package util

import "math"

func HaversineDistanceMeters(lat1 float64, lon1 float64, lat2 float64, lon2 float64) float64 {
	const earthRadius = 6371000.0

	lat1Rad := lat1 * math.Pi / 180
	lat2Rad := lat2 * math.Pi / 180
	dLat := (lat2 - lat1) * math.Pi / 180
	dLon := (lon2 - lon1) * math.Pi / 180

	sinLat := math.Sin(dLat / 2)
	sinLon := math.Sin(dLon / 2)

	h := sinLat*sinLat + math.Cos(lat1Rad)*math.Cos(lat2Rad)*sinLon*sinLon
	return 2 * earthRadius * math.Atan2(math.Sqrt(h), math.Sqrt(1-h))
}