getDatesInRangeByDaysInMonth.php

<?php

/**
 * Returns all days between two dates matching a wanted position in a week, in a month.
 *
 * For instance, in order to get all dates matching the request:
 * "First and third monday and friday of each month between 2022-01-08 and 2022-06-15" :
 *
 * $days = getDatesInRangeByDaysInMonth(new DateTimeImmutable('2022-01-08'), new DateTimeImmutable('2022-06-15'), [1, 5], [1, 3]);
 *
 * @param DateTimeInterface $startDate
 * @param DateTimeInterface $endDate
 * @param int[] $daysOfWeek
 * @param int[] $daysOfWeekInMonth
 * @return DateTimeImmutable[]
 */
function getDatesInRangeByDaysInMonth(DateTimeInterface $startDate, DateTimeInterface $endDate, array $daysOfWeek, array $daysOfWeekInMonth): array
{
    $days = [1 => 'Monday', 2 => 'Tuesday', 3 => 'Wednesday', 4 => 'Thursday', 5 => 'Friday', 6 => 'Saturday', 7 => 'Sunday'];
    $ordinals = [1 => 'first', 2 => 'second', 3 => 'third', 4 => 'fourth', 5 => 'fifth'];

    // Clean passed variables
    $startDate = $startDate instanceof DateTime ? DateTimeImmutable::createFromMutable($startDate) : $startDate;
    $endDate = $endDate instanceof DateTime ? DateTimeImmutable::createFromMutable($endDate) : $endDate;
    $daysOfWeek = array_unique(array_filter($daysOfWeek, static fn($d) => array_key_exists((int)$d, $days)));
    $daysOfWeekInMonth = array_unique(array_filter($daysOfWeekInMonth, static fn($d) => array_key_exists((int)$d, $ordinals)));

    /** @var DateTimeImmutable[] $result */
    $result = [];

    // Iterator
    $period = new DatePeriod($startDate->modify('first day of this month'), new DateInterval('P1M'), $endDate);

    foreach ($period as $firstDayOfMonth) {
        /** @var DateTimeImmutable $firstDayOfMonth */

        foreach ($daysOfWeekInMonth as $dayOfWeekInMonth) {
            foreach ($daysOfWeek as $dayOfWeek) {
                $newDate = $firstDayOfMonth->modify(sprintf('%s %s of this month', $ordinals[$dayOfWeekInMonth], $days[$dayOfWeek]));
                if ($newDate < $startDate || $newDate > $endDate) {
                    continue;
                }
                $result[] = $newDate;
            }
        }
    }
    return $result;
}

$startDate = new DateTimeImmutable('2022-01-08');
$endDate = new DateTimeImmutable('2022-06-15');
$daysOfWeek = [1, 5]; // 1 = monday, 5 = friday
$daysOfWeekInMonth = [1, 3]; // First and third monday and friday of each month

$days = getDatesInRangeByDaysInMonth($startDate, $endDate, $daysOfWeek, $daysOfWeekInMonth);
print_r($days);