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.plan.visualizer;
  
  import org.apache.calcite.rel.RelNode;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.Collections;
  import java.util.LinkedHashMap;
  import java.util.List;
  import java.util.Map;
  import java.util.Objects;
  
  /**
   * Helper class to create the node update.
   */
  class NodeUpdateHelper {
  
    private final String key;
    private final @Nullable RelNode rel;
    private final NodeUpdateInfo state;
    private @Nullable NodeUpdateInfo update = null;
  
    NodeUpdateHelper(String key, @Nullable RelNode rel) {
      this.key = key;
      this.rel = rel;
      this.state = new NodeUpdateInfo();
    }
  
    String getKey() {
      return key;
    }
  
    @Nullable RelNode getRel() {
      return this.rel;
    }
  
    void updateAttribute(final String attr, final Object newValue) {
      if (Objects.equals(newValue, state.get(attr))) {
        return;
      }
  
      state.put(attr, newValue);
  
      if (update == null) {
        update = new NodeUpdateInfo();
      }
  
      if (newValue instanceof List
          && ((List<?>) newValue).isEmpty()
          && !update.containsKey(attr)) {
        return;
      }
  
      update.put(attr, newValue);
    }
  
    boolean isEmptyUpdate() {
      return this.update == null || update.isEmpty();
    }
  
    /**
     * Gets an object representing all the changes since the last call to this method.
     *
     * @return an object or null if there are no changes.
     */
    @Nullable Object getAndResetUpdate() {
      if (isEmptyUpdate()) {
        return null;
      }
      NodeUpdateInfo update = this.update;
      this.update = null;
      return update;
    }
  
    Map<String, Object> getState() {
      return Collections.unmodifiableMap(this.state);
    }
  
    /**
     * Get the current value for the attribute.
     */
    @Nullable Object getValue(final String attr) {
      return this.state.get(attr);
    }
  
    /**
     * Type alias.
     */
    private static class NodeUpdateInfo extends LinkedHashMap<String, Object> {
    }
  }
  