Reminder.php

<?php

namespace ReminderNamespace;

class Reminder {

	private $logo_url = 'logo-url';

	public function __construct() {
		add_action( 'admin_enqueue_scripts', array( $this, 'enqueue_reminder_script' ) );
		add_action( 'admin_footer', array( $this, 'display_html_element' ) );
	}

	public function enqueue_reminder_script() {
		if ( ! $this->is_plugin_activated() ) {
			wp_enqueue_script(
				'wpdesk-activation-reminder',
				plugins_url( 'popup-javascript-file' ),
				array(),
				'script-version',
				true
			);

			wp_enqueue_style(
				'wpdesk-activation-reminder',
				plugins_url( 'popup-css-file' ),
				array(),
				'script-version'
			);
		}
	}

	public function display_html_element() {
		if ( ! $this->is_plugin_activated() ) {
			$logo_url          = plugins_url( 'plugin-dir' . '/' . $this->logo_url );
			$cookie_name       = md5( site_url() . 'plugin-dir' );
			$subscriptions_url = admin_url( 'admin.php?page=wpdesk-licenses' );
			$read_more_url     = 'https://flexibleshipping.com';
			echo "<span class=\"wpdesk-activation-reminder\" data-plugin_title=\"plugin-title\" data-plugin_dir=\"plugin-dir\" data-logo_url=\"$logo_url\" data-cookie_name=\"$cookie_name\" data-subscriptions_url=\"$subscriptions_url\" data-buy_plugin_url=\"buy-plugin-url\" data-read_more_url=\"$read_more_url\"></span>";
		}
	}

	private function is_plugin_activated() {
		return get_option( 'api_plugin-dir_activated', '' ) === 'Activated';
	}

}

new Reminder();