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.pig;
  
  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.Expressions;
  import org.apache.calcite.plan.ConventionTraitDef;
  import org.apache.calcite.plan.RelOptCluster;
  import org.apache.calcite.plan.RelTraitSet;
  import org.apache.calcite.rel.RelNode;
  import org.apache.calcite.rel.convert.ConverterImpl;
  import org.apache.calcite.runtime.Hook;
  import org.apache.calcite.util.BuiltInMethod;
  
  import java.util.List;
  
  /**
   * Relational expression representing a scan of a table in a Pig data source.
   */
  public class PigToEnumerableConverter
      extends ConverterImpl
      implements EnumerableRel {
    /** Creates a PigToEnumerableConverter. */
    protected PigToEnumerableConverter(
        RelOptCluster cluster,
        RelTraitSet traits,
        RelNode input) {
      super(cluster, ConventionTraitDef.INSTANCE, traits, input);
    }
  
    @Override public RelNode copy(RelTraitSet traitSet, List<RelNode> inputs) {
      return new PigToEnumerableConverter(
          getCluster(), traitSet, sole(inputs));
    }
  
    /**
     * {@inheritDoc}
     *
     * <p>This implementation does not actually execute the associated Pig Latin
     * script and return results. Instead it returns an empty
     * {@link org.apache.calcite.adapter.enumerable.EnumerableRel.Result}
     * in order to allow for testing and verification of every step of query
     * processing up to actual physical execution and result verification.
     *
     * <p>Next step is to invoke Pig from here, likely in local mode, have it
     * store results in a predefined file so they can be read here and returned as
     * a {@code Result} object.
     */
    @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
      final BlockBuilder list = new BlockBuilder();
      final PhysType physType =
          PhysTypeImpl.of(implementor.getTypeFactory(), rowType,
              pref.prefer(JavaRowFormat.ARRAY));
      PigRel.Implementor impl = new PigRel.Implementor();
      impl.visitChild(0, getInput());
      Hook.QUERY_PLAN.run(impl.getScript()); // for script validation in tests
      list.add(
          Expressions.return_(null,
              Expressions.call(
                  BuiltInMethod.EMPTY_ENUMERABLE.method)));
      return implementor.result(physType, list.toBlock());
    }
  }
  