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.calcite.materialize;
  
  import org.apache.calcite.util.Util;
  
  import com.google.common.cache.CacheBuilder;
  import com.google.common.cache.CacheLoader;
  import com.google.common.cache.LoadingCache;
  import com.google.common.collect.ImmutableList;
  import com.google.common.util.concurrent.UncheckedExecutionException;
  
  import java.util.ArrayList;
  import java.util.List;
  import java.util.concurrent.ExecutionException;
  
  /**
   * Implementation of {@link LatticeStatisticProvider} that caches single-column
   * statistics and computes multi-column statistics from these.
   */
  class CachingLatticeStatisticProvider implements LatticeStatisticProvider {
    private final Lattice lattice;
    private final LoadingCache<Lattice.Column, Double> cache;
  
    /** Creates a CachingStatisticProvider. */
    CachingLatticeStatisticProvider(final Lattice lattice,
        final LatticeStatisticProvider provider) {
      this.lattice = lattice;
      cache =
          CacheBuilder.newBuilder().build(
              CacheLoader.from(key ->
                  provider.cardinality(ImmutableList.of(key))));
    }
  
    @Override public double cardinality(List<Lattice.Column> columns) {
      final List<Double> counts = new ArrayList<>();
      for (Lattice.Column column : columns) {
        try {
          counts.add(cache.get(column));
        } catch (UncheckedExecutionException | ExecutionException e) {
          throw Util.throwAsRuntime(Util.causeOrSelf(e));
        }
      }
      return (int) Lattice.getRowCount(lattice.getFactRowCount(), counts);
    }
  }
  