/***********************************************************************
  MySQL Session class

  This class encapsulates everything needed to store your PHP sessions
  in a MySQL database. To use it simply call Session::start() instead
  of session_start().

  You'll need a table like this in your database. You can change the
  name but the fields should remain as they are defined here.

  CREATE TABLE `sessions` (
    `id` varchar(50) NOT NULL,
    `name` varchar(50) NOT NULL,
    `expires` int(10) unsigned NOT NULL default '0',
    `data` text,
    PRIMARY KEY  (`id`, `name`)
  ) TYPE=InnoDB;
***********************************************************************/
class Session
{
  protected $_lifetime = 900;
  protected $_db = false;
  protected $_table = 'sessions';
  protected $_name = 'phpsess';

  static public function start($host = 'localhost', $username = 'root', $password = '', $db = 'sessionstore', $table = 'sessions', $_lifetime = 0)
  {
    // Create the object
    $GLOBALS['_SESSION_OBJ_'] = new self($host, $username, $password, $db, $table, $lifetime);
    // Hook up the handler
    session_set_save_handler(
            array($GLOBALS['_SESSION_OBJ_'], 'open'),
            array($GLOBALS['_SESSION_OBJ_'], 'close'),
            array($GLOBALS['_SESSION_OBJ_'], 'read'),
            array($GLOBALS['_SESSION_OBJ_'], 'write'),
            array($GLOBALS['_SESSION_OBJ_'], 'destroy'),
            array($GLOBALS['_SESSION_OBJ_'], 'gc')
          );
    // Start the session
    session_start();
  }

  private function __construct($host = 'localhost', $username = 'root', $password = '', $db = 'sessionstore', $table = 'sessions', $_lifetime = 0)
  {
    // By default we use the session _lifetime in php.ini, but this can be overridden in code
    $this->_lifetime = ($_lifetime == 0 ? get_cfg_var('session.gc_max_lifetime') : $_lifetime);
    // This is the table where session data is to be stored
    $this->_table = $table;
    // Now we connect to the database, throwing expections if anything fails
    $this->_db = @mysql_connect($host, $username, $password);
    if ($this->_db === false)
      throw new Exception('Failed to connect to the session store', 1);
    if (false === @mysql_select_db($db, $this->_db))
      throw new Exception('Failed to select session store', 2);
  }

  public function open($path, $name)
  {
    // Store the session name for future use, we don't have any use for the path
    $this->_name = $name;
    // Everything is OK if we have a connection to the database
    return ($this->_db !== false);
  }

  public function close()
  {
    // Run the garbage collector 10% of the time
    if (rand(1, 10) == 5) {
      $this->gc($this->_lifetime);
    }
    // Close the database connection
    return @mysql_close($this->_db);
  }

  public function read($id)
  {
    // By default we return nothing
    $retval = '';

    // Try to read an entry from the database
    $result = mysql_query('select data from `'.$this->_table.'` where id = "'.mysql_real_escape_string($id, $this->_db).'" and name = "'.mysql_real_escape_string($this->_name, is->_db).'" and expires > '.time().' order by expires desc', $this->_db);
    if ($result !== false and mysql_num_rows($result) > 0) {
      // Found one, get it
      $retval = mysql_result($result, 0, 0);
    }

    return $retval;
  }

  public function write($id, $data)
  {
    $retval = false;
    // Build the query. We use the MySQL ON DUPLICATE KEY feature to do an insert/update in one query.
    $sql = 'insert into `'.$this->_table.'` set ';
    $sql.= 'id = "'.mysql_real_escape_string($id, $this->_db).'", ';
    $sql.= 'name = "'.mysql_real_escape_string($this->_name, $this->_db).'", ';
    $sql.= 'expires = '.(time() + $this->_lifetime).', ';
    $sql.= 'data = "'.mysql_real_escape_string($data, $this->_db).'" ';
    $sql.= 'on duplicate key update expires = values(expires), data = values(data)';
    // Run it and return true if it was successful
    $result = mysql_query($sql, $this->_db);
    if ($result !== false and mysql_affected_rows($this->_db) > 0) {
      $retval = true;
    }
    @mysql_free_result($result);
    return $retval;
  }

  public function destroy($id)
  {
    // Remove this session from the database
    $result = mysql_query('delete from `'.$this->_table.'` where id = "'.mysql_real_escape_string($id, $this->_db).'" and name = "'.mysql_real_escape_string($this->_name, s->_db).'"', $this->_db);
    if ($result !== false and mysql_affected_rows($this->_db) > 0) {
      return true;
    }
    return false;
  }

  public function gc($_lifetime)
  {
    // Remove any sessions that have expired
    $result = mysql_query('delete from `'.$this->_table.'` where expires < '.time(), $this->_db);
    return ($result === false ? 0 : mysql_affected_rows($this->_db));
  }
}