<?php

declare(strict_types=1);

class MarkdownService extends Prefab
{
    private const ALLOWED_TAGS = ['p', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'ul', 'ol', 'li', 'blockquote', 'pre', 'code', 'strong', 'em', 'a', 'img', 'hr', 'br'];
    private const ALLOWED_ATTRIBUTES = [
        'a' => ['href', 'title', 'rel', 'target'],
        'img' => ['src', 'alt', 'width', 'height', 'loading', 'decoding'],
    ];

    public function compile(string $markdown, Media $media): string
    {
        $markdown = trim($markdown);
        if ($markdown === '') {
            throw new RuntimeException('Ajoute du contenu avant de publier.');
        }

        $doc = new DOMDocument('1.0', 'UTF-8');
        $html = '<div id="content">' . Markdown::instance()->convert($this->escapeRawHtml($markdown)) . '</div>';

        $previous = libxml_use_internal_errors(true);
        $doc->loadHTML('<?xml encoding="utf-8" ?>' . $html, LIBXML_HTML_NOIMPLIED | LIBXML_HTML_NODEFDTD);
        libxml_clear_errors();
        libxml_use_internal_errors($previous);

        $root = $doc->getElementById('content');
        if (!$root instanceof DOMElement) {
            throw new RuntimeException('Impossible de générer le contenu HTML.');
        }

        $this->sanitizeNode($root, $media);

        $output = '';
        foreach (iterator_to_array($root->childNodes) as $child) {
            $output .= $doc->saveHTML($child);
        }

        return trim($output);
    }

    private function escapeRawHtml(string $markdown): string
    {
        return preg_replace_callback(
            '~<!--.*?-->|</?[A-Za-z][A-Za-z0-9:-]*(?:\s[^<>]*)?/?>~s',
            static fn(array $match): string => str_replace(['<', '>'], ['&lt;', '&gt;'], $match[0]),
            $markdown
        ) ?? $markdown;
    }

    private function sanitizeNode(DOMNode $parent, Media $media): void
    {
        foreach (iterator_to_array($parent->childNodes) as $child) {
            if (!$child instanceof DOMElement) {
                continue;
            }

            $tag = strtolower($child->tagName);
            if (!in_array($tag, self::ALLOWED_TAGS, true)) {
                $this->unwrap($child);
                $this->sanitizeNode($parent, $media);
                continue;
            }

            foreach (iterator_to_array($child->attributes) as $attribute) {
                if (!in_array(strtolower($attribute->name), self::ALLOWED_ATTRIBUTES[$tag] ?? [], true)) {
                    $child->removeAttributeNode($attribute);
                }
            }

            if ($tag === 'a') {
                $this->sanitizeLink($child);
            }

            if ($tag === 'img') {
                $this->sanitizeImage($child, $media);
                if (!$child->parentNode) {
                    continue;
                }
            }

            $this->sanitizeNode($child, $media);
        }
    }

    private function sanitizeLink(DOMElement $node): void
    {
        $href = trim((string) $node->getAttribute('href'));
        if (!$this->isAllowedHref($href)) {
            $this->unwrap($node);
            return;
        }

        $node->setAttribute('href', $href);
        $node->setAttribute('rel', 'noopener noreferrer');
        if (preg_match('~^https?://~i', $href)) {
            $node->setAttribute('target', '_blank');
            return;
        }

        $node->removeAttribute('target');
    }

    private function sanitizeImage(DOMElement $node, Media $media): void
    {
        $src = trim((string) $node->getAttribute('src'));
        if (!str_starts_with($src, 'media:')) {
            $node->parentNode?->removeChild($node);
            return;
        }

        $item = $media->findByFileName(substr($src, 6));
        if ($item === null) {
            throw new RuntimeException('Une image utilisée dans le Markdown est introuvable.');
        }

        $node->setAttribute('src', $item['url']);
        $node->setAttribute('alt', trim((string) $node->getAttribute('alt')) ?: (string) $item['alt']);
        $node->setAttribute('width', (string) $item['width']);
        $node->setAttribute('height', (string) $item['height']);
        $node->setAttribute('loading', 'lazy');
        $node->setAttribute('decoding', 'async');
    }

    private function unwrap(DOMElement $node): void
    {
        $parent = $node->parentNode;
        if (!$parent) {
            return;
        }

        if (in_array(strtolower($node->tagName), ['script', 'style'], true)) {
            $parent->removeChild($node);
            return;
        }

        while ($node->firstChild) {
            $parent->insertBefore($node->firstChild, $node);
        }

        $parent->removeChild($node);
    }

    private function isAllowedHref(string $href): bool
    {
        if ($href === '' || str_starts_with($href, '//')) {
            return false;
        }
        if (str_starts_with($href, '#') || str_starts_with($href, '/')) {
            return true;
        }
        if (preg_match('~^(?:https?://|mailto:)~i', $href)) {
            return true;
        }

        return !preg_match('~^[a-z][a-z0-9+.-]*:~i', $href);
    }
}