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.cassandra;
  
  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.config.CalciteSystemProperty;
  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.RelOptTable;
  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.runtime.Hook;
  import org.apache.calcite.util.BuiltInMethod;
  import org.apache.calcite.util.Pair;
  import org.apache.calcite.util.Util;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.AbstractList;
  import java.util.ArrayList;
  import java.util.List;
  import java.util.Map;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * Relational expression representing a scan of a table in a Cassandra data source.
   */
  public class CassandraToEnumerableConverter
      extends ConverterImpl
      implements EnumerableRel {
    protected CassandraToEnumerableConverter(
        RelOptCluster cluster,
        RelTraitSet traits,
        RelNode input) {
      super(cluster, ConventionTraitDef.INSTANCE, traits, input);
    }
  
    @Override public RelNode copy(RelTraitSet traitSet, List<RelNode> inputs) {
      return new CassandraToEnumerableConverter(
          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 implementor, Prefer pref) {
      // Generates a call to "query" with the appropriate fields and predicates
      final BlockBuilder list = new BlockBuilder();
      final CassandraRel.Implementor cassandraImplementor = new CassandraRel.Implementor();
      cassandraImplementor.visitChild(0, getInput());
      final RelDataType rowType = getRowType();
      final PhysType physType =
          PhysTypeImpl.of(
                  implementor.getTypeFactory(), rowType,
                  pref.prefer(JavaRowFormat.ARRAY));
      final Expression fields =
          list.append("fields",
              constantArrayList(
                  Pair.zip(CassandraRules.cassandraFieldNames(rowType),
                      new AbstractList<Class<?>>() {
                        @Override public Class<?> get(int index) {
                          return physType.fieldClass(index);
                        }
  
                        @Override public int size() {
                          return rowType.getFieldCount();
                        }
                      }),
                  Pair.class));
      List<Map.Entry<String, String>> selectList = new ArrayList<>();
      for (Map.Entry<String, String> entry
              : Pair.zip(cassandraImplementor.selectFields.keySet(),
                  cassandraImplementor.selectFields.values())) {
        selectList.add(entry);
      }
      final Expression selectFields =
          list.append("selectFields", constantArrayList(selectList, Pair.class));
      final RelOptTable cassandraTable =
          requireNonNull(cassandraImplementor.table);
      final Expression table =
          list.append("table",
              requireNonNull(
                  cassandraTable.getExpression(
                      CassandraTable.CassandraQueryable.class)));
      final Expression predicates =
          list.append("predicates",
              constantArrayList(cassandraImplementor.whereClause, String.class));
      final Expression order =
          list.append("order",
              constantArrayList(cassandraImplementor.order, String.class));
      final Expression offset =
          list.append("offset",
              Expressions.constant(cassandraImplementor.offset));
      final Expression fetch =
          list.append("fetch",
              Expressions.constant(cassandraImplementor.fetch));
      Expression enumerable =
          list.append("enumerable",
              Expressions.call(table,
                  CassandraMethod.CASSANDRA_QUERYABLE_QUERY.method, fields,
                  selectFields, predicates, order, offset, fetch));
      if (CalciteSystemProperty.DEBUG.value()) {
        System.out.println("Cassandra: " + predicates);
      }
      Hook.QUERY_PLAN.run(predicates);
      list.add(
          Expressions.return_(null, enumerable));
      return implementor.result(physType, list.toBlock());
    }
  
    /** E.g. {@code constantArrayList("x", "y")} returns
     * "Arrays.asList('x', 'y')". */
    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")}}. */
    private static <T> List<Expression> constantList(List<T> values) {
      return Util.transform(values, Expressions::constant);
    }
  }
  