/*
    * Copyright 2006-2008 the original author or authors.
    *
    * 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 org.springframework.batch.item.database.support;
  
  /**
   * H2 implementation of a {@link org.springframework.batch.item.database.PagingQueryProvider} using database specific features.
   *
   * @author Dave Syer
   * @since 2.1
   */
  public class H2PagingQueryProvider extends AbstractSqlPagingQueryProvider {
  
  	@Override
  	public String generateFirstPageQuery(int pageSize) {
  		return SqlPagingQueryUtils.generateTopSqlQuery(this, false, buildTopClause(pageSize));
  	}
  
  	@Override
  	public String generateRemainingPagesQuery(int pageSize) {
  		return SqlPagingQueryUtils.generateTopSqlQuery(this, true, buildTopClause(pageSize));
  	}
  
  	private String buildTopClause(int pageSize) {
  		return new StringBuilder().append("TOP ").append(pageSize).toString();
  	}
  
  	@Override
  	public String generateJumpToItemQuery(int itemIndex, int pageSize) {
  		int page = itemIndex / pageSize;
  		int offset = (page * pageSize) - 1;
  		offset = offset<0 ? 0 : offset;
  
  		String topClause = new StringBuilder().append("LIMIT ").append(offset).append(" 1").toString();
  		return SqlPagingQueryUtils.generateTopJumpToQuery(this, topClause);
  	}
  
  }