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.core;
  
  import com.google.common.collect.ImmutableSet;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.Set;
  
  import static java.lang.Integer.parseInt;
  
  /**
   * Describes the necessary parameters for an implementation in order to
   * identify and set dynamic variables.
   */
  public class CorrelationId implements Cloneable, Comparable<CorrelationId> {
    /**
     * Prefix to the name of correlating variables.
     */
    public static final String CORREL_PREFIX = "$cor";
  
    private final int id;
    private final String name;
  
    /**
     * Creates a correlation identifier.
     */
    private CorrelationId(int id, String name) {
      this.id = id;
      this.name = name;
    }
  
    /**
     * Creates a correlation identifier.
     * This is a type-safe wrapper over int.
     *
     * @param id     Identifier
     */
    public CorrelationId(int id) {
      this(id, CORREL_PREFIX + id);
    }
  
    /**
     * Creates a correlation identifier from a name.
     *
     * @param name     variable name
     */
    public CorrelationId(String name) {
      this(parseInt(name.substring(CORREL_PREFIX.length())), name);
      assert name.startsWith(CORREL_PREFIX)
          : "Correlation name should start with " + CORREL_PREFIX
          + " actual name is " + name;
    }
  
    /**
     * Returns the identifier.
     *
     * @return identifier
     */
    public int getId() {
      return id;
    }
  
    /**
     * Returns the preferred name of the variable.
     *
     * @return name
     */
    public String getName() {
      return name;
    }
  
    @Override public String toString() {
      return name;
    }
  
    @Override public int compareTo(CorrelationId other) {
      return id - other.id;
    }
  
    @Override public int hashCode() {
      return id;
    }
  
    @Override public boolean equals(@Nullable Object obj) {
      return this == obj
          || obj instanceof CorrelationId
          && this.id == ((CorrelationId) obj).id;
    }
  
    /** Converts a set of correlation ids to a set of names. */
    public static ImmutableSet<CorrelationId> setOf(Set<String> set) {
      if (set.isEmpty()) {
        return ImmutableSet.of();
      }
      final ImmutableSet.Builder<CorrelationId> builder = ImmutableSet.builder();
      for (String s : set) {
        builder.add(new CorrelationId(s));
      }
      return builder.build();
    }
  
    /** Converts a set of names to a set of correlation ids. */
    public static Set<String> names(Set<CorrelationId> set) {
      if (set.isEmpty()) {
        return ImmutableSet.of();
      }
      final ImmutableSet.Builder<String> builder = ImmutableSet.builder();
      for (CorrelationId s : set) {
        builder.add(s.name);
      }
      return builder.build();
    }
  }
  