update

pkg/types/stop.go

@@ -2,6 +2,7 @@ package types
 
 import (
 	"iter"
+	"math"
 	"time"
 )
 
@@ -51,6 +52,19 @@ func (s *Stop) GetTripsAfter(when time.Time) iter.Seq[*TripWithDepartureTime] {
 	}
 }
 
+func (s *Stop) HaversineDistance(other *Stop) float64 {
+	return haversine(s.StopLat, s.StopLon, other.StopLat, other.StopLon)
+}
+
+func haversine(lat1, lon1, lat2, lon2 float64) float64 {
+	const R = 6371 // Earth radius in km
+	dLat := (lat2 - lat1) * math.Pi / 180
+	dLon := (lon2 - lon1) * math.Pi / 180
+	a := math.Sin(dLat/2)*math.Sin(dLat/2) + math.Cos(lat1*math.Pi/180)*math.Cos(lat2*math.Pi/180)*math.Sin(dLon/2)*math.Sin(dLon/2)
+	c := 2 * math.Atan2(math.Sqrt(a), math.Sqrt(1-a))
+	return R * c
+}
+
 func (s *Stop) GetUpcomingStops(start *StopTime) iter.Seq[*StopTime] {
 	return func(yield func(*StopTime) bool) {
 		found := false