Caching currency conversion using Google Calculator.

google_convert_currency.php

<?php

$currencyCache = array();

/**
 * Looks for unquoted keys in a json string and fixes them ie: {a:"b"} => {"a":"b"}
 * @param string $string A json string that is suspect
 * @return string A valid json string
 */ 
function fix_json($string){
	// (no qupte) (word) (no quote) (semicolon)
	$regex = '/(?<!")([a-zA-Z0-9_]+)(?!")(?=:)/i';
	return preg_replace($regex, '"$1"', $string);
}

/**
 * Change one currency into another using google's currency calculator
 * @param string $fromCurrency The currency you are starting with
 * @param string $toCurrency The currency you want to calculate
 * @param float $amount The amount of money you want to check
 * @return float The amount in a new currency
 */
function currency($fromCurrency,$toCurrency,$amount) {
	global $currencyCache;
	$key = $fromCurrency.'-'.$toCurrency;
	if ( !array_key_exists($key, $currencyCache) ) {
		$amount = urlencode($amount);
		$fromCurrency = urlencode($fromCurrency);
		$toCurrency = urlencode($toCurrency);
		$url = 'http://www.google.com/ig/calculator?hl=en&q=1' . $fromCurrency . '=?' . $toCurrency;
		$ch = curl_init();
		$timeout = 0;
		curl_setopt ($ch, CURLOPT_URL, $url);
		curl_setopt ($ch, CURLOPT_RETURNTRANSFER, 1);
		curl_setopt($ch,  CURLOPT_USERAGENT , "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1)");
		curl_setopt ($ch, CURLOPT_CONNECTTIMEOUT, $timeout);
		$rawdata = curl_exec($ch);
		curl_close($ch);
		//since google is returning invalid json, add the quotes back in
		$data = fix_json($rawdata);
		$data = json_decode($data, true);
		$currencyCache[$key] = $data['rhs'];
	}
	return round($amount * $currencyCache[$key], 2);
}

/* Example usage: echo currency('USD', 'GBP', 100); */

?>