First draft

main.go

@@ -0,0 +1,129 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"image"
+	"image/draw"
+	"image/png"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"os"
+	"os/exec"
+	"time"
+)
+
+var level = 4
+var width = 550
+var delay = 8 // delay in hours, so that I can see daylight on my wallpaper during the day!
+
+type latestData struct {
+	Date string `json:"date"`
+	File string `json:"file"`
+}
+
+func main() {
+	// Define work directory and files
+	var home = os.Getenv("HOME")
+	var work_dir = home + "/.himawari"
+	var image_file = work_dir + "/latest.png"
+	var dat_file = work_dir + "/data"
+
+	// Read the last date from dat_file if it exists
+	data, err := ioutil.ReadFile(dat_file)
+	oldData := new(latestData)
+	if err != nil {
+		data = nil
+	} else {
+		err = json.Unmarshal(data, oldData)
+		if err != nil {
+			oldData = nil
+		}
+	}
+
+	// Get the data about the last image
+	initData := new(latestData)
+	err = getJson("http://himawari8-dl.nict.go.jp/himawari8/img/D531106/latest.json", initData)
+	if err != nil {
+		log.Fatal("error getting json :", err)
+	}
+
+	location, _ := time.LoadLocation("Asia/Tokyo")
+	t, _ := time.ParseInLocation("2006-01-02 15:04:05", initData.Date, location)
+	if oldData != nil && oldData.Date == initData.Date {
+		log.Print("No new image, keeping the old one")
+		os.Exit(0)
+	}
+	t = t.Add(time.Duration(-delay) * time.Hour)
+
+	// Get all the chunks from the latest image and assemble them
+	output := image.NewRGBA(image.Rect(0, 0, level*width, level*width))
+	for x := 0; x < level; x++ {
+		for y := 0; y < level; y++ {
+			url := fmt.Sprintf("http://himawari8.nict.go.jp/img/D531106/%dd/%d/%s_%d_%d.png",
+				level, width, t.Format("2006/01/02/150405"), x, y)
+
+			var buff image.Image
+			err = getPng(url, &buff)
+			if err != nil {
+				err = getPng(url, &buff)
+				if err != nil {
+					log.Fatal("Error getting png :", url)
+				}
+			}
+
+			draw.Draw(output, image.Rect(x*width, y*width, (x+1)*width, (y+1)*width), buff, image.Point{0, 0}, draw.Src)
+		}
+	}
+
+	// Write output to file
+	out, err := os.Create(image_file)
+	if err != nil {
+		err := os.Mkdir(work_dir, 0755)
+		if err != nil {
+			log.Fatal("error creating :", err)
+		}
+		out, err = os.Create(image_file)
+		if err != nil {
+			log.Fatal("error creating :", err)
+		}
+	}
+	defer out.Close()
+	err = png.Encode(out, output)
+	if err != nil {
+		log.Fatal("Error writing output:", err)
+	}
+
+	// Write dat file
+	buff, err := json.Marshal(initData)
+	ioutil.WriteFile(dat_file, buff, 0644)
+
+	// Exec feh
+	cmd := exec.Command("feh", "--bg-max", image_file)
+	err = cmd.Run()
+	if err != nil {
+		log.Fatal("Error launching feh :", err)
+	}
+}
+
+func getJson(url string, target interface{}) error {
+	r, err := http.Get(url)
+	if err != nil {
+		return err
+	}
+	defer r.Body.Close()
+
+	return json.NewDecoder(r.Body).Decode(target)
+}
+
+func getPng(url string, image *image.Image) error {
+	r, err := http.Get(url)
+	if err != nil {
+		return err
+	}
+	defer r.Body.Close()
+
+	*image, err = png.Decode(r.Body)
+	return err
+}