// Copyright (C) 2025 Marius Schellenberger
package main
import (
"cmp"
"errors"
"flag"
"fmt"
"image"
"image/color"
"image/png"
"net/http"
"os"
"strconv"
"sync"
"time"
"git.giftfish.de/ston1th/godrop/v2"
)
var (
version string
listen string
)
const bfsURL = "https://uvi.bfs.de/Tagesgrafiken"
var allowedFiles = []string{
"/etc/resolv.conf",
"/etc/localtime",
"/etc/hosts",
"/etc/ssl/cert.pem",
}
func main() {
flag.StringVar(&listen, "l", ":7878", "listen addr")
flag.Parse()
if len(cityList) != len(fileList) {
fatal(errors.New("city and file list length differ"))
}
if err := godrop.PledgePromises("stdio inet rpath unveil"); err != nil {
fatal(err)
}
for _, file := range allowedFiles {
if err := godrop.Unveil(file, "r"); err != nil {
fatal(err)
}
}
if err := godrop.UnveilBlock(); err != nil {
fatal(err)
}
ic := &ImageCrawler{
url: bfsURL,
c: &http.Client{},
m: make(map[int]*Image),
}
http.HandleFunc("/set", func(w http.ResponseWriter, r *http.Request) {
if r.Method == "POST" {
r.ParseForm()
loc := r.PostForm.Get("loc")
_, ok := locFromString(loc)
if !ok {
http.Redirect(w, r, "/", http.StatusMovedPermanently)
return
}
setCookie(w, loc)
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 = cc[0]
} else {
c = setCookie(w, DefaultCity)
}
num, ok := locFromString(c.Value)
if !ok {
writeError(w, "Error", "Error")
return
}
img, mod, err := ic.getImage(num)
mod = mod.Local()
location := cityList[num]
if err != nil {
writeError(w, mod.Format(time.RFC1123), location)
return
}
vals := getUV(img)
if len(vals) == 0 {
writeError(w, mod.Format(time.RFC1123), location)
return
}
last := vals[len(vals)-1]
imgURL := bfsURL + "/" + fileList[num]
fmt.Fprintf(w, indexPage,
getColor(last),
fmt.Sprintf("%.2f", last),
mod.Format(time.RFC1123),
time.Now().Format(time.RFC1123),
location,
imgURL,
version,
)
})
err := http.ListenAndServe(listen, nil)
if err != nil {
fatal(err)
}
}
func setCookie(w http.ResponseWriter, loc string) *http.Cookie {
c := &http.Cookie{
Name: "loc",
Path: "/",
Value: loc,
Secure: true,
HttpOnly: true,
SameSite: http.SameSiteStrictMode,
}
http.SetCookie(w, c)
return c
}
func writeError(w http.ResponseWriter, mod, location string) {
fmt.Fprintf(w, indexPage,
"000000",
"Error",
mod,
time.Now().Format(time.RFC1123),
location,
version,
)
}
func fatal(err error) {
if err != nil {
fmt.Println(err)
os.Exit(1)
}
}
type ImageCrawler struct {
mu sync.RWMutex
url string
c *http.Client
m map[int]*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 int) (img image.Image, mod time.Time, err error) {
file := fileList[loc]
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
}
req.Header.Set("user-agent", "uvgo/"+version)
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")
}
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
}
func between[T cmp.Ordered](v, min, max T) bool {
return v >= min && v <= max
}
func getColor(v float64) string {
switch {
case between(v, 0, 1):
return "006300"
case between(v, 1, 2):
return "00a014"
case between(v, 2, 3):
return "81c600"
case between(v, 3, 4):
return "fff800"
case between(v, 4, 5):
return "ffd100"
case between(v, 5, 6):
return "ffa600"
case between(v, 6, 7):
return "ff7200"
