/*
    * Copyright 2006-2012 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;
  
  import java.util.Map;
  
  import org.springframework.batch.item.database.Order;
  
  /**
   * Oracle implementation of a
   * {@link org.springframework.batch.item.database.PagingQueryProvider} using
   * database specific features.
   * 
   * @author Thomas Risberg
   * @author Michael Minella
   * @since 2.0
   */
  public class OraclePagingQueryProvider extends AbstractSqlPagingQueryProvider {
  
  	@Override
  	public String generateFirstPageQuery(int pageSize) {
  		return SqlPagingQueryUtils.generateRowNumSqlQuery(this, false, buildRowNumClause(pageSize));
  	}
  
  	@Override
  	public String generateRemainingPagesQuery(int pageSize) {
  		return SqlPagingQueryUtils.generateRowNumSqlQuery(this, true, buildRowNumClause(pageSize));
  	}
  
  	@Override
  	public String generateJumpToItemQuery(int itemIndex, int pageSize) {
  		int page = itemIndex / pageSize;
  		int offset = (page * pageSize);
  		offset = offset == 0 ? 1 : offset;
  		String sortKeySelect = this.getSortKeySelect();
  		return SqlPagingQueryUtils.generateRowNumSqlQueryWithNesting(this, sortKeySelect, sortKeySelect, false, "TMP_ROW_NUM = "
  				+ offset);
  	}
  	
  	private String getSortKeySelect() {
  		StringBuilder sql = new StringBuilder();
  		String prefix = "";
  		
  		for (Map.Entry<String, Order> sortKey : this.getSortKeys().entrySet()) {
  			sql.append(prefix);
  			prefix = ", ";
  			sql.append(sortKey.getKey());
  		}
  		
  		return sql.toString();
  	}
  
  	private String buildRowNumClause(int pageSize) {
  		return new StringBuilder().append("ROWNUM <= ").append(pageSize).toString();
  	}
  
  }