get_theme_update_available( WP_Theme $theme )

function get_theme_update_available( $theme ) {
	static $themes_update = null;

	if ( !current_user_can('update_themes' ) )
		return false;

	if ( !isset($themes_update) )
		$themes_update = get_site_transient('update_themes');

	if ( ! ( $theme instanceof WP_Theme ) ) {
		return false;
	}

	$stylesheet = $theme->get_stylesheet();

	$html = '';

	if ( isset($themes_update->response[ $stylesheet ]) ) {
		$update = $themes_update->response[ $stylesheet ];
		$theme_name = $theme->display('Name');
		$details_url = add_query_arg(array('TB_iframe' => 'true', 'width' => 1024, 'height' => 800), $update['url']); //Theme browser inside WP? replace this, Also, theme preview JS will override this on the available list.
		$update_url = wp_nonce_url( admin_url( 'update.php?action=upgrade-theme&theme=' . urlencode( $stylesheet ) ), 'upgrade-theme_' . $stylesheet );

		if ( !is_multisite() ) {
			if ( ! current_user_can('update_themes') ) {
				/* translators: 1: theme name, 2: theme details URL, 3: additional link attributes, 4: version number */
				$html = sprintf( '<p><strong>' . __( 'There is a new version of %1$s available. <a href="%2$s" %3$s>View version %4$s details</a>.' ) . '</strong></p>',
					$theme_name,
					esc_url( $details_url ),
					sprintf( 'class="thickbox open-plugin-details-modal" aria-label="%s"',
						/* translators: 1: theme name, 2: version number */
						esc_attr( sprintf( __( 'View %1$s version %2$s details' ), $theme_name, $update['new_version'] ) )
					),
					$update['new_version']
				);
			} elseif ( empty( $update['package'] ) ) {
				/* translators: 1: theme name, 2: theme details URL, 3: additional link attributes, 4: version number */
				$html = sprintf( '<p><strong>' . __( 'There is a new version of %1$s available. <a href="%2$s" %3$s>View version %4$s details</a>. <em>Automatic update is unavailable for this theme.</em>' ) . '</strong></p>',
					$theme_name,
					esc_url( $details_url ),
					sprintf( 'class="thickbox open-plugin-details-modal" aria-label="%s"',
						/* translators: 1: theme name, 2: version number */
						esc_attr( sprintf( __( 'View %1$s version %2$s details' ), $theme_name, $update['new_version'] ) )
					),
					$update['new_version']
				);
			} else {
				/* translators: 1: theme name, 2: theme details URL, 3: additional link attributes, 4: version number, 5: update URL, 6: additional link attributes */
				$html = sprintf( '<p><strong>' . __( 'There is a new version of %1$s available. <a href="%2$s" %3$s>View version %4$s details</a> or <a href="%5$s" %6$s>update now</a>.' ) . '</strong></p>',
					$theme_name,
					esc_url( $details_url ),
					sprintf( 'class="thickbox open-plugin-details-modal" aria-label="%s"',
						/* translators: 1: theme name, 2: version number */
						esc_attr( sprintf( __( 'View %1$s version %2$s details' ), $theme_name, $update['new_version'] ) )
					),
					$update['new_version'],
					$update_url,
					sprintf( 'aria-label="%s" id="update-theme" data-slug="%s"',
						/* translators: %s: theme name */
						esc_attr( sprintf( __( 'Update %s now' ), $theme_name ) ),
						$stylesheet
					)
				);
			}
		}
	}

	return $html;
}