<?php

declare(strict_types=1);

class MarkdownService extends Prefab
{
    private const TAGS = ['p', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'ul', 'ol', 'li', 'blockquote', 'pre', 'code', 'strong', 'em', 'a', 'img', 'hr', 'br'];
    private const ATTRS = [
        '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.');
        }

        $markdown = $this->neutralizeRawHtml($markdown);

        $doc = new DOMDocument('1.0', 'UTF-8');
        $html = '<div id="content">' . Markdown::instance()->convert($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) {
            return '';
        }

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

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

        return trim($out);
    }

    private function neutralizeRawHtml(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 sanitizeChildren(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::TAGS, true)) {
                $this->unwrap($child);
                $this->sanitizeChildren($parent, $media);
                continue;
            }

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

            if ($tag === 'a') {
                $href = trim((string) $child->getAttribute('href'));
                if (!$this->allowedHref($href)) {
                    $this->unwrap($child);
                    $this->sanitizeChildren($parent, $media);
                    continue;
                }

                $child->setAttribute('href', $href);
                $child->setAttribute('rel', 'noopener noreferrer');

                if (preg_match('~^https?://~i', $href)) {
                    $child->setAttribute('target', '_blank');
                } else {
                    $child->removeAttribute('target');
                }
            }

            if ($tag === 'img') {
                $src = trim((string) $child->getAttribute('src'));
                if (!str_starts_with($src, 'media:')) {
                    $child->parentNode?->removeChild($child);
                    continue;
                }

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

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

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

    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 allowedHref(string $href): bool
    {
        if ($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);
    }
}