<?php

//input
$numberStirng = $_GET["numbersString"];
$dateString = $_GET["dateString"];
//get all numbers
preg_match_all("/[^A-Za-z0-9](\d+)[^A-Za-z0-9]/", $numberStirng, $outputNumbers);
$revertedSum = revertSumOfArr($outputNumbers[1]);
preg_match_all("/\d{4}-(0[1-9]|1[0-2])-(0[0-9]|[12][0-9]|3[01])/", $dateString, $outputDates);
//no result output
if (count($outputDates[0]) == 0) {
    echo "<p>No dates</p>";
    die;
}
//rest of the logic
$outputArray = addDaysToArray($outputDates[0], $revertedSum);
//output
printOutput($outputArray);

function revertSumOfArr($data) {
    $sum = 0;
    foreach ($data as $v) {
        $sum += $v;
    }
    $sum = (string) $sum;
    $sum = strrev($sum);
    return intval($sum);
}

function addDaysToArray($datesArray, $days) {
    $outputArray = array();
//My solution 1
    date_default_timezone_set("Europe/Sofia");
    foreach ($datesArray as $v) {
        array_push($outputArray, date('Y-m-d', strtotime($v . " + " . $days . " days")));
    }
//My solution 2
//    date_default_timezone_set('Europe/Sofia');
//    foreach ($datesArray as $date) {
//
//        $date = new DateTime($date);
//        $date->add(new DateInterval("P".$days."D"));
//        array_push($outputArray, $date);
//    }
 //Author solution
//    foreach ($datesArray as $da) {
//        $tempDate = date_create($date, timezone_open("Europe/Sofia"));
//        date_add($tempDate, date_interval_create_from_date_string("$days days"));
//        array_push($outputArray, $tempDate);
//    }
//end of author solution
    return $outputArray;
}

function printOutput($outputArray) {
    echo "<ul>";
    foreach ($outputArray as $v) {
        //My Solution 1
        echo "<li>" . $v . "</li>";
        //My Solution 2
        //echo "<li>" . date_format($v, "Y-m-d") . "</li>";
        //Author solution
        //echo "<li>" . date_format($v, "Y-m-d") . "</li>";
    }
    echo "</ul>";
}