PHP - Calculate the next occurrence of a given date

next_occurrence.php

<?php

// Usage
$occurrences = next_occurrence('Friday', 13);
foreach($occurrences as $day) {
    echo $day->format('D M j, Y') . PHP_EOL;
}



/**
 * Find the next occurrence(s) of a given date
 * 
 * @param  string   $day_name          The full name of the day (Monday-Friday)
 * @param  integer  $day_num           The day number (1-31)
 * @param  string   $month_name        [optional] The abbreviated month name (Jan-Dec)
 * @param  integer  $num_occurrences    The number of occurrences to show
 * @return array                       All of the occurrences 
 * 
 */
function next_occurrence($day_name='Friday', $day_num=13, $month_name=null, $num_occurrences=20)
{
    
    $first_day = new DateTime($day_name);

    // Calculate the end date
    // note: use "clone" first because "modify" changes the original instance
    $last_day = clone $first_day; 
    $last_day->modify("+$num_occurrences years");

    // Select the format based on whether or not the month is included
    if (is_null($month_name)) {
        $format = 'l j';
        $long_format = "$day_name $day_num";
    } else {
        $format = 'M l j';
        $long_format = "$month_name $day_name $day_num"; 
    }

    // Iterate over each day for the next $num_occurrences, and see if the date matches the given format
    $dates = array();
    while($first_day < $last_day) {
        if($first_day->format($format) == $long_format) {
            $dates[] = clone $first_day;
        }
        $first_day->modify('+7 days');
    }
    return $dates;
}