case between(v, 7, 8):
return "ff4a00"
case between(v, 8, 9):
return "ff0000"
case between(v, 9, 10):
return "ff0078"
case v >= 10:
return "a80080"
}
return "000000"
}
func colorIs(c color.RGBA, v uint8) bool {
return c.R == v && c.G == v && c.B == v
}
func isWhite(col color.Color) bool {
col = color.RGBAModel.Convert(col)
c, ok := col.(color.RGBA)
if !ok {
return false
}
return colorIs(c, 255)
}
func isBlack(col color.Color) bool {
col = color.RGBAModel.Convert(col)
c, ok := col.(color.RGBA)
if !ok {
return false
}
return colorIs(c, 0)
}
func isStop(col color.Color) bool {
col = color.RGBAModel.Convert(col)
c, ok := col.(color.RGBA)
if !ok {
return false
}
if colorIs(c, 241) || colorIs(c, 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 colorIs(c, 241) || colorIs(c, 214) || colorIs(c, 0) {
return true
}
return false
}
// DefaultCity is Muenchen
// Array index 24
const DefaultCity = "24"
var fileList = []string{
"EEr_Andernach_today.png",
"EEr_Berlin_Potsdamer_Platz_today.png",
"EEr_Bonn_today.png",
"EEr_Boesel_B_today.png",
"EEr_Chieming_today.png",
"EEr_Cuxhaven_B_today.png",
"EEr_Dortmund_today.png",
"EEr_Duderstadt_B_today.png",
"EEr_Eckernfoerde_today.png",
"EEr_Fichtelberg_today.png",
"EEr_Friedrichshafen_today.png",
"EEr_Genthin_today.png",
"EEr_Giessen-Wettenberg_today.png",
"EEr_Goerlitz_today.png",
"EEr_Groemitz_today.png",
"EEr_Hamburg_today.png",
"EEr_Hohenpeissenberg_today.png",
"EEr_Kassel_today.png",
"EEr_Klippeneck_today.png",
"EEr_Kulmbach_today.png",
"EEr_Langen_today.png",
"EEr_Lindenberg_today.png",
"EEr_Lueneburg_today.png",
"EEr_Melpitz_today.png",
"EEr_Muenchen_today.png",
"EEr_Norderney_today.png",
"EEr_Belm-Osnabrueck_today.png",
"EEr_Salzgitter_today.png",
"EEr_Sankt Augustin_today.png",
"EEr_Schauinsland_today.png",
"EEr_Schweinfurt_Wasserlosen_today.png",
"EEr_Stuttgart_today.png",
"EEr_Sylt_Tinnum_today.png",
"EEr_Tholey_today.png",
"EEr_Todendorf_today.png",
"EEr_Waldhof_Falkenstein_today.png",
"EEr_Waldmuenchen_today.png",
"EEr_Wasserkuppe bei Fulda_today.png",
"EEr_Weissenburg_today.png",
"EEr_Wurmberg_B_today.png",
"EEr_Zingst_today.png",
"EEr_Zirchow_today.png",
"EEr_Schneefernerhaus_today.png",
}
func locFromString(s string) (i int, ok bool) {
i, err := strconv.Atoi(s)
if err != nil {
return
}
return i, validLoc(i)
}
func validLoc(loc int) bool {
return loc >= 0 && loc < len(cityList)
}
var cityList = []string{
"Andernach",
"Berlin",
"Bonn",
"Bösel",
"Chieming",
"Cuxhaven",
"Dortmund",
"Duderstadt",
"Eckernförde",
"Fichtelberg",
"Friedrichshafen",
"Genthin",
"Gießen",
"Görlitz",
"Grömitz",
"Hamburg",
"Hohenpeißenberg",
"Kassel",
"Klippeneck",
"Kulmbach",
"Langen",
"Lindenberg",
"Lüneburg",
"Melpitz",
"München",
"Norderney",
"Osnabrück",
"Salzgitter",
"Sankt Augustin",
"Schauinsland",
"Schweinfurt",
"Stuttgart",
"Sylt (Westerland)",
"Tholey",
"Todendorf",
"Waldhof",
"Waldmünchen",
"Wasserkuppe",
"Weißenburg",
"Wurmberg",
"Zingst",
"Zirchow",
"Zugspitze (Schneefernerhaus)",
}
func generateLocPage() string {
loc := `
UV Index Change Location
Change Location
`
return loc
}
var locPage = generateLocPage()
var indexPage = `
UV Index
UV Index
%s
Updated: %s
Server: %s
`