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/**
 *  This file is part of MetaModel.
 *
 *  MetaModel is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  MetaModel is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with MetaModel.  If not, see .
 */
package dk.eobjects.metamodel.data;

import java.util.Iterator;
import java.util.List;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import dk.eobjects.metamodel.DataContext;
import dk.eobjects.metamodel.MetaModelException;
import dk.eobjects.metamodel.query.Query;
import dk.eobjects.metamodel.query.SelectItem;

/**
 * DataSet strategy for split queries. Queries will be executed as needed, not
 * at once.
 * 
 * @see dk.eobjects.metamodel.QuerySplitter
 */
public class SplitQueriesDataSetStrategy implements IDataSetStrategy {

	private static final Log _log = LogFactory
			.getLog(SplitQueriesDataSetStrategy.class);
	private DataContext _dataContext;
	private Iterator _queryIterator;
	private DataSet _currentDataSet;
	private SelectItem[] _selectItems;
	private int _queryIndex = 0;

	public SplitQueriesDataSetStrategy(DataContext dataContext,
			List splitQueries) {
		if (dataContext == null || splitQueries == null) {
			throw new IllegalArgumentException("Arguments cannot be null");
		}
		_dataContext = dataContext;
		_queryIterator = splitQueries.iterator();
		if (splitQueries.size() == 0) {
			_selectItems = new SelectItem[0];
		} else {
			_selectItems = splitQueries.get(0).getSelectClause().getItems()
					.toArray(new SelectItem[0]);
		}
	}

	public void close() {
		if (_currentDataSet != null) {
			_log.debug("currentDataSet.close() and System.gc()");
			_currentDataSet.close();
			System.gc();
		}
		_currentDataSet = null;
		_dataContext = null;
		_queryIterator = null;
	}

	public Row getRow() throws MetaModelException {
		if (_currentDataSet != null) {
			return _currentDataSet.getRow();
		}
		throw new IllegalStateException(
				"No rows available. Either DataSet is closed or next() hasn't been called");
	}

	public SelectItem[] getSelectItems() {
		return _selectItems;
	}

	public boolean next() {
		boolean result;
		if (_currentDataSet == null) {
			result = false;
		} else {
			result = _currentDataSet.next();
		}
		if (!result && _queryIterator.hasNext()) {
			if (_currentDataSet != null) {
				_log.debug("currentDataSet.close() and System.gc()");
				_currentDataSet.close();
				System.gc();
			}
			Query q = _queryIterator.next();
			_currentDataSet = _dataContext.executeQuery(q);
			if (_log.isDebugEnabled()) {
				_queryIndex++;
				_log.debug("Executing query #" + _queryIndex);
			}
			result = next();
		}
		return result;
	}
}