content: 
  /*
   * Copyright 2021-2022 Alibaba Group Holding Ltd.
   *
   *    Licensed 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 com.aliyun.fastmodel.core.tree.expr.window;
  
  import java.util.List;
  
  import com.aliyun.fastmodel.core.tree.AbstractNode;
  import com.aliyun.fastmodel.core.tree.IAstVisitor;
  import com.aliyun.fastmodel.core.tree.Node;
  import com.aliyun.fastmodel.core.tree.NodeLocation;
  import com.aliyun.fastmodel.core.tree.expr.enums.WindowFrameType;
  import com.google.common.collect.ImmutableList;
  import lombok.EqualsAndHashCode;
  import lombok.Getter;
  import lombok.ToString;
  
  import static java.util.Objects.requireNonNull;
  
  /**
   * @author panguanjing
   */
  @Getter
  @ToString
  @EqualsAndHashCode(callSuper = false)
  public class WindowFrame
      extends AbstractNode {
  
      private final WindowFrameType type;
      private final FrameBound start;
      private final FrameBound end;
  
      public WindowFrame(WindowFrameType type, FrameBound start, FrameBound end) {
          this(null, type, start, end);
      }
  
      public WindowFrame(NodeLocation location, WindowFrameType type, FrameBound start, FrameBound end) {
          super(location);
          this.type = requireNonNull(type, "type is null");
          this.start = requireNonNull(start, "start is null");
          this.end = end;
      }
  
      @Override
      public <R, C> R accept(IAstVisitor<R, C> visitor, C context) {
          return visitor.visitWindowFrame(this, context);
      }
  
      @Override
      public List<? extends Node> getChildren() {
          ImmutableList.Builder<Node> nodes = ImmutableList.builder();
          nodes.add(start);
          if (end != null) {
              nodes.add(end);
          }
          return nodes.build();
      }
  
  }
  