Best practices and cosmetics

main.go

@@ -11,12 +11,15 @@ import (
 	"net/http"
 	"os"
 	"os/exec"
+	"path"
 	"time"
 )
 
-var level = 4
+const (
-var width = 550
+	level = 4
-var delay = 8 // delay in hours, so that I can see daylight on my wallpaper during the day!
+	width = 550
+	delay = 8 // delay in hours, so that I can see daylight on my wallpaper during the day!
+)
 
 type latestData struct {
 	Date string `json:"date"`
@@ -25,14 +28,23 @@ type latestData struct {
 
 func main() {
 	// Define work directory and files
-	var home = os.Getenv("HOME")
+	var (
-	var work_dir = home + "/.himawari"
+		home      = os.Getenv("HOME")
-	var image_file = work_dir + "/latest.png"
+		workDir   = path.Join(home, ".himawari")
-	var dat_file = work_dir + "/data"
+		imageFile = path.Join(workDir, "/latest.png")
+		dataFile  = path.Join(workDir, "/data")
+		data      []byte
+		err       error
+		oldData   = new(latestData)
+		initData  = new(latestData)
+		t         time.Time
+		location  *time.Location
+		output    *image.RGBA
+		out       *os.File
+	)
 
-	// Read the last date from dat_file if it exists
+	// Read the last date from dataFile if it exists
-	data, err := ioutil.ReadFile(dat_file)
+	data, err = ioutil.ReadFile(dataFile)
-	oldData := new(latestData)
 	if err != nil {
 		data = nil
 	} else {
@@ -43,14 +55,16 @@ func main() {
 	}
 
 	// Get the data about the last image
-	initData := new(latestData)
+	err = getJSON("http://himawari8-dl.nict.go.jp/himawari8/img/D531106/latest.json", initData)
-	err = getJson("http://himawari8-dl.nict.go.jp/himawari8/img/D531106/latest.json", initData)
 	if err != nil {
-		log.Fatal("error getting json :", err)
+		log.Fatal("error getting json data from himawari server: ", err)
 	}
 
-	location, _ := time.LoadLocation("Asia/Tokyo")
+	location, err = time.LoadLocation("Asia/Tokyo")
-	t, _ := time.ParseInLocation("2006-01-02 15:04:05", initData.Date, location)
+	if err != nil {
+		log.Fatal("error loading Asia/Tokyo time zone data: ", err)
+	}
+	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)
@@ -58,72 +72,70 @@ func main() {
 	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))
+	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)
+			err = getPNG(url, &buff)
 			if err != nil {
-				err = getPng(url, &buff)
+				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)
+	out, err = os.Create(imageFile)
 	if err != nil {
-		err := os.Mkdir(work_dir, 0755)
+		err := os.Mkdir(workDir, 0755)
 		if err != nil {
-			log.Fatal("error creating :", err)
+			log.Fatal("error creating output directory:", err)
 		}
-		out, err = os.Create(image_file)
+		out, err = os.Create(imageFile)
 		if err != nil {
-			log.Fatal("error creating :", err)
+			log.Fatal("error creating output file:", err)
 		}
 	}
 	defer out.Close()
 	err = png.Encode(out, output)
 	if err != nil {
-		log.Fatal("Error writing output:", err)
+		log.Fatal("Error writing output file:", err)
 	}
 
 	// Write dat file
 	buff, err := json.Marshal(initData)
-	ioutil.WriteFile(dat_file, buff, 0644)
+	ioutil.WriteFile(dataFile, buff, 0644)
 
 	// Exec feh
-	cmd := exec.Command("feh", "--bg-max", image_file)
+	cmd := exec.Command("feh", "--bg-max", imageFile)
 	err = cmd.Run()
 	if err != nil {
 		log.Fatal("Error launching feh :", err)
 	}
 }
 
-func getJson(url string, target interface{}) error {
+func getJSON(url string, target interface{}) (err error) {
-	r, err := http.Get(url)
+	var r *http.Response
-	if err != nil {
+	r, err = http.Get(url)
-		return err
+	if err == nil {
+		defer r.Body.Close()
+		err = json.NewDecoder(r.Body).Decode(target)
 	}
-	defer r.Body.Close()
+	return
-
-	return json.NewDecoder(r.Body).Decode(target)
 }
 
-func getPng(url string, image *image.Image) error {
+func getPNG(url string, image *image.Image) (err error) {
-	r, err := http.Get(url)
+	var r *http.Response
-	if err != nil {
+	r, err = http.Get(url)
-		return err
+	if err == nil {
+		defer r.Body.Close()
+		*image, err = png.Decode(r.Body)
 	}
-	defer r.Body.Close()
+	return
-
-	*image, err = png.Decode(r.Body)
-	return err
 }