public static function writeable() {
		if ( self::$disabled ) {
			return false;
		}

		// If we have already determined files to not be writeable, go ahead and return.
		if ( true != get_option( 'pum_files_writeable', true ) ) {
			return false;
		}

		global $wp_filesystem;

		if ( ! function_exists( 'WP_Filesystem' ) ) {
			require_once( ABSPATH . 'wp-admin/includes/file.php' );
		}

		$results = WP_Filesystem();

		if ( true !== $results ) {
			// Prevents this from running again and set to show the admin notice.
			update_option( 'pum_files_writeable', false );
			update_option( '_pum_writeable_notice_dismissed', false );
			if ( ! is_null( $results ) && is_wp_error( $wp_filesystem->errors ) && $wp_filesystem->errors->has_errors() ) {
				$error = $wp_filesystem->errors->get_error_message();
				PUM_Utils_Logging::instance()->log( sprintf( 'Cache directory is not writeable due to filesystem error. Error given: %s', esc_html( $error ) ) );
			} else {
				PUM_Utils_Logging::instance()->log( 'Cache directory is not writeable due to incorrect filesystem method.' );
			}
			return false;
		}

		// Checks and create cachedir.
		if ( false !== self::$cache_dir && ! is_dir( self::$cache_dir ) ) {

			/** @var WP_Filesystem_Base $wp_filesystem */
			$wp_filesystem->mkdir( self::$cache_dir );
		}

		return false !== self::$cache_dir && is_writable( self::$cache_dir ) && ! isset( $_POST['wp_customize'] );
	}