package util

import "math"

func HaversineDistance(lat1 float64, lon1 float64, lat2 float64, lon2 float64) float64 {
	const earthRadiusKm = 6371
	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 earthRadiusKm * c * 1000
}