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.rel.rules;
  
  import org.apache.calcite.plan.RelOptPredicateList;
  import org.apache.calcite.plan.RelOptRuleCall;
  import org.apache.calcite.plan.RelOptUtil;
  import org.apache.calcite.plan.RelRule;
  import org.apache.calcite.rel.RelNode;
  import org.apache.calcite.rel.core.Union;
  import org.apache.calcite.rel.metadata.RelMetadataQuery;
  import org.apache.calcite.rel.type.RelDataTypeField;
  import org.apache.calcite.rex.RexBuilder;
  import org.apache.calcite.rex.RexInputRef;
  import org.apache.calcite.rex.RexNode;
  import org.apache.calcite.rex.RexUtil;
  import org.apache.calcite.tools.RelBuilder;
  import org.apache.calcite.tools.RelBuilderFactory;
  import org.apache.calcite.util.ImmutableBitSet;
  import org.apache.calcite.util.Pair;
  import org.apache.calcite.util.mapping.Mappings;
  
  import org.immutables.value.Value;
  
  import java.util.ArrayList;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  
  /**
   * Planner rule that pulls up constants through a Union operator.
   *
   * @see CoreRules#UNION_PULL_UP_CONSTANTS
   */
  @Value.Enclosing
  public class UnionPullUpConstantsRule
      extends RelRule<UnionPullUpConstantsRule.Config>
      implements SubstitutionRule {
  
    /** Creates a UnionPullUpConstantsRule. */
    protected UnionPullUpConstantsRule(Config config) {
      super(config);
    }
  
    @Deprecated // to be removed before 2.0
    public UnionPullUpConstantsRule(Class<? extends Union> unionClass,
        RelBuilderFactory relBuilderFactory) {
      this(Config.DEFAULT.withRelBuilderFactory(relBuilderFactory)
          .as(Config.class)
          .withOperandFor(unionClass));
    }
  
    @Override public void onMatch(RelOptRuleCall call) {
      final Union union = call.rel(0);
  
      final RexBuilder rexBuilder = union.getCluster().getRexBuilder();
      final RelMetadataQuery mq = call.getMetadataQuery();
      final RelOptPredicateList predicates = mq.getPulledUpPredicates(union);
      if (RelOptPredicateList.isEmpty(predicates)) {
        return;
      }
  
      final Map<Integer, RexNode> constants = new HashMap<>();
      for (Map.Entry<RexNode, RexNode> e : predicates.constantMap.entrySet()) {
        if (e.getKey() instanceof RexInputRef) {
          constants.put(((RexInputRef) e.getKey()).getIndex(), e.getValue());
        }
      }
  
      // None of the expressions are constant. Nothing to do.
      if (constants.isEmpty()) {
        return;
      }
  
      // Create expressions for Project operators before and after the Union
      List<RelDataTypeField> fields = union.getRowType().getFieldList();
      List<RexNode> topChildExprs = new ArrayList<>();
      List<String> topChildExprsFields = new ArrayList<>();
      List<RexNode> refs = new ArrayList<>();
      ImmutableBitSet.Builder refsIndexBuilder = ImmutableBitSet.builder();
      for (RelDataTypeField field : fields) {
        final RexNode constant = constants.get(field.getIndex());
        if (constant != null) {
          if (constant.getType().equals(field.getType())) {
            topChildExprs.add(constant);
          } else {
            topChildExprs.add(rexBuilder.makeCast(field.getType(), constant, true, false));
          }
          topChildExprsFields.add(field.getName());
        } else {
          final RexNode expr = rexBuilder.makeInputRef(union, field.getIndex());
          topChildExprs.add(expr);
          topChildExprsFields.add(field.getName());
          refs.add(expr);
          refsIndexBuilder.set(field.getIndex());
        }
      }
      ImmutableBitSet refsIndex = refsIndexBuilder.build();
  
      // Update top Project positions
      final Mappings.TargetMapping mapping =
          RelOptUtil.permutation(refs, union.getInput(0).getRowType()).inverse();
      topChildExprs = RexUtil.apply(mapping, topChildExprs);
  
      // Create new Project-Union-Project sequences
      final RelBuilder relBuilder = call.builder();
      for (RelNode input : union.getInputs()) {
        List<Pair<RexNode, String>> newChildExprs = new ArrayList<>();
        for (int j : refsIndex) {
          newChildExprs.add(
              Pair.of(rexBuilder.makeInputRef(input, j),
                  input.getRowType().getFieldList().get(j).getName()));
        }
        if (newChildExprs.isEmpty()) {
          // At least a single item in project is required.
          newChildExprs.add(
              Pair.of(topChildExprs.get(0), topChildExprsFields.get(0)));
        }
        // Add the input with project on top
        relBuilder.push(input);
        relBuilder.project(Pair.left(newChildExprs), Pair.right(newChildExprs));
      }
      relBuilder.union(union.all, union.getInputs().size());
      // Create top Project fixing nullability of fields
      relBuilder.project(topChildExprs, topChildExprsFields);
      relBuilder.convert(union.getRowType(), false);
  
      call.transformTo(relBuilder.build());
      call.getPlanner().prune(union);
    }
  
    /** Rule configuration. */
    @Value.Immutable
    public interface Config extends RelRule.Config {
      Config DEFAULT = ImmutableUnionPullUpConstantsRule.Config.of()
          .withOperandFor(Union.class);
  
      @Override default UnionPullUpConstantsRule toRule() {
        return new UnionPullUpConstantsRule(this);
      }
  
      /** Defines an operand tree for the given classes. */
      default Config withOperandFor(Class<? extends Union> unionClass) {
        return withOperandSupplier(b ->
            b.operand(unionClass)
                // If field count is 1, then there's no room for
                // optimization since we cannot create an empty Project
                // operator. If we created a Project with one column,
                // this rule would cycle.
                .predicate(union -> union.getRowType().getFieldCount() > 1)
                .anyInputs())
            .as(Config.class);
      }
    }
  }
  