<?php
class Post
{
    private PDO $pdo;

    public function __construct(PDO $pdo)
    {
        $this->pdo = $pdo;
    }

    /** Return all published posts, newest first */
    public function all(): array
    {
        $stmt = $this->pdo->query(
            "SELECT id, title, slug, excerpt, author, created_at
             FROM posts
             WHERE published = 1
             ORDER BY created_at DESC"
        );
        return $stmt->fetchAll(PDO::FETCH_ASSOC);
    }

    /** Return one post by slug, or null if not found */
    public function findBySlug(string $slug): ?array
    {
        $stmt = $this->pdo->prepare(
            "SELECT * FROM posts WHERE slug = ? AND published = 1 LIMIT 1"
        );
        $stmt->execute([$slug]);
        $row = $stmt->fetch(PDO::FETCH_ASSOC);
        return $row ?: null;
    }
}

<?php
class PostController
{
    public function __construct(
        private PDO           $pdo,
        private Tplix\Engine  $tplix
    ) {}

    /** GET /  — list all posts */
    public function index(): void
    {
        $model = new Post($this->pdo);
        $posts = $model->all();

        $this->tplix->assign('posts',      $posts);
        $this->tplix->assign('page_title', 'Blog');
        $this->tplix->display('index.tpl');
    }

    /** GET /{slug}  — single post */
    public function show(string $slug): void
    {
        $model = new Post($this->pdo);
        $post  = $model->findBySlug($slug);

        if (!$post) {
            http_response_code(404);
            echo '<h1>Post not found</h1>';
            return;
        }

        $this->tplix->assign('post',       $post);
        $this->tplix->assign('page_title', $post['title']);
        $this->tplix->display('post.tpl');
    }
}