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.core.Intersect;
  import org.apache.calcite.rel.core.Minus;
  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.RelBuilderFactory;
  
  import org.immutables.value.Value;
  
  /**
   * <code>UnionEliminatorRule</code> checks to see if its possible to optimize a
   * Union call by eliminating the Union operator altogether in the case the call
   * consists of only one input.
   *
   * <p>Originally written for {@link Union} (hence the name),
   * but now also applies to {@link Intersect} and {@link Minus}.
   *
   * @see CoreRules#UNION_REMOVE
   */
  @Value.Enclosing
  public class UnionEliminatorRule
      extends RelRule<UnionEliminatorRule.Config>
      implements SubstitutionRule {
  
    /** Creates a UnionEliminatorRule. */
    protected UnionEliminatorRule(Config config) {
      super(config);
    }
  
    @Deprecated // to be removed before 2.0
    public UnionEliminatorRule(Class<? extends SetOp> setOpClass,
        String description, RelBuilderFactory relBuilderFactory) {
      super(Config.DEFAULT.withRelBuilderFactory(relBuilderFactory)
          .withDescription(description)
          .as(Config.class)
          .withOperandFor(setOpClass));
    }
  
    @Deprecated // to be removed before 2.0
    public UnionEliminatorRule(Class<? extends Union> unionClass,
        RelBuilderFactory relBuilderFactory) {
      super(Config.DEFAULT.withRelBuilderFactory(relBuilderFactory)
          .as(Config.class)
          .withOperandFor(unionClass));
    }
  
    //~ Methods ----------------------------------------------------------------
  
    @Override public boolean matches(RelOptRuleCall call) {
      SetOp setOp = call.rel(0);
      return setOp.all && setOp.getInputs().size() == 1;
    }
  
    @Override public void onMatch(RelOptRuleCall call) {
      SetOp setOp = call.rel(0);
      call.transformTo(setOp.getInputs().get(0));
    }
  
    @Override public boolean autoPruneOld() {
      return true;
    }
  
    /** Rule configuration. */
    @Value.Immutable
    public interface Config extends RelRule.Config {
      Config DEFAULT = ImmutableUnionEliminatorRule.Config.of()
              .withDescription("UnionEliminatorRule")
              .withOperandFor(LogicalUnion.class);
  
      Config INTERSECT = ImmutableUnionEliminatorRule.Config.of()
              .withDescription("IntersectEliminatorRule")
              .withOperandFor(LogicalIntersect.class);
  
      Config MINUS = ImmutableUnionEliminatorRule.Config.of()
              .withDescription("MinusEliminatorRule")
              .withOperandFor(LogicalMinus.class);
  
      @Override default UnionEliminatorRule toRule() {
        return new UnionEliminatorRule(this);
      }
  
      /** Defines an operand tree for the given classes. */
      default Config withOperandFor(Class<? extends SetOp> setOpClass) {
        return withOperandSupplier(b -> b.operand(setOpClass).anyInputs())
            .as(Config.class);
      }
    }
  }
  