geocoder.go

// It will get coordinates for a given address.
package geocoder

import (
	"encoding/json"
	"errors"
	"io/ioutil"
	"net/http"
	"strconv"
	"strings"
)

// The expected reply from API (the bit we need).
type Reply struct {
	Response struct {
		GeoObjectCollection struct {
			FeatureMember []struct {
				GeoObject struct {
					Point struct {
						Pos string
					}
				}
			}
		}
	}
}

// Coordinates.
type Coordinates struct {
	Latitude  float32
	Longitude float32
}

// The url of Yandex Geocoder API.
const API_URL = "http://geocode-maps.yandex.ru/1.x/?format=json&results=1&geocode="

// Request calls Yandex Geocoder API.
func Request(address string) (Reply, error) {
	url := API_URL + address
	resp, err := http.Get(url)
	defer resp.Body.Close()
	if err != nil {
		return Reply{}, err
	}
	body, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		return Reply{}, err
	}
	var r Reply
	err = json.Unmarshal(body, &r)
	if err != nil {
		return Reply{}, err
	}
	return r, nil
}

// AddressToCoordinates converts address to coordinates.
func AddressToCoordinates(address string) (Coordinates, error) {
	r, err := Request(address)
	if err != nil {
		return Coordinates{}, err
	}
	if len(r.Response.GeoObjectCollection.FeatureMember) == 0 {
		return Coordinates{}, errors.New("geocoder: the place hasn't been found: " + address)
	}
	pos := r.Response.GeoObjectCollection.FeatureMember[0].GeoObject.Point.Pos
	points := strings.Split(pos, " ")
	if len(points) < 2 {
		return Coordinates{}, errors.New("geocoder: unexpected format of points (" + pos + ")")
	}
	lat, err := strconv.ParseFloat(points[1], 32)
	if err != nil {
		return Coordinates{}, err
	}
	lon, err := strconv.ParseFloat(points[0], 32)
	if err != nil {
		return Coordinates{}, err
	}
	c := Coordinates{float32(lat), float32(lon)}
	return c, nil
}