/**

     * 获取指定日期所在月的开始日期与结束日期

     * @param string $date

     * @param boolean 为true返回开始日期，否则返回结束日期

     * @return array

     * @author zyb <zyb.allwell@gmail.com>

     * @access private

     */

    private function getMonthRange( $date, $returnFirstDay = true ) {

        $timestamp = strtotime( $date );

        if ( $returnFirstDay ) {

            $monthFirstDay = date( 'Y-m-1 00:00:00', $timestamp );

            return $monthFirstDay;

        } else {

            $mdays = date( 't', $timestamp );

            $monthLastDay = date( 'Y-m-' . $mdays . ' 23:59:59', $timestamp );

            return $monthLastDay;

        }

    }