// Copyright (C) 2025 Marius Schellenberger
package main
import (
"cmp"
"errors"
"flag"
"fmt"
"image"
"image/color"
"image/png"
"iter"
"net/http"
"os"
"slices"
"sync"
"time"
)
const (
X = 82
maxX = 574
maxStart = 150
Y = 431
)
func scale(img image.Image) int {
startY := Y
for y := Y; y > 0; y-- {
col := img.At(X, y)
if !isBlack(col) {
startY = y
break
}
}
c := 0
for y := startY; y > 0; y-- {
col := img.At(X, y)
if isWhite(col) {
c = startY - y
startY = y
break
}
}
for y := startY; y > 0; y-- {
col := img.At(X, y)
if !isWhite(col) {
return (startY + c) - y
}
}
return -1
}
func start(img image.Image) int {
for x := X; x < maxStart; x++ {
col := img.At(x, Y)
if !isStart(col) {
return x
}
}
return -1
}
func uv(img image.Image, x, s int) float64 {
start := Y
end := Y
for y := start; y > 0; y-- {
col := img.At(x, y)
if isBlack(col) || isWhite(col) {
end = y - 1
break
}
}
v := start - end
if v <= s {
return float64(v) / float64(s)
}
return float64(v+s) / 2 / float64(s)
}
func getUV(img image.Image) (vals []float64) {
s := scale(img)
if s == -1 {
return
}
x := start(img)
if x == -1 {
return
}
for ; x < maxX; x++ {
col := img.At(x, Y)
if isStop(col) {
break
}
vals = append(vals, uv(img, x, s))
}
return
}
var tmp = `
UV Index
UV Index
%s
Updated: %s
Server: %s
`
func getColor(v float64) string {
if v < 1.0 {
return "006300"
} else if v >= 1.0 && v <= 2.0 {
return "00a014"
} else if v >= 2.0 && v <= 3.0 {
return "81c600"
} else if v >= 3.0 && v <= 4.0 {
return "fff800"
} else if v >= 4.0 && v <= 5.0 {
return "ffd100"
} else if v >= 5.0 && v <= 6.0 {
return "ffa600"
} else if v >= 6.0 && v <= 7.0 {
return "ff7200"
} else if v >= 7.0 && v <= 8.0 {
return "ff4a00"
} else if v >= 8.0 && v <= 9.0 {
return "ff0000"
} else if v >= 9.0 && v <= 10.0 {
return "ff0078"
} else if v >= 10.0 {
return "a80080"
}
return "000000"
}
var (
locPage string
version string
listen string
)
func main() {
flag.StringVar(&listen, "l", ":7878", "listen addr")
flag.Parse()
url := "https://uvi.bfs.de/Tagesgrafiken"
generateLocPage()
ic := &ImageCrawler{
url: url,
c: &http.Client{},
m: make(map[string]*Image),
}
http.HandleFunc("/set", func(w http.ResponseWriter, r *http.Request) {
if r.Method == "POST" {
r.ParseForm()
loc := r.PostForm.Get("loc")
if _, ok := locations[loc]; ok {
c := &http.Cookie{
Name: "loc",
Path: "/",
Value: loc,
Secure: true,
HttpOnly: true,
SameSite: http.SameSiteStrictMode,
}
http.SetCookie(w, c)
http.Redirect(w, r, "/", http.StatusMovedPermanently)
return
}
}
w.Write([]byte(locPage))
})
http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
cc := r.CookiesNamed("loc")
var c *http.Cookie
if len(cc) == 0 {
c = &http.Cookie{
Name: "loc",
Path: "/",
Value: "24",
Secure: true,
HttpOnly: true,
SameSite: http.SameSiteStrictMode,
}
http.SetCookie(w, c)
} else {
c = cc[0]
}
loc := c.Value
img, mod, err := ic.getImage(loc)
mod = mod.Local()
location := selectListReverse[loc]
if err != nil {
fmt.Fprintf(w, tmp,
"000000",
"Err",
mod.Format(time.RFC1123),
time.Now().Format(time.RFC1123),
location,
version,
)
return
