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.enumerable;
  
  import org.apache.calcite.linq4j.tree.BlockBuilder;
  import org.apache.calcite.linq4j.tree.Expression;
  import org.apache.calcite.linq4j.tree.Expressions;
  import org.apache.calcite.plan.RelOptCluster;
  import org.apache.calcite.plan.RelTraitSet;
  import org.apache.calcite.rel.RelCollation;
  import org.apache.calcite.rel.RelNode;
  import org.apache.calcite.rel.core.Sort;
  import org.apache.calcite.rex.RexNode;
  import org.apache.calcite.util.BuiltInMethod;
  import org.apache.calcite.util.Pair;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import static org.apache.calcite.adapter.enumerable.EnumerableLimit.getExpression;
  
  /**
   * Implementation of {@link org.apache.calcite.rel.core.Sort} in
   * {@link org.apache.calcite.adapter.enumerable.EnumerableConvention enumerable calling convention}.
   * It optimizes sorts that have a limit and an optional offset.
   */
  public class EnumerableLimitSort extends Sort implements EnumerableRel {
  
    /**
     * Creates an EnumerableLimitSort.
     *
     * <p>Use {@link #create} unless you know what you're doing.
     */
    public EnumerableLimitSort(
        RelOptCluster cluster,
        RelTraitSet traitSet,
        RelNode input,
        RelCollation collation,
        @Nullable RexNode offset,
        @Nullable RexNode fetch) {
      super(cluster, traitSet, input, collation, offset, fetch);
      assert this.getConvention() instanceof EnumerableConvention;
      assert this.getConvention() == input.getConvention();
    }
  
    /** Creates an EnumerableLimitSort. */
    public static EnumerableLimitSort create(
        RelNode input,
        RelCollation collation,
        @Nullable RexNode offset,
        @Nullable RexNode fetch) {
      final RelOptCluster cluster = input.getCluster();
      final RelTraitSet traitSet =
          cluster.traitSetOf(EnumerableConvention.INSTANCE).replace(collation);
      return new EnumerableLimitSort(cluster, traitSet, input, collation, offset, fetch);
    }
  
    @Override public EnumerableLimitSort copy(
        RelTraitSet traitSet,
        RelNode newInput,
        RelCollation newCollation,
        @Nullable RexNode offset,
        @Nullable RexNode fetch) {
      return new EnumerableLimitSort(
          this.getCluster(),
          traitSet,
          newInput,
          newCollation,
          offset,
          fetch);
    }
  
    @Override public Result implement(EnumerableRelImplementor implementor, Prefer pref) {
      final BlockBuilder builder = new BlockBuilder();
      final EnumerableRel child = (EnumerableRel) this.getInput();
      final Result result = implementor.visitChild(this, 0, child, pref);
      final PhysType physType =
          PhysTypeImpl.of(implementor.getTypeFactory(), this.getRowType(),
              result.format);
      final Expression childExp = builder.append("child", result.block);
  
      final PhysType inputPhysType = result.physType;
      final Pair<Expression, Expression> pair =
          inputPhysType.generateCollationKey(this.collation.getFieldCollations());
  
      final Expression fetchVal;
      if (this.fetch == null) {
        fetchVal = Expressions.constant(Integer.MAX_VALUE);
      } else {
        fetchVal = getExpression(this.fetch);
      }
  
      final Expression offsetVal;
      if (this.offset == null) {
        offsetVal = Expressions.constant(0);
      } else {
        offsetVal = getExpression(this.offset);
      }
  
      builder.add(
          Expressions.return_(null,
              Expressions.call(BuiltInMethod.ORDER_BY_WITH_FETCH_AND_OFFSET.method,
                  Expressions.list(childExp,
                          builder.append("keySelector", pair.left))
                      .appendIfNotNull(
                          builder.appendIfNotNull("comparator", pair.right))
                      .appendIfNotNull(
                          builder.appendIfNotNull("offset",
                              Expressions.constant(offsetVal)))
                      .appendIfNotNull(
                          builder.appendIfNotNull("fetch",
                              Expressions.constant(fetchVal))))));
      return implementor.result(physType, builder.toBlock());
    }
  }
  