<?php
/**
 * TMsssqlCommandBuilder class file.
 *
 * @author Wei Zhuo <weizhuo[at]gmail[dot]com>
 * @link http://www.pradosoft.com/
 * @copyright Copyright &copy; 2005-2014 PradoSoft
 * @license http://www.pradosoft.com/license/
 * @package System.Data.Common
 */

Prado::using('System.Data.Common.TDbCommandBuilder');

/**
 * TMssqlCommandBuilder provides specifics methods to create limit/offset query commands
 * for MSSQL servers.
 *
 * @author Wei Zhuo <weizho[at]gmail[dot]com>
 * @package System.Data.Common
 * @since 3.1
 */
class TMssqlCommandBuilder extends TDbCommandBuilder
{
	/**
	 * Overrides parent implementation. Uses "SELECT @@Identity".
	 * @return integer last insert id, null if none is found.
	 */
	public function getLastInsertID()
	{
		foreach($this->getTableInfo()->getColumns() as $column)
		{
			if($column->hasSequence())
			{
				$command = $this->getDbConnection()->createCommand('SELECT @@Identity');
				return intval($command->queryScalar());
			}
		}
	}

	/**
	 * Overrides parent implementation. Alters the sql to apply $limit and $offset.
	 * The idea for limit with offset is done by modifying the sql on the fly
	 * with numerous assumptions on the structure of the sql string.
	 * The modification is done with reference to the notes from
	 * http://troels.arvin.dk/db/rdbms/#select-limit-offset
	 *
	 * <code>
	 * SELECT * FROM (
	 *  SELECT TOP n * FROM (
	 *    SELECT TOP z columns      -- (z=n+skip)
	 *    FROM tablename
	 *    ORDER BY key ASC
	 *  ) AS FOO ORDER BY key DESC -- ('FOO' may be anything)
	 * ) AS BAR ORDER BY key ASC    -- ('BAR' may be anything)
	 * </code>
	 *
	 * <b>Regular expressions are used to alter the SQL query. The resulting SQL query
	 * may be malformed for complex queries.</b> The following restrictions apply
	 *
	 * <ul>
	 *   <li>
	 * In particular, <b>commas</b> should <b>NOT</b>
	 * be used as part of the ordering expression or identifier. Commas must only be
	 * used for separating the ordering clauses.
	 *  </li>
	 *  <li>
	 * In the ORDER BY clause, the column name should NOT be be qualified
	 * with a table name or view name. Alias the column names or use column index.
	 * </li>
	 * <li>
	 * No clauses should follow the ORDER BY clause, e.g. no COMPUTE or FOR clauses.
	 * </li>
	 * </ul>
	 *
	 * @param string SQL query string.
	 * @param integer maximum number of rows, -1 to ignore limit.
	 * @param integer row offset, -1 to ignore offset.
	 * @return string SQL with limit and offset.
	 */
	public function applyLimitOffset($sql, $limit=-1, $offset=-1)
	{
		$limit = $limit!==null ? intval($limit) : -1;
		$offset = $offset!==null ? intval($offset) : -1;
		if ($limit > 0 && $offset <= 0) //just limit
			$sql = preg_replace('/^([\s(])*SELECT( DISTINCT)?(?!\s*TOP\s*\()/i',"\\1SELECT\\2 TOP $limit", $sql);
		else if($limit > 0 && $offset > 0)
			$sql = $this->rewriteLimitOffsetSql($sql, $limit,$offset);
		return $sql;
	}

	/**
	 * Rewrite sql to apply $limit > and $offset > 0 for MSSQL database.
	 * See http://troels.arvin.dk/db/rdbms/#select-limit-offset
	 * @param string sql query
	 * @param integer $limit > 0
	 * @param integer $offset > 0
	 * @return sql modified sql query applied with limit and offset.
	 */
	protected function rewriteLimitOffsetSql($sql, $limit, $offset)
	{
		$fetch = $limit+$offset;
		$sql = preg_replace('/^([\s(])*SELECT( DISTINCT)?(?!\s*TOP\s*\()/i',"\\1SELECT\\2 TOP $fetch", $sql);
		$ordering = $this->findOrdering($sql);

		$orginalOrdering = $this->joinOrdering($ordering);
		$reverseOrdering = $this->joinOrdering($this->reverseDirection($ordering));
		$sql = "SELECT * FROM (SELECT TOP {$limit} * FROM ($sql) as [__inner top table__] {$reverseOrdering}) as [__outer top table__] {$orginalOrdering}";
		return $sql;
	}

	/**
	 * Base on simplified syntax http://msdn2.microsoft.com/en-us/library/aa259187(SQL.80).aspx
	 *
	 * @param string $sql
	 * @return array ordering expression as key and ordering direction as value
	 */
	protected function findOrdering($sql)
	{
		if(!preg_match('/ORDER BY/i', $sql))
			return array();
		$matches=array();
		$ordering=array();
		preg_match_all('/(ORDER BY)[\s"\[](.*)(ASC|DESC)?(?:[\s"\[]|$|COMPUTE|FOR)/i', $sql, $matches);
		if(count($matches)>1 && count($matches[2]) > 0)
		{
			$parts = explode(',', $matches[2][0]);
			foreach($parts as $part)
			{
				$subs=array();
				if(preg_match_all('/(.*)[\s"\]](ASC|DESC)$/i', trim($part), $subs))
				{
					if(count($subs) > 1 && count($subs[2]) > 0)
					{
						$ordering[$subs[1][0]] = $subs[2][0];
					}
					//else what?
				}
				else
					$ordering[trim($part)] = 'ASC';
			}
		}
		return $ordering;
	}

	/**
	 * @param array ordering obtained from findOrdering()
	 * @return string concat the orderings
	 */
	protected function joinOrdering($orders)
	{
		if(count($orders)>0)
		{
			$str=array();
			foreach($orders as $column => $direction)
				$str[] = $column.' '.$direction;
			return 'ORDER BY '.implode(', ', $str);
		}
	}

	/**
	 * @param array original ordering
	 * @return array ordering with reversed direction.
	 */
	protected function reverseDirection($orders)
	{
		foreach($orders as $column => $direction)
			$orders[$column] = strtolower(trim($direction))==='desc' ? 'ASC' : 'DESC';
		return $orders;
	}
}