func eventCancel(w http.ResponseWriter, r *http.Request, t auth.Token) error {
	uuid := r.URL.Query().Get(":uuid")
	if !bson.IsObjectIdHex(uuid) {
		msg := fmt.Sprintf("uuid parameter is not ObjectId: %s", uuid)
		return &errors.HTTP{Code: http.StatusBadRequest, Message: msg}
	}
	objID := bson.ObjectIdHex(uuid)
	e, err := event.GetByID(objID)
	if err != nil {
		return &errors.HTTP{Code: http.StatusNotFound, Message: err.Error()}
	}
	reason := InputValue(r, "reason")
	if reason == "" {
		return &errors.HTTP{Code: http.StatusBadRequest, Message: "reason is mandatory"}
	}
	scheme, err := permission.SafeGet(e.AllowedCancel.Scheme)
	if err != nil {
		return err
	}
	allowed := permission.Check(t, scheme, e.AllowedCancel.Contexts...)
	if !allowed {
		return permission.ErrUnauthorized
	}
	err = e.TryCancel(reason, t.GetUserName())
	if err != nil {
		if err == event.ErrNotCancelable {
			return &errors.HTTP{Code: http.StatusBadRequest, Message: err.Error()}
		}
		return err
	}
	w.WriteHeader(http.StatusNoContent)
	return nil
}
func eventCancel(w http.ResponseWriter, r *http.Request, t auth.Token) error {
	uuid := r.URL.Query().Get(":uuid")
	if !bson.IsObjectIdHex(uuid) {
		msg := fmt.Sprintf("uuid parameter is not ObjectId: %s", uuid)
		return &errors.HTTP{Code: http.StatusBadRequest, Message: msg}
	}
	objID := bson.ObjectIdHex(uuid)
	e, err := event.GetByID(objID)
	if err != nil {
		return &errors.HTTP{Code: http.StatusNotFound, Message: err.Error()}
	}
	reason := InputValue(r, "reason")
	if reason == "" {
		return &errors.HTTP{Code: http.StatusBadRequest, Message: "reason is mandatory"}
	}
	scheme, err := permission.SafeGet(e.AllowedCancel.Scheme)
	if err != nil {
		return err
	}
	allowed := permission.Check(t, scheme, e.AllowedCancel.Contexts...)
	if !allowed {
		return permission.ErrUnauthorized
	}
	err = e.TryCancel(reason, t.GetUserName())
	if err != nil {
		if err == event.ErrNotCancelable {
			return &errors.HTTP{Code: http.StatusBadRequest, Message: err.Error()}
		}
		return err
	}
	w.WriteHeader(http.StatusNoContent)
	return nil
}
// title: event cancel
// path: /events/{uuid}/cancel
// method: POST
// produce: application/json
// responses:
//   204: OK
//   400: Invalid uuid or empty reason
//   401: Unauthorized
//   404: Not found