URL Validation in PHP

if (empty($_POST["website"])) {
  $website = "";
} else {
  $website = test_input($_POST["website"]);
  // check syntax of the URL (dashes allowed)
  if (!preg_match("/\b(?:(?:https?|ftp):\/\/|www\.)[-a-z0-9+&@#\/%?=~_|!:,.;]*[-a-z0-9+&@#\/%=~_|]/i",$website)) {
    $website_error = "URL Invalid.";
  }
}