package main

import (
	"math"
	"strconv"
	"strings"
)

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 angleDifference(a, b float64) float64 {
	diff := math.Mod(math.Abs(a-b), 360)
	if diff > 180 {
		diff = 360 - diff
	}
	return diff
}

func bearing(lat1, lon1, lat2, lon2 float64) float64 {
	lat1Rad := lat1 * math.Pi / 180
	lat2Rad := lat2 * math.Pi / 180
	dLon := (lon2 - lon1) * math.Pi / 180

	y := math.Sin(dLon) * math.Cos(lat2Rad)
	x := math.Cos(lat1Rad)*math.Sin(lat2Rad) - math.Sin(lat1Rad)*math.Cos(lat2Rad)*math.Cos(dLon)

	brng := math.Atan2(y, x) * 180 / math.Pi
	if brng < 0 {
		brng += 360
	}
	return brng
}

func parseTime(s string) float64 {
	parts := strings.Split(s, ":")
	if len(parts) != 3 {
		return 0
	}
	h, _ := strconv.Atoi(parts[0])
	m, _ := strconv.Atoi(parts[1])
	sec, _ := strconv.Atoi(parts[2])
	return float64(h*3600 + m*60 + sec)
}