CartoGo/osm.go at main · fezcode/CartoGo · GitHub

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package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"math"
	"net/http"
	"strings"
	"time"
)

type OverpassResponse struct {
	Elements []Element `json:"elements"`
}

type Element struct {
	Type     string            `json:"type"`
	ID       int64             `json:"id"`
	Lat      float64           `json:"lat,omitempty"`
	Lon      float64           `json:"lon,omitempty"`
	Nodes    []int64           `json:"nodes,omitempty"`
	Tags     map[string]string `json:"tags,omitempty"`
	Members  []Member          `json:"members,omitempty"`
	Geometry []Point           `json:"geometry,omitempty"`
}

type Member struct {
	Type     string  `json:"type"`
	Ref      int64   `json:"ref"`
	Role     string  `json:"role"`
	Geometry []Point `json:"geometry,omitempty"`
}

type Point struct {
	Lat float64 `json:"lat"`
	Lon float64 `json:"lon"`
}

func fetchOSMData(lat, lon float64, dist float64) (*OverpassResponse, error) {

	const degPerMeter = 1.0 / 111320.0

	latDelta := dist * degPerMeter

	lonDelta := dist * degPerMeter / math.Cos(lat*math.Pi/180.0)


	s, w, n, e := lat-latDelta, lon-lonDelta, lat+latDelta, lon+lonDelta


	query := fmt.Sprintf(`

[out:json][timeout:120];

(

  way["highway"](%f,%f,%f,%f);

  way["natural"="water"](%f,%f,%f,%f);

  relation["natural"="water"](%f,%f,%f,%f);

  way["waterway"="riverbank"](%f,%f,%f,%f);

  way["leisure"="park"](%f,%f,%f,%f);

  way["landuse"="grass"](%f,%f,%f,%f);

  relation["leisure"="park"](%f,%f,%f,%f);

  relation["landuse"="grass"](%f,%f,%f,%f);

);

out body geom;

`, s, w, n, e, s, w, n, e, s, w, n, e, s, w, n, e, s, w, n, e, s, w, n, e, s, w, n, e, s, w, n, e)


	var lastErr error

	for i := 0; i < 3; i++ {

		if i > 0 {

			fmt.Printf("⚠ Overpass server busy, retrying in 5 seconds... (Attempt %d/3)\n", i+1)

			time.Sleep(5 * time.Second)

		}


		req, err := http.NewRequest("POST", "https://overpass-api.de/api/interpreter", bytes.NewBufferString(query))

		if err != nil {

			return nil, err

		}

		req.Header.Set("Content-Type", "application/x-www-form-urlencoded")

		req.Header.Set("User-Agent", "CartoGo/1.0")


		client := &http.Client{Timeout: 150 * time.Second}

		resp, err := client.Do(req)

		if err != nil {

			lastErr = err

			continue

		}

		defer resp.Body.Close()


		if resp.StatusCode != http.StatusOK {

			body, _ := io.ReadAll(resp.Body)

			lastErr = fmt.Errorf("overpass api error: %s", string(body))

			if strings.Contains(string(body), "Dispatcher_Client::request_read_and_idx::timeout") || resp.StatusCode == 429 {

				continue // Retry on timeout or rate limit

			}

			return nil, lastErr

		}


		var overpassResp OverpassResponse

		if err := json.NewDecoder(resp.Body).Decode(&overpassResp); err != nil {

			return nil, err

		}


		return &overpassResp, nil

	}


	return nil, fmt.Errorf("failed after 3 attempts: %v", lastErr)

}