//-----------------
// controllers/InvitationController
//-----------------
    @RequestMapping(value = "/invite/{link}", method = RequestMethod.GET)
    public ModelAndView acceptingInvitation(@PathVariable String link) {
        User user = getLoggedUser();
        Result result = invitationService.tryAcceptInvitation(link, user);
        ModelAndView view;
        if (result.getType() != ResultType.ERROR) {
            view = new ModelAndView(new RedirectView("/tasks/" + (Long)result.getObject(), true));
            view.addObject("permissionMessage", result.getMessage());
        }
        else {
            view = new ModelAndView("/home/index");
            view.addObject("invalidLinkMessage", result.getMessage());
        }
        return view;
    }

//---------------------
// service/implementations/InvitationService
//--------------------
    @Override
    public Result tryAcceptInvitation(String link, User user) {
        if (this.isInvitationValid(link)) {
            Invitation invitation = this.getInvitationByLink(link);
            Permission existingPermission = permissionService.findPermissionByUserAndTask(user, invitation.getTask());

            if (existingPermission == null) {
                Permission newPermission = new Permission();
                newPermission.setId(new PermissionKey(user, invitation.getTask()));
                newPermission.setPermission(invitation.getPermission());
                permissionService.addPermission(newPermission);
                return new Result(ResultType.SUCCESS, "Permission to the task has been granted!", invitation.getTask().getId());

            } else if (existingPermission.getPermission() == invitation.getPermission()) {
                return new Result(ResultType.ENTITY_EXISTS, "You already have permission to the note!", invitation.getTask().getId());

            } else {
                existingPermission.setPermission(invitation.getPermission());
                permissionService.updatePermission(existingPermission);
                return new Result(ResultType.ENTITY_UPDATED,"Permission to the note has been changed!", invitation.getTask().getId());
            }
        } else {
            return new Result(ResultType.ERROR, "Invalid link!");
        }
    }

// ----------------------
// updatePermission() potom volá metodu z repozitáře která provede manuální update (ačkoliv možná by na to stačil opět jen save())
// ----------------------
    @Modifying
    @Transactional
    @Query("UPDATE Permission p SET p.permission = :permission WHERE p.id.user.id = :userId and p.id.task.id = :taskId")
    void updateByUserAndTaskId(@Param("userId") long userId, @Param("taskId") long taskId, @Param("permission") UserRight permission);