在线Crontab表达式执行时间验证

<?php

class Cron
{
    const MINUTE = 0;
    const HOUR = 1;
    const DAY = 2;
    const MONTH = 3;
    const WEEKDAY = 4;
    const YEAR = 5;

    private static $order = array(self::YEAR, self::MONTH, self::DAY, self::WEEKDAY, self::HOUR, self::MINUTE);
    public static function factory($expression)
    public function __construct($expression, FieldFactory $fieldFactory)
    public function setExpression($value)
    public function setPart($position, $value)
    public function getNextRunDate($currentTime = 'now', $nth = 0, $allowCurrentDate = false)
    public function getPreviousRunDate($currentTime = 'now', $nth = 0, $allowCurrentDate = false)
    public function getMultipleRunDates($total, $currentTime = 'now', $invert = false, $allowCurrentDate = false)
    public function getExpression($part = null)
    public function __toString()
    public function isDue($currentTime = 'now')

    protected function getRunDate($currentTime = null, $nth = 0, $invert = false, $allowCurrentDate = false)
}