class curs
{
 const REFRESH_INTERVAL=3600;
 private $dataFile;
 private $source = "http://www.cbr.ru/scripts/XML_daily.asp";
 private $refreshTime;
 public $cursNew;
 public $cursOld;

 private $error;

 public function __construct($dataFile)
 {
  $this->dataFile=$dataFile;

  if(!$f=fopen($this->dataFile, "r")) {
   $this->refresh();
   $this->error=true;
   return false;
  }
  $data=fread($f, filesize($this->dataFile));
  fclose($f);
  $data=unserialize($data);
  $this->refreshTime=$data['refresh_time'];
  $this->cursNew=$data['curs']['new'];
  $this->cursOld=$data['curs']['old'];
  $this->refresh();
 }

 public function save()
 {
  $data=array(
   "refresh_time"=>$this->refreshTime,
   "curs" => array(
    "new"=>$this->cursNew,
    "old"=>$this->cursOld
   )
  );


  if(!$f=fopen($this->dataFile, "w+")) return false;
  fwrite($f, serialize($data));
  fclose($f);
 }

 public function refresh()
 {
  if((time()-self::REFRESH_INTERVAL)<$this->refreshTime) return true;

  if(isset($this->cursNew['date']) && $this->cursNew['date']>=$this->get_timestamp(date("d.m.y"))) return true;

  $new_data=$this->readFromCbr();
  $this->refreshTime=time();
  if(is_array($new_data)){
   if($new_data['date']>$this->cursNew['date']){
    $this->cursOld=$this->cursNew;
    $this->cursNew=$new_data;
    $this->save();
   } else {
    return true;
   }
  } else {
   return false;
  }
 }

 private function readFromCbr()
 {
  if(!$xml=simplexml_load_file($this->source)) return false;
  $curs['date']=self::get_timestamp($xml->attributes()->Date);
  foreach($xml->Valute as $m){
   if($m->CharCode=="USD" || $m->CharCode=="EUR"){
    $curs[(string)$m->CharCode]=(float)str_replace(",", ".", (string)$m->Value);
   }
  }
  return $curs;
 }

 public static function get_timestamp($date)
 {
     list($d, $m, $y) = explode('.', $date);
     return mktime(0, 0, 0, $m, $d, $y);
 }
}