core/src/main/java/org/apache/calcite/rex/RexPermuteInputsShuttle.java

/*
 * 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.rex;

import org.apache.calcite.rel.RelNode;
import org.apache.calcite.rel.type.RelDataTypeField;
import org.apache.calcite.util.mapping.Mappings;

import com.google.common.collect.ImmutableList;

import org.checkerframework.checker.nullness.qual.Nullable;

import java.util.List;

/**
 * Shuttle which applies a permutation to its input fields.
 *
 * @see RexPermutationShuttle
 * @see RexUtil#apply(org.apache.calcite.util.mapping.Mappings.TargetMapping, RexNode)
 */
public class RexPermuteInputsShuttle extends RexShuttle {
  //~ Instance fields --------------------------------------------------------

  private final Mappings.TargetMapping mapping;
  private final ImmutableList<RelDataTypeField> fields;

  //~ Constructors -----------------------------------------------------------

  /**
   * Creates a RexPermuteInputsShuttle.
   *
   * <p>The mapping provides at most one target for every source. If a source
   * has no targets and is referenced in the expression,
   * {@link org.apache.calcite.util.mapping.Mappings.TargetMapping#getTarget(int)}
   * will give an error. Otherwise the mapping gives a unique target.
   *
   * @param mapping Mapping
   * @param inputs  Input relational expressions
   */
  public RexPermuteInputsShuttle(
      Mappings.TargetMapping mapping,
      RelNode... inputs) {
    this(mapping, fields(inputs));
  }

  private RexPermuteInputsShuttle(
      Mappings.TargetMapping mapping,
      ImmutableList<RelDataTypeField> fields) {
    this.mapping = mapping;
    this.fields = fields;
  }

  /** Creates a shuttle with an empty field list. It cannot handle GET calls but
   * otherwise works OK. */
  public static RexPermuteInputsShuttle of(Mappings.TargetMapping mapping) {
    return new RexPermuteInputsShuttle(mapping,
        ImmutableList.of());
  }

  //~ Methods ----------------------------------------------------------------

  private static ImmutableList<RelDataTypeField> fields(RelNode[] inputs) {
    final ImmutableList.Builder<RelDataTypeField> fields =
        ImmutableList.builder();
    for (RelNode input : inputs) {
      fields.addAll(input.getRowType().getFieldList());
    }
    return fields.build();
  }

  @Override public RexNode visitInputRef(RexInputRef local) {
    final int index = local.getIndex();
    int target = mapping.getTarget(index);
    return new RexInputRef(
        target,
        local.getType());
  }

  @Override public RexNode visitCall(RexCall call) {
    if (call.getOperator() == RexBuilder.GET_OPERATOR) {
      final String name =
          (String) ((RexLiteral) call.getOperands().get(1)).getValue2();
      final int i = lookup(fields, name);
      if (i >= 0) {
        return RexInputRef.of(i, fields);
      }
    }
    return super.visitCall(call);
  }

  private static int lookup(List<RelDataTypeField> fields, @Nullable String name) {
    for (int i = 0; i < fields.size(); i++) {
      final RelDataTypeField field = fields.get(i);
      if (field.getName().equals(name)) {
        return i;
      }
    }
    return -1;
  }
}