actuel-inactuel/site/plugins/toc/index.php

<?php

const HEADING_PATTERN = '/<(h[34])(.*?)>(.*?)<\/\1>/';

function getContent($page) {
    if ($page->intendedTemplate() == 'grid') return $page->body()->toBlocks();
    
    if ($page->intendedTemplate() == 'linear') {     
        if ($page->isBlockMode()->isTrue()) return $page->bodyBlocks()->toBlocks();
        if ($page->isBlockMode()->isFalse()) return $page->body();
    }

    return null;
}

function getTocContent($page) {
    if (!$page->parent()?->parent()?->is('textes')) return null;

    $content = (string) getContent($page);

    return $content ?: null;
}

Kirby::plugin('actuel-inactuel/toc', [
    'pageMethods' => [
        'hasToc' => function(): bool {
            return count($this->tocItems()) > 0;
        },

        'tocItems' => function(): array {
            $content = getTocContent($this);
            if (!$content) return [];

            preg_match_all(HEADING_PATTERN, $content, $matches, PREG_SET_ORDER);

            $items = [];
            foreach ($matches as $m) {
                $entry = ['title' => $m[3], 'slug' => Str::slug($m[3])];

                if ($m[1] === 'h3') {
                    $entry['children'] = [];
                    $items[] = $entry;
                } elseif ($m[1] === 'h4' && count($items) > 0) {
                    $items[count($items) - 1]['children'][] = $entry;
                }
            }

            return $items;
        },

        'bodyWithAnchors' => function(): string {
            $content = getTocContent($this);
            if (!$content) return '';

            return preg_replace_callback(
                HEADING_PATTERN,
                fn($m) => '<' . $m[1] . ' id="' . Str::slug($m[3]) . '"' . $m[2] . '>' . $m[3] . '</' . $m[1] . '>',
                $content
            );
        }
    ]
]);