private function getCSSThemeFile()
 {
     $current_user = UserManager::instance()->getCurrentUser();
     $theme_variant = new ThemeVariant();
     $css_file_provider = new FlamingParrot_CSSFilesProvider($theme_variant);
     $variant_used = $theme_variant->getVariantForUser($current_user);
     return $css_file_provider->getCSSFileForVariant($variant_used);
 }
<?php

/**
 * Copyright (c) Enalean, 2014. All rights reserved
 *
 * This file is a part of Tuleap.
 *
 * Tuleap is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * Tuleap is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Tuleap. If not, see <http://www.gnu.org/licenses/
 */
require_once 'pre.php';
$available_theme_variants = array('selected' => false, 'values' => array());
if ($request->get('theme') === 'FlamingParrot') {
    require_once '../themes/FlamingParrot/FlamingParrot_CSSFilesProvider.class.php';
    $theme_variant = new ThemeVariant();
    $css_file_selector = new FlamingParrot_CSSFilesProvider($theme_variant);
    $available_theme_variants['selected'] = $theme_variant->getVariantForUser($request->getCurrentUser());
    $available_theme_variants['values'] = $theme_variant->getAllowedVariants();
    $available_theme_variants['css_files'] = $css_file_selector->getCSSFilesForAllAvailableVariants();
}
$GLOBALS['Response']->sendJSON($available_theme_variants);