add first ical implementation

service/ical/ical.go

@@ -0,0 +1,79 @@
+package ical
+
+import (
+	"bytes"
+	"crypto/rand"
+	"fmt"
+	"github.com/jordic/goics"
+	"github.com/labstack/echo/v5"
+	"github.com/pocketbase/pocketbase"
+	"htwk-planner/service/db"
+	"log"
+	"net/http"
+	"time"
+)
+
+const expirationTime = 5 * time.Minute
+
+var cache = make(map[string]*FeedModel)
+
+func FeedURL(c echo.Context, app *pocketbase.PocketBase) error {
+	token := randomToken(20)
+	_, err := createFeedForToken(app, token)
+	if err != nil {
+		return err
+	}
+	return c.JSON(http.StatusOK, fmt.Sprintf("FeedToken: %s", token))
+}
+
+func Feed(c echo.Context, app *pocketbase.PocketBase) error {
+
+	var result string
+	var responseWriter http.ResponseWriter
+	token := c.Request().Header.Get("token")
+	log.Print("iCal feed Token: " + token)
+	feed, ok := cache[token]
+	if !ok || feed == nil {
+		return c.JSON(http.StatusNotFound, "No FeedModel for this Token")
+	}
+
+	result = feed.Content
+	if feed.ExpiresAt.Before(time.Now()) {
+		newFeed, err := createFeedForToken(app, token)
+		if err != nil {
+			return c.JSON(http.StatusInternalServerError, err)
+		}
+		result = newFeed.Content
+	}
+
+	responseWriter.Header().Set("Content-type", "text/calendar")
+	responseWriter.Header().Set("charset", "utf-8")
+	responseWriter.Header().Set("Content-Disposition", "inline")
+	responseWriter.Header().Set("filename", "calendar.ics")
+	writeSuccess(result, responseWriter)
+	c.Response().Writer = responseWriter
+	return nil
+}
+
+func createFeedForToken(app *pocketbase.PocketBase, token string) (*FeedModel, error) {
+	res := db.GetPlanForCourseAndSemester(app, "22INM", "ws")
+	b := bytes.Buffer{}
+	goics.NewICalEncode(&b).Encode(res)
+	feed := &FeedModel{Content: b.String(), ExpiresAt: time.Now().Add(expirationTime)}
+	cache[token] = feed
+	return feed, nil
+}
+
+func randomToken(len int) string {
+	b := make([]byte, len)
+	read, err := rand.Read(b)
+	if err != nil {
+		return ""
+	}
+	return fmt.Sprintf("%x", read)
+}
+
+func writeSuccess(message string, w http.ResponseWriter) {
+	w.WriteHeader(http.StatusOK)
+	w.Write([]byte(message))
+}