You can use my service, the http://ipinfo.io API to get the country code:
function get_country($ip) {
return file_get_contents("http://ipinfo.io/{$ip}/country");
}
echo get_country("8.8.8.8"); // => US
If you're interested in other details you could make a more generic function:
function ip_details($ip) {
$json = file_get_contents("http://ipinfo.io/{$ip}");
$details = json_decode($json);
return $details;
}
$details = ip_details("8.8.8.8");
echo $details->city; // => Mountain View
echo $details->country; // => US
echo $details->org; // => AS15169 Google Inc.
echo $details->hostname; // => google-public-dns-a.google.com
I've used the IP 8.8.8.8 in these examples, but if you want details for the user's IP just pass in $_SERVER['REMOTE_ADDR'] instead. More details are available at http://ipinfo.io/developers
You can get a mapping of country codes to currency codes from http://country.io/data/ and add that to your code. Here's a simple example:
function getCurrenyCode($country_code) {
$currency_codes = array(
'GB' => 'GBP',
'FR' => 'EUR',
'DE' => 'EUR',
'IT' => 'EUR',
);
if(isset($currency_codes[$country_code])) {
return $curreny_codes[$country_code];
}
return 'USD'; // Default to USD
}