnFamilyStores(), ColumnFamilyStore::getLiveSSTables));
      }
  }
  