macker/server/geocode.go

package main

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"math"
	"net/http"
	"net/url"
	"strconv"
	"strings"
	"sync"
	"time"
)

const addressCacheRadius = 25.0 // Metres from the coordinates used for the lookup.
const addressCacheTTL = 5 * time.Minute

type nearbyAddress struct {
	Label          string  `json:"label"`
	DistanceMeters float64 `json:"distance_meters"`
	Attribution    string  `json:"attribution"`
}
type addressResult struct {
	Status  string         `json:"status"`
	Address *nearbyAddress `json:"address,omitempty"`
}
type cachedAddress struct {
	queryLat, queryLon, lat, lon float64
	label                        string
	at                           time.Time
}
type geocoder struct {
	endpoint, key string
	client        *http.Client
	mu            sync.RWMutex
	cache         []cachedAddress
	lastAttempt   time.Time
	failed        bool
}

func newGeocoder(endpoint, key string) (*geocoder, error) {
	if endpoint == "" {
		return nil, nil
	}
	u, err := url.Parse(endpoint)
	if err != nil || u.Host == "" || (u.Scheme != "http" && u.Scheme != "https") || u.User != nil {
		return nil, fmt.Errorf("geocoder URL must be an HTTP(S) endpoint without embedded credentials")
	}
	if strings.EqualFold(u.Hostname(), "nominatim.openstreetmap.org") {
		return nil, fmt.Errorf("use a tracking-compatible provider or your own Nominatim instance")
	}
	return &geocoder{endpoint: endpoint, key: key, client: &http.Client{Timeout: 8 * time.Second}}, nil
}

// Straight-line distance between WGS84 coordinates, in metres.
func distanceMeters(lat1, lon1, lat2, lon2 float64) float64 {
	const rad = math.Pi / 180
	a := math.Pow(math.Sin((lat2-lat1)*rad/2), 2) + math.Cos(lat1*rad)*math.Cos(lat2*rad)*math.Pow(math.Sin((lon2-lon1)*rad/2), 2)
	return 6371000 * 2 * math.Asin(math.Sqrt(math.Max(0, math.Min(1, a))))
}
func (g *geocoder) cached(lat, lon float64, now time.Time) *cachedAddress {
	for i := len(g.cache) - 1; i >= 0; i-- {
		c := &g.cache[i]
		if now.Sub(c.at) < addressCacheTTL && distanceMeters(lat, lon, c.queryLat, c.queryLon) <= addressCacheRadius {
			return c
		}
	}
	return nil
}
func (g *geocoder) view(lat, lon float64, now time.Time) addressResult {
	if g == nil {
		return addressResult{Status: "disabled"}
	}
	g.mu.RLock()
	defer g.mu.RUnlock()
	if c := g.cached(lat, lon, now); c != nil {
		return addressResult{Status: "ready", Address: &nearbyAddress{Label: c.label, DistanceMeters: distanceMeters(lat, lon, c.lat, c.lon), Attribution: "© OpenStreetMap contributors"}}
	}
	if g.failed {
		return addressResult{Status: "unavailable"}
	}
	return addressResult{Status: "pending"}
}

func (g *geocoder) update(ctx context.Context, lat, lon float64, now time.Time) {
	g.mu.Lock()
	if g.cached(lat, lon, now) != nil || (!g.lastAttempt.IsZero() && now.Sub(g.lastAttempt) < 30*time.Second) {
		g.mu.Unlock()
		return
	}
	g.lastAttempt = now
	g.mu.Unlock()
	c, err := g.lookup(ctx, lat, lon)
	g.mu.Lock()
	defer g.mu.Unlock()
	g.failed = err != nil
	if err != nil {
		return
	} // Keep provider errors and credentials out of API responses and logs.
	c.at = now
	if len(g.cache) >= 128 {
		g.cache = g.cache[1:]
	}
	g.cache = append(g.cache, c)
}
func (g *geocoder) lookup(ctx context.Context, lat, lon float64) (cachedAddress, error) {
	u, _ := url.Parse(g.endpoint)
	q := u.Query()
	q.Set("lat", strconv.FormatFloat(lat, 'f', 7, 64))
	q.Set("lon", strconv.FormatFloat(lon, 'f', 7, 64))
	q.Set("format", "jsonv2")
	q.Set("zoom", "18")
	q.Set("addressdetails", "1")
	u.RawQuery = q.Encode()
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u.String(), nil)
	if err != nil {
		return cachedAddress{}, err
	}
	req.Header.Set("User-Agent", "Macker/1.0")
	if g.key != "" {
		req.Header.Set("Authorization", "Bearer "+g.key)
	}
	res, err := g.client.Do(req)
	if err != nil {
		return cachedAddress{}, err
	}
	defer res.Body.Close()
	if res.StatusCode != http.StatusOK {
		return cachedAddress{}, fmt.Errorf("geocoder status %d", res.StatusCode)
	}
	raw, err := io.ReadAll(io.LimitReader(res.Body, 1<<20+1))
	if err != nil {
		return cachedAddress{}, err
	}
	if len(raw) > 1<<20 {
		return cachedAddress{}, fmt.Errorf("geocoder response too large")
	}
	var v struct {
		Lat         string `json:"lat"`
		Lon         string `json:"lon"`
		DisplayName string `json:"display_name"`
	}
	if err = json.Unmarshal(raw, &v); err != nil {
		return cachedAddress{}, err
	}
	alat, e1 := strconv.ParseFloat(v.Lat, 64)
	alon, e2 := strconv.ParseFloat(v.Lon, 64)
	if e1 != nil || e2 != nil || math.IsNaN(alat) || math.IsNaN(alon) || math.IsInf(alat, 0) || math.IsInf(alon, 0) || math.Abs(alat) > 90 || math.Abs(alon) > 180 || strings.TrimSpace(v.DisplayName) == "" {
		return cachedAddress{}, fmt.Errorf("no usable address")
	}
	return cachedAddress{queryLat: lat, queryLon: lon, lat: alat, lon: alon, label: v.DisplayName}, nil
}

func (t *tracker) runGeocoder(ctx context.Context) {
	ticker := time.NewTicker(time.Second)
	defer ticker.Stop()
	for {
		select {
		case <-ctx.Done():
			return
		case now := <-ticker.C:
			t.mu.RLock()
			var current *location
			if t.latest != nil {
				copy := *t.latest
				current = &copy
			}
			t.mu.RUnlock()
			if current != nil && now.Sub(current.UpdatedAt) <= 30*time.Second {
				t.geocoder.update(ctx, current.Point.Lat, current.Point.Long, now)
			}
		}
	}
}