}
vals := getUV(img)
if len(vals) == 0 {
fmt.Fprintf(w, tmp,
"000000",
"Err",
mod.Format(time.RFC1123),
time.Now().Format(time.RFC1123),
location,
version,
)
return
}
last := vals[len(vals)-1]
fmt.Fprintf(w, tmp,
getColor(last),
fmt.Sprintf("%.2f", last),
mod.Format(time.RFC1123),
time.Now().Format(time.RFC1123),
location,
version,
)
})
err := http.ListenAndServe(listen, nil)
if err != nil {
fatal(err)
}
}
type ImageCrawler struct {
mu sync.RWMutex
url string
c *http.Client
m map[string]*Image
}
type Image struct {
mu sync.RWMutex
ic *ImageCrawler
file string
img image.Image
etag string
modified time.Time
lastGet time.Time
}
func (ic *ImageCrawler) getImage(loc string) (img image.Image, mod time.Time, err error) {
file, ok := locations[loc]
if !ok {
return nil, time.Time{}, errors.New("invalid location")
}
ic.mu.RLock()
if i, ok := ic.m[loc]; ok {
ic.mu.RUnlock()
return i.getImage()
}
ic.mu.RUnlock()
ic.mu.Lock()
i := &Image{
ic: ic,
file: file,
}
ic.m[loc] = i
ic.mu.Unlock()
return i.getImage()
}
func (i *Image) getImage() (img image.Image, mod time.Time, err error) {
i.mu.RLock()
if !i.lastGet.IsZero() &&
time.Now().Sub(i.lastGet) < time.Minute*3 {
defer i.mu.RUnlock()
return i.img, i.modified, nil
}
i.mu.RUnlock()
req, err := http.NewRequest("GET", i.ic.url+"/"+i.file, nil)
if err != nil {
return
}
i.mu.RLock()
if !i.modified.IsZero() {
req.Header.Set("if-modified-since", i.modified.Format(time.RFC1123))
}
if i.etag != "" {
req.Header.Set("if-none-match", i.etag)
}
i.mu.RUnlock()
resp, err := i.ic.c.Do(req)
if err != nil {
return
}
defer resp.Body.Close()
if resp.StatusCode == http.StatusNotModified {
i.mu.RLock()
defer i.mu.RUnlock()
return i.img, i.modified, nil
}
if resp.StatusCode == http.StatusOK {
img, err = png.Decode(resp.Body)
if err != nil {
return
}
i.mu.Lock()
i.img = img
modTime, err := time.Parse(time.RFC1123, resp.Header.Get("last-modified"))
if err == nil {
i.modified = modTime
}
i.etag = resp.Header.Get("etag")
i.lastGet = time.Now()
defer i.mu.Unlock()
return i.img, i.modified, nil
}
i.mu.RLock()
defer i.mu.RUnlock()
if i.img != nil {
return i.img, i.modified, nil
}
return nil, time.Time{}, errors.New("error getting image")
}
func isWhite(col color.Color) bool {
col = color.RGBAModel.Convert(col)
c, ok := col.(color.RGBA)
if !ok {
return false
}
if c.R == 255 &&
c.G == 255 &&
c.B == 255 {
return true
}
return false
}
func isBlack(col color.Color) bool {
col = color.RGBAModel.Convert(col)
c, ok := col.(color.RGBA)
if !ok {
return false
}
if c.R == 0 &&
c.G == 0 &&
c.B == 0 {
return true
}
return false
}
func isStop(col color.Color) bool {
col = color.RGBAModel.Convert(col)
c, ok := col.(color.RGBA)
if !ok {
return false
}
if c.R == 241 &&
c.G == 241 &&
c.B == 241 {
return true
}
if c.R == 88 &&
c.G == 88 &&
c.B == 88 {
return true
}
return false
}
func isStart(col color.Color) bool {
col = color.RGBAModel.Convert(col)
c, ok := col.(color.RGBA)
if !ok {
return false
}
if c.R == 241 &&
c.G == 241 &&
c.B == 241 {
return true
}
if c.R == 214 &&
c.G == 214 &&
c.B == 214 {
