A Geocoder

geocoder.php

<?php

    class ReportableHTTPGeocodingFailure extends Exception {}
    class HTTPGeocodingFailure extends Exception {}

    class GeoLocation {
        function __construct($lng, $lat) {
            $this->lng = $lng;
            $this->lat = $lat;
        }

        function __toString() {
            return sprintf('<GeoLocation(%s, %s)>', $this->lng, $this->lat);
        }
    }

    interface Geocoder {
        function _geocode($q, $country);
    }

    class HTTPGeocoder {

        private function normalise($q) {
            return trim(strtolower($q));
        }

        final public function geocode($q, $country='GB') {
            $q = $this->normalise($q);
            $failed = array('geocoded' => false);

            try {
                $query = $this->_geocode($q, $country);    
            }
            catch (ReportableHTTPGeocodingFailure $e) {
                return array_merge($failed, array('message' => $e->getMessage()));
            }
            catch (HTTPGeocodingFailure $e) {
                return array_merge($failed, array('message' => $e->getMessage()));
            }
            catch (Exception $e) {
                return array_merge(
                    $failed,
                    array('message' => sprintf('General error: %s', $e->getMessage()))
                );   
            }

            return array(
                'geocoded' => true,
                'geolocation' => $query,
                'query' => $q
            );
        }
    }

    class GoogleGeocoder extends HTTPGeocoder {
        private $endpoint = "http://maps.google.com/maps/api/geocode/json";


        protected function _geocode($q, $country) {
            $params = array(
                "sensor" => "false",
                "region" => $country,
                "address" => $q
            );

            $url = sprintf(
                "%s?%s",
                $this->endpoint,
                http_build_query($params)
            );

            // make request
            $resp = @file_get_contents($url);
            if (false === $resp) {
                throw new Exception('HTTP Error [no response?]');
            }

            // parse json
            $json = @json_decode($resp, true);
            if (null === $json) {
                throw new Exception('Response Decode Error');
            }

            if ('ZERO_RESULTS' == $json['status']) {
                throw new HTTPGeocodingFailure($json['status']);
            }
            elseif ('OK' !== $json['status']) {
                throw new ReportableHTTPGeocodingFailure($json['status']);
            }

            $place = $json['results'][0];
            return array(
                'geolocation' => array(
                    'lng' =>  $place['geometry']['location']['lng'],
                    'lat' => $place['geometry']['location']['lat']
                )
            );
        }
    }

    function error_response($msg, $and_exit=true) {
        echo json_encode(array('success' => false, 'msg' => $msg));
        if ($and_exit) {
            exit();
        }
    }

    function success_response($resp) {
        echo json_encode(array('success' =>$resp));
    }

    // -- init --

    header('Content-type: application/json');

    // check backend specified
    if (!isset($_GET['backend'])) {
        error_response('Please specify a backend');
    }

    $backend = $_GET['backend'];
    if (!class_exists($backend)) {
        error_response('Backend not found');
    }

    if (!isset($_GET['q'])) {
        error_response('Please specify a query');
    }

    // should be good to go
    $backend = new $backend();
    $result = $backend->geocode($_GET['q']);
    success_response($result);