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.mongodb;
  
  import org.apache.calcite.adapter.java.JavaTypeFactory;
  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.core.Project;
  import org.apache.calcite.rel.metadata.RelMetadataQuery;
  import org.apache.calcite.rel.type.RelDataType;
  import org.apache.calcite.rex.RexNode;
  import org.apache.calcite.util.Pair;
  import org.apache.calcite.util.Util;
  
  import com.google.common.collect.ImmutableList;
  import com.google.common.collect.ImmutableSet;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.ArrayList;
  import java.util.List;
  
  /**
   * Implementation of {@link org.apache.calcite.rel.core.Project}
   * relational expression in MongoDB.
   */
  public class MongoProject extends Project implements MongoRel {
    public MongoProject(RelOptCluster cluster, RelTraitSet traitSet,
        RelNode input, List<? extends RexNode> projects, RelDataType rowType) {
      super(cluster, traitSet, ImmutableList.of(), input, projects, rowType, ImmutableSet.of());
      assert getConvention() == MongoRel.CONVENTION;
      assert getConvention() == input.getConvention();
    }
  
    @Deprecated // to be removed before 2.0
    public MongoProject(RelOptCluster cluster, RelTraitSet traitSet,
        RelNode input, List<RexNode> projects, RelDataType rowType, int flags) {
      this(cluster, traitSet, input, projects, rowType);
      Util.discard(flags);
    }
  
    @Override public Project copy(RelTraitSet traitSet, RelNode input,
        List<RexNode> projects, RelDataType rowType) {
      return new MongoProject(getCluster(), traitSet, input, projects,
          rowType);
    }
  
    @Override public @Nullable RelOptCost computeSelfCost(RelOptPlanner planner,
        RelMetadataQuery mq) {
      return super.computeSelfCost(planner, mq).multiplyBy(0.1);
    }
  
    @Override public void implement(Implementor implementor) {
      implementor.visitChild(0, getInput());
  
      final MongoRules.RexToMongoTranslator translator =
          new MongoRules.RexToMongoTranslator(
              (JavaTypeFactory) getCluster().getTypeFactory(),
              MongoRules.mongoFieldNames(getInput().getRowType()));
      final List<String> items = new ArrayList<>();
      for (Pair<RexNode, String> pair : getNamedProjects()) {
        final String name = pair.right;
        final String expr = pair.left.accept(translator);
        items.add(expr.equals("'$" + name + "'")
            ? MongoRules.maybeQuote(name) + ": 1"
            : MongoRules.maybeQuote(name) + ": " + expr);
      }
      final String findString = Util.toString(items, "{", ", ", "}");
      final String aggregateString = "{$project: " + findString + "}";
      final Pair<String, String> op = Pair.of(findString, aggregateString);
      implementor.add(op.left, op.right);
    }
  }
  