mark.php

<?php

require 'app/init.php';

if(isset($_GET['as'], $_GET['item'])) {
    $as     = $_GET['as'];
    $item   = $_GET['item'];
    
    switch($as) {
        case 'done':
            $doneQuery = $db->prepare("
                UPDATE items
                SET done = 1
                WHERE id = :item
                AND user = :user
            ");
            
            $doneQuery->execute([
               'item'   => $item,
               'user'   => $_SESSION['user_id'] 
            ]);
            break;
        case 'undone':
            $undoneQuery = $db->prepare("
                UPDATE items
                SET done = 0
                WHERE id = :item
                AND user = :user
            ");
            
            $undoneQuery->execute([
               'item'   => $item,
               'user'   => $_SESSION['user_id'] 
            ]);            
            break;
    }
}

header('Location: index.php');