content: /**
   * Copyright (C) 2024 AIDC-AI
   *
   * 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.langengine.core.doctransformer;
  
  import com.alibaba.langengine.core.indexes.Document;
  import com.alibaba.langengine.core.textsplitter.BaseDocumentTransformer;
  
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  
  /**
   * Lost in the middle:
   * Performance degrades when models must access relevant information in the middle of long contexts.
   * See: https://arxiv.org/abs//2307.03172
   *
   * @author xiaoxuan.lp
   */
  public class LongContextReorder extends BaseDocumentTransformer {
  
      @Override
      public List<Document> transformDocuments(List<Document> documents) {
          return litmReordering(documents);
      }
  
      private List<Document> litmReordering(List<Document> documents) {
          List reorderedResult = new ArrayList<>();
          Collections.reverse(documents);
          for (int i = 0; i < documents.size(); i++) {
              if (i % 2 == 1) {
                  reorderedResult.add(documents.get(i));
              } else {
                  reorderedResult.add(0, documents.get(i));
              }
          }
          return reorderedResult;
      }
  }
  