package client

import (
	"math"
)

//https://gist.github.com/cdipaolo/d3f8db3848278b49db68
func getDistanceFrom(lat1, lon1, lat2, lon2 float64) float64 {
	var la1, lo1, la2, lo2, r float64
	la1 = lat1 * math.Pi / 180
	lo1 = lon1 * math.Pi / 180
	la2 = lat2 * math.Pi / 180
	lo2 = lon2 * math.Pi / 180

	r = 6378100 // Earth radius in METERS

	// calculate
	h := hsin(la2-la1) + math.Cos(la1)*math.Cos(la2)*hsin(lo2-lo1)

	return 2 * r * math.Asin(math.Sqrt(h))
}

func hsin(theta float64) float64 {
	return math.Pow(math.Sin(theta/2), 2)
}