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.adapter.elasticsearch;
  
  import org.apache.calcite.adapter.enumerable.EnumerableRel;
  import org.apache.calcite.adapter.enumerable.EnumerableRelImplementor;
  import org.apache.calcite.adapter.enumerable.JavaRowFormat;
  import org.apache.calcite.adapter.enumerable.PhysType;
  import org.apache.calcite.adapter.enumerable.PhysTypeImpl;
  import org.apache.calcite.linq4j.tree.BlockBuilder;
  import org.apache.calcite.linq4j.tree.Expression;
  import org.apache.calcite.linq4j.tree.Expressions;
  import org.apache.calcite.linq4j.tree.MethodCallExpression;
  import org.apache.calcite.plan.ConventionTraitDef;
  import org.apache.calcite.plan.RelOptCluster;
  import org.apache.calcite.plan.RelOptCost;
  import org.apache.calcite.plan.RelOptPlanner;
  import org.apache.calcite.plan.RelTraitSet;
  import org.apache.calcite.rel.RelNode;
  import org.apache.calcite.rel.convert.ConverterImpl;
  import org.apache.calcite.rel.metadata.RelMetadataQuery;
  import org.apache.calcite.rel.type.RelDataType;
  import org.apache.calcite.util.BuiltInMethod;
  import org.apache.calcite.util.Pair;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.AbstractList;
  import java.util.List;
  import java.util.stream.Collectors;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * Relational expression representing a scan of a table in an Elasticsearch data source.
   */
  public class ElasticsearchToEnumerableConverter extends ConverterImpl implements EnumerableRel {
    ElasticsearchToEnumerableConverter(RelOptCluster cluster, RelTraitSet traits,
        RelNode input) {
      super(cluster, ConventionTraitDef.INSTANCE, traits, input);
    }
  
    @Override public RelNode copy(RelTraitSet traitSet, List<RelNode> inputs) {
      return new ElasticsearchToEnumerableConverter(getCluster(), traitSet, sole(inputs));
    }
  
    @Override public @Nullable RelOptCost computeSelfCost(RelOptPlanner planner,
        RelMetadataQuery mq) {
      final RelOptCost cost = requireNonNull(super.computeSelfCost(planner, mq));
      return cost.multiplyBy(.1);
    }
  
    @Override public Result implement(EnumerableRelImplementor relImplementor, Prefer prefer) {
      final BlockBuilder block = new BlockBuilder();
      final ElasticsearchRel.Implementor implementor = new ElasticsearchRel.Implementor();
      implementor.visitChild(0, getInput());
  
      final RelDataType rowType = getRowType();
      final PhysType physType =
          PhysTypeImpl.of(relImplementor.getTypeFactory(),
              rowType, prefer.prefer(JavaRowFormat.ARRAY));
      final Expression fields =
          block.append("fields",
              constantArrayList(
                  Pair.zip(ElasticsearchRules.elasticsearchFieldNames(rowType),
                      new AbstractList<Class>() {
                        @Override public Class get(int index) {
                          return physType.fieldClass(index);
                        }
  
                        @Override public int size() {
                          return rowType.getFieldCount();
                        }
                      }),
                  Pair.class));
      final Expression table =
          block.append("table",
              requireNonNull(
                  implementor.table.getExpression(
                      ElasticsearchTable.ElasticsearchQueryable.class)));
      final Expression ops = block.append("ops", Expressions.constant(implementor.list));
      final Expression sort = block.append("sort", constantArrayList(implementor.sort, Pair.class));
      final Expression nullsSort =
          block.append("nullsSort", constantArrayList(implementor.nullsSort, Pair.class));
      final Expression groupBy = block.append("groupBy", Expressions.constant(implementor.groupBy));
      final Expression aggregations =
          block.append("aggregations",
              constantArrayList(implementor.aggregations, Pair.class));
  
      final Expression mappings =
          block.append("mappings",
              Expressions.constant(implementor.expressionItemMap));
  
      final Expression offset = block.append("offset", Expressions.constant(implementor.offset));
      final Expression fetch = block.append("fetch", Expressions.constant(implementor.fetch));
  
      Expression enumerable =
          block.append("enumerable",
              Expressions.call(table,
                  ElasticsearchMethod.ELASTICSEARCH_QUERYABLE_FIND.method, ops,
                  fields, sort, nullsSort, groupBy, aggregations, mappings, offset, fetch));
      block.add(Expressions.return_(null, enumerable));
      return relImplementor.result(physType, block.toBlock());
    }
  
    /** E.g. {@code constantArrayList("x", "y")} returns
     * "Arrays.asList('x', 'y')".
     *
     * @param values list of values
     * @param clazz runtime class representing each element in the list
     * @param <T> type of elements in the list
     * @return method call which creates a list
     */
    private static <T> MethodCallExpression constantArrayList(List<T> values, Class clazz) {
      return Expressions.call(BuiltInMethod.ARRAYS_AS_LIST.method,
          Expressions.newArrayInit(clazz, constantList(values)));
    }
  
    /** E.g. {@code constantList("x", "y")} returns
     * {@code {ConstantExpression("x"), ConstantExpression("y")}}.
     *
     * @param values list of elements
     * @param <T> type of elements inside this list
     * @return list of constant expressions
     */
    private static <T> List<Expression> constantList(List<T> values) {
      return values.stream().map(Expressions::constant).collect(Collectors.toList());
    }
  }
  