How to calculate date in PHP using variables - php

Question

Can anyone help create this logic? Kind of difficult to explain...
Looking to take a date, add 3 days then select the next date based on a database value.
Say we start with:
$end_date = "2017-08-23 23:59:59"
$payday = 5; //1=monday, 2=tuesday, 3=wednesday, 4=thursday, 5=friday
//And we want to calculate $paydate:
$temp_date = $end_date + 3 days;
$pay_date = the first $payday(day of week) after $temp_date
Any ideas how to write this in php? This one is stumping me. Thanks!

Answer 1

To add three days you can do this:
$date = new DateTime('2017-08-23 23:59:59');
$date->add(new DateInterval('P3D'));
$date->modify("next friday");
echo $date->format('Y-m-d') . "\n";
You could also use a lookup table, or array, that matches number to named days of the week and use something like $date->modify("next $days[$payday]");
where
$days = [ [1] => "monday",
.... etc

Answer 2

How about this? It will get a date, add 3 days, and then loop through the next days until it finds a day in the $days array (which you can get from a database):
<?php
$date = new DateTime('2017-08-23 23:59:59');
function nextPayday($date) {
$date->add(new DateInterval('P3D'));
echo "Date + 3 days: ".$date->format('D Y-m-d') . "<br>";
$payDate = $date->add(new DateInterval('P1D'));
$days = ["1", "2", "3", "4", "5"];
while (!in_array($payDate->format("N"), $days)) {
$payDate->add(new DateInterval('P1D'));
}
return $payDate->format("D Y-m-d");
}
echo "Date + 3 days: ".$date->format('D Y-m-d') . "<br>";
echo "Next payday: ".nextPayday($date);
Demo
Or, if you need to find a next specific day, use this function instead:
function nextPayday($date) {
$date->add(new DateInterval('P3D'));
echo "Date + 3 days: ".$date->format('D Y-m-d') . "<br>";
$payDate = $date->add(new DateInterval('P1D'));
$day = "5";
while ($payDate->format("N") !== $day) {
$payDate->add(new DateInterval('P1D'));
}
return $payDate->format("D Y-m-d");
}

Answer 3

Jeff, take a look at Carbon which extends PHP's DateTime object.
It allows you to deal with dates in a very clean and intuitive way. Based on your example:
$date = Carbon::parse('next monday')->toDateString();
Adjust that to your exact case.

Answer 4

Another version to achieve the objective:
function nextPayday($dateString, $paydayNum) {
$paydays = [
1=>'monday',
2=>'tuesday',
3=>'wednesday',
4=>'thursday',
5=>'friday'
];
$temp_date_stamp = date('d-m-Y H:i:s', strtotime($dateString.' +3 days'));
$pay_date_stamp = strtotime('first '.$paydays[$paydayNum].' '.$temp_date_stamp);
return date('d-m-Y H:i:s', $pay_date_stamp);
}
$end_date = "2017-08-23 23:59:59";
$payday = 5;
echo nextPayday($end_date, $payday);
result:
01-09-2017 23:59:59