installment due by period - PHP - php

Question

the code snippet below shows a simulation of installments, with fixed expiration dates, divided every 30 days!
I would like to include a periodic expiration date, for example, every 20 days, or 10 every 10, depending on the variable $periodicity;
I have no idea how to do it?
<?php
function calculate_due($num_installment, $first_due_date = null){
if($first_due_date != null)
{
$first_due_date = explode('/',$first_due_date);
$day = $first_due_date[0];
$month = $first_due_date[1];
$year = $first_due_date[2];
}
else
{
$day = date('d');
$month = date('m');
$year = date('Y');
}
$periodicity = 20;
for($installment = 0; $installment < $num_installment; $installment++)
{
if ($periodicity == 30)
echo date('d/m/Y', strtotime('+'.$installment. " month", mktime(0, 0, 0, $month, $day, $year))),'<br/>';
else
echo date('d/m/Y', strtotime('+'.$installment. " month", mktime(0, 0, 0, $month, $periodicity, $year))),'<br/>';
}
}
echo 'Calculates installments from an informed date<br/>';
calculate_due(5, '10/10/2020');

Answer 1

Try this,
<?php
function calculate_due($num_installment, $first_due_date = null, $days = 1){
$start = DateTime::createFromFormat('d/m/Y', $first_due_date);
$end = DateTime::createFromFormat('d/m/Y', $first_due_date);
$end->add(new DateInterval('P'.($num_installment * $days).'D'));
$period = new DatePeriod(
$start,
new DateInterval('P'.$days.'D'),
$end
);
$return = [];
foreach ($period as $date) {
$return[] = $date->format('d/m/Y');
}
return $return;
}
echo 'Calculates installments from an informed date<br/>'.PHP_EOL;
echo implode("\n", calculate_due(5, '10/10/2020', 20));
https://3v4l.org/TLR8a
Change 20 (the last function parameter) to suit the number of days between.
Result:
Calculates installments from an informed date<br/>
10/10/2020<br/>
30/10/2020<br/>
19/11/2020<br/>
09/12/2020<br/>
29/12/2020<br/>