<?php
/**
 * DataReader class file
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @link http://www.yiiframework.com/
 * @copyright Copyright &copy; 2008-2012 Yii Software LLC
 * @license http://www.yiiframework.com/license/
 */

namespace yii\db\dao;

/**
 * DataReader represents a forward-only stream of rows from a query result set.
 *
 * To read the current row of data, call [[read]]. The method [[readAll]]
 * returns all the rows in a single array.
 *
 * One can also retrieve the rows of data in DataReader by using `foreach`:
 *
 * ~~~
 * foreach($reader as $row) {
 *     // $row represents a row of data
 * }
 * ~~~
 *
 * Since DataReader is a forward-only stream, you can only traverse it once.
 *
 * It is possible to use a specific mode of data fetching by setting
 * [[fetchMode]]. See the [PHP manual](http://www.php.net/manual/en/function.PDOStatement-setFetchMode.php)
 * for more details about possible fetch mode.
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @since 2.0
 */
class DataReader extends \yii\base\Component implements \Iterator, \Countable
{
	private $_statement;
	private $_closed = false;
	private $_row;
	private $_index = -1;

	/**
	 * Constructor.
	 * @param Command $command the command generating the query result
	 */
	public function __construct(Command $command)
	{
		$this->_statement = $command->getPdoStatement();
		$this->_statement->setFetchMode(\PDO::FETCH_ASSOC);
	}

	/**
	 * Binds a column to a PHP variable.
	 * When rows of data are being fetched, the corresponding column value
	 * will be set in the variable. Note, the fetch mode must include PDO::FETCH_BOUND.
	 * @param mixed $column Number of the column (1-indexed) or name of the column
	 * in the result set. If using the column name, be aware that the name
	 * should match the case of the column, as returned by the driver.
	 * @param mixed $value Name of the PHP variable to which the column will be bound.
	 * @param integer $dataType Data type of the parameter
	 * @see http://www.php.net/manual/en/function.PDOStatement-bindColumn.php
	 */
	public function bindColumn($column, &$value, $dataType = null)
	{
		if ($dataType === null) {
			$this->_statement->bindColumn($column, $value);
		}
		else {
			$this->_statement->bindColumn($column, $value, $dataType);
		}
	}

	/**
	 * Set the default fetch mode for this statement
	 * @param mixed $mode fetch mode
	 * @see http://www.php.net/manual/en/function.PDOStatement-setFetchMode.php
	 */
	public function setFetchMode($mode)
	{
		$params = func_get_args();
		call_user_func_array(array($this->_statement, 'setFetchMode'), $params);
	}

	/**
	 * Advances the reader to the next row in a result set.
	 * @return array|false the current row, false if no more row available
	 */
	public function read()
	{
		return $this->_statement->fetch();
	}

	/**
	 * Returns a single column from the next row of a result set.
	 * @param integer $columnIndex zero-based column index
	 * @return mixed|false the column of the current row, false if no more row available
	 */
	public function readColumn($columnIndex)
	{
		return $this->_statement->fetchColumn($columnIndex);
	}

	/**
	 * Returns an object populated with the next row of data.
	 * @param string $className class name of the object to be created and populated
	 * @param array $fields Elements of this array are passed to the constructor
	 * @return mixed|false the populated object, false if no more row of data available
	 */
	public function readObject($className, $fields)
	{
		return $this->_statement->fetchObject($className, $fields);
	}

	/**
	 * Reads the whole result set into an array.
	 * @return array the result set (each array element represents a row of data).
	 * An empty array will be returned if the result contains no row.
	 */
	public function readAll()
	{
		return $this->_statement->fetchAll();
	}

	/**
	 * Advances the reader to the next result when reading the results of a batch of statements.
	 * This method is only useful when there are multiple result sets
	 * returned by the query. Not all DBMS support this feature.
	 * @return boolean Returns true on success or false on failure.
	 */
	public function nextResult()
	{
		if (($result = $this->_statement->nextRowset()) !== false) {
			$this->_index = -1;
		}
		return $result;
	}

	/**
	 * Closes the reader.
	 * This frees up the resources allocated for executing this SQL statement.
	 * Read attemps after this method call are unpredictable.
	 */
	public function close()
	{
		$this->_statement->closeCursor();
		$this->_closed = true;
	}

	/**
	 * whether the reader is closed or not.
	 * @return boolean whether the reader is closed or not.
	 */
	public function getIsClosed()
	{
		return $this->_closed;
	}

	/**
	 * Returns the number of rows in the result set.
	 * Note, most DBMS may not give a meaningful count.
	 * In this case, use "SELECT COUNT(*) FROM tableName" to obtain the number of rows.
	 * @return integer number of rows contained in the result.
	 */
	public function getRowCount()
	{
		return $this->_statement->rowCount();
	}

	/**
	 * Returns the number of rows in the result set.
	 * This method is required by the Countable interface.
	 * Note, most DBMS may not give a meaningful count.
	 * In this case, use "SELECT COUNT(*) FROM tableName" to obtain the number of rows.
	 * @return integer number of rows contained in the result.
	 */
	public function count()
	{
		return $this->getRowCount();
	}

	/**
	 * Returns the number of columns in the result set.
	 * Note, even there's no row in the reader, this still gives correct column number.
	 * @return integer the number of columns in the result set.
	 */
	public function getColumnCount()
	{
		return $this->_statement->columnCount();
	}

	/**
	 * Resets the iterator to the initial state.
	 * This method is required by the interface Iterator.
	 * @throws Exception if this method is invoked twice
	 */
	public function rewind()
	{
		if ($this->_index < 0) {
			$this->_row = $this->_statement->fetch();
			$this->_index = 0;
		}
		else {
			throw new Exception('DataReader cannot rewind. It is a forward-only reader.');
		}
	}

	/**
	 * Returns the index of the current row.
	 * This method is required by the interface Iterator.
	 * @return integer the index of the current row.
	 */
	public function key()
	{
		return $this->_index;
	}

	/**
	 * Returns the current row.
	 * This method is required by the interface Iterator.
	 * @return mixed the current row.
	 */
	public function current()
	{
		return $this->_row;
	}

	/**
	 * Moves the internal pointer to the next row.
	 * This method is required by the interface Iterator.
	 */
	public function next()
	{
		$this->_row = $this->_statement->fetch();
		$this->_index++;
	}

	/**
	 * Returns whether there is a row of data at current position.
	 * This method is required by the interface Iterator.
	 * @return boolean whether there is a row of data at current position.
	 */
	public function valid()
	{
		return $this->_row !== false;
	}
}