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.RelOptRuleCall;
  import org.apache.calcite.plan.RelRule;
  import org.apache.calcite.rel.RelNode;
  import org.apache.calcite.rel.core.Intersect;
  import org.apache.calcite.rel.core.Minus;
  import org.apache.calcite.rel.core.RelFactories;
  import org.apache.calcite.rel.core.SetOp;
  import org.apache.calcite.rel.core.Union;
  import org.apache.calcite.rel.logical.LogicalIntersect;
  import org.apache.calcite.rel.logical.LogicalMinus;
  import org.apache.calcite.rel.logical.LogicalUnion;
  import org.apache.calcite.tools.RelBuilder;
  import org.apache.calcite.tools.RelBuilderFactory;
  import org.apache.calcite.util.Util;
  
  import org.immutables.value.Value;
  
  /**
   * UnionMergeRule implements the rule for combining two
   * non-distinct {@link org.apache.calcite.rel.core.SetOp}s
   * into a single {@link org.apache.calcite.rel.core.SetOp}.
   *
   * <p>Originally written for {@link Union} (hence the name),
   * but now also applies to {@link Intersect} and {@link Minus}.
   */
  @Value.Enclosing
  public class UnionMergeRule
      extends RelRule<UnionMergeRule.Config>
      implements TransformationRule {
  
    /** Creates a UnionMergeRule. */
    protected UnionMergeRule(Config config) {
      super(config);
    }
  
    @Deprecated // to be removed before 2.0
    public UnionMergeRule(Class<? extends SetOp> setOpClass, String description,
        RelBuilderFactory relBuilderFactory) {
      this(Config.DEFAULT.withRelBuilderFactory(relBuilderFactory)
          .withDescription(description)
          .as(Config.class)
          .withOperandFor(setOpClass));
    }
  
    @Deprecated // to be removed before 2.0
    public UnionMergeRule(Class<? extends Union> setOpClass,
        RelFactories.SetOpFactory setOpFactory) {
      this(Config.DEFAULT.withRelBuilderFactory(RelBuilder.proto(setOpFactory))
          .as(Config.class)
          .withOperandFor(setOpClass));
    }
  
    //~ Methods ----------------------------------------------------------------
  
    @Override public boolean matches(RelOptRuleCall call) {
      // It avoids adding the rule match to the match queue in case the rule is known to be a no-op
      final SetOp topOp = call.rel(0);
      @SuppressWarnings("unchecked") final Class<? extends SetOp> setOpClass =
          (Class<? extends SetOp>) operands.get(0).getMatchedClass();
      final SetOp bottomOp;
      if (setOpClass.isInstance(call.rel(2))
          && !Minus.class.isAssignableFrom(setOpClass)) {
        bottomOp = call.rel(2);
      } else if (setOpClass.isInstance(call.rel(1))) {
        bottomOp = call.rel(1);
      } else {
        return false;
      }
  
      if (topOp.all && !bottomOp.all) {
        return false;
      }
  
      return true;
    }
  
    @Override public void onMatch(RelOptRuleCall call) {
      final SetOp topOp = call.rel(0);
      @SuppressWarnings("unchecked") final Class<? extends SetOp> setOpClass =
          (Class) operands.get(0).getMatchedClass();
  
      // For Union and Intersect, we want to combine the set-op that's in the
      // second input first.
      //
      // For example, we reduce
      //    Union(Union(a, b), Union(c, d))
      // to
      //    Union(Union(a, b), c, d)
      // in preference to
      //    Union(a, b, Union(c, d))
      //
      // But for Minus, we can only reduce the left input. It is not valid to
      // reduce
      //    Minus(a, Minus(b, c))
      // to
      //    Minus(a, b, c)
      //
      // Hence, that's why the rule pattern matches on generic RelNodes rather
      // than explicit sub-classes of SetOp.  By doing so, and firing this rule
      // in a bottom-up order, it allows us to only specify a single
      // pattern for this rule.
      final SetOp bottomOp;
      if (setOpClass.isInstance(call.rel(2))
          && !Minus.class.isAssignableFrom(setOpClass)) {
        bottomOp = call.rel(2);
      } else if (setOpClass.isInstance(call.rel(1))) {
        bottomOp = call.rel(1);
      } else {
        return;
      }
  
      // Can only combine (1) if all operators are ALL,
      // or (2) top operator is DISTINCT (i.e. not ALL).
      // In case (2), all operators become DISTINCT.
      if (topOp.all && !bottomOp.all) {
        return;
      }
  
      // Combine the inputs from the bottom set-op with the other inputs from
      // the top set-op.
      final RelBuilder relBuilder = call.builder();
      if (setOpClass.isInstance(call.rel(2))
          && !Minus.class.isAssignableFrom(setOpClass)) {
        relBuilder.push(topOp.getInput(0));
        relBuilder.pushAll(bottomOp.getInputs());
        // topOp.getInputs().size() may be more than 2
        for (int index = 2; index < topOp.getInputs().size(); index++) {
          relBuilder.push(topOp.getInput(index));
        }
      } else {
        relBuilder.pushAll(bottomOp.getInputs());
        relBuilder.pushAll(Util.skip(topOp.getInputs()));
      }
      int n = bottomOp.getInputs().size()
          + topOp.getInputs().size()
          - 1;
      if (topOp instanceof Union) {
        relBuilder.union(topOp.all, n);
      } else if (topOp instanceof Intersect) {
        relBuilder.intersect(topOp.all, n);
      } else if (topOp instanceof Minus) {
        relBuilder.minus(topOp.all, n);
      }
      call.transformTo(relBuilder.build());
    }
  
    /** Rule configuration. */
    @Value.Immutable
    public interface Config extends RelRule.Config {
      Config DEFAULT = ImmutableUnionMergeRule.Config.of()
          .withDescription("UnionMergeRule")
          .withOperandFor(LogicalUnion.class);
  
      Config INTERSECT = ImmutableUnionMergeRule.Config.of()
          .withDescription("IntersectMergeRule")
          .withOperandFor(LogicalIntersect.class);
  
      Config MINUS = ImmutableUnionMergeRule.Config.of()
          .withDescription("MinusMergeRule")
          .withOperandFor(LogicalMinus.class);
  
      @Override default UnionMergeRule toRule() {
        return new UnionMergeRule(this);
      }
  
      /** Defines an operand tree for the given classes. */
      default Config withOperandFor(Class<? extends RelNode> setOpClass) {
        return withOperandSupplier(b0 ->
            b0.operand(setOpClass).inputs(
                b1 -> b1.operand(RelNode.class).anyInputs(),
                b2 -> b2.operand(RelNode.class).anyInputs()))
            .as(Config.class);
      }
    }
  }
  