--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/calsync/notificationrouter/notificationrouter.go	Fri Sep 06 16:43:14 2024 -0700
@@ -0,0 +1,47 @@
+package notificationrouter
+
+// Holds the map of (random) watchIds and the sync functions for the affected calendars.
+
+import (
+	"log"
+	"net/http"
+	"time"
+
+	"github.com/dchest/uniuri"
+)
+
+type SyncFunc func()
+
+type NotificationRouter struct {
+	handlers map[string]SyncFunc
+}
+
+func New() *NotificationRouter {
+	return &NotificationRouter{
+		handlers: make(map[string]SyncFunc),
+	}
+}
+
+func (nr *NotificationRouter) AddHandler(watchId string, handler SyncFunc, lifetime time.Duration) {
+	nr.handlers[watchId] = handler
+	go func() {
+		time.Sleep(lifetime)
+		delete(nr.handlers, watchId)
+	}()
+}
+
+func (nr *NotificationRouter) NotificationHandler(w http.ResponseWriter, r *http.Request) {
+	watchId := r.Header.Get("X-Goog-Channel-ID")
+	if nr.handlers[watchId] == nil {
+		log.Println("incoming notification for unknown watch id", watchId, "(ignoring)")
+	} else {
+		// todo: The first notification on a given watchId is the confirmation,
+		// and the sync func is probably (surely?) not needed.
+		log.Println("incoming notification for known watch id", watchId)
+		nr.handlers[watchId]()
+	}
+}
+
+func NewWatchId() string {
+	return uniuri.New() + "_" + time.Now().Format("15_04_05")
+}