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

<?php

const H3_PATTERN = '/<h3>(.*?)<\/h3>/';

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(H3_PATTERN, $content, $matches);

            return array_map(fn($title) => [
                'title' => $title,
                'slug' => Str::slug($title)
            ], $matches[1]);
        },

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

            return preg_replace_callback(
                H3_PATTERN,
                fn($m) => '<h3 id="' . Str::slug($m[1]) . '">' . $m[1] . '</h3>',
                $content
            );
        }
    ]
]);