return true
}
if c.R == 0 &&
c.G == 0 &&
c.B == 0 {
return true
}
return false
}
func fatal(err error) {
if err != nil {
fmt.Println(err)
os.Exit(1)
}
}
func generateLocPage() {
loc := `
UV Index Change Location
Change Location
`
locPage = loc
}
var locations = map[string]string{
"0": "EEr_Andernach_today.png",
"1": "EEr_Berlin_Potsdamer_Platz_today.png",
"2": "EEr_Bonn_today.png",
"3": "EEr_Boesel_B_today.png",
"4": "EEr_Chieming_today.png",
"5": "EEr_Cuxhaven_B_today.png",
"6": "EEr_Dortmund_today.png",
"7": "EEr_Duderstadt_B_today.png",
"8": "EEr_Eckernfoerde_today.png",
"9": "EEr_Fichtelberg_today.png",
"10": "EEr_Friedrichshafen_today.png",
"11": "EEr_Genthin_today.png",
"12": "EEr_Giessen-Wettenberg_today.png",
"13": "EEr_Goerlitz_today.png",
"14": "EEr_Groemitz_today.png",
"15": "EEr_Hamburg_today.png",
"16": "EEr_Hohenpeissenberg_today.png",
"17": "EEr_Kassel_today.png",
"18": "EEr_Klippeneck_today.png",
"19": "EEr_Kulmbach_today.png",
"20": "EEr_Langen_today.png",
"21": "EEr_Lindenberg_today.png",
"22": "EEr_Lueneburg_today.png",
"23": "EEr_Melpitz_today.png",
"24": "EEr_Muenchen_today.png",
"25": "EEr_Norderney_today.png",
"26": "EEr_Belm-Osnabrueck_today.png",
"27": "EEr_Salzgitter_today.png",
"28": "EEr_Sankt Augustin_today.png",
"29": "EEr_Schauinsland_today.png",
"30": "EEr_Schweinfurt_Wasserlosen_today.png",
"31": "EEr_Stuttgart_today.png",
"32": "EEr_Sylt_Tinnum_today.png",
"33": "EEr_Tholey_today.png",
"34": "EEr_Todendorf_today.png",
"35": "EEr_Waldhof_Falkenstein_today.png",
"36": "EEr_Waldmuenchen_today.png",
"37": "EEr_Wasserkuppe bei Fulda_today.png",
"38": "EEr_Weissenburg_today.png",
"39": "EEr_Wurmberg_B_today.png",
"40": "EEr_Zingst_today.png",
"41": "EEr_Zirchow_today.png",
"42": "EEr_Schneefernerhaus_today.png",
}
var selectList = map[string]string{
"Andernach": "0",
"Berlin": "1",
"Bonn": "2",
"Bösel": "3",
"Chieming": "4",
"Cuxhaven": "5",
"Dortmund": "6",
"Duderstadt": "7",
"Eckernförde": "8",
"Fichtelberg": "9",
"Friedrichshafen": "10",
"Genthin": "11",
"Gießen": "12",
"Görlitz": "13",
"Grömitz": "14",
"Hamburg": "15",
"Hohenpeißenberg": "16",
"Kassel": "17",
"Klippeneck": "18",
"Kulmbach": "19",
"Langen": "20",
"Lindenberg": "21",
"Lüneburg": "22",
"Melpitz": "23",
"München": "24",
"Norderney": "25",
"Osnabrück": "26",
"Salzgitter": "27",
"Sankt Augustin": "28",
"Schauinsland": "29",
"Schweinfurt": "30",
"Stuttgart": "31",
"Sylt (Westerland)": "32",
"Tholey": "33",
"Todendorf": "34",
"Waldhof": "35",
"Waldmünchen": "36",
"Wasserkuppe": "37",
"Weißenburg": "38",
"Wurmberg": "39",
"Zingst": "40",
"Zirchow": "41",
"Zugspitze (Schneefernerhaus)": "42",
}
var selectListReverse = reverseMap(selectList)
func reverseMap[K, V comparable](v map[K]V) map[V]K {
m := make(map[V]K)
for k, v := range v {
m[v] = k
}
return m
}
func sortedMap[K cmp.Ordered, V any](m map[K]V) iter.Seq2[K, V] {
a := make([]K, len(m))
i := 0
for k := range m {
a[i] = k
i++
}
slices.Sort(a)
return func(yield func(K, V) bool) {
for _, k := range a {
v := m[k]
if !yield(k, v) {
return
}
}
}
}