cx-newsletter/database/02-database_versions_manager.php

<?php

namespace cx_newsletter;
use \get_option;
use \update_option;
use \delete_option;
use \exception;

class database_versions_manager {
    public function get_installed() : ?int {
        $version = get_option($this->get_database_version_name(), null);

        if ($version === null) {
            return null;
        }

        $version = intval($version);

        if ($version === 0) {
            return null;
        }

        return $version;
    }

    public function is_installed() : bool {
        return $this->get_installed() !== null;
    }   

    public function set_installed(?int $version) : void {
        if ($version === null) {
            delete_option($this->get_database_version_name());
            return;
        }

        if ($version <= 0) {
            throw new exception('Version must be greaten than 0.');
        }
        
        update_option($this->get_database_version_name(), strval($version));
    }

    private function get_database_version_name() : string {
        return 'cx_newsletter_database_version';
    }
}