A new multi-currency fxConverter (including historic rates)

<?php
/** example usage **/
$f = new fxConverter();
$result = $f->convert('USD', 'GBP', 1, '1 October 1999');
print_r($result);
/** end example usage **/
class fxConverter{
 
	/**
	 * constructor
	 * @return 
	 */
	public function __construct(){
		date_default_timezone_set('UTC');
		$this->pdo = new PDO ('sqlite:fxrates.sqlite');
		$this->pdo->exec('create table if not exists fxRates  (fxDate int, fxCurrency text, fxRate real, primary key (fxDate, fxCurrency) on conflict replace)');
		$this->pdo->exec('create table if not exists fxTime (updateID integer primary key autoincrement, updateDate int)');
		if ( 0 < ($lastUpdate = $this->needsUpdate())) $this->updateFx($lastUpdate);
	}
 
	/**
	 * helper method to set the required date.  
	 * @param object $date in unixtimestamp or text based format
	 * @return 
	 */	
	public function setDate($date){
		if(is_string($date)) $this->date = date('Y-m-d', strtotime($date));
		if(is_numeric($date)) $this->date = date('Y-m-d', $date);
	}
 
	/**
	 * main public method for converting amounts from one currency to another
	 * @param string $from - a supported currency
	 * @param string $to - a supported currency
	 * @param float $amount [optional] - the amount to be converted, defaults to 1
	 * @param int|string $date [optional] - the date for the conversion, specified in text form ('2011-01-01', '1 Jan 2011') or a unix timestamp
	 * @param int|string $offset [optional] - an offset to apply.  can be a percentage between 0 and 5 or one of the following string 'bank, 'credit card', 'cash')
	 * @return either an error object or an array with the converted amount and the date of the currency pair used.
	 */
	public function convert($from, $to, $amount = 1, $date = NULL, $offset = NULL){
		if(!$this->supportedCurrency($from, $to)) return $this->raiseError('This currency pair is not supported');
		if($amount == 0) return 0;
		if (empty($date) && empty($this->date)) $this->setDate(time());
		if(!empty($date)) $this->setDate($date);
		switch (strtolower($offset)):
			case 'creditcard':
				$offset = 0.97;
			break;	
			case 'atm':
				$offset = 0.98;
			break;
			case 'bureau':
			case 'kiosk':
				$offset = 0.95;
			break;
			case '':
			case NULL:
				$offset = 1;
			break;
			default:
				$offset = 1 - $offset/100;
		endswitch;
		//get conversion rate for $from and $to
		$rate = $this->getFX($from, $to, $amount, $offset);
		return $rate;
	}
 
	/**
	 * private method to ensure that the requested currency pairs are retrievable
	 * @param object $from
	 * @param object $to
	 * @return 
	 */
	private function supportedCurrency($from, $to){
		$sql = <<<SQL
SELECT	COUNT(DISTINCT fxCurrency) as c
FROM 	fxRates
WHERE	fxCurrency IN (?, ?)
SQL;
		$s = $this->pdo->prepare($sql);
		$s->execute(array(strtoupper($from), strtoupper($to)));
		$row = $s->fetchObject();
		return ($row->c == 2); 
	}
 
	/**
	 * private method to convert the requested amount by the rxrate.
	 * 
	 * @param object $from
	 * @param object $to
	 * @param object $amount
	 * @param object $offset [optional]
	 * @return 
	 */
	private function getFX($from, $to, $amount, $offset=NULL){
		$sql = <<<SQL
SELECT 		(b.fxRate/a.fxRate) * ? AS convertedAmount,
			(b.fxRate/a.fxRate) * ? * ? AS adjustedConvertedAmount, 
			a.fxDate as fxDate,
			? as 'interbank rate' 
FROM 		fxRates a 
JOIN		fxRates b 
ON 			a.fxDate = b.fxDate 
WHERE 		a.fxCurrency=?
			AND 
			b.fxCurrency=?
			AND
			a.fxDate <= round(julianday(?)) 
			AND 
			a.fxDate >= round(julianday(?)) - 5
ORDER BY	a.fxDate DESC 
LIMIT 		1
SQL;
		$s = $this->pdo->prepare($sql);
		$s->execute(array(	 $amount, $amount, $offset, $offset, $from, $to, $this->date, $this->date));
		$row = $s->fetchObject();
		if(is_null($row) || $row === false) return $this->raiseError('No recent rate for this currency pair');
		return get_object_vars($row); //$row;
	}
 
	/**
	 * private function to determine whether a new set of fx rates should be retrieved
	 * @return true|false
	 */
	private function needsUpdate(){
		$s = $this->pdo->prepare(<<<SQL
SELECT
		IFNULL(
			(CASE 
				WHEN 	(round(julianday('now')) > max(updateDate)) 
				THEN 	(round(julianday('now')) - max(updateDate))
				ELSE	0
			END), 
			10000
			)  as lastUpdate 
FROM 	fxTime
SQL
		);
		if(!$s) die(print_r($this->pdo->errorInfo()));
		$s->execute();
		$o = $s->fetchObject();
		return isset($o->lastUpdate) ? $o->lastUpdate : 0;
	}
 
	/**
	 * private method to retrieve and update currency pairs from the ECB website
	 * @param object $lastUpdate [optional]
	 * @return 
	 */
	private function updateFx($lastUpdate = NULL){
		if( $lastUpdate > 90 || is_null($lastUpdate)):
			$url = 'http://www.ecb.europa.eu/stats/eurofxref/eurofxref-hist.xml';
		else:
			$url = 'http://www.ecb.europa.eu/stats/eurofxref/eurofxref-hist-90d.xml';
		endif;
		$XML=simplexml_load_file($url);
		if($XML === false) return $this->raiseError('Cannot update fxRates');
		$query = 'insert into fxRates (fxDate, fxCurrency, fxRate) values (round(julianday(?)),?,?)';
		$s = $this->pdo->prepare($query);
		if($s === false) print_r($this->pdo->errorInfo());
		//work out the comparitive date
		$cDate = strtotime('-' . ($lastUpdate + 1) .' day' );
		foreach($XML->Cube->Cube as $data):
			set_time_limit(30);	
			$i = $data->attributes();
			$date = $i['time'];
			if(strtotime($date) < $cDate) continue;
			$s->execute(array($date, 'EUR', 1));
			foreach ($data->children() as $blob):
				set_time_limit(10);
				$d = $blob->attributes();
				$s->execute(array( $date, $d['currency'], $d['rate']));
			endforeach;
		endforeach;
		$this->pdo->exec("insert into fxTime values (NULL, round(julianday('now')))");
		$this->pdo->exec('VACUUM');
	}
 
	private function raiseError($message){
		$this->hasErrors = true;
		$this->errors[] = new fxError($message); 
		return $this->errors;
	}
}
class fxError{
	public function __construct($message){ $this->message = $message; }
}