public static function init() {
		if ( ! self::$initialized ) {
			self::$cache_dir = self::get_cache_dir();
			self::$debug     = Popup_Maker::debug_mode() || ( defined( 'SCRIPT_DEBUG' ) && SCRIPT_DEBUG );
			self::$suffix    = self::$debug ? '' : '.min';
			self::$asset_url = Popup_Maker::$URL . 'assets/';
			self::$js_url    = self::$asset_url . 'js/';
			self::$css_url   = self::$asset_url . 'css/';
			if ( defined( 'IS_WPCOM' ) && IS_WPCOM ) {
				self::$disabled = true;
			} else {
				self::$disabled  = pum_get_option( 'disable_asset_caching', false );
			}

			add_action( 'pum_extension_updated', array( __CLASS__, 'reset_cache' ) );
			add_action( 'pum_extension_deactivated', array( __CLASS__, 'reset_cache' ) );
			add_action( 'pum_extension_activated', array( __CLASS__, 'reset_cache' ) );
			add_action( 'pum_regenerate_asset_cache', array( __CLASS__, 'reset_cache' ) );
			add_action( 'pum_save_settings', array( __CLASS__, 'reset_cache' ) );
			add_action( 'pum_save_popup', array( __CLASS__, 'reset_cache' ) );
			add_action( 'pum_save_theme', array( __CLASS__, 'reset_cache' ) );
			add_action( 'pum_update_core_version', array( __CLASS__, 'reset_cache' ) );

			if ( isset( $_GET['flush_popup_cache'] ) ) {
				add_action( 'init', array( __CLASS__, 'reset_cache' ) );
			}

			add_filter( 'pum_alert_list', array( __CLASS__, 'cache_alert' ) );

			add_action( 'pum_styles', array( __CLASS__, 'global_custom_styles' ) );

			if ( null === get_option( 'pum_files_writeable', null ) ) {
				add_option( 'pum_files_writeable', true );
				add_option( '_pum_writeable_notice_dismissed', true );
				pum_reset_assets();
			}

			if ( is_admin() && current_user_can( 'edit_posts' ) ) {
				add_action( 'init', array( __CLASS__, 'admin_notice_check' ) );
			}

			// Prevent reinitialization.
			self::$initialized = true;
		}
	}