/**
 * @var Employee[]|EmployeeGroup[] $newAssignees
 * @var Employee[]|EmployeeGroup[] $oldAssignees
 * @return array
 */
private function getAssigneesTypes($oldAssignees, $newAssignees) {
    $deleted = [];
    $added = [];
    $modified = [];

    foreach ($oldAssignees as $old) {
        $mod = false;
        foreach ($newAssignees as $new) {
            if ($old->getId() == $new->getId()) {
                $modified[] = $old;
                $mod = true;
            }
        }

        if (!$mod) {
            $deleted[] = $old;
        }
    }

    foreach ($newAssignees as $new) {
        $mod = false;
        foreach ($oldAssignees as $old) {
            if ($old->getId() == $new->getId()) {
                $mod = true;
            }
        }

        if (!$mod) {
            $added[] = $new;
        }
    }

    return [
        'deleted' => $deleted,
        'added' => $added,
        'modified' => $modified,
    ];
}