rename backend to core

core/internal/server/wayland/suncalc.go

@@ -0,0 +1,86 @@
+package wayland
+
+import (
+	"math"
+	"time"
+)
+
+const (
+	degToRad     = math.Pi / 180.0
+	radToDeg     = 180.0 / math.Pi
+	solarNoon    = 12.0
+	sunriseAngle = -0.833
+)
+
+func CalculateSunTimes(lat, lon float64, date time.Time) SunTimes {
+	utcDate := date.UTC()
+	year, month, day := utcDate.Date()
+	loc := date.Location()
+
+	dayOfYear := utcDate.YearDay()
+
+	gamma := 2 * math.Pi / 365 * float64(dayOfYear-1)
+
+	eqTime := 229.18 * (0.000075 +
+		0.001868*math.Cos(gamma) -
+		0.032077*math.Sin(gamma) -
+		0.014615*math.Cos(2*gamma) -
+		0.040849*math.Sin(2*gamma))
+
+	decl := 0.006918 -
+		0.399912*math.Cos(gamma) +
+		0.070257*math.Sin(gamma) -
+		0.006758*math.Cos(2*gamma) +
+		0.000907*math.Sin(2*gamma) -
+		0.002697*math.Cos(3*gamma) +
+		0.00148*math.Sin(3*gamma)
+
+	latRad := lat * degToRad
+
+	cosHourAngle := (math.Sin(sunriseAngle*degToRad) -
+		math.Sin(latRad)*math.Sin(decl)) /
+		(math.Cos(latRad) * math.Cos(decl))
+
+	if cosHourAngle > 1 {
+		return SunTimes{
+			Sunrise: time.Date(year, month, day, 0, 0, 0, 0, time.UTC).In(loc),
+			Sunset:  time.Date(year, month, day, 0, 0, 0, 0, time.UTC).In(loc),
+		}
+	}
+	if cosHourAngle < -1 {
+		return SunTimes{
+			Sunrise: time.Date(year, month, day, 0, 0, 0, 0, time.UTC).In(loc),
+			Sunset:  time.Date(year, month, day, 23, 59, 59, 0, time.UTC).In(loc),
+		}
+	}
+
+	hourAngle := math.Acos(cosHourAngle) * radToDeg
+
+	sunriseTime := solarNoon - hourAngle/15.0 - lon/15.0 - eqTime/60.0
+	sunsetTime := solarNoon + hourAngle/15.0 - lon/15.0 - eqTime/60.0
+
+	sunrise := timeOfDayToTime(sunriseTime, year, month, day, time.UTC).In(loc)
+	sunset := timeOfDayToTime(sunsetTime, year, month, day, time.UTC).In(loc)
+
+	return SunTimes{
+		Sunrise: sunrise,
+		Sunset:  sunset,
+	}
+}
+
+func timeOfDayToTime(hours float64, year int, month time.Month, day int, loc *time.Location) time.Time {
+	h := int(hours)
+	m := int((hours - float64(h)) * 60)
+	s := int(((hours-float64(h))*60 - float64(m)) * 60)
+
+	if h < 0 {
+		h += 24
+		day--
+	}
+	if h >= 24 {
+		h -= 24
+		day++
+	}
+
+	return time.Date(year, month, day, h, m, s, 0, loc)
+}