Add sun cmd

cmd/sun/main.go

@@ -0,0 +1,69 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"log"
+	"time"
+
+	"github.com/nathan-osman/go-sunrise"
+
+	"code.chimeric.al/dwrz/sun/pkg/geo"
+)
+
+var (
+	coordinates = flag.String("c", "", "coordinates")
+	date        = flag.String("d", "", "date in YYYY-MM-DD format")
+	tz          = flag.String("z", "", "timezone")
+	f           = flag.String("f", "", "output time format")
+)
+
+func main() {
+	flag.Parse()
+	if *coordinates == "" {
+		log.Fatalf("missing coordinates")
+	}
+
+	c, err := geo.ParseCoordinates(*coordinates)
+	if err != nil {
+		log.Fatalf("failed to parse coordinates: %v", err)
+	}
+
+	var now = time.Now()
+	if *date != "" {
+		var err error
+		now, err = time.Parse(time.DateOnly, *date)
+		if err != nil {
+			log.Fatalf("failed to parse date: %v", err)
+		}
+	}
+
+	var loc *time.Location = time.UTC
+	if *tz != "" {
+		var err error
+		loc, err = time.LoadLocation(*tz)
+		if err != nil {
+			log.Fatalf("failed to parse timezone: %v", err)
+		}
+	}
+
+	// https://en.wikipedia.org/wiki/Sunrise_equation
+	rise, set := sunrise.SunriseSunset(
+		c.Latitude, c.Longitude,
+		now.Year(), now.Month(), now.Day(),
+	)
+
+	if *f == "" {
+		fmt.Println(
+			rise.In(loc).Format(time.RFC3339),
+			set.In(loc).Format(time.RFC3339),
+			set.Sub(rise),
+		)
+	} else {
+		fmt.Println(
+			rise.In(loc).Format(*f),
+			set.In(loc).Format(*f),
+			set.Sub(rise),
+		)
+	}
+}