/**
* xDate wrapps Zend_Date. It adds lazyness, so the many dates
* our objects are using will consume performance only if
* really required. Published first at www.trash-factor.com
*/
class xDate {
	private $_isoDate; // iso date string like 'YYYY-MM-dd HH:mm:ss'
	private $_zendDate; // Zend_Date instantiated on demand
 
	public function __construct($value=null) {
		if (!is_null($value)) {
			$this->set($value); // initialize with $value
		}
	}
 
	public function __toString() {
		// lazyness: create the _isoDate once and cache the result
		if (is_null($this->_isoDate)) {
			// build the ISO date string
			$zendDate = $this->getZendDate();
			$this->_isoDate = $zendDate->toString('YYYY-MM-dd HH:mm:ss');
		}
		return $this->_isoDate;
	}
 
	public function set($value) {
		if ($value instanceof Zend_Date) {
			$this->_zendDate = $value;
			$this->_isoDate = null; // ISO date becomes invalid
		}else{
			$this->_zendDate = null; // Zend_Date becomes invalid
			$this->_isoDate = $value;
		}
	}
 
	public function addSecond($seconds) {
		$this->_isoDate = null;
		$zendDate = $this->getZendDate();
		return $zendDate->addSecond($seconds);
	}
 
	public function subSecond($seconds) {
		$this->_isoDate = null;
		$zendDate = $this->getZendDate();
		return $zendDate->subSecond($seconds);
	}
 
 
	public function compare($value) {
		$zendDate = $this->getZendDate();
		return $zendDate->compare($value);
	}
 
	public function sub($value) {
		$this->_isoDate = null;
		$zendDate = $this->getZendDate();
		return $zendDate->sub($value);
	}
 
	/**
	* Get the current Zend_Date instance.
	* Instantiate the Zend_Date on demand and cache it.
	* So it's created once and maintained for later use.
	*/
	private function getZendDate() {
		if (is_null($this->_zendDate)) {
			if (is_null($this->_isoDate)) {
				$this->_zendDate = Zend_Date::now();
			}else{
				$this->_zendDate = new Zend_Date($this->_isoDate, Zend_Date::ISO_8601);
			}
		}
		return $this->_zendDate;
	}
}