/*
    * 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.shardingsphere.sharding.merge.dql.pagination;
  
  import org.apache.shardingsphere.infra.merge.result.MergedResult;
  import org.apache.shardingsphere.infra.merge.result.impl.decorator.DecoratorMergedResult;
  import org.apache.shardingsphere.infra.binder.context.segment.select.pagination.PaginationContext;
  
  import java.sql.SQLException;
  
  /**
   * Decorator merged result for top and row number pagination.
   */
  public final class TopAndRowNumberDecoratorMergedResult extends DecoratorMergedResult {
      
      private final PaginationContext paginationContext;
      
      private final boolean skipAll;
      
      private long rowNumber;
      
      public TopAndRowNumberDecoratorMergedResult(final MergedResult mergedResult, final PaginationContext paginationContext) throws SQLException {
          super(mergedResult);
          this.paginationContext = paginationContext;
          skipAll = skipOffset();
      }
      
      private boolean skipOffset() throws SQLException {
          long end = paginationContext.getActualOffset();
          for (int i = 0; i < end; i++) {
              if (!getMergedResult().next()) {
                  return true;
              }
          }
          rowNumber = end + 1;
          return false;
      }
      
      @Override
      public boolean next() throws SQLException {
          if (skipAll) {
              return false;
          }
          if (!paginationContext.getActualRowCount().isPresent()) {
              return getMergedResult().next();
          }
          return rowNumber++ <= paginationContext.getActualRowCount().get() && getMergedResult().next();
      }
  }