Substract a date compared to current date and show actual remaining days - php

Question

This is my function below:
function Active()
{
............
$num_rows = $db->doQuery('SELECT PremiumDays, PremiumStartTime FROM Premium WHERE AccountID = ?', $_SESSION['AccountID']);
if ($num_rows == -1)
{
$this->Error('ERROR');
$db->getError();
return;
}
$data = $db->doRead();
$data['Status'] = $num_rows == 0 ? '<:SHOW_PREMIUM_STATUS:>' : '<b><font size="2" color="red">Premium is active - <%Days_Remaining%> days remaining.</font></b>';
$replace = array
(
'account_status' => $data['Status'],
'days_remaining' => number_format($data['PremiumDays'])
);
$this->content = Template::Load('account-template', $replace);
}
PremiumDays column contains numbers like 10,15,30 etc.
PremiumStartTime contains a date in this format 2018-12-17 21:13:00
What I am trying to achieve is to show the actual days of premium remaining with days_remaining. So, I believe I need to substract from PremiumDays the days that passed since the premium started based on the second column PremiumStartTime.
Something like that I believe, however, I am not sure how to implement it correctly in PHP. Any help is greatly appreciated. Thank you in advance!
days_remaining = PremiumDays - (NumberOfDaysSincePremiumStarted(DateToday - PremiumStartTime))

Answer 1

To get the difference in PHP, you can create a DateInterval object using DateTime::diff between the current time (output of date_create()) and a DateTime object created from your PremiumStartTime variable. You can then access the days value of this object to get the total number of days from the PremiumStartTime to the current time. For example:
$data['PremiumStartTime'] = '2018-12-12 21:13:00';
$data['PremiumDays'] = 20;
$days_remaining = $data['PremiumDays'] - date_create($data['PremiumStartTime'])->diff(date_create())->days;
echo number_format($days_remaining);
Output:
13
Demo on 3v4l.org

Answer 2

Do it in the DB as follows:
//SQL Server
$num_rows = $db->doQuery('SELECT PremiumDays, PremiumStartTime,
(PremiumDays - datediff(day,PremiumStartTime,getdate())) DaysRemaining
FROM Premium WHERE AccountID = ?', $_SESSION['AccountID']);
//MySQL
$num_rows = $db->doQuery('SELECT PremiumDays, PremiumStartTime,
(PremiumDays - datediff(now(),PremiumStartTime)) DaysRemaining
FROM Premium WHERE AccountID = ?', $_SESSION['AccountID']);
Then:
$replace = array
(
'account_status' => $data['Status'],
'days_remaining' => $data['DaysRemaining']
);
Proof here: https://www.db-fiddle.com/f/xzuc89C9gQUHpdTTy9M4vf/0
Or if you really want to do it in PHP:
$replace = array
(
'account_status' => $data['Status'],
'days_remaining' => $data['PremiumDays'] - date_diff(date_create(), date_create($data['PremiumStartTime']))->days
);