content: /*
   * Copyright 2020 Alibaba Group Holding Limited.
   *
   * 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.alibaba.graphscope.common.antlr4;
  
  import com.google.common.collect.Sets;
  
  import org.apache.calcite.sql.validate.SqlValidatorUtil;
  
  import java.util.Set;
  
  /**
   * infer a unique alias (which not contained in the uniqueNameList) for expression.
   */
  public class ExprUniqueAliasInfer {
      private final Set<String> uniqueNameList;
  
      public ExprUniqueAliasInfer() {
          this.uniqueNameList = Sets.newHashSet();
      }
  
      public String infer() {
          String name;
          int j = 0;
          do {
              name = SqlValidatorUtil.EXPR_SUGGESTER.apply(null, j++, 0);
          } while (uniqueNameList.contains(name));
          uniqueNameList.add(name);
          return name;
      }
  }
  