<?php

namespace Cron;

/**
 * Day of month field.	Allows: * , / - ? L W
 *
 * 'L' stands for "last" and specifies the last day of the month.
 *
 * The 'W' character is used to specify the weekday (Monday-Friday) nearest the
 * given day. As an example, if you were to specify "15W" as the value for the
 * day-of-month field, the meaning is: "the nearest weekday to the 15th of the
 * month". So if the 15th is a Saturday, the trigger will fire on Friday the
 * 14th. If the 15th is a Sunday, the trigger will fire on Monday the 16th. If
 * the 15th is a Tuesday, then it will fire on Tuesday the 15th. However if you
 * specify "1W" as the value for day-of-month, and the 1st is a Saturday, the
 * trigger will fire on Monday the 3rd, as it will not 'jump' over the boundary
 * of a month's days. The 'W' character can only be specified when the
 * day-of-month is a single day, not a range or list of days.
 *
 * @author Michael Dowling <mtdowling@gmail.com>
 */
class DayOfMonthField extends AbstractField
{
	/**
	 * Get the nearest day of the week for a given day in a month
	 *
	 * @param int $currentYear	Current year
	 * @param int $currentMonth Current month
	 * @param int $targetDay	Target day of the month
	 *
	 * @return \DateTime Returns the nearest date
	 */
	private static function getNearestWeekday($currentYear, $currentMonth, $targetDay)
	{
		$tday = str_pad($targetDay, 2, '0', STR_PAD_LEFT);
		$target = \DateTime::createFromFormat('Y-m-d', "$currentYear-$currentMonth-$tday");
		$currentWeekday = (int) $target->format('N');

		if ($currentWeekday < 6) {
			return $target;
		}

		$lastDayOfMonth = $target->format('t');

		foreach (array(-1, 1, -2, 2) as $i) {
			$adjusted = $targetDay + $i;
			if ($adjusted > 0 && $adjusted <= $lastDayOfMonth) {
				$target->setDate($currentYear, $currentMonth, $adjusted);
				if ($target->format('N') < 6 && $target->format('m') == $currentMonth) {
					return $target;
				}
			}
		}
	}

	public function isSatisfiedBy(\DateTime $date, $value)
	{
		// ? states that the field value is to be skipped
		if ($value == '?') {
			return true;
		}

		$fieldValue = $date->format('d');

		// Check to see if this is the last day of the month
		if ($value == 'L') {
			return $fieldValue == $date->format('t');
		}

		// Check to see if this is the nearest weekday to a particular value
		if (strpos($value, 'W')) {
			// Parse the target day
			$targetDay = substr($value, 0, strpos($value, 'W'));
			// Find out if the current day is the nearest day of the week
			return $date->format('j') == self::getNearestWeekday(
				$date->format('Y'),
				$date->format('m'),
				$targetDay
			)->format('j');
		}

		return $this->isSatisfied($date->format('d'), $value);
	}

	public function increment(\DateTime $date, $invert = false)
	{
		if ($invert) {
			$date->modify('previous day');
			$date->setTime(23, 59);
		} else {
			$date->modify('next day');
			$date->setTime(0, 0);
		}

		return $this;
	}

	public function validate($value)
	{
		return (bool) preg_match('/^[\*,\/\-\?LW0-9A-Za-z]+$/', $value);
	}
}
