PHP - Calculating An Older Date/time Based On A Desired Interval

<header>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.5.1/jquery.min.js"></script>
<script src="Time/detect_timezone.js"></script>
<script src="Time/jquery.detect_timezone.js"></script>
<script>
$(document).ready(function(){
  $('#tzvalue').set_timezone({'default' : 'America/Los_Angeles'});
});
</script>
</header>

I'm working on a project that has a lot of different timezone options, and all I have from the users is their UTC offset.

After weeks of doing tweaks, I come to new issues every time I add something, one would think it would be a lot easier to just get the correct time and day :)

The latest issue is that when I try to rewrite a date to a better fomat, it disregards the GMT offset. Like this:

4/14/19, 12:00 PM GMT+2 (=$date) becomes ... 14-04-2019 10:00 when using this code:

$bp_date_to_format = date_create_from_format('Y-m-d\TH:i:sP', $date);
echo date_format($bp_date_to_format, 'd-m-Y H:i');

I figured it would just rewrite the format, keeping the exact time. It isn't.

We do have all these sorts of localization functions as well, but because there doesn't seem to be one single standard (each 3rd party API connection we have uses its own default datetime format so it seems).

        // Remove UTC Text
        $UTC_offset = str_replace('UTC', '', $timezone);

        // Get Offset in Minutes
        if (stripos($UTC_offset, ':') !== false) {
            // Calculate seconds from offset
            list($hours, $minutes) = explode(':', $offset);
            $seconds = $hours * 60 * 60 + $minutes * 60;
        } else {
            $seconds = $UTC_offset * 60 * 60;
        }

        // Get User timezone name from seconds
        $timezone = timezone_name_from_abbr('', $seconds, 1);
        if ($timezone === false) {
            $timezone = timezone_name_from_abbr('', $seconds, 0);
        }
        // Set new TZ
        return date_default_timezone_set($timezone);

Isn't there any "one way"solution that can be used? It's confusing to say the least.

Cheers.

$stmt = $pdo->query("SELECT recurring, due_date FROM $table");
while($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
    $recur = $row['recurring'];
    $date_due = $row['due_date'];
}
$weekly = "Weekly";
$bi_monthly = "Bi-Monthly";
$monthly = "Monthly";
$quarterly = "Quarterly";
$half_yearly = "Half Yearly";
$yearly = "Yearly";

if(strcmp($recur, $weekly) == 0){
    $recurs = "7 DAY";
}elseif(strcmp($recur, $bi_monthly) == 0){
    $recurs = "14 DAY";
}elseif(strcmp($recur, $monthly) == 0){
    $recurs = "1 MONTH";
}elseif(strcmp($recur, $quarterly) == 0){
    $recurs = "3 MONTH";
}elseif(strcmp($recur, $half_yearly) == 0){
    $recurs = "6 MONTH";
}elseif(strcmp($recur, $yearly) == 0){
    $recurs = "1 YEAR";
}

$stmt = $pdo->query("SELECT ADDDATE('$date_due', INTERVAL $recurs) as nex_due FROM

$table");
$row = $stmt->fetch(PDO::FETCH_ASSOC);
$nex_due = $row['nex_due'];


$stmt = $pdo->prepare("SELECT * FROM $table ORDER BY trans_id DESC");
$stmt->execute();
$num_rows = $stmt->rowCount();
    
while($row = $stmt->fetch(PDO::FETCH_ASSOC)) {
    // Print out the contents of each row into a table
echo "<tr><td>";
echo $row['trans_ref'];
echo "</td><td>";
echo $row['acct_num'];
echo "</td><td>";
echo ucwords($row['payee']);
echo "</td><td>";
echo ucwords($row['company']);
echo "</td><td>";
echo $row['acct_no'];
echo "</td><td>";
echo number_format($row['amt'],2);
echo "</td><td>";
echo $row['purpose'];
echo "</td><td>";
echo $row['recurring'];
echo "</td><td>";
echo $row['due_date'];
echo "</td><td>";
echo $nex_due;
echo "</td><td>";
echo "<strong>".$row['status']."</strong>";
echo "</td><td>";
echo "<strong>".$row['pay_status']."</strong>";
echo "</td><td>";
}