How to stop the continous fines using php - php

Question

I want to stop the continous fines in my codes after I click it and save it in database my problem is because if i click the button it's only save in the return.php but the counting is continuous every day like in the picture, I already try it but it didn't work
view_borrow.php
<div class="container">
<form method="POST" action="return_save.php">
<div class="margin-top">
<div class="row">
<div class="span12">
<div class="alert alert-info"><strong>Borrowed Books</strong></div>
<table cellpadding="0" cellspacing="0" border="0" class="table" id="example">
<thead>
<tr>
<th>Book title</th>
<th>Borrower</th>
<th>Type</th>
<th>Date Borrow</th>
<th>Due Date</th>
<th>Date Returned</th>
<th>Fines</th>
<th>Borrow Status</th>
</tr>
</thead>
<tbody>
<?php $user_query=mysqli_query($dbcon,"select * from borrow
LEFT JOIN member ON borrow.member_id = member.member_id
LEFT JOIN borrowdetails ON borrow.borrow_id = borrowdetails.borrow_id
LEFT JOIN book on borrowdetails.book_id = book.book_id
ORDER BY borrow.borrow_id DESC
")or die(mysqli_error());
while($row=mysqli_fetch_array($user_query)){
$currentdate = date('Y/m/d');
$start = new DateTime($returndate=$row['due_date']);
$end = new DateTime($currentdate);
$fines =0;
if(strtotime($currentdate) > strtotime($returndate)){
$days= $start->diff($end, true)->days;
$fines = $days > 0 ? intval(floor($days)) * 15 : 0;
$fi = $row['borrow_details_id'];
mysqli_query($dbcon,"update borrowdetails set fines='$fines' where borrow_details_id = '$fi'");
}
$id=$row['borrow_id'];
$book_id=$row['book_id'];
$borrow_details_id=$row['borrow_details_id'];
?>
<tr class="del<?php echo $id ?>">
<td class="test"><?php echo $row['book_title']; ?></td>
<td class="test"><?php echo $row['firstname']." ".$row['lastname']; ?></td>
<td class="test"><?php echo $row['type']; ?></td>
<td class="test"><?php echo $row['date_borrow']; ?></td>
<td class="test"><?php echo $row['due_date']; ?> </td>
<td class="test"><?php echo $row['date_return']; ?> </td>
<td class="test"><?php echo "₱ ".$fines; ?></td>
<td class="test"><?php echo $row['borrow_status'];?></td>
<td > <a rel="tooltip" title="Return" id="<?php echo $borrow_details_id; ?>"
href="#delete_book<?php echo $borrow_details_id; ?>" data-toggle="modal"
class="btn btn-success"><i class="icon-check icon-large"></i>Return</a>
<?php include('modal_return.php'); ?>
<td></td>
</tr>
<?php } ?>
</tbody>
</table>
</div>
</div>
</div>
</form>
</div>
this is the modal where I click the return button
modal_return.php
<div id="delete_book<?php echo $borrow_details_id; ?>" class="modal hide fade" tabindex="-1" role="dialog" aria-labelledby="myModalLabel" aria-hidden="true">
<div class="modal-body">
<div class="alert alert-success">Do you want to Return this Book?</div>
</div>
<div class="modal-footer">
<a class="btn btn-success" href="return_save.php<?php echo '?id='.$id; ?>&<?php echo 'book_id='.$book_id; ?>">Yes</a>
<button class="btn" data-dismiss="modal" aria-hidden="true"><i class="icon-remove icon-large"></i> Close</button>
</div>
</div>
This is the table

Answer 1

You're doing a date diff between $start and $end ($currentdate) but never using $returndate. PHP 7 has a null coalesce operator ?? that would be handy for your scenario (otherwise just use a normal if/else or its ternary equivalent ?:).
Your fees will always be from borrowdate to currentdate with your existing code. The code below should fix your issue.
$borrowdate = new Datetime($row['due_date']);
$currentdate = new Datetime();
$returndate = new Datetime($row['date_return']);
// PHP >= 7
$days = $borrowdate->diff($returndate ?? $currentdate, true)->days;
// PHP < 7
$days = $borrowdate->diff($returndate ?: $currentdate, true)->days;