package utils

import (
	"math"
)

const (
	earthRadiusMi = 3958
	earthRaidusKm = 6371
)

type Coord struct {
	Lat float64
	Lon float64
}

func degreesToRadians(d float64) float64 {
	return d * math.Pi / 180
}

func Distance(p, q Coord) (mi, km float64) {
	lat1 := degreesToRadians(p.Lat)
	lon1 := degreesToRadians(p.Lon)
	lat2 := degreesToRadians(q.Lat)
	lon2 := degreesToRadians(q.Lon)

	diffLat := lat2 - lat1
	diffLon := lon2 - lon1

	a := math.Pow(math.Sin(diffLat/2), 2) + math.Cos(lat1)*math.Cos(lat2)*
		math.Pow(math.Sin(diffLon/2), 2)

	c := 2 * math.Atan2(math.Sqrt(a), math.Sqrt(1-a))

	mi = c * earthRadiusMi
	km = c * earthRaidusKm

	return mi, km
}