ReverseGeoLookup/ReverseGeoLookup.go

package ReverseGeoLookup

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

const (
	timeout            = time.Minute * 10
	maxHttpRespBytes   = 8 * 1024 * 1024
	addressCache       = "knownAddresses.json"
	marshalIndent      = "  "
	sleepBetweenLookup = time.Second
)

type Location struct {
	Latitude  float64
	Longitude float64
}

type Address struct {
	Street string
	House  string
	Town   string
	Error  error
}

func (l *Location) values() (float64, float64) {
	if l == nil {
		return 0, 0
	}
	return l.Latitude, l.Longitude
}

func (l *Location) isEmpty() bool {
	if l == nil {
		return true
	}
	return l.Latitude == 0 || l.Longitude == 0
}

var knownAddresses map[string]Address

func (l *Location) cachedAddress() (Address, bool) {
	if l == nil {
		return Address{}, false
	}
	val, ok := knownAddresses[l.String()]
	return val, ok
}

func (l *Location) fetchAddress() Address {
	if l == nil {
		return Address{}
	}
	if cachedAddress, hasKey := l.cachedAddress(); hasKey {
		return cachedAddress
	}
	content, err := NominatimRequest(l)
	if err == nil && len(content) > 0 {
		var d Nominatim
		err = json.Unmarshal(content, &d)
		if err == nil {
			address := d.Address.simpleAddress()
			knownAddresses[l.String()] = address
			return address
		}
	}
	return Address{Error: errors.New("fetchAddress: " + err.Error())}
}

func (l *Location) String() string {
	if l == nil {
		return ""
	}
	return fmt.Sprintf("%v, %v", l.Latitude, l.Longitude)
}

func fetchAddresses(locations []Location) map[Location]Address {
	addresses := make(map[Location]Address)
	for i, location := range locations {
		addresses[location] = location.fetchAddress()
		if i < len(locations)-1 {
			time.Sleep(sleepBetweenLookup) //  TODO: unnötig bei gecacheten
		}
	}
	return addresses
}

func (a Address) fields() []string {
	return []string{a.Street, a.House, a.Town}
}

func (a Address) isValid() bool {
	if a.Error != nil {
		return false
	}
	for _, field := range a.fields() {
		if field != "" {
			return true
		}
	}
	return false
}

func (a Address) String() string {
	s := ""
	for _, field := range a.fields() {
		if field != "" {
			s += " " + field
		}
	}
	return strings.TrimSpace(s)
}

/* ----- Nominatim ----- */

func NominatimRequest(l *Location) ([]byte, error) {
	lat, lon := l.values()
	return httpRequest(fmt.Sprintf("http://nominatim.openstreetmap.org/reverse?format=jsonv2&addressdetails=1&lat=%v&lon=%v", lat, lon))
}

type Nominatim struct {
	Address NominatimAddress
}

type NominatimAddress struct {
	House_Number string
	Path         string
	Footway      string
	Pedestrian   string
	Road         string
	Suburb       string
	Village      string
	Town         string
	City         string
}

func first(values []string) string {
	for _, v := range values {
		if v != "" {
			return v
		}
	}
	return ""
}

func (a *NominatimAddress) simpleAddress() Address {
	if a == nil {
		return Address{}
	}
	street := a.getStreet()
	town := a.getTown()
	house := a.House_Number
	return Address{street, house, town, nil}
}

func (a NominatimAddress) getStreet() string {
	prio := []string{a.Path, a.Footway, a.Pedestrian, a.Road}
	return first(prio)
}

func (a NominatimAddress) getTown() string {
	prio := []string{a.Village, a.Suburb, a.Town, a.City}
	return first(prio)
}

/* ----- End Nominatim ----- */

func httpRequest(address string) ([]byte, error) {
	resp, err := http.Get(address)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()
	content, err := ioutil.ReadAll(io.LimitReader(resp.Body, maxHttpRespBytes))
	return content, err
}

func loadKnownAddresses() {
	knownAddresses = make(map[string]Address, 0)
	data, err := ioutil.ReadFile(addressCache)
	if err == nil {
		err = json.Unmarshal(data, &knownAddresses)
		if err != nil {
			knownAddresses = make(map[string]Address, 0)
		}
	}
}

func saveKnownAddresses() error {
	data, err := json.MarshalIndent(knownAddresses, "", marshalIndent)
	if err == nil {
		ioutil.WriteFile(addressCache, []byte(data), 0644)
	} else {
		err = errors.New("saveKnownAddresses: " + err.Error())
	}
	return err
}

func GetAddresses(locations []Location) (map[Location]Address, []error) {
	errs := make([]error, 0)
	loadKnownAddresses()
	addresses := fetchAddresses(locations)
	for _, addr := range addresses {
		if addr.Error != nil {
			errs = append(errs, addr.Error)
		}
	}
	err := saveKnownAddresses()
	if err != nil {
		errs = append(errs, err)
	}
	return addresses, errs
}