// FILE: internal/normalizers/nws/day_night.go
package nws

import (
	"math"
	"time"
)

const (
	degToRad = math.Pi / 180.0
	radToDeg = 180.0 / math.Pi
)

func observationLatLon(coords []float64) (lat *float64, lon *float64) {
	if len(coords) < 2 {
		return nil, nil
	}
	latVal := coords[1]
	lonVal := coords[0]
	return &latVal, &lonVal
}

// isDayFromLatLonTime estimates day/night from solar elevation.
// Uses a refraction-adjusted cutoff (-0.833 degrees).
func isDayFromLatLonTime(lat, lon float64, ts time.Time) *bool {
	if ts.IsZero() || math.IsNaN(lat) || math.IsNaN(lon) || math.IsInf(lat, 0) || math.IsInf(lon, 0) {
		return nil
	}
	if lat < -90.0 || lat > 90.0 || lon < -180.0 || lon > 180.0 {
		return nil
	}

	t := ts.UTC()
	day := float64(t.YearDay())
	hour := float64(t.Hour())
	min := float64(t.Minute())
	sec := float64(t.Second()) + float64(t.Nanosecond())/1e9
	utcHours := hour + min/60.0 + sec/3600.0

	gamma := 2.0 * math.Pi / 365.0 * (day - 1.0 + (utcHours-12.0)/24.0)

	eqtime := 229.18 * (0.000075 + 0.001868*math.Cos(gamma) - 0.032077*math.Sin(gamma) -
		0.014615*math.Cos(2.0*gamma) - 0.040849*math.Sin(2.0*gamma))

	decl := 0.006918 - 0.399912*math.Cos(gamma) + 0.070257*math.Sin(gamma) -
		0.006758*math.Cos(2.0*gamma) + 0.000907*math.Sin(2.0*gamma) -
		0.002697*math.Cos(3.0*gamma) + 0.00148*math.Sin(3.0*gamma)

	timeOffset := eqtime + 4.0*lon
	trueSolarMinutes := hour*60.0 + min + sec/60.0 + timeOffset
	for trueSolarMinutes < 0 {
		trueSolarMinutes += 1440.0
	}
	for trueSolarMinutes >= 1440.0 {
		trueSolarMinutes -= 1440.0
	}

	hourAngleDeg := trueSolarMinutes/4.0 - 180.0
	ha := hourAngleDeg * degToRad
	latRad := lat * degToRad

	cosZenith := math.Sin(latRad)*math.Sin(decl) + math.Cos(latRad)*math.Cos(decl)*math.Cos(ha)
	if cosZenith > 1.0 {
		cosZenith = 1.0
	} else if cosZenith < -1.0 {
		cosZenith = -1.0
	}

	zenith := math.Acos(cosZenith)
	elevation := 90.0 - zenith*radToDeg

	isDay := elevation > -0.833
	return &isDay
}