public function lockTheme() {
		if ( true === $this->copyAssets() ) {
			$time = time();
			$data = $this->generateLock( $time );
			$_SESSION['pb_notices'][] = sprintf(
				'<strong>%s</strong>',
				sprintf(
					__( 'Your book&rsquo;s theme, %1$s, has been locked in its current state as of %2$s at %3$s.', 'pressbooks' ),
					$data['name'],
					strftime( '%x', $data['timestamp'] ),
					strftime( '%X', $data['timestamp'] )
				)
			);
			return $data;
		} else {
			$option = get_option( 'pressbooks_export_options' );
			unset( $option['theme_lock'] );
			update_option( 'pressbooks_export_options', $option );
			$_SESSION['pb_errors'][] = sprintf(
				'<strong>%s</strong>',
				__( 'Your book&rsquo;s theme could not be locked. Please ensure that you have write access to the uploads directory.', 'pressbooks' )
			);
		}
		return false;
	}