openstamanager/plugins/importFE/view.php

<?php
/*
 * OpenSTAManager: il software gestionale open source per l'assistenza tecnica e la fatturazione
 * Copyright (C) DevCode s.n.c.
 *
 * This program 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 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 this program. If not, see <https://www.gnu.org/licenses/>.
 */

include_once __DIR__.'/../../core.php';

$directory = Plugins\ImportFE\FatturaElettronica::getImportDirectory();
$filename = get('filename');

$content = file_get_contents($directory.'/'.$filename);

// XML
$xml = new DOMDocument();
$xml->loadXML($content);

// XSL
$xsl = new DOMDocument();
$xsl->load(DOCROOT.'/plugins/xml/asso-invoice.xsl');

// XSLT
$xslt = new XSLTProcessor();
$xslt->importStylesheet($xsl);

echo $xslt->transformToXML($xml);