<?php
/* Icinga Web 2 | (c) 2021 Icinga GmbH | GPLv2+ */

namespace Icinga\Web\Helper\Markdown;

use HTMLPurifier_AttrTransform;
use HTMLPurifier_Config;
use ipl\Stdlib\Str;
use ipl\Web\Url;

class LinkTransformer extends HTMLPurifier_AttrTransform
{
    /**
     * Link targets with such a file extension are not loaded by an iFrame
     *
     * @var string[]
     */
    public static $NON_IFRAME_FILES = [
        'html',
        'htm',
        'php',
        'svg',
        'aspx',
        'cshtml',
        'vbhtml'
    ];

    /**
     * Link targets that are considered to have a thumbnail
     *
     * @var string[]
     */
    public static $IMAGE_FILES = [
        'jpg',
        'jpeg',
        'png',
        'bmp',
        'gif',
        'heif',
        'heic',
        'webp'
    ];

    public function transform($attr, $config, $context)
    {
        if (! isset($attr['href'])) {
            return $attr;
        }

        $url = Url::fromPath($attr['href']);

        list($_, $ext) = Str::symmetricSplit($url->getPath(), '.', 2);

        $hasThumbnail = $ext !== null && in_array($ext, static::$IMAGE_FILES, true);
        $useIframe = $ext !== null && ! in_array($ext, static::$NON_IFRAME_FILES, true);

        if ($hasThumbnail) {
            // I would have liked to not only base this off of the extension, but also by
            // whether there is an actual img tag inside the anchor. Seems not possible :(
            $attr['class'] = 'with-thumbnail';
        }

        if ((! isset($attr['target']) || ! in_array($attr['target'], ['_blank', '_self']))
            && ($useIframe || $url->isExternal())
        ) {
            $attr['href'] = Url::fromPath('iframe', ['url' => $url])->getAbsoluteUrl();
        }

        return $attr;
    }

    public static function attachTo(HTMLPurifier_Config $config)
    {
        $module = $config->getHTMLDefinition(true)
            ->getAnonymousModule();

        if (isset($module->info['a'])) {
            $a = $module->info['a'];
        } else {
            $a = $module->addBlankElement('a');
        }

        $a->attr_transform_post[] = new self();
    }
}