Skyfeed_archive/internal/geo/stations.go

package geo

import (
	"encoding/json"
	"encoding/xml"
	"errors"
	"fmt"
	"io"
	"math"
	"net/http"
	"os"
	"path/filepath"
	"time"

	"github.com/leaktechnologies/skyfeed/internal/config"
)

// Station represents an Environment Canada citypage station.
type Station struct {
	Name     string  `json:"name"`
	Code     string  `json:"code"`
	Province string  `json:"province"`
	Lat      float64 `json:"lat"`
	Lon      float64 `json:"lon"`
}

// stationCacheFile defines where we persist the station index locally.
const stationCacheFile = "stations.json"

// FindNearestStation locates the closest Environment Canada weather station to given coordinates.
func FindNearestStation(lat, lon float64) (Station, error) {
	if lat == 0 && lon == 0 {
		return Station{}, errors.New("invalid coordinates: cannot locate nearest station")
	}

	stations, err := ensureStationCache()
	if err != nil {
		return Station{}, fmt.Errorf("failed to load station list: %w", err)
	}

	var nearest Station
	minDist := math.MaxFloat64

	for _, s := range stations {
		d := Haversine(lat, lon, s.Lat, s.Lon)
		if d < minDist {
			minDist = d
			nearest = s
		}
	}

	if nearest.Code == "" {
		return Station{}, errors.New("no station found in index")
	}

	fmt.Printf("[geo] Nearest station: %s (%s, %.2f km)\n", nearest.Name, nearest.Province, minDist)
	return nearest, nil
}

// ensureStationCache loads the cached station list or updates it if missing/outdated.
func ensureStationCache() ([]Station, error) {
	cachePath := filepath.Join(config.DataDir, stationCacheFile)

	info, err := os.Stat(cachePath)
	if os.IsNotExist(err) {
		fmt.Println("[geo] No station cache found, fetching from Environment Canada...")
		return updateStationCache(cachePath)
	}
	if err != nil {
		return nil, err
	}

	// Refresh monthly
	modTime := info.ModTime().UTC()
	now := time.Now().UTC()
	firstOfMonth := time.Date(now.Year(), now.Month(), 1, 0, 0, 0, 0, time.UTC)
	if modTime.Before(firstOfMonth) {
		fmt.Println("[geo] Station cache is older than this month, refreshing...")
		return updateStationCache(cachePath)
	}

	// Load existing JSON cache
	f, err := os.Open(cachePath)
	if err != nil {
		return nil, err
	}
	defer f.Close()

	var stations []Station
	if err := json.NewDecoder(f).Decode(&stations); err != nil {
		return nil, err
	}

	return stations, nil
}

// updateStationCache fetches and parses Environment Canada's current site list (XML).
func updateStationCache(dest string) ([]Station, error) {
	const ecURL = "https://geo.weather.gc.ca/geomet/features/collections/citypage_weather:siteList/items?f=xml"

	fmt.Println("[geo] Downloading station list from:", ecURL)

	client := &http.Client{Timeout: 25 * time.Second}
	resp, err := client.Get(ecURL)
	if err != nil {
		return nil, fmt.Errorf("failed to fetch EC station list: %w", err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		body, _ := io.ReadAll(resp.Body)
		return nil, fmt.Errorf("unexpected HTTP status: %s — %s", resp.Status, string(body))
	}

	type Site struct {
		Code     string  `xml:"properties>code"`
		NameEn   string  `xml:"properties>nameEn"`
		NameFr   string  `xml:"properties>nameFr"`
		Province string  `xml:"properties>provinceCode"`
		Lat      float64 `xml:"geometry>coordinates>1"` // Note: GeoJSON order is [lon, lat]
		Lon      float64 `xml:"geometry>coordinates>0"`
	}

	var parsed struct {
		Sites []Site `xml:"member"`
	}

	if err := xml.NewDecoder(resp.Body).Decode(&parsed); err != nil {
		return nil, fmt.Errorf("failed to parse site list XML: %w", err)
	}

	stations := make([]Station, 0, len(parsed.Sites))
	for _, s := range parsed.Sites {
		if s.Code == "" || s.Lat == 0 || s.Lon == 0 {
			continue
		}
		name := s.NameEn
		if name == "" {
			name = s.NameFr
		}
		stations = append(stations, Station{
			Name:     name,
			Code:     s.Code,
			Province: s.Province,
			Lat:      s.Lat,
			Lon:      s.Lon,
		})
	}

	if err := os.MkdirAll(filepath.Dir(dest), 0755); err != nil {
		return nil, err
	}

	f, err := os.Create(dest)
	if err != nil {
		return nil, err
	}
	defer f.Close()

	enc := json.NewEncoder(f)
	enc.SetIndent("", "  ")
	if err := enc.Encode(stations); err != nil {
		return nil, err
	}

	fmt.Printf("[geo] Saved %d Environment Canada stations → %s\n", len(stations), dest)
	return stations, nil
}

// Haversine computes the great-circle distance (in km) between two coordinates.
func Haversine(lat1, lon1, lat2, lon2 float64) float64 {
	const R = 6371
	dLat := toRadians(lat2 - lat1)
	dLon := toRadians(lon2 - lon1)
	lat1R := toRadians(lat1)
	lat2R := toRadians(lat2)
	a := math.Sin(dLat/2)*math.Sin(dLat/2) +
		math.Cos(lat1R)*math.Cos(lat2R)*math.Sin(dLon/2)*math.Sin(dLon/2)
	c := 2 * math.Atan2(math.Sqrt(a), math.Sqrt(1-a))
	return R * c
}

func toRadians(deg float64) float64 { return deg * math.Pi / 180 }