Add code

.gitignore

@@ -0,0 +1,4 @@
+cache.gob
+prayercal
+.env
+prayercal.ics

main.go

@@ -0,0 +1,192 @@
+package main
+
+import (
+	"io"
+	"log"
+	"net/http"
+	"os"
+	"encoding/json"
+	"github.com/joho/godotenv"
+
+	"time"
+	"encoding/gob"
+	"bytes"
+
+	"fmt"
+	"sync"
+	_ "time/tzdata"
+
+	ics "github.com/arran4/golang-ical"
+)
+
+type prayerTimes struct {
+	FetchedAt int64
+	Times     map[string]string
+}
+
+func main() {
+	// load the env and check for API key, but its ok if there is no .env as there is (hopefully) env variables in the envrionment itself or whatever
+	_ = godotenv.Load()
+	var mu sync.Mutex
+	
+	apiKey := os.Getenv("LPT_API_KEY")
+	if apiKey == "" {
+		log.Fatal("LPT_API_KEY is not set")
+	}
+	url := "https://www.londonprayertimes.com/api/times/?format=json&24hours=true&key=" + apiKey
+
+	// times := getTimes(url, "./cache.gob")
+	// example {1791571473 map[Asr:15:43 Dhuhr:12:53 Fajr:05:41 Isha:19:45 Maghrib:18:24 Sunrise:07:11]}
+
+	loc, err := time.LoadLocation("Europe/London")
+	time.Local = loc
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	http.HandleFunc("/prayercal.ics", func(w http.ResponseWriter, r *http.Request) {
+		mu.Lock()
+		times, err := getTimes(url, "/data/cache.gob")
+		mu.Unlock()
+		if err != nil {
+			log.Println(err)
+			http.Error(w, "upstream error", http.StatusBadGateway)
+			return
+		}
+
+		out, err := buildCal(times, loc)
+		if err != nil {
+			log.Println(err)
+			http.Error(w, "bad prayer data", http.StatusBadGateway)
+			return
+		}
+
+		w.Header().Set("Content-Type", "text/calendar; charset=utf-8")
+		io.WriteString(w, out)
+	})
+	log.Fatal(http.ListenAndServe(":5543", nil))
+}
+
+func buildCal(times prayerTimes, loc *time.Location) (string, error) {
+	cal := ics.NewCalendar()
+	cal.SetMethod(ics.MethodPublish)
+
+	for _, name := range prayerNames {
+		start, err := parseToday(times.Times[name], loc)
+		if err != nil {
+			return "", fmt.Errorf("%s: %w", name, err)
+		}
+
+		ev := cal.AddEvent(name + "-" + start.Format("20060102") + "@prayercal")
+		ev.SetCreatedTime(time.Now())
+		ev.SetDtStampTime(time.Now())
+		ev.SetModifiedAt(time.Now())
+		ev.SetStartAt(start)
+		ev.SetEndAt(start.Add(20 * time.Minute))
+		ev.SetSummary(name)
+		ev.SetDescription(name + " prayer time")
+
+		for _, a := range []struct{ trigger, desc string }{
+			{"-PT15M", name + " in 15 minutes"},
+			{"PT0S", name + " time now"},
+		} {
+			alarm := ev.AddAlarm()
+			alarm.SetAction(ics.ActionDisplay)
+			alarm.SetTrigger(a.trigger)
+			alarm.SetDescription(a.desc)
+		}
+	}
+
+	return cal.Serialize(), nil
+}
+
+var prayerNames = []string{"Fajr", "Sunrise", "Dhuhr", "Asr", "Maghrib", "Isha"}
+
+var httpClient = &http.Client{Timeout: 10 * time.Second}
+
+func parseToday(hhmm string, loc *time.Location) (time.Time, error) {
+	t, err := time.Parse("15:04", hhmm)
+	if err != nil {
+		return time.Time{}, fmt.Errorf("bad time %q: %w", hhmm, err)
+	}
+	now := time.Now().In(loc)
+	return time.Date(now.Year(), now.Month(), now.Day(), t.Hour(), t.Minute(), 0, 0, loc), nil
+}
+
+func readCache(path string) (prayerTimes, bool) {
+	file, err := os.Open(path)
+	if err != nil {
+		if !os.IsNotExist(err) {
+			log.Println("cache open error:", err)
+		}
+		return prayerTimes{}, false
+	}
+	defer file.Close()
+
+	var cached prayerTimes
+	if err := gob.NewDecoder(file).Decode(&cached); err != nil {
+		log.Println("cache decode error, refetching:", err)
+		return prayerTimes{}, false
+	}
+	y1, m1, d1 := time.Unix(cached.FetchedAt, 0).Date()
+	y2, m2, d2 := time.Now().Date()
+	return cached, y1 == y2 && m1 == m2 && d1 == d2
+}
+
+func getTimes(url, cache string) (prayerTimes, error) {
+	if cached, ok := readCache(cache); ok {
+		log.Println("cache hit")
+		return cached, nil
+	}
+	log.Println("cache miss")
+
+	resp, err := httpClient.Get(url)
+	if err != nil {
+		return prayerTimes{}, fmt.Errorf("fetch: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return prayerTimes{}, fmt.Errorf("fetch: status %s", resp.Status)
+	}
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return prayerTimes{}, fmt.Errorf("read body: %w", err)
+	}
+
+	var raw map[string]string
+	if err := json.Unmarshal(body, &raw); err != nil {
+		return prayerTimes{}, fmt.Errorf("unmarshal: %w", err)
+	}
+
+	form := prayerTimes{
+		FetchedAt: time.Now().Unix(),
+		Times: map[string]string{
+			"Fajr":    raw["fajr"],
+			"Sunrise": raw["sunrise"],
+			"Dhuhr":   raw["dhuhr"],
+			"Asr":     raw["asr"],
+			"Maghrib": raw["magrib"],
+			"Isha":    raw["isha"],
+		},
+	}
+
+	// don't cache a response with missing fields
+	for _, name := range prayerNames {
+		if form.Times[name] == "" {
+			return prayerTimes{}, fmt.Errorf("api response missing %s", name)
+		}
+	}
+
+	var buf bytes.Buffer
+	if err := gob.NewEncoder(&buf).Encode(form); err != nil {
+		log.Println("cache encode error:", err) // still serve the data
+		return form, nil
+	}
+	if err := os.WriteFile(cache, buf.Bytes(), 0644); err != nil {
+		log.Println("cache write error:", err)
+	}
+
+	return form, nil
+}