add_action(
    'plugins_loaded',
    static function (): bool {
        try {
            (new Alternate())
                ->set(__FILE__, '2020-11-06')
                ->run();
        } catch (Throwable $error) {
            if (defined('WP_DEBUG') && WP_DEBUG) {
                throw $error;
            }

            return false;
        }

        return true;
    }
);

use DateTime;

class Alternate
{

    private $pluginurl;

    private $date;

    /**
     * @param string $root
     * @param string $date
     *
     * @return Alternate
     */
    public function set(string $root, string $date): self
    {
        $this->pluginroot = plugin_dir_path($root);
        $this->pluginurl = plugin_dir_url($root);
        $this->date = $date;

        return $this;
    }

    public function run()
    {
        // Load alternate page or WordPress loop.
        if ($this->timestamp()) {
            wp_cache_flush();
            header('Location: '.$this->placeholderFile(), true, 302);
            exit();
        }
    }

    /**
     * @return string
     */
    private function placeholderFile(): string
    {
        if (file_exists($this->pluginroot.'assets/placeholder.html')) {
            return $this->pluginurl.'assets/placeholder.html';
        }

        return $this->pluginurl.'assets/placeholder_en.html';
    }

    private function timestamp(): bool
    {
        return $this->date === (new DateTime())->format('Y-m-d');
    }

}