PHP - 找到下一个未来的重复日期？

I have a database of events that are both "static" (on a specific day) and "recurring" (starting on a specific day, but set to be "recurring" either every week or every other week). I understand that there needs to be intervals of 7 and 14, but I don't know how to get to that point to find a date > today and spit it out.

so example;

I want to find the next upcoming recurring events and spit out their relevant dates. Side note: the data I'm stuck working with is in strings (I know, I know) of Ymd so 20150821 would be Aug 21st 2015.

if today was Aug 21 2015 and there's a recurring event for "Every other Friday" starting on Aug 7, it would be +14 which would get you to today, Friday Aug 21.

But say there was one for "Every Wednesday" starting Aug 19, I'd want to get the date for Wednesday, Aug 26 and spit that out.

This would need to work for infinite dates in the future, with the start dates never changing.

So running the script on Jan 1 2016, I'd need to know that the next "Every Wednesday" was Jan 6 2016.

pseudo code:

if(start_date < today_date) {
    // start date is in the past
    add recurring_inverval to start_date until result >= today_date
    echo result
} elseif(start_date > today_date {
    // start date is in the future
    echo start_date
}

it's the adding until x that I'm lost at. not sure how to do that within an if statement.

also not sure if that's the best way to go about it. I know PHP can also do complicated strings and convert them to a date. like "Next Saturday"

solved it myself:

$begin = new DateTime($start_date); // start searching on the start date of the event
$end = new DateTime(date('Ymd')); // end on today's date
$end = $end->modify('+1 month'); // extend search to the next month

$interval = new DateInterval('P'. $freq_math .'D'); // intervals of Plus X Days - uses frequency math of 7 or 14 for every or every other
$daterange = new DatePeriod($begin, $interval, $end);


foreach($daterange as $date) {
    if($date->format('Ymd') >= date('Ymd')) {
        $next_recurring_date = $date->format('Ymd');
        break;
    }
}

echo $next_recurring_date;

I know you answered this yourself, however another option is to just use the modulus (remainder after devision) of the current date minus the start date to compute your next date. Here is a quick script to do just that :

<?php
function nextDate($start_date,$interval_days,$output_format){
    $start = strtotime($start_date);
    $end = strtotime(date('Y-m-d'));
    $days_ago = ($end - $start) / 24 / 60 / 60;
    if($days_ago < 0)return date($output_format,$start);
    $remainder_days = $days_ago % $interval_days;
    if($remainder_days > 0){
        $new_date_string = "+" . ($interval_days - $remainder_days) . " days";
    } else {
        $new_date_string = "today";
    }
    return date($output_format,strtotime($new_date_string));
}
echo nextDate('20151210',14,'Ymd') . "<br />";
echo nextDate('20150808',14,'Ymd') . "<br />";
?>

You also don't want to return an early date if the "start date" is in the distant future. Code updated to prevent that.