$listingId = $_GET['listing_id'];

if(isset($_POST['submit']))
{
  $target_dir = "./images/listing_images/";
  $target_file = $target_dir . basename($_FILES["file_selected"]["name"]);

  //temp varriables for file details
  $file_name = $_FILES["file_selected"]["name"];
  $file_type = strtolower(pathinfo($target_file, PATHINFO_EXTENSION));
  $file_size = $_FILES["file_selected"]["size"];
  $is_valid = 1;

  if($file_type != "jpg")
  {
    $is_valid = 0;
    echo "File must be a jpg!";
  }
  if($file_size > MAX_FILE_SIZE)
  {
    $is_valid = 0;
    echo "File cannot be larger than " + MAX_FILE_SIZE;
  }
  if ($is_valid == 1)
  {
    move_uploaded_file($_FILES["file_selected"]["tmp_name"], $target_file);

    echo "Success!";
  }