protected static function guessCurrencySymbol($currency)
{
switch (strtolower($currency)) {
case 'usd':
case 'aud':
case 'cad':
return '$';
case 'eur':
return '€';
case 'gbp':
return '£';
default:
throw new Exception("Unable to guess symbol for currency. Please explicitly specify it.");
